Photovoltaic System Integration
Short Description
The main objective of this thesis is to design a photovoltaic system to be optimally integrated with the electrical syst...
Description
Photovoltaic System Integration for Roehampton Vale Campus, Kingston University London
Omar Hamdan Supervised by: Dr. Paul Wagstaff MSc Renewable Energy Engineering October 2012
Faculty of SEC, Kingston University
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Synopsis This thesis is divided in a way to permit the reader to follow the content in a logical sequence. The main objective of this thesis is to design a photovoltaic system to be optimally integrated with the electrical system in Kingston University London, Roehampton Vale campus. This system main objective is to supply the electrical demand of the facility. The thesis presents a piece of work to calculate the power output of the photovoltaic system in hand calculations and software simulation. The thesis will evaluate the location of the installation by means of radiation falls on the location, construction of the photovoltaic system, sizing the system by evaluate the options according to area available and capital cost. The hand calculation will present a model develop on excel to calculate the power output by calculating the solar irradiances on a tilted surface, converting the irradiances to electrical power and considering the effect of temperature on photovoltaic cells. The simulation part will present an entire design of the system by means of calculating the power output, losses associated with the conversion process and connection, shade study and result analysis The sizing of the system was carried out through hand calculation, simulation and economical analysis. Finally an economical evaluation for many models will be presented.
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Table of Contents List of Figures ............................................................................................................................... VI List of Tables............................................................................................................................... VIII List of Equations ........................................................................................................................... IX Chapter One .................................................................................................................................. 1 1.1.0 Introduction .......................................................................................................................... 2 1.2.0 Building Integrated PV System .............................................................................................. 5 1.3.0 Solar Radiation and Solar Constant ....................................................................................... 7 1.4.0 Geometrical Considerations: ................................................................................................. 8 1.4.1 The Declination angle............................................................................................................ 9 1.4.2 Solar Hour Angle ................................................................................................................... 9 1.4.3 The Latitude angle .............................................................................................................. 10 1.4.4 The Sunset Hour angle ........................................................................................................ 10 1.4.5 Slope Angle ......................................................................................................................... 10 1.4.6 Surface Azimuth angle ........................................................................................................ 10 1.4.7 Angle of Incident ................................................................................................................. 10 1.4.8 Zenith Angle........................................................................................................................ 11 1.5.0 Solar Radiations reaches a specific tilted surface ................................................................. 11 1.5.1 Clearness Index: .................................................................................................................. 12 1.5.2 Calculating of Hourly Global and Diffused Irradiance ........................................................... 12 Chapter Two ................................................................................................................................ 15 2.1.0 System Components ........................................................................................................... 16 2.1.1 Solar Cell Basics: ................................................................................................................. 16 2.1.2 Light characteristics ............................................................................................................ 17 2.1.3 Electrical Characteristics of a PV-Cell: .................................................................................. 18 2.1.4 Voltage and Current in PV Plant .......................................................................................... 21 2.2.0 Electrical Power Output: ..................................................................................................... 22 2.3.0 Components Selection PV panel .......................................................................................... 23 2.3.1 PV Panel Selection Methodology ......................................................................................... 24 2.3.2 Chosen Panel ...................................................................................................................... 24 2.4.0 Inverter and Control............................................................................................................ 26 2.4.1 Maximum Power Point Tracking (MPPT): ............................................................................ 26 2.4.2 Connection of Inverter to Array........................................................................................... 26 2.4.3 Inverter, process and Functions .......................................................................................... 28 Omar Hamdan | Kingston University London
IV 2.4.4 Component Selection, Inverter ........................................................................................... 29 2.4.5 Summary ............................................................................................................................ 30 2.5.0 Shading: .............................................................................................................................. 33 Chapter Three ............................................................................................................................. 34 3.1.0 Project Demand and Hand Calculations ............................................................................... 35 3.1.1 Process of progression: ....................................................................................................... 35 3.1.2 Overview, System Demand and Electrical System Review:................................................... 36 3.2.1 Hand Calculation: ................................................................................................................ 38 3.2.2 Summary and Assumptions: ................................................................................................ 38 3.2.3 Calculating the hourly solar radiation on the system: .......................................................... 39 3.2.4 Calculation: ......................................................................................................................... 41 3.2.5 Hand Calculation Results and Analysis: ................................................................................ 46 3.2.6 Area optimising and assessment ......................................................................................... 52 3.2.7 shading consideration ......................................................................................................... 53 3.3.0 calculating the hourly electrical power produced through all the year ................................. 55 3.3.1 System sizing ...................................................................................................................... 55 Chapter Four ............................................................................................................................... 60 4.1.0 Project Simulation............................................................................................................... 61 4.1.1 Preliminary Design .............................................................................................................. 61 4.2.0 Full Project Design .............................................................................................................. 64 4.2.1 Shade Simulation ................................................................................................................ 65 4.2.2 Electrical Layout .................................................................................................................. 70 4.2.3 Panel Layout Design ............................................................................................................ 71 4.2.4 Simulation Results and Review ............................................................................................ 73 Chapter Five ................................................................................................................................ 78 5.1.0 Electrical Configurations ..................................................................................................... 79 5.1.1 Measurement of the Energy Produced and Sold to the Grid ................................................ 80 5.2.0 Protection and Earthing of the System: ............................................................................... 81 5.3.0 Protection Against Over Current on AC Side: ....................................................................... 82 5.4.0 Comparison between Hand Calculation and Simulation....................................................... 82 Chapter Six .................................................................................................................................. 83 6.1.0 Economical Evaluation ........................................................................................................ 84 6.1.1 Assumptions ....................................................................................................................... 84 6.2.0 Sizing the System Based on Data from the Economic Model ................................................ 85 Omar Hamdan | Kingston University London
V 6.2.1 Maximum Power Output..................................................................................................... 85 6.2.2 System Limited by the Minimum Demand of December ...................................................... 87 6.2.3 Using the Data from Simulation for 20% of December System Size ...................................... 87 6.3.0 Analysis............................................................................................................................... 93 Chapter Seven ............................................................................................................................. 94 7.1.0 Critical Review .................................................................................................................... 95 7.2.0 Further Work ...................................................................................................................... 95 Chapter Eight............................................................................................................................... 96 7.1.0 Conclusion .......................................................................................................................... 97 References .................................................................................................................................. 98 Bibliographies ............................................................................................................................ 100 Appendix A ................................................................................................................................ 101 Appendix B ................................................................................................................................ 102 Appendix C ................................................................................................................................ 104
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List of Figures Figure 1: GHG and CO2 emissions by sector. (EC, 2010) ...................................................................... 3 Figure 2: Electricity consumptions by Sector. (DECC, 2009) ................................................................ 4 Figure 3: Electrical PV generation (European commission, 2010) ....................................................... 5 Figure 4: Grid-connected photovoltaic system. (Luque and Hegedus, 2011). ...................................... 6 Figure 5: Earth Positions around the sun (Scharmer, 2000) ................................................................ 8 Figure 6: Solar Geometry Angles (Duffie and Beckman, 2006). ......................................................... 11 Figure 7: Schematic of a solar cell. The solid white lines indicate the conduction and valence bands of the semiconductor layers; the dotted white lines indicate the Fermi level in the dark. .................... 16 Figure 8: Light wavelength ranges ................................................................................................... 18 Figure 9 Equivalent circuit of Photovoltaic ....................................................................................... 19 Figure 10 Voltage-Current characteristics example (ABB, 2010) ....................................................... 20 Figure 11 Selected Panel Dimensions ............................................................................................... 25 Figure 12 photovoltaic panel curves with different irradiances. ....................................................... 25 Figure 13 typical circuit used in PV inverters. ................................................................................... 28 Figure 14 inverter combination ....................................................................................................... 32 Figure 15 PWM DC to AC process .................................................................................................... 32 Figure 16 By-Pass diode under shading ............................................................................................ 33 Figure 17 system demand in kW ...................................................................................................... 37 Figure 18 Day Length for each month .............................................................................................. 47 Figure 19 Clearness Index and the diffused radiation ratio ............................................................... 47 Figure 20 total irradiance on a tilted surface per hour for each month............................................. 49 Figure 21 total estimated electrical output per hour each month. ................................................... 51 Figure 22 The monthly production of the system ............................................................................. 51 Figure 23 Roof Top of the Location. ................................................................................................. 52 Figure 24 calculating the area of shade effect .................................................................................. 54 Figure 25 Monthly Percentage of the total demand when maximum power produced. ................... 56 Figure 26 Percentage of the Supply to the Demand ......................................................................... 58 Figure 27 Monthly Demand Vs. Production. ..................................................................................... 58 Figure 28 Program's first interface page .......................................................................................... 61 Figure 29 Site data entry. ................................................................................................................. 62 Figure 30 mutual shading Visualisation/optimisation ....................................................................... 63 Figure 31 Sun Path and Mutual shading. .......................................................................................... 63 Figure 32 Preliminary Power Output, Horizontal and tilt surface comparison. .................................. 64 Figure 33 Near Shading design tool interface ................................................................................... 64 Figure 34 building a new object to simulate the shading .................................................................. 65 Figure 35 the final built structure. ................................................................................................... 66 Figure 36 PV panels build user interface. ......................................................................................... 66 Figure 37 Final system before the shade simulation......................................................................... 67 Figure 38 Top View, photovoltaic generator position ....................................................................... 68 Figure 39 Shading process ............................................................................................................... 68 Figure 40 shading when the system is placed at the eastern side of the building. ............................ 69 Figure 41 shading when the system is placed at the western side of the building............................. 70 Figure 42 System Design interface ................................................................................................... 72 Figure 43 Array power optimisation graph. ...................................................................................... 72 Omar Hamdan | Kingston University London
VII Figure 44 Module Layout design and layout tool interface. .............................................................. 73 Figure 45 Simulation Production vs. Demand ................................................................................... 74 Figure 46 loss Diagram of the whole system along the year. ............................................................ 75 Figure 47 Daily input/output diagram .............................................................................................. 76 Figure 48 Array voltage distribution ................................................................................................. 76 Figure 49 Daily Power output along the year. .................................................................................. 77 Figure 50 Performance Ratio for each month. ................................................................................. 77 Figure 51 Electrical System Layout. .................................................................................................. 80 Figure 52 kWh meter integration with the system ........................................................................... 81 Figure 53 Cash Flow when installing 250 kWp as maximum assumption .......................................... 87 Figure 54 Cash flow of system sized based on 20% of December demand. ....................................... 89 Figure 55 Cash flow of System sized based on 20% of December demand. Simulation results .......... 89 Figure 56 Saving on Electricity bill in first model .............................................................................. 92 Figure 57 Saving on Electricity bill in the second model ................................................................... 92 Figure 58 Demand and Production for the first model ..................................................................... 93 Figure 59 Demand and Production for the second model ................................................................ 93
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List of Tables Table 1 System Demand kW ............................................................................................................ 37 Table 2. Monthly Ground Reflectance, (Albedo) .............................................................................. 39 Table 3 Monthly average meteorological data (EUROPEAN COMMISSION) ...................................... 40 Table 4 Site Data and Calculated information for one hour of the year ............................................ 40 Table 5 Irradiance Ht according to day hours for each month along the year.................................... 48 Table 6 Average kWh production per hour for each month. ............................................................. 50 Table 7 Maximum power system production and comparison with the system demand .................. 55 Table 8 Minimum Production considering 20% of the Demand in December. .................................. 57 Table 9 Shading factor for the beam radiation at different sun positions. ........................................ 70 Table 10 Simulation Data Output. .................................................................................................... 74 Table 11 Maximum power output applied on the built economical model (in £) .............................. 86 Table 12 20% of December production assumption applied on the built economical model (in £).... 88 Table 13 20% of December production assumption applied on the built economical model/ simulation result (in £) ..................................................................................................................... 90
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List of Equations Equation 1 Extraterrestrial Radiation ................................................................................................. 8 Equation 2 Declination Angle ............................................................................................................. 9 Equation 3 Solar Time ........................................................................................................................ 9 Equation 4 E value. ............................................................................................................................ 9 Equation 5 Sunset Hour Angle ......................................................................................................... 10 Equation 6 Incident Angle ................................................................................................................ 10 Equation 7 Zenith Angle .................................................................................................................. 11 Equation 8 Clearness Index .............................................................................................................. 12 Equation 9 global Hourly irradiance on horizontal surface ............................................................... 12 Equation 10 Diffused Radiation Ratio ws ≤ 81.4˚ ............................................................................... 13 Equation 11 Diffused Radiation Ratio ws > 81.4˚ ............................................................................... 13 Equation 12 Average Daily irradiance .............................................................................................. 13 Equation 13 rt ratio ......................................................................................................................... 13 Equation 14 constant a .................................................................................................................... 13 Equation 15 constant b .................................................................................................................... 13 Equation 16 Diffused irradiance ....................................................................................................... 13 Equation 17 Beam irradiance ........................................................................................................... 14 Equation 18 rd ratio......................................................................................................................... 14 Equation 19 Total irradiance on tilted surface.................................................................................. 14 Equation 20 Rb Value ....................................................................................................................... 14 Equation 21 Photon Energy ............................................................................................................. 17 Equation 22 Atmospheric Mass ....................................................................................................... 18 Equation 23 Diode current............................................................................................................... 19 Equation 24 current delivered by the photovoltaic panel ................................................................. 19 Equation 25 Filling Factor ................................................................................................................ 21 Equation 26 Cell temperature effect on the cell Efficiency ............................................................... 22 Equation 27 Ambient temperature relation with the cell temperature ............................................ 22 Equation 28 tilt angle correction factor for the cell temperature ..................................................... 22 Equation 29 Energy supplied to the building and the electrical grid ................................................. 23
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Chapter One
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1.1 Introduction
Since the first public power distribution system was developed, in 1882, by the famous Thomas Edison, our modern life style started to shape. Electricity made a shift for human history, bringing all life’s modern luxuries into being (Chapman, 2005). Before electricity became available over 100 years ago, houses were lit with kerosene lamps, food was cooled in iceboxes, and wood-burning or coal-burning stoves warmed rooms. In other words, Electricity has changed that and become a key driver in our modern life development. Electrical power generation started in the form of cool power plants using Steam turbines to drive Direct Current generators. That was followed by huge developments in electrical power generation methods. Combined cycle power plant, Nuclear Power Plant and Hydroelectric Power Plant are the latest forms of power generation methods. Although those types of power plants are considered to have high reliability and low loss of load probability (LOLP) fraction, they still suffer from many major issues threatening the globe indirectly, by increasing Green House Gases (GHG), and increasing the availability of some types of fuel, which might not be available for all nations, either now or in the future. Waldau A. J. et al, (2011) mentioned that "besides the increasing pressure on the supply side of energy by the increasing world energy demand, environmental concerns shared by a majority of the public and add to the list of weaknesses of fossil fuels and the problems of nuclear energy. These concerns include the societal damage caused by the existing energy supply system, whether such damage is of accidental origin (oil slicks, nuclear accidents, methane leaks) or connected to emissions of pollutants". Baker, (2004) added that generating electricity has made major damages to the environment which might, in the end, cause global catastrophes. Green House Gases (GHG) and CO2 emissions in particular cause environmental damages. The Global warming or the expansion of the ozone hole, which could lead to the melting of more ice in Antarctica and increase the water level in the seas, represent clear examples of the danger of GHG. Such Issues have led scientists to search for other alternatives, which might balance the scales.
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Renewable Power Generation is being strongly considered. The technology offers a free fuel energy that is free of GHG emissions. Solar Power Generation has a long history and a promising future. Generally, Photovoltaic Power Systems helped to supply electricity to many rural places but since 1991, this case has changed. In Aachen, Germany (1991), the first installation of building-integrated photovoltaic's (BIPV) was realized. In addition, the energy market in the UK is growing, according to many market analysts. In December 1997, the European Council and the European Parliament adopted the “White Paper for a Community Strategy and action Plan”. In this paper, the aims are described as follows, “Renewable energy sources may help to reduce dependence on imports and increase security of supply. Positive effects also anticipated in terms of CO2 emissions and job creation. Renewable energy sources accounted in 1996 for 6% of the union’s overall gross internal energy consumption. The union’s aim is to double this figure by 2010” (European Commission, 2010). The UK government is stating policies to support renewable projects. Subsequently, seeking sustainable and cleaner energy to provide a secure energy level of consumption is an international concern. Residential Buildings contribute in a large way to the total GHG and CO2 emissions. In the UK, residential CO2 and GHG emissions are 14% and 12% respectively. The commercial institutions contribute in 3.8% and 3.2% (European Commission, 2010). Figure (1) illustrates GHG and CO2 emissions by each sector. As well, Domestic and household consumption of electricity represents 32% of the total electricity generation, while the commercial sector consumes 19% of the total electricity produced. (DECC, 2010). Refer to Figure (2).
Figure 1: GHG and CO2 emissions by sector. (EC, 2010)
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Consequently, it is important to consider better solutions for residential sector
electricity
production.
If
the
nineteenth century was the age of coal and the twenty century is the age of oil, then definitely the twenty one century is the age of sun and solar power. Building Integrated PV system (BIPV) considered being one of most efficient solutions. PV system
integration
in
buildings
can
overcome all the above problems and achieve most of the required objectives to
Figure 2: Electricity consumptions by Sector. (DECC, 2009)
certain extend. Furthermore, PV systems on roof or on Façade become more challenging. The UK market faces a short drop in demand, due to reduction on feed in tariff (FIT) by UK government. As a result, most of the PV panels prices dropped dramatically. On the other hand, installation cost still almost the same. For sure, the competitiveness among the market contractors has increased which opened a space for less installation prices. On the other hand, the UK electricity production using solar cell has increased dramatically. The total production in 2005 is 10.9 MW; this number has jumped in 2011 to be 975.8 MW (DECC, 2012). This is an indication on how promising is the photovoltaic market is. The total consumption of electricity from photovoltaic in 1999 used to be only 1000 MWh this number has increase along the decade to be 11000 MWh in 2007. Figure (3) shows the increase along nine years (European Commission, 2010) Finally, it is important to note that the UK photovoltaic market now is under uncertainty conditions due to the change of the incentives and feed in tariff low. All the calculations of the financial part have been done under this assumption, which might decrease the figure. On the other hand, when the market returns to a stable situation the figures are expected to increase.
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Gross Electricity Generation of Photovoltaic GWh Gross Electricity Generation of Photovoltaic GWh
8 1
1
1999
2000
3
4
3
4
2001
2002
2003
2004
2005
10
11
2006
2007
Figure 3: Electrical PV generation (European commission, 2010)
1.2 Building Integrated PV System Examining Photovoltaic modules for building integration, produced as a standard building product that fit into standard façade
and roof structures (IEA,
1996). Since the first integration for Photovoltaic into buildings, it has become one of the fastest growth market segments in photovoltaic (Benemann J. et al, 2001). There are several reasons for the great interest in PV systems in buildings. Its image as a high-tech and its futuristic technology makes it more interesting for engineers, architect and consumers. As well, integration of PV is technically simple to install compared with other solar technologies such as solar thermal (Fieber A., 2005). Furthermore, the price of PV panel integration in building is economically attractive where its profit expectation is promising. A roof or façade element with photovoltaic can be used in all kind of building's structures, curtain wall façade (with isolating glass), rear vented curtain wall façade , structural glazing and tilted façade . It is expected from the photovoltaic system to cover day lighting, reduce the noise and produce electricity (Benemann J. Et al, 2001). While Thomas R. and Fordham M. argued (2001) that the reasons of why Photovoltaic is attractive technology is that using it includes supplying all, or most likely the largest portion, of the annual electricity requirement of a building, making a contribution to the environment, making a statement about innovative architectural Omar Hamdan | Kingston University London
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and engineering design and using them as a demonstration or educational project (Thomas R. and Fordham M., 2001). To integrate a PV system in any building, many considerations must be taken into account by the designer and engineers. One of the crucial points is the orientation of the building and tilt angle of the PV panel, solar irradiations and the electrical system used including the proposed inverter and control methods. In general, any BIPV system consists of Photovoltaic panel(s), inverter(s) and accessories, which are usually referred to as Balance of System (BOS) and switchgears. PV panels are the main component used to convert the energy carried by the photons, particles that exist in sunlight, into electrical power. The inverter will convert the produced DC electrical power by the PV panels to an AC usable electrical power. The BOS includes kWh meter(s), cables, fuses, combiners, fittings, grounding connections, switchgear and strings, DC and AC switches and connectors. The PV system integrated into a building would not need a storage system, batteries; since the storage system is normally used to supply the load during the night hours or when there is not enough radiation to produce electricity into the PV panels. In this case, the national grid will act as a storage system (Luque and Hegedus, 2011). Figure (4) illustrates a basic grid connected (On-Grid) schematic of PV system. More details about each component of the system are presented later; specifically on PV cell, module and array and on the conditioning system (inverter).
Figure 4: Grid-connected photovoltaic system. (Luque and Hegedus, 2011).
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To explain how the solar system does work, it is important to describe the nature of the sun light and the radiations that fall on earth's surface. As well, a short introduction about the sun and earth position should be presented to be able to elucidate sunlight, radiation analysis and solar system.
1.3 Solar Radiation and Solar Constant It is obvious that the Photovoltaic system is related to the sun and the earth's movement around it, thus, studying this movement and the way the radiation will fall into the earth's surface has great importance, in order to achieve the highest possible performance. In addition, it is important to understand the geometric relationships between a planet relative to the earth at anytime and the incoming radiation. This will make it possible to find the power output for any system intended to be installed. The sun is a sphere containing hot gaseous matter and has a diameter of 1.39 x 109 m. On average, the earth is 1.5 x 10 11 meter away from the sun. This distance equals about 12000 times the earth's diameter. The earth revolves around the sun in an elliptical unusual orbit that varies the distance between the sun and the earth by 1.7%. The day of the closest approach in the northern hemisphere is known as Perihelion and occurs on the 2nd of January, whilst on 2nd of July, the earth is at its greatest distance from the sun, this distance is known as Aphelion, see Figure (5) (Scharmer, 2000). The sun has an effective blackbody temperature of 5777 K. The radiation emitted by the sun and its spatial relationship to the earth result in a nearly fixed intensity of solar radiation outside the earth's atmosphere, often referred to as extraterrestrial radiation. The extraterrestrial radiation's values, referred to as solar constant, found in the literature vary slightly due to the measurement techniques or assumptions for necessary estimations. The World Radiation Centre (WRC) has adopted a value of 1367 W/m2, with 1% uncertainty (IEA, 1996). The Solar Radiation outside the earth's atmosphere changes throughout the year due to the change in the distance from the sun and the rotation of earth around its axis. The solar radiation outside the atmosphere is then calculated depending on the eccentricity correction factor ( ) and the day of the year (Luque and Hegedus,
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2011). According to (Duffie and Beckman, 2006),
depends on the distance of the
earth from the sun, which will vary by ± 1.7% of its mean value 1.495×10
11
, which is equal to
m. A simple equation for engineering proposes combines the change in
the day and distance and defines the solar radiation outside the earth's atmosphere as following:
Equation 1 Extraterrestrial Radiation
Where Gsc: solar constant, 1367 W/m2. n: is the day number of the year.
Figure 5: Earth Positions around the sun (Scharmer, 2000)
1.4 Geometrical Considerations: To put a formula to find the radiation received on the system's surface, tilted surface, by only knowing the total radiation on the horizontal surface. It is important to know the direction from which the beam or the diffused radiations are received. The geometrical properties should be studied. The next definitions and equations are used in the calculation later in this paper.
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1.4.1 The Declination Angle : It is the key input for the solar geometry. It is defined by (UNESCO and NELP, 1978) as "the angle between the Equatorial Plane and the line joining the centre of the Earth's sphere to the centre of the solar disk. The axis of rotation of the Earth about the poles is set at an angle to that so called Plane of the Ecliptic. "The angle varies along the Julian days between 23.45˚ and -23.45˚. The following equation relates to the declination angle and the day number n, along the year.
Equation 2 Declination Angle
1.4.2 Solar Hour Angle : According to (PEN, 2012), is the angular displacement of the sun east and west of the local meridian. It changes 1˚ each for minutes and 15˚ each hour. It changes 15˚ each hour after the solar noon and -15 each hour before the solar noon. The solar noon corresponds to the moment when the sun at the highest point in the sky. So the solar noon does not depend on the local time but on the solar time. The solar time can be found as following:
Equation 3 Solar Time
Where Lst is the standard meridian for the local time zone, L loc is the longitude of the specific location in degree. E is the equation of time in minutes which equals to:
Equation 4 E value.
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1.4.3 The Latitude angle : It is the angular location north of the equator as positive and south of the equator as negative. Its values range between -90˚ and +90˚.
1.4.4 The Sunset Hour angle: According to (RETScreen International, 2005) is the angle of the sun at the sunset solar hour. It can be found using the following equation:
Equation 5 Sunset Hour Angle
1.4.5 Slope Angle : This is the tilt angle where the Photovoltaic panel or array is tilted from the horizontal. Generally, as a rule of thumb, to collect maximum annual energy, a surface slope angle should be adjusted to be equal to the latitude angle. For the summer maximum energy gain, slope angle should be approximately 10˚ to 15˚ less than the latitude and for the winter, maximum energy gain can be acquired when the angle is adjusted to be 10˚ to 15˚ more than the latitude. (Duffie and Beckman, 2006).
1.4.6 Surface Azimuth angle : This is the deviation of the projection, on a horizontal plane, of the normal to the surface from local meridian. It is equal to zero when it is pointed to the south, negative to the east and positive to the west. It ranges between
.
1.4.7 Angle of Incident This is the angle between the beam radiation on a surface and the normal to that surface. It can be calculated as follows:
Equation 6 Incident Angle
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1.4.8 Zenith Angle
:
It is the angle between the vertical of the sun and the incident solar beam. Its value must be between 0˚ and 90˚. For a horizontal surface the zenith angle can be calculated using the following equation.
Equation 7 Zenith Angle
The following figure (6) illustrates the angles on a tilted surface. Please note that the previous equations will be implemented in a hand calculation for the total power output of the proposed system, later in this paper. The calculation will be done using Microsoft Excel.
Figure 6: Solar Geometry Angles (Duffie and Beckman, 2006).
1.5 Solar Radiations reaches a specific tilted surface The directions from which solar radiation reaches a specific tilted surface are a dependent on conditions of cloudiness and atmospheric clarity (Duffie and Beckman, 2006). Those radiations are considered to be distributed over the sky dome. In general, the data of cloudiness and clarity are widely available. Omar Hamdan | Kingston University London
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In this paper radiations have been dealt with as three parts; Beam radiation, Diffused radiations and Ground reflected or what is known as Albedo. The beam radiations are the amount of radiations that have been received on a specific surface without scattering; it will be represented as H b. The diffused radiations are those radiations, which their direction have been changed before they receive a specific surface. Finally, the ground reflected radiations are the radiations received on a specific surface after they have been reflected from the ground.
1.5.1 Clearness Index: The Clearness index gives a measure of atmospheric transparency. It shows the relation between solar radiation at the Earth's surface and extraterrestrial radiation. It is related to the path of which the solar radiations have been received on earth's surface, which will be illustrated in a later section, referred to as atmospheric AM value. It also represents the composition and the cloud content of the atmosphere (Luque and Hegedus, 2011). Thus, the Clearness Index is defined as:
Equation 8 Clearness Index
Where, and
is the monthly average daily solar radiation on a horizontal surface
is the monthly average extraterrestrial daily solar radiation, which can be
found from the following equation:
Equation 9 global Hourly irradiance on horizontal surface
1.5.2 Calculating of Hourly Global and Diffused Irradiance
To calculate the hourly irradiances, a developed method by Erbs et al and introduced by (Duffie and Beckman, 2006), was used. It is obvious that the amount of the diffused radiations will be a function of Kt, thus the theory developed the monthly average diffused fraction correlation. Equations for these correlations are as following, for
:
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Equation 10 Diffused Radiation Ratio ws ≤ 81.4˚
For
:
Equation 11 Diffused Radiation Ratio ws > 81.4˚
The average daily irradiance is now broken into hourly values. To do so, the equation developed by Collares-Pereira is used in the calculations. The formulas are as following:
Equation 12 Average Daily irradiance
Where
is:
Equation 13 rt ratio
Where (a) and (b) are values can be found as follows:
Equation 14 constant a
Equation 15 constant b
Note that the values of sunset angle and the hour angles are in radians. Then the values of both the diffused and the Beam irradiances can be calculated as follows:
Equation 16 Diffused irradiance
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Equation 17 Beam irradiance
can be found using this equation:
Equation 18 rd ratio
The calculation of the total hourly irradiance is a combination of the three irradiances values; the beam irradiance, diffused irradiance and the ground reflectance. This equation was developed upon an Isotropic Model, which had been derived by Jordan and Liu in 1963 (Duffie and Beckman, 2006). The equation equals to:
Equation 19 Total irradiance on tilted surface
Where:
Equation 20 Rb Value
Moreover,
is the average diffused ground reflectance, Albedo.
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Chapter Two
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2.1 System Components 2.1.1 Solar Cell Basics: The Solar cell is a solid-state device that absorbs light and converts part of its energy- directly into electricity. The process is done within the solid work structure; the solar cell does not have any moving parts (Richard J. K., 1995). The photovoltaic cell is manufactured by combining two layers of semiconductors differently doped, a p-type and an n-type layer. The combination will result of a matching between holes and electrons which will lead to creating a potential layer. This is why the solar cells are usually referred to as "Photovoltaic cells", the photovoltaic effect. Photovoltaic effect is the electrical potential, developed between the two dissimilar materials. When the two dissimilar material's common junction, or what is called the depletion layer, is illuminated with radiation of photons, thus an electrical potential gradient will be created (Mukund R. P., 1999). Each photon, if it has enough energy, is capable of releasing an electron, which has a negative charge, or creating a hole, which has positive charge. The accumulated process will result in a current and potential difference on cell's sides, the p-type and the n-type. The released electrons will be accelerated because of the resultant gradient, which is called Fermi level, and can then be circulated as a current through an external circuit, see figure (7) (Mukund R. P., 1999).
Figure 7: Schematic of a solar cell. The solid white lines indicate the conduction and valence bands of the semiconductor layers; the dotted white lines indicate the Fermi level in the dark.
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2.1.2 Light characteristics All electromagnetic radiations can be viewed as being composed of particles called Photons. According to the theory of quantum, the photons are particles that travel in vacuum with the speed of light and have no mass. Each photon carries specific amounts of energy as a packet, referred to as an electron volt (ev). The amount of energy is related to the proton's source spectral properties. The shorter the wavelength of the proton, the larger the packet (Richard J. K., 1995). The sunlight spectral is divided into three regions see figure (8). The first region has a wavelength between 400 to 700 nanometres. At 700 nanometres, the visible spectrum appears red and on the shorter end of 400 nanometres it appears violate. All other colours appear in between. Our eyes are most sensitive to the spectrum around 500 nanometres. At 400 nanometres and less, the spectrum is called Ultraviolet (UV) wavelength and most of it is filtered or absorbed by the Ozone or the transparent material before it reaches the earth's surface. Our skin perceives the spectrum as radiant heat spectrums above 700 nanometres, which is referred to as Infrared (Clark and Eckert, 1975). The water vapour, CO2 and other substances in our atmosphere absorb most of the Infrared spectrums. On the other hand, Most of those absorptions become longer wavelengths than the wavelengths the solar system uses. While the solar system effectively collects wavelengths less than 2000 nanometres, thus its efficiency is not significantly affected (Duffie and Beckman, 2006). Photon's energy can be calculated as follows:
Equation 21 Photon Energy
Where
is the wavelength,
speed of light (
is Plank's constant (
) and
is the
m/s).
As well as this, the energy held by a photon is affected by Air Mass. The Air Mass is the path length which light takes through the atmosphere normalized to the shortest possible path length (the shortest path is when the sun is directly overhead). The Air Mass quantifies the reduction in the energy of light as it passes through the atmosphere and is absorbed by air, dust, ozone (O3), carbon dioxide (CO2), and water vapour (H2O) with the last three having a high absorption for photons that have Omar Hamdan | Kingston University London
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energies close to their bond energies. The air mass (AM) is defined using the following equation (noting that
is defined later in this paper):
Equation 22 Atmospheric Mass
Figure 8: Light wavelength ranges
2.1.3 Electrical Characteristics of a PV-Cell: A PV cell equivalent circuit is similar to that of the diode, since they have similar structures. A photovoltaic cell is considered as a current generator and can be represented by the equivalent circuit of Figure (9). The current I at the outgoing terminals is equal to the current generated through the PV effect I PV by the ideal current generator, decreased by the diode current Id and by the ground leakage current Ish. The resistance in series Rs represents the internal resistance to the flow of generated current and depends on the thickness of the junction P-N, the present impurities and on contacts resistances. The shunt resistance Rsh takes into account the current to earth under normal operational conditions. In an ideal cell the values of Rs is zero while the value of Rsh is maximum. On the contrary, in a high-quality silicon cell the typical value of Rs is around five milliohm and the shunt resistance is around 285 ohm. The conversion Omar Hamdan | Kingston University London
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efficiency of the PV cell is greatly affected also by a small variation of R s, whereas it is not affected by the variation of Rsh too much.
Figure 9 Equivalent circuit of Photovoltaic
The no-load voltage Voc, open circuit voltage, occurs when the load does not absorb any current, i.e. IL equals zero, thus according to ohms law, the open circuit voltage will be the current passing through the shunt resistance, times the shunt resistance Voc =IshRsh (Luque and Hegedus, 2011) In addition, the diode current is given by the classical formula for the direct current:
Equation 23 Diode current
Where: ID is the diode's saturation current, Q is the charge of the electron (1.6×10-19 C), A is the identity factor of the diode and it depends on the recombination factor between the holes and electron inside the diode itself (for crystalline silicon it is about 2). K is the Boltzmann constant (1.38×10 -23 J/K). Finally, T is the absolute temperature in Kelvin degree. Therefore, the current supplied to the load is given by:
Equation 24 current delivered by the photovoltaic panel
The final term, the ground-leakage current, in practical cells is small compared to Iph and ID, thus it can be ignored. The diode-saturation current can be Omar Hamdan | Kingston University London
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determined experimentally by applying the open circuit voltage Voc in the dark (when Iph is zero) and measuring the current going into the cell. This current is usually referred to as the dark current or the reverse diode-saturation current. (Mukund R. P., 1999). The voltage-current characteristic curve of a PV module is shown in Figure10. The generated current is at its highest under short-circuit conditions (Isc), whereas with the circuit open, the voltage (Voc=open circuit voltage) is at the highest. Under the two of those conditions, the electric power produced in the module is equal to zero, whereas under all the other conditions, when the voltage increases, the produced power rises too; at first, it reaches the maximum power point (Pm) and then it falls suddenly near to the no-load voltage value. (Sera, D et al, 2007)
Figure 10 Voltage-Current characteristics example (ABB, 2010)
In summary, the electrical characteristics needed to be known about for a photovoltaic module is as follows:
Isc short-circuit current;
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Voc no-load voltage;
Pm maximum produced power under standard conditions (STC);
Im current produced at the maximum power point;
Vm voltage at the maximum power point;
FF filling factor: this is a parameter which determines the form of the characteristic curve V-I. It can be defined as the actual maximum power divided by the ideal power value; the ideal power is that value that would be obtained under ideal conditions. i.e. when the voltage is equal to the open voltage and the current is equal to the short circuit current. The filling factor is:
Equation 25 Filling Factor
It should be pointed that all those data can be found in the manufacturer data sheet. Most of the information is experimentally distinguished. There are some methods to calculate the series resistance value but it will not be needed in this paper, thus it will not be presented.
2.1.4 Voltage and Current in PV Plant PV modules generate a current from 4 to 10 A at a voltage from 30 to 40 V. To achieve the projected peak power, the panels are electrically connected in series to form the strings, which are connected in parallel. The trend is developing strings constituted by as many panels as possible, given the complexity and cost of wiring, in particular of the paralleling switchboards between the strings. The maximum number of panels which can be connected in series (and therefore the highest reachable voltage) to form a string is determined by the operational range of the inverter and by the availability of the disconnection and protection devices suitable for the voltage reached. In particular, the voltage of the inverter is bound, due to reasons of efficiency, to its power. Generally, when using inverters with power lower than 10 kW, the voltage range most commonly used is from 250V to 750V, whereas if the power of the inverter exceeds 10 kW, the voltage range usually is from 500V to 900V. (ABB, 2010)
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2.2.0 Electrical Power Output: The electrical power output of the system will depend on three values, the total hourly irradiance, and the efficiencies of the electrical components used and the total area of the panels. The values of total hourly irradiance will be found as described previously in this thesis. The efficiency of the Photovoltaic's arrays will be characterised by the average module temperature T c. Thus, the efficiency will depend on the ambient temperature (RETScreen International, 2005). The efficiency equation using the calculation for this study purpose is as follows:
Equation 26 Cell temperature effect on the cell Efficiency
Where
is the temperature coefficient for the module efficiency and
and
are the efficiency and the temperature of the panel under the Standard Testing Conditions (STC). Normally the testing temperature is equal to 25C˚. In addition, the standard testing conditions will define the Nominal Operating Cell Temperature NOCT. NOCT values normally ranges from 42C˚ to 46C˚ (Luque and Hegedus, 2011). The average module temperature T c is related to the mean monthly ambient temperature through the following equation, which had been developed by Evans in 1981 (Duffie and Beckman, 2006):
Equation 27 Ambient temperature relation with the cell temperature
Furthermore, the equation above is valid when the tilting angle is equal to the latitude angle minus the declination angle, when the tilt angle is different, then the right side of the equation has be multiplied by a correction factor defined as C f. (RETScreen International, 2005). It can be found using the following equation:
Equation 28 tilt angle correction factor for the cell temperature
Where sM is equal to the latitude angle minus the declination angle and s is the current tilt angle. Omar Hamdan | Kingston University London
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On the other hand, STC efficiency will vary for each type of module. In general, the efficiency values range between 5%, for example for a module of a-Si type, up to about 15%, for example a mono-crystalline silicon module. Finally, the power output of the PV generator can be defined as the total reached irradiances multiplied by the final efficiency
and the total area used S. The
equation can be shown below:
Equation 29 Energy supplied to the building and the electrical grid
To calculate the electrical power delivered by the PV generator, which is received by the building or the grid, the EP must be multiplied by the inverter efficiency and the electrical losses due to the wiring. As well, other miscellaneous losses of the BOS should be deducted from the total power production (RETScreen International, 2005). In later sections, a method to calculate the power output will be presented and illustrated systematically giving one example of the whole system. The codes and work sheet of the hand model can be found in the appendix A.
2.3.0 Components Selection PV panel In order to optimise the system for the best conditions, it is highly required to choose the most suitable component in the system. Reliable, high efficient and low cost components are the optimal components to choose. In the following, the detailed process for the main component selection is presented. There are many kinds of photovoltaic panels which vary in material used, technology, manufacturing process and size. Looking into the features of each panel then comparing it with its price and its installation cost can be a very difficult process, especially if the life time of the PV panel, warranty, market availability and efficiency are taken into account as well. Therefore, the selection process can be narrowed by specifying the priority features needed in the panel.
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2.3.1 PV Panel Selection Methodology The selection of the PV panel for this project was based on three aspect as priority features; the efficiency of the photovoltaic panel, the panel price and the market availability. In addition to those characteristics, an additional facet took priority when the economical evaluation had been completed. The project life-time needed to be increased because the payback and the breakeven level of output, was found to be longer than 20 years. Hence, the PV panel life-time and the entire project studies have been extended to 25 years.
2.3.2 Chosen Panel The panel which has the highest efficiency is mostly mono-crystalline, thus the panel's types have been narrowed by only mono-crystalline panels. One of the most established, experienced brands in the market of manufacturing panels is SHARP, when the panel specifications have been studied, and only the panels with life-time of 25 years are used. They had a higher level of efficiency was compared to the other panels in the market. The panel is mono-crystalline which has 14.14% efficiency and lower sensitivity to the variation of the temperature, the voltage variation is only a decreasing of 104 mV/˚C. The peak power of the panel is 185 W P. The voltage at maximum power point is 24 while the current is 7.71 Amp. The filling factor is 71.75%. The Nominal Operation Cell Temperature (NOCT) is 47.5 ˚C. The Panel dimensions as show in figure 11 is 1.318×0.994 m. the panel has a bypass diodes which, as mentioned before, will minimise the loss in output when shading occurs. The panel behaviour with different irradiances is shown in figure 12. Additional data about the panel which might be useful for the installer:
156.5 mm × 156.5 mm mono-crystalline solar cells
48 cells in series
2,400 N/m2 mechanical load-bearing capacity (245 kg/m2)
1,000 V DC maximum system voltage
IEC/EN 61215, IEC/EN 61730, Class II (VDE: 40021391) Finally, a vital point need for economical evaluation purposes; a full
performance of the panel is guaranteed for five years, a 90% of the full performance Omar Hamdan | Kingston University London
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for ten years and an 80% for twenty five years. Therefore, it will be possible to extend the project life time to twenty five years. (A detailed data sheet is attached in appendix C for the reader to refer to if needed).
Figure 11 Selected Panel Dimensions
Figure 12 photovoltaic panel curves with different irradiances.
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2.4.0 Inverter and Control 2.4.1 Maximum Power Point Tracking (MPPT): A maximum Power Tracker is a device that keeps the impedance of the circuit of the cells at levels corresponding to best operation. It also converts the resulting power from the PV array, so its voltage is that required by the load. There is some power losses associated with the power tracking process Any PV array, however its size or sophistication, is only capable of producing Direct Current (DC) power, thus for the system to be integrated into the building it is necessary to have a methodology to convert the produced DC power into the building integrated AC power system. The DC to AC Inverter, sometimes referred to as converter, is used to achieve this function. The System might require more than one inverter depending on the system size and sophistication.
2.4.2 Connection of Inverter to Array For many systems, a three-phase inverter is used. In addition, in some cases, single phase inverter is only needed with a final decision taken by knowing whether the grid supply is single or three phases; this is because the system should be coupled with the electrical grid. The system can be connected to the inverters with three deferent methods depending on the rating of both the PV Generator and the inverter. The first method is a single inverter plant, which might consist of single or several strings; a string is a connection of many modules to form one DC output, positive wire and negative wire. The single inverter plant implies that the rating of both the PV generator and the inverter required is relatively small. This method has many advantages in terms of lower investment cost and low maintenance; but on the other hand, using one inverter will reduce the reliability of the system since a total stoppage of power production will occur in case of inverter failure. In addition, this solution is not suitable for increasing the size of the system, since these increases the problems of protection against over currents and the problems deriving from different shading that is when the exposition of the panels is not the same in the whole plant (Esram and Chapman, 2007).
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The second method is to have many strings with an inverter for each string. In this layout, the blocking diode will prevent the source direction from being reversed; it is usually included in the inverter. The diagnosis on production is carried out directly by the inverter, which in addition can provide protection against the overcurrent and under-voltage on the DC side. Moreover, having an inverter on each string will reduce the coupling problems between the modules and inverters and the reduction of the performances caused by shading or different exposition. Again, in different strings, modules with different characteristics may be used, thus increasing the efficiency and reliability of the whole plant. (Esram and Chapman, 2007). Finally, the last method is to have a combination of large-size plants, the PV field is generally divided into more parts (subfields), each of them served by an inverter of one’s own to which different strings in parallel are connected. In comparison with the layout previously described, in this case there are a smaller number of inverters with a consequent reduction of the investment and maintenance costs. However it maintains the advantage of reducing the problems of shading, different expositions of the strings and of those due to the use of modules that are different from one another, if subfield strings with equal modules and with equal exposition are connected to the same inverter. Besides, the failure of an inverter does not involve the loss of production of the whole plant (as in the case of singleinverter), but of the relevant subfield only. It is advisable that each string can be disconnected separately, so that the necessary operation and maintenance verifications can be carried out without putting the whole PV generator out of service. When installing a parallel switchboard on the DC side, it is necessary to provide for the insertion on each string of a device for the protection against over-currents and reverse currents so that the supply of shaded or faulted strings from the other ones in parallel is avoided. Protection against over-currents can be obtained by means of either a thermo-magnetic circuit breaker or a fuse, whereas protection against reverse current is obtained through blocking diodes. With this configuration, the diagnosis of the plant is assigned to a supervision system, which checks the production of the different strings (ABB, 2010).
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2.4.3 Inverter, process and Functions Inverters take a great role in photovoltaic electrical production; the inverter makes it possible to convert the DC power to an AC power used in the building's systems. It will add a great flexibility with dealing with the produced power since the dealing with DC power can often be difficult and dangerous. It is important to present a brief introduction about the inverter in order to be able to understand the basic methodology of how the inverter works. The circuit used in the inverter is usually a three phase bridge inverter. This circuit is used to convert the DC power to three phase AC power, which will make it easy to connect, and to, integrate, the whole new photovoltaic system into the existing system in the building. Moreover, after integrating both systems together; it is possible to connect their integration to the electrical grid through a bidirectional kWh meter to calculate the spending and selling. The typical circuit used in the inverter can be seen in figure 13.
Figure 13 typical circuit used in PV inverters.
The process of inverting the DC power to an AC power inside the inverter is done using mostly a Pulse Width Modulator PWM to great a sinusoidal AC output. The process can be explained using figure 13. The battery in the figure represent the PV panels production, they are connected to the inputs of three legs, two transistors, and are protected from the reverse current by a diode connected in parallel with each of them. The DC voltage should be converted to a three phase, lines, AC output, therefore, each transistor, of the six transistors, will be triggered sequentially by a controller. The controller has a reference PWM wave, Sinusoidal
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form. The controller will trigger one of the transistors in a process and will form three phase AC power. Each of the phases is shifted by 120˚ electrical degree. Furthermore, in this process the inverter is able to vary the voltage and frequency at the output. For the case of building integration, the frequency required to be fixed to either 50 Hz in the UK or 60 Hz in other places. On the other hand, the inverter need to be able to cope with the variation in the voltage level, hence the PV generator, relatively, does not have a fixed voltage. The voltage variation can be due to the change in the temperature of the cell or due to the voltage drop caused by the resistance of wiring. The output wave ought to be filtered to lower the effect of any ripples or harmonics, which might be caused during the conversion process.
2.4.4 Component Selection, Inverter In conjunction with the photovoltaic panel, the selection of an optimal inverter to use for the project can be a difficult process since there are many issues to be considered. One of the main issues when selecting an inverter is to consider the Maximum Power Point Tracking MPPT voltage range which might affect the final performance of the system. Any inverter with MPPT will be able to optimally decrease the effect of shadowing. In order to select a suitable inverter to be used in the system, some aspects should be considered. The capability of the inverter to cope with the variation in voltage is an important matter. The system size is determined according to much iteration to evaluate the system technically and economically. According to the system size the inverter rated power will be distinguished. Therefore, the options to choose an inverter will be limited to a certain level. It is better to choose an inverter rating half the system size. In this way, two inverters will be installed instead of one. The main purpose of this is to increase the reliability of the system. When one of the inverters is out of service only half of the system is lost. Under certain circumstances, one inverter could be selected, especially if the system rating is low. The inverter type chosen for this project is going to be able to handle the whole system solely, since the system size is relatively small compared other projects. After considering many aspects the system's voltage and current have been Omar Hamdan | Kingston University London
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stated. Hence, the voltage rating is also known. The system voltage is ranging between 540 V and 576 V, 576 V to be the maximum power point voltage. Now, the options to choose an inverter, are narrowed, due to the fact that only the inverters have voltages around this range. ±25% of the maximum and the minimum voltage are considered as a good estimation because a margin of variation above or below the maximum or the minimum level must be considered. Finally, the market availability, quality guarantee and the cost should be taken into account.
2.4.5 Summary In summary, the selection of the inverter, depending on size, is carried out according to the PV array rated power that the inverter should manage. The size of the inverter can be determined, from 0.8 to 0.9 for the ratio between the active power delivered to the network and the PV generator. This ratio considers the power under real operational conditions (working temperature, voltage drops on the electrical connection...etc) in addition to the efficiency of the inverter itself. Finally, the choice of correct size, for the inverter, must be done by taking the following considerations: - DC Side:
rated power and maximum power;
rated voltage and maximum admitted voltage;
variation field of the MPPT tracking voltage under standard operating conditions;
- AC Side:
rated power and maximum power which can be continuatively delivered by the conversion group, as well as the field of ambient temperature at which such power can be supplied;
rated current supplied;
maximum delivered current allowing the calculation of the contribution of the PV plant to the short circuit current;
maximum voltage and power factor distortion;
maximum conversion efficiency;
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Efficiency at partial load and at 100%.
- Other:
Market availability
Life time
Cost The chosen inverter is a tri-phased Sinvert 60 M from Siemens with 50 Hz
frequency and has a nominal power of 65 kVA (apparent). The inverter has a minimum MPP voltage of 450 V and a maximum MPP voltage of 750 V. The power conditioning unit consists of Isolated Gate Bipolar Transistor (IGBT) inverter, DC/AC distribution, isolating transformer and a controller number SIMATIC S7. It also has a MPP tracking for optimum utilisation of PV field power. In addition, it has an optional Voltage Ampere Reactive (VAR) controller for three-phase network. The unit comes with a control panel with display of operating states and actual values for the user to interface in order to set the parameters of the inverter. Furthermore, it does have a switch-over in both manual and automatic mode by integrated key-switch. Moreover, the following features are included in the unit, isolation monitoring with selective fault allocation and safety disconnection; visualization and service software Power Protect solar; interface for process visualization and an optional integration in management systems via Ethernet, cabinets for floor mounting, forced ventilation by fan, air intake through lower cabinet front and cabinet bottom, air discharge through the cabinet roof; cable entry at base from. Figure 14 shows the component's internal combination. Figure 15 shows the process in PWM to convert the DC power to an AC power.
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Figure 14 inverter combination
Figure 15 PWM DC to AC process
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2.5.0 Shading: Taking into consideration the area occupied by the modules of a PV plant, part of them (one or more cells) may be shaded by trees, fallen leaves, chimneys, clouds or by PV panels installed nearby. In the case of shading, a PV cell consisting in a junction P-N stops producing energy and becomes a passive load. This cell behaves as a diode, which blocks the current produced by the other cells connected in series, thus jeopardizing the whole production of the module (Seung-Ho and EunTack, 2002). Moreover the diode is subject to the voltage of the other cells which may cause the perforation of the junction due to localized overheating (hot spot) and damages to the module. In order to avoid that one or more shaded cells prevent the production of a whole string, some diodes which by-pass the shaded or damaged part of module are inserted at the module level. Thus, the functioning of the module is guaranteed even if with reduced efficiency. In theory, it would be necessary to insert a by-pass diode in parallel to each single cell, but this would be too onerous for the ratio costs/benefits. Therefore, by-pass diodes are usually installed for each module (Kajihara and Harakawa, 2005). See figure 16
Figure 16 By-Pass diode under shading
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Chapter Three
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3.1.0 Project Demand and Hand Calculations This approach is to decide whether the system will be feasible or not. The feasibility study will be done through a hand calculation and system simulation using PVsyst. The Use of both methods; hand and simulation will make it easier to decide the system size and specification. In addition, the hand calculation will present a power output at an hourly pace which then can be compared with hourly demand if available. The hand calculation will make it easier to predict the hourly share of the proposed system to set an economical plan for the building. The first section will describe the hand calculation of the system. The calculation will use one day, as an example to demonstrate the method. Starting with only one monthly value, for each month, the hand calculation will find the hourly estimated power output throughout the day, then, the estimated daily total kWh that can be produced. It is important to note that the hand calculation does not consider the system losses, since it is going to be considered in the simulation more precisely. The simulation will be produced using PVsyst, as quoted from the user help booklet of the program, "PVsyst is a PC software package for the study, sizing and data analysis of complete PV systems. It deals with grid-connected, stand-alone, pumping and DC-grid (public transport) PV systems, and includes extensive meteorological and PV systems components databases, as well as general solar energy tools."(PVsyst., 2012) Comparison between both calculations will be presented.
3.1.1 Process of progression: The system to be proposed will be installed in Kingston University London, Roehampton campus. The campus is positioned at 15° 26ˈ and -00° 15ˈ latitude and longitude. The system proposed is to integrate a photovoltaic system with the existing electrical system. The main objective of the project is to, fully or partially; supply the facility’s electrical demand throughout the year. This will be done by: This chapter: -
Calculating the system demand and electric system review,
-
Calculating the hourly solar radiation on the system,
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-
Hand Calculation the hourly electrical power produced annually,
-
Optimising the area used and evaluating the available options, system sizing, Next Chapters:
-
Calculating the monthly power production, losses and shading effect using a simulating program,
-
Electrical consideration and power layout,
-
Economical Evaluation of the project,
-
Comparison of the hand calculation and the simulation results,
The integration of a PV system with a building will be carried out while carefully considering all the aspects.
3.1.2 Overview, System Demand and Electrical System Review: The site consists of a main building, which is composed of a library, lecture rooms, and engineering laboratories, and a secondary building, which mainly consists of lecture rooms. The building’s total area is approximately 4730 m2, the total useful area, which is above the main building, is around 3030 m2. The electrical load main consumptions are air chillers, laboratories machines, wind tunnel; which is used for experimental purposes and derived by two main electrical motors, lights, personal computers and printers. Similar to all the building's systems in the UK, the facility has 240 Volt/ 50 Hz electrical systems, which will be supplied through a three phase main incomer connected on the main board with electrical meters. The main electrical board is located at the east gate of the building. This main incomer is supplying both buildings through two sub-boards and connected to monitoring system. The calculation of the electrical demand of the facility had been carried out based on electrical monthly bill readings over a period of three years. This monthly bills had been converted from kWh consumption to kW consumption. The final monthly demand is shown in figure 17 and table 1. For the sake of comparison, the electrical demand is kept in kWh in later sections. Omar Hamdan | Kingston University London
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400 300
Monthly Average System Demand
200
December
November
October
September
August
January February March April May June July
100 0
Figure 17 system demand in kW Table 1 System Demand kW
Month January February March April May June July August September October November December
Electrical Demand (kW) 345.4943727 324.6823017 264.0997798 200.4881069 182.0981522 152.2148372 156.0801467 164.6080031 219.5328399 287.221441 355.4871879 341.3481184
The data in both the figure and the table above shows the variation of the electrical demand from one month to another. It can be shown that the highest demand had been consumed in November while the least consumption takes place in June. This situation, unfortunately, contradicts with the incident solar radiations during each month, i.e. the highest measured incident solar radiation occurs in June and July when the lowest electrical consumption takes place, and the lowest measured incident solar radiation occurs in November, December and January. This is why system sizing should be carried out with cautious consideration of all the aspects, since the main purpose of the project is only to supply the facility consumption. Not taking this into account would lead to an unnecessary increase of the investment cost. This point shall later be discussed in detail.
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3.2.1 Hand Calculation: The hand calculations have been done using a Microsoft Excel data sheet. All the data and the codes can be found in appendix A. The calculations have been done for all the days in the same method; therefore, one-hour example will be presented to demonstrate the methodology of the power output calculation followed. Power output calculation for a specific site will predict the long term system performance. Many methods have been developed to calculate the power output of a PV system. (Duffie and Bickman, 2006) demonstrated many theories, (the reader can refer to this reference for further reading). For the purpose of this project, one method has been selected for implementation, with occasional adjustments from other theories.
3.2.2 Summary and Assumptions: The aim of this calculation is to estimate the total irradiance on a tilted surface with knowledge of only one value of, average monthly radiation on a horizontal surface. Location latitude and the slope angle are primarily data in addition with the monthly average radiation. Knowing that solar constant is equal to 1367 W/m2 will make it possible to find the extraterrestrial radiation on a horizontal surface and likewise, the clearness index. Ideally, the building should be oriented to the south to optimally make use of the direct (beam) and diffuse radiation throughout the year. However, as the system is planned to be installed on an already built building's surface azimuth angle might be considered if the building conditions does not allow a south facing system. The buildings for the proposed system do not face south, but south-east (SE) with an angle estimated to be approximately 23.2˚ from the south or 156.8˚ from the north. The surface azimuth angle is calculated from the south, thus the used angle in the calculation will be 23.2˚. The average daily monthly radiation on September is 2800 Wh/m2. The selected day is the 3rd of September and the selected hour is between 12:00 and 13:00 (day time). The ground reflectance can be found in the NASA solar database and its average for September is 0.09. Monthly ground reflectance (Albedo) can be seen in table 2.
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Month
Albedo Value
Month
Albedo value
January
0.1
July
0.11
February
0.1
August
0.1
March
0.09
September
0.09
April
0.10
October
0.08
May
0.11
November
0.10
June
0.11
December
0.10
3.2.3 Calculating the hourly solar radiation on the system: The hourly solar radiations that fall on the system will be calculated using the methodology mentioned in previous sections of this paper. The calculation for one hour in one day will be presented. The selected day is the 3rd of September and the selected hour will be between 12:00 and 13:00 (day time).Table 3 shows the monthly global irradiation data on the proposed location and its general information, while table 4 shows the day information. All the metrological data is taken from European Commission (EC) solar database. It should be established that this calculation is done to find the maximum power production in this specific day and hour based on the final total useful area calculated later in area assessment section, 408 m2. The optimal area is found after many iteration calculations to size the system. Table 3 illustrates the basic information about the day of the study and the specific hour, which has been carried out as follows.
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Month
H Wh/m2
Day Time Ave. Temperature C˚
Ave. Temperature C˚
Albedo
Jan
736
5.9
5.2
0.1
Feb
1360
6.5
5.8
0.1
Mar
2210
8.2
7.2
0.09
Apr
3680
10.4
9.4
0.1
May
4650
13.5
15.6
0.11
Jun
4820
16.4
15.6
0.11
Jul
4860
18.7
17.8
0.11
Aug
4140
19.2
18.2
0.1
Sep
2800
16.7
15.5
0.09
Oct
1690
13.3
12.2
0.08
Nov
902
9
8.1
0.1
Dec
527
6.1
5.4
0.1
Year
2697.916667
12
11.1
0.099
Table 4 Site Data and Calculated information for one hour of the year
Global Irradiation On Horizontal Plane (Wh/m2)
2800
Day Length
13.174 Equals to 13h 27m
Day of Month
3
H0 (J/m2)
28688146
Month
9
H (J/m2)
10080000
Day of Year
246
Kt
0.351365
Declination Angle
6.958˚
Hd/H
0.593271
Latitude Angle
51.43˚
Hd (J/m2)
5980176
Tilt Angle
51˚
Sunrise (hours)
06:16
Azimuth Angle
-23.2˚
Sunset
19:43
Cos (Ws)
-0.153079527
Solar Noon
13:00
Sunset Angle Ws
98.80543208˚
Hour Angle W
7.5˚
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3.2.4 Calculation: All the calculation is done on the 3rd day of September thus the day number is 246. Latitude angle is 51.43˚. Declination angle can be calculated from equation 2 as following:
To find out the sunset angle equation 5 can be used as the following:
The daily extraterrestrial radiation on a horizontal surface has been calculated using the following:
To find the clearness index, equation 8 can be applied. However, before, the value of the average radiation on a horizontal surface, should be calculated in J/m 2, thus, the value in Wh can be multiplied by 3600 to be 10.08 MJ/m 2. Now, the clearness index can be found as following:
Now, to find the percentage of diffused radiation to the global radiation, equation 10 or equation 11 can be applied depending on ws. In the studied hour case equation 10 should be used.
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The diffused radiations can be found by multiplying this ratio by the global irradiation on a horizontal surface.
Sunrise hour and sunset hour has been calculated for this day to be 6:16 and 19:43 consequently. The length of this day is found to be 13 hours and 27 minutes. The solar noon takes place at 13:00. (Note that all those values are at the local time, and consider the one hour shift forward to start at 25th of March and ending at 28th of October). To calculate the hour angle, as mentioned before, the hour angle is -15˚ for each hour before noon and +15˚ for each hour after the solar noon. In the case of the example, the hour intended to find the power output at, is between 12:00 and 13:00, local time. While the time used is local time and is shifted one hour forward, the solar noon should be calculated according to one hour earlier. The solar noon occurs at 12:00 exactly, 13:00 at the local time, thus the hour angle between 12 and 13 becomes the hour angle between 11 and 12. It is thus calculated to be -15/2, which is -7.5˚. Now, Collares-Pereira's equation can be used to break the daily radiation into an hourly global irradiance. The equation applied in the hand calculation is as follows:
So rt is found as follows
Constant (a) and constant (b) is found as follow, noting that the angles are used in radians. For ws = 98.81˚, the angle in radians equals to 1.724, thus:
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And (b) found as follow:
So, rt can be found to be:
The hourly diffused irradiance can be broken down using the Jordan and Liu equation:
So,
And:
The final irradiance on a tilted surface can now be found using equation 19, introduced by Jordan and Liu (Duffie and Beckman, 2006) mentioned. Considering the slope angle of the PV panel to be 51˚, this can be used as following:
Where
thus,
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And,
Then, this value can be found in Watt as the following:
This is the maximum power that can be extracted from the sun at the latitude mentioned and the specifications stated. Now the electrical power output depends on the efficiency of the PV panel and its efficiency variation with the ambient temperature. Furthermore, the electrical connection and the electrical losses will take an effect on the power output mentioned. Those calculations were done using a simulation program which will help to design the system's specification more accurately. Finally, it is important to show the effect of the temperature on the PV panel's efficiency, thus calculations were carried out, whilst consider the power output. It can be presented for the case study stating that the efficiency is going to change according to the internal temperature T c of the PV cells. Each material and each manufacturer type PV will vary differently according to its internal temperature. The ruling coefficient for this change is the
, the temperature coefficient for efficiency.
The PV used in this project has a maximum power point voltage equal to 24 Volts. The temperature coefficient for open circuit voltage is equal to -104 mV for each ˚C degree. From this data the efficiency temperature coefficient can be found, due to the relationship between the voltage and efficiency being linear. Thus the efficiency coefficient is:
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The relationship between the efficiency and the internal temperature is stated in equation 26. Applying it to the studied hour will need to find the value of T c which in its place will vary according to the ambient temperature. The average ambient temperature of September is 16.7 ˚C. The reference PV efficiency is found under Standard Testing Conditions (STC), while under those conditions, the temperature is known as Nominal Operation Cell Temperature (NOCT). The slope angle that used in calculation does not equal to the latitude angle minus the declination angle. In this case a correction factor should be used by applying equation 28, the optimal angle for Cf is equal to 44.0421˚, so:
The PV selected has a NOCT equals to 47.5 ˚C. Equation 26 can be applied to find Tc as following but the first part, excluding T a, has to be multiplied by Cf as following:
Now, efficiency equation that relates the temperature with the reference temperature can be applied:
Finally, the final power (W/m2) can be found. The power produced between 12:00 and 13:00 on the 3rd of September, when using the specified PV panel, is:
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The system will produce, at the specified time, 22708.4047 Wh when the optimal area is used. The optimal area is calculated for the site to be 408 m 2. (see the area assessment section for more details about the system size and area assessment).
3.2.5 Hand Calculation Results and Analysis: The hand calculations offer a great material for study and analysis. The site data is available with the exception of some sophisticated calculations such as shade assessments, which will be conducted using a simulation program and will be presented in later sections. The day length has an impact on the produced power throughout the year, and the variation of the day length is going to affect the delivered demand. In summer months of longer days, the production is expected to increase. The change in day length is shown in figure 18. The relation between the clearness index and the diffuse radiation ratio is shown in figure 19. The relationship between the clearness index changes throughout the year and diffused radiation ratio is taking a linear shape. See figure 19. It can be seen that the clearness index is governing the diffuse ratio since the diffuse radiation amount is affected by the amount of dust, gases and water vapour. As mentioned before, the hourly irradiance on a tilted surface was calculated. Its profile alongside the day changes with the day hours. Average irradiance H t for each hour can be seen in table 5 and figure 20. In table 5, the maximum average irradiance occurs at 12:00 in August. The irradiance average acts according to the day hours as expected. This, thus, indicates that the results are correct.
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Hours/day
Monthly Average Daily Daylight Hours 17 16 15 14 13 12 11 10 9 8 7 6
16.30805395 15.38278881 15.86715824 14.31161552 13.62388931 12.33584107 11.59721747
10.31258186
9.685236872
8.567491142
8.187874362
7.687702537
Month
Kt
Figure 18 Day Length for each month
1 0.95 0.9 0.85 0.8 0.75 0.7 0.65 0.6 0.55 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0
0.504399652
0.256432765
0.35
0.4
0.45
0.5
0.55
0.6
Hd/H
Figure 19 Clearness Index and the diffused radiation ratio
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0.7
0.75
Kt vs. Hd/H
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Table 5 Irradiance Ht according to day hours for each month along the year.
Hour
Janua ry
Febru ary
Marc h
April
May
June
July
Augu st
Septe mber
Octo ber
Nove mber
Dece mber
4.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
5.00
0.00
0.00
0.00
1.87
2.75
1.92
0.00
0.09
0.00
0.00
0.00
0.00
6.00
0.00
0.00
95.39
85.27
0.00
0.00
0.00
176.4 5 239.5 3 310.2 7 350.0 4 362.8 3 347.7 6 305.8 7 240.0 1 154.6 9
195.5 3 280.8 0 346.3 4 387.6 7 401.9 8 388.2 7 347.5 0 282.4 4 197.5 3
196.2 1 308.5 9 402.2 9 470.9 3 509.8 1 516.2 8 489.8 9 432.4 5 347.8 8 241.9 5 121.8 9
102.0 8 220.8 9 329.7 7 421.3 0 489.2 2 528.8 9 537.6 2 514.7 9 461.9 7 382.7 6 282.5 8 168.2 6
39.76
0.00
113.0 1 222.3 7 322.1 0 405.3 8 466.5 3 501.3 7 507.5 3 484.5 7 434.0 8 359.5 0 265.9 1 159.7 1
83.51
7.00
113.7 1 233.7 8 342.5 5 432.5 8 497.7 3 533.5 6 537.6 1 509.6 1 451.4 6 367.1 5 262.4 2 144.4 2
207.8 9 323.0 7 419.5 1 490.6 3 531.5 6 539.5 2 513.9 6 456.6 1 371.4 1 264.1 6 142.1 9
168.7 8 274.3 0 361.5 9 424.7 1 459.3 4 463.1 1 435.7 7 379.1 9 297.2 2 195.4 6
118.3 1 244.5 9 322.8 6 376.8 2 402.7 9 399.0 0 365.6 9 305.1 5 221.5 1 122.3 8
80.86
8.00 9.00 10.00 11.00 12.00 13.00 14.00
169.3 9 215.5 4 246.6 5 256.4 2 244.1 8 210.7 6 158.4 5
15.00
89.38
16.00
24.37
57.18
98.58
17.00
0.00
7.15
12.81
18.00
0.00
0.00
0.00
4.60
21.22
48.14
47.59
17.76
19.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
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71.96 230.4 2 279.1 4 304.4 8 304.7 1 279.8 2 231.5 0 163.0 6
127.7 5 166.6 6 190.2 2 195.9 2 183.3 6 153.4 0 108.0 9 53.71
79.17
0.00
2.77
0.00
25.04
0.00
0.00
0.43
0.00
0.00
0.00
0.00
0.00
0.00
0.00
49 550.00 500.00
450.00 400.00
January February
350.00
March
Ht W/m2
April 300.00
May June
250.00
July August
200.00
September October
150.00
November December
100.00 50.00 0.00 4.00
5.00
6.00
7.00
8.00
9.00 10.00 11.00 12.00 13.00 14.00 15.00 16.00 17.00 18.00 19.00 20.00 21.00 Day Light Hours
Figure 20 total irradiance on a tilted surface per hour for each month.
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The final electrical power, after considering the thermal effect on the photovoltaic panel efficiency, was calculated for each hour of the month. The average hourly electrical power is presented in table 6. It can be seen that the change in the electrical power production starts with medium production and then reaches the maximum at noon. The production in the afternoon drops dramatically until it reaches zero. The hourly demand of the building is similar to production since, the university opens its doors in the early morning, and the consumption is relatively low. Then at the noon the consumption is estimated to be high and might drop afternoon. The consumption of the university may continue one, two or three hours after the production stops, depending on the month. It is important to mention that the consumption is less in summer, because the university is partially close and the working hours are less while it can be seen from the demand figure that the highest consumption takes place in December. This situation is not perfect in the case of solar electricity production since the production is going to be higher in summer and lower in winter. This must be considered when sizing the system, in order to avoid the over sizing or the under sizing of the system, which will, consequently be reflected in the investment cost. Table 6 Average kWh production per hour for each month.
Hour 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 12.00 13.00 14.00 15.00 16.00 17.00 18.00 19.00 Total
January February March April May June July August September October November December 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 5.70 0.11 0.16 0.11 0.19 0.01 0.00 0.00 0.00 0.00 0.00 0.00 11.45 4.93 6.58 6.54 6.13 4.84 2.24 0.00 0.30 0.00 0.00 10.20 16.36 11.35 13.52 12.86 12.98 12.06 9.80 6.03 4.59 0.00 9.79 13.85 20.12 17.84 19.81 18.63 19.25 18.75 15.93 13.94 13.22 7.38 12.86 17.94 22.47 23.26 25.02 23.45 24.50 24.35 20.99 18.54 15.95 9.63 14.72 20.23 23.26 27.23 28.79 26.98 28.38 28.48 24.65 21.74 17.35 10.99 15.30 20.97 22.42 29.48 30.86 29.00 30.62 30.85 26.66 23.33 17.32 11.32 14.57 20.10 20.03 29.85 31.09 29.36 31.06 31.31 26.87 23.19 15.86 10.60 12.57 17.68 16.23 28.33 29.47 28.03 29.68 29.82 25.28 21.34 13.07 8.87 9.45 13.87 11.29 25.01 26.11 25.11 26.58 26.48 21.99 17.90 9.14 6.25 5.33 8.94 5.55 20.12 21.23 20.79 21.96 21.53 17.23 13.11 4.37 3.10 1.45 3.31 0.58 13.99 15.18 15.38 16.13 15.30 11.31 7.31 0.14 0.00 0.00 0.41 0.00 7.05 8.35 9.24 9.51 8.21 4.66 1.43 0.00 0.00 0.00 0.00 0.00 0.27 1.23 2.78 2.66 0.99 0.03 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 96.05 147.51 175.46 238.82 257.40 248.27 259.63 252.95 207.64 167.87 111.32 68.14
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35 January
30
February March
25
April May
kWh
20
June 15
July August
10
September October
5
November December
0 4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19
Yearly Average
Hour of the Day
Figure 21 total estimated electrical output per hour each month.
Figure 21 shows the variation of production per hour for each month. It is observed that the highest production is estimated to be at 12:00 in August. Monthly production is shown in figure 22.
10000 8000 kWh
6000
4000 2000 0
Month kWh…
Figure 22 The monthly production of the system
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3.2.6 Area optimising and assessment Area assessment has been done on the site to consider all the possible locations for installing the proposed solar system. The location drawings can be found in appendix 22. The total useful area was calculated to be 3030 m2. The area is a tilted surface with two sides, upside-down "V" shape, one side facing south with azimuth angle of -23.2˚ SE while the other is facing north. Thus the useful area is less since the northern side will not be useful. The second problem of the useful area is that it contains obstacles which might cause shading and difficulty to install the PV panels. See appendix B. Finally, the roof top useful area is a corrugated roof with low loading withstand. See figure 23.
Figure 23 Roof Top of the Location.
Taking all those issues into consideration has led to the considerations of other options. The suggested idea is to erect a structure above the roof top to set the panels tilted with the optimal tilt angle. This idea has many advantages. Erecting whole new structure above the building, will increase the power output in a way and decrease the used area in another way due to the consideration that the optimally tilted panels, which will perform better than the normally tilted panels, which will allow higher solar radiations collections. Furthermore, this erection shall decrease the effect of shading associated with existing obstacles. Omar Hamdan | Kingston University London
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Moreover, it is important to mention that the roof top contains some ventilation exhausts which, by installing the panels above it, might obstruct the exit air. Those ventilation areas are assumed to be avoidable by placing the panels away from them. Thus, the selected option will be to erect the structure above the top roof.
3.2.7 shading consideration The possible shading of the area is either on a higher floor next to the top building on the southern side or by the panels shading. The building has a higher floor on the southern side, which might contribute to annual shading. On the other hand, the panels should be positioned in a way that their shadows minimise the effect on performance but do not interfere with the building's primary objects e.g. the ventilation, skylights...etc. This can be done by following simple rules in array geometry. The main factors ruling the geometry are the latitude and the climate of the location but the design will also include the spacing between rows, array tilt angle and azimuth angle and in addition to the module orientation. The standard limitation for the shading losses is between 2-4%. For spacing the rows, a setback ration (SBR) should be assigned. For many places the SBR is 2:1 while in the sunny locations and lower regions it is at least 3:1. (Luque and Hegedus, 2011) defined the SBR as "the horizontal distance, or gap, between rows, divided by the vertical distance between the high and low sides of adjoining rows". See figure 24. According to this the SBR is the angle . In this case, the height of the panel which is ruled by the tilt angle will waver the spacing required. The case of this project the tilt angle is fixed. Furthermore, the Ground cover ration GCR is correlated to the tilted angle. The GCR is defined as "the array area divided by the ground area, or, for an array of unit depth, as the row width, c, divided by the row spacing, d." (Luque and Hegedus, 2011) Thus, the equation ruling the spacing ration will be:
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Figure 24 calculating the area of shade effect
Solving for the project situation when giving that c = 1.316 m (Panel width) . SBR = 2:1, soving for the height a:
So the pitch equals to 1.34 m. but because the area available is wide spread, this value will be increased to 2 m. From appendix B, the dimensions of the building can be calculated when it is printed on (A3) paper using the scale. The dimensions found the useful area to be only, (60.76×49.91 m). Due to the need of distancing from the southern side in order to avoid the shadow of the higher floor, spacing of 10 m is considered to be deducted from the total width which will make the total area, (60.76×39.91 m). By dividing the width by pitch value, it can be found that it is possible to install approximately 20 rows. Thus the total width available is 1.316×20 which equals to 26.32 m. If it is considered to have spacing between arrays, (along the building), 15% is considered to be a good value. Therefore, the length decreases to 51.646 m.
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The final area which will be covered by the PV panels is 26.32×51.646 that equals to approximately 1356 m2.
3.3.0 calculating the hourly electrical power produced through all the year 3.3.1 System sizing The system sizing is done with consideration of area available, system demand and installation cost. The area available has been assessed in a previous section and was found to be 1356 m2. Taking into account this aspect, the system size based on this area can be considered to be the maximum possible system. The figures for this size of the system has been calculated and compared with the system demand to see how much of the total demand the proposed system will supply. See table 7 and figure 25. It can be seen that the system, if installed to the maximum will be oversized, this is because only the building electricity demand needs to be supplied. Thus, this system is not feasible to install and the investment cost will be much higher than it should be. Table 7 Maximum power system production and comparison with the system demand
Month
Maximum possible Power Produced Percentage
January February March April May June July August September October November December Yearly or Average
9844.597755 13660.27358 17989.30002 23695.32654 26390.64852 24632.79406 26618.92997 25875.19094 20551.31597 17210.73493 11165.04505 6986.619537 224620.7769
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System Demand kWh 10710.32555 9091.104447 8187.093173 6014.643208 5645.042719 4566.445117 4838.484549 5102.848096 6585.985196 8903.864671 10664.61564 10581.79167 7574.35367
% 91.92% 150.26% 219.73% 393.96% 467.50% 539.43% 550.15% 507.07% 312.05% 193.30% 104.69% 66.02%
56
Maximum possible Power Produced Percentage 104.69% 193.30%
66.02% 91.92% 150.26% 219.73%
January
February March April
312.05% 393.96%
May June
507.07%
July 467.50%
August September October
550.15% 539.43%
November December
Figure 25 Monthly Percentage of the total demand when maximum power produced.
Looking to the figures, it can be inferred that the system size should be reduced in order to cover a percentage of the demand in the lowest month of production while taking advantage of the system in the highest month of production. In this case, the system will cover the system demand in most of the months and will have a very good percentage in the low months of production. The lowest production will be in December, while the highest production will be in July. The system should be reduce and levelized to a certain amount. It is known that the extra produced power can be sold to the electrical grid through the Feed in Tariff (FIT) system. (This point will be illustrated in more detail in the economical evaluation to follow later in this paper) Now the system will be limited to minimum level to be sure that the size of the system will cover at least a small amount of the energy in the low months of production. The lowest production, as seen in table 8, is in December, consequently, the system should supply at least 20% of the system demand to be economically feasible. To find out the minimum production, the system demand in December should be levelled to 20% of it is actual level to ensure that the system will be able to
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supply this amount. Then, the area needed to supply the minimum level is calculated. The average figures must be used to estimate the area. Twenty percent of the system demand is calculated to be 2116.36 kWh. The average efficiency of the panels in December is 14.10% and the average daily H t is around 1180 W/m2. This means the total monthly average is approximately 36552 W/m2 for 31 days of the month. The final minimum area found to be 410 m2. Table 8 shows the produced power when this area is used while figure 26 shows the percentage in each month and figure 27 shows the demand vs. the production. Table 8 Minimum Production considering 20% of the Demand in December.
Month January February March April May June July August Septemb er October Novemb er Decemb er Yearly
Minimum Power to be produced 2986.443997 4145.725021 5455.236162 7178.322731 7976.504384 7425.626379 8016.335699 7793.994859
System Demand kWh 10710.32555 9091.104447 8187.093173 6014.643208 5645.042719 4566.445117 4838.484549 5102.848096
Percentage OF THE SUPPLY OF THE DEMAND 27.88% 45.60% 66.63% 119.35% 141.30% 162.61% 165.68% 152.74%
6199.55965
6585.985196
94.13%
5201.836239
8903.864671
58.42%
3380.659849
10664.61564
31.70%
2116.820611
10581.79167
20.00%
67877.06558
90892.24404
The main purpose of this project is to supply most of the demand of the facility and when looking at the figures above, it can be noticed that the system with its current sizing is capable of supplying more than 100% of the demand in some months. The proposed system, under the mentioned conditions, is capable of supplying the total demand and supplying the grid with the extra produced power during months like April, May, June, July and August. In addition, the system delivers the needed power in the building by almost 100%. The system is capable of providing the electrical demand by around 94% in September. February, March and October are supplied by electrical power by percentages between 45% and 66%
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whilst the rest of the months, November, December and January, will be supplied limitedly of values between 20% and slightly above 30% of the demand.
Percentage of the Supply to the Demand 10581.79167
10710.32555
January February 9091.104447
10664.61564
March April May
8187.093173
8903.864671
June July August
6014.643208
6585.985196
September October
5102.848096
4838.484549
5645.042719
November
4566.445117
Figure 26 Percentage of the Supply to the Demand
12000
Demand Vs. Production
10000
8000
6000
4000
2000
0
Figure 27 Monthly Demand Vs. Production.
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Power Produced based on 20% of … System Demand kWh
59
The system size seems to be viable thus further study can be applied on the system. Now, the panel area should be considered to find the optimal number of panels based on the minimum value. The area is divided by the panel area to find out the number of panels, and then the number of arrays can be decided. The number of panels, based on those calculations, is found to be 313 panels. For electrical configuration issues, this number should be reduced to 312 panels. The total area of the panels will be 409 m2. The final size of the system will be as follows:
The total installed PV panels are 312 panels.
The total area covered by the PV panels is 408.13 m2.
The total used area to install the system will be approximately 33×26 = 858 m2.
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Chapter Four
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4.1.0 Project Simulation As mentioned before, the program used to do the simulation process is PVsyst. It is highly efficient and has most of the features needed to accurately size, design and calculate the power output for any photovoltaic system. It contains a data base of many locations around the world consisting of meteorological data and solar radiation data for any location. It has the data from many meteorology centres around the globe and data from NASA solar data base, (different source than the one used for hand calculations).
4.1.1 Preliminary Design The program introduces options to do preliminary design, full project design and many tools to evaluate many aspects of the system to optimally design the system. See figure 28. The system designed in this project started with preliminary design after calculating the azimuth angle and deciding the slope angle. In this case the project will be grid connected, so this option should be selected when starting the design.
Figure 28 Program's first interface page
The selection is presented in the preliminary design step. This is important since it is going to decide whether the system proposed is feasible or not. The Omar Hamdan | Kingston University London
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program has a data of solar radiation from NASA solar data base of a period of ten years. The data of the location of the proposed system is taken during the period between 1983 and 1993. This data is considered to be old hence, a newer data from the European commission has been used as what was done in the hand calculation. To setup a new location and solar radiation data, the program has a tool called "Geographical sites" which enable the user to enter a new data and modify its specifications. The new location had been created and the data used in the hand calculation was entered to the data base of the program, see figure 29.
Figure 29 Site data entry.
In the preliminary design step, the tilt angle, azimuth angle and the active area used is entered and a visualisation/optimisation of shade option is available. According to hand calculations and panel's data sheet the pitch distance and the dimension of the panel were entered into a sun path which was created. (See figure 30 and figure 31.).
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The preliminary design step shows, roughly, a promising output. The program includes a price list in its data base which cannot be considered to be reliable information since the market undergoing continuous change. Now, a comparison between the global radiation on horizontal surface, tilted surface and considering the shading effect is presented. It can be noticed that the tilted angle set for the system is improving the system output in winter months, which is what is needed according to the system demand figures, also, it can be seen that this increase in winter months is a compromise on the summer months, see figure 32.
Figure 30 mutual shading Visualisation/optimisation
Figure 31 Sun Path and Mutual shading.
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Figure 32 Preliminary Power Output, Horizontal and tilt surface comparison.
4.2.0 Full Project Design The project is now ready to be entirely designed and many considerations should be set to the optimal values. To design the project fully, many steps should be taken, which may affect the power output. The project meteorology, solar data and orientation of the panel can be modified before proceeding in the full simulation and design. The near shading and variant can be defined and simulated using the "Near Shading" tool. The tool interface can be shown in figure 33.
Figure 33 Near Shading design tool interface
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4.2.1 Shade Simulation The first step to simulate the shade is to construct the objects which might shade the panels, thus the following steps were done:
Calculating the dimensions of the building where the system intended to be installed.
Predict any object might cause any possible shading.
Construct the main body of buildings, shading objects and position them in the right places and distances.
Direct the whole built structures to the right surface azimuth angle.
Build the photovoltaic panel with the exact dimensions
Arrange the arrays and strings.
Place the system built in the right pitch distance and tilt angle
Optimise the photovoltaic system's position on the roof of the building using hand calculation data, as previously mentioned, and the building span distance. The building structure can be built using object build tool in the shading interface window, see figure 34. The tool will allow the user to choose the shape type and ease the building of the whole body of the structure. The built object can be modified to the orientation and the slope needed accurately. The parameter and the dimension of any object selected can be modified to the required shape in real life standard.
Figure 34 building a new object to simulate the shading
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The main building and hawker wings building in the facility were the main source of shading to the photovoltaic system. In addition trees on the southern side of the building were considered in the shadow assessment. The final achieved structure can be seen from the southern side in figure 35.
Figure 35 the final built structure.
Figure 36 PV panels build user interface.
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Now the structure of the building is ready. To build the photovoltaic system a new PV plane in shade can be added from the object menu, see figure 36. The user interface window allows the user to specify the panel dimensions, the pitch distance, the tilt angle and the number of sheds. The colour of each object and component can be modified to visualise the scene easily. As well, the program will assist and give the user advice to optimally design the objects. The panel's positions and directions on the scene can be modified to be positioned in the most optimal situations. The shadowing simulating will allow the user to find the shadow ratio and the sun path specification and it will show the time where the plane will be in shadow. Much iteration approaches can be done to optimally decide the best positions of the panels. The shading simulation can be done for any day of the year and output will defer from day to another due to the change in the sun position, figure 37, 38 and 39 shows this process. The simulation was applied on two possible positions and the results made it possible to decide which position is optimal for placing the photovoltaic system. See figure 40 and 41 to compare the results.
Figure 37 Final system before the shade simulation
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Figure 38 Top View, photovoltaic generator position
Figure 39 Shading process
There were two possible positions, one near the eastern edge of the main building and the other possible position is near to the western edge. When the shade simulation was applied to those two positions the results showed that the system will be behind the plane at 5:00 p.m. when the system is placed at the eastern side of Omar Hamdan | Kingston University London
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the building whilst the system will be start to be behind the plane at 6 p.m. which will give the system more time to produce electricity from the beam radiations. On the other hand, the losses due to the shading where almost the same for both sides. The attenuation factors for diffused and Albedo radiation were slightly deferent, the attenuation is higher at the western side of the building. In general, both results are almost the same, keeping in mind that the effect of reducing the diffuse and the Albedo radiations is much less than the effect of decreasing the beam radiations. Therefore, the selected position was to install the system at the western side of the building. The shading factor for the beam radiations at different heights of the sun and different azimuth angle can be seen in table 9. The table shows where the system will be behind the plane corresponding to the sun positions and movements during the day.
Figure 40 shading when the system is placed at the eastern side of the building.
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Figure 41 shading when the system is placed at the western side of the building.
Table 9 Shading factor for the beam radiation at different sun positions.
4.2.2 Electrical Layout Furthermore, the system will be designed, electrically, with two different options, either the required peak power of the system (kWp) or by stating the available area. In the case of this project the area is an important issue since the Omar Hamdan | Kingston University London
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system will be mostly restricted by the area. The total useful area and the system area are already calculated by hand calculation and the area assessment as mention in previous section, therefore, the system was built according to the area calculated on the area assessment section. The area used is 409 m 2. System design interface page is shown in figure 42 The data of the selected components, Sharpe PV-NU-S5E3E and Siemens inverter Sinvert 60M, were selected from the options given by the program in the system design window. The optimisation of number of modules in series and parallel was done using the array graph drawing tool in the program. The graph showed the better results than any other condition when the twenty four panels are connected in series and when thirteen arrays placed in parallel. All the possible options were limited by both the inverter's MPP tracking voltage and current. The optimisation graph can be seen in figure 43. The graph shows a comparison between the power at the STC and the array arrangement used. The final configuration of the system is to use 312 panels with peak power of 57.7 kWp. Twenty four panels will be placed in series and 13 arrays in parallel. The voltage and the current of the photovoltaic generator with the suggested configuration will be around 576 V and 102 A, before considering the losses. The nominal PV power is 51.6 kWdc while the AC nominal power is 57 kWpac.
4.2.3 Panel Layout Design panel's layout was designed using the program's tool for building layouts. The area calculated in the area assessment section was used. The tool will use the dimensions of the PV panel used in the system design and will place automatically the maximum possible panels on the given area. The tool will not consider the pitch distance, thus, this process must done by placing "inactive area". When creating inactive area, the tool will avoid placing any panel on this area. The total area used for placing the system was calculated to be 858 with dimensions of 33×26 m. The active area calculated for the system is 409 m2. Thus, the layout was configured to have only 312 panel with the arrangement suggested in the system design array, 24 panels in series and 13 arrays in parallel. The designed layout is shown in figure 44.
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Figure 42 System Design interface
Figure 43 Array power optimisation graph.
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Figure 44 Module Layout design and layout tool interface.
Now, the system is ready to be Simulated. All the data for the design have been entered and all the configurations and optimisation have been done. Before running the simulation, all the data have been review to make sure that the enter data, specification and configurations are stated as required from the design. Any required graph or table, other than the default, can be added before running the simulation. The simulation had been done and the results are presented in the next section.
4.2.4 Simulation Results and Review The results of the simulation consider mostly all the aspect of the system design. The data given to the program is the same data used in the hand calculations. The program will produce a short report of five pages summarising the project done. Table 10 shows the output data after the simulation. E_Grid is the total electrical power produced to the building and the electrical network. It shows the total kWh produced by the suggested system for each month. Thus, a comparison between the demand and the produced kWh is shown in figure 45. Omar Hamdan | Kingston University London
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The produced kWh using simulation program found to be less than that calculated by hand. The main reason is that the hand calculation did not consider any losses and only considered the variation in the efficiency with the change in the temperature. The output energy by the simulation might indicate that the result produced is accurate since all the losses are calculated. This cannot be true for many reasons. The main reason that those data output is provisional data and the simulation has an error percentage that might increase or decrease the results. Table 10 Simulation Data Output.
12000 10000 8000 D (kWh)
6000
sim kWh 4000 2000
0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Figure 45 Simulation Production vs. Demand
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Figure 46 loss Diagram of the whole system along the year.
The simulation program will build a loss diagram for the whole year. The loss diagram shows all the possible losses along the year and deducts it from the total production. The losses of the shading and AM factor are shown to be 20%. The module losses are around 13.2% of the total energy supposed to be produced by the photovoltaic generator. Finally, the inverter losses are equal to 8.2%. All the details of the mentioned losses above can be seen in figure 46. The net energy generated from the system to either the building network or the electrical network will be 37490 kWh. It can be seen that the shading has a very great impact on the energy output with approximately 17% losses. This is why an accurate study on the shading must always be done.
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Figure 47 shows the daily input/output diagram of the suggested system. It can be seen that the does not exceed 300 kWh for any day while the global incident radiation on the system does not exceed seven kWh/m2.
Figure 47 Daily input/output diagram
Figure 48 shows the Voltage distribution for the array along the day. The maximum voltage is recorded to be around 620 V while the minimum is around 450 V.
Figure 48 Array voltage distribution
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Figure 49 Daily Power output along the year.
Figure 49 shows the daily power output along the whole year. It can be seen that the energy produced in the summer months are much higher than that produced in the winter. Performance Ratio (PR) is calculated to be 64.6% yearly. The highest performance ratio recorded is on April to be around 70%. Figure 50 shows the performance ratio for each month.
Figure 50 Performance Ratio for each month.
The system has been built and now ready to be evaluated economically. Further calculation will present how the project evaluated economically and how the economical models help to size the system in its current conditions. Final models of both hand and simulation calculation should be presented. Omar Hamdan | Kingston University London
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Chapter Five
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5.1.0 Electrical Configurations The electrical configurations are going to be decided based on both the size and range of the inverter. As mentioned before, the selected inverter is Sinvert 60M. This inverter has a nominal power of 68 kW, a minimum MPP voltage (DC) of 450 V and a maximum MPP voltage of 750 V. The maximum DC current is 149 A. This data should be taken into consideration when the array is designed. The number of panels is 312, therefore, approximately 49% of the area used to install the system will be covered by the PV modules while the other 51% of the area will be used for spacing and stringing. The inverter control room can be placed on a nearby roof of another building, hence the cable length has been estimated to be 80 m and its cross sectional area is 35 mm2, the material suggested is copper thus the resistance due to wiring is going to be 0.05 Ohm. Under those considerations the array design can be set. The suggested number of modules in series is 24 modules accumulating of 576 Volt and 13 strings which will provide 100.23 Amp. to the inverter. The inverter has only one DC input and the arrangements are within the inverter rating. The output power will be 400V L-L and the current will change according to the demand and consumption. The nominal AC power is 68 kW. Normally, any grid connect photovoltaic system is composed mainly of photovoltaic panels, inverter, kWh meter and switches. The electrical layout for an integrated commercial might need some additional feature and extra considerations. Figure 51 shows the system layout. The layout shows the optimal electrical circuit for the system starting from the photovoltaic panels as a power generator for the system. On the DC side of the inverter, it is important to include a DC circuit breaker with specific protection. On the AC side, an AC isolator is needed to isolate the whole system from the newly integrated photovoltaic system. The output of the inverter is connected to a contactor which is driven by a protective relay. The relay is an over current relay to protect the circuit from any accidental rise in the current. This relay makes it possible to control the system remotely. In case of an over current, the relay will sense the current through a coil connected in line with the each phase, then its contactors will send a signal to the main power contactor, 4 pole contactor. Finally, the energy will go Omar Hamdan | Kingston University London
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through a kWh meter to calculate the produced energy. The energy status can be observed through a display unit installed remotely.
Figure 51 Electrical System Layout.
5.1.1 Measurement of the Energy Produced and Sold to the Grid It is important to measure the kWh and keep it under control for both intensive purposes and energy consumption track. The state of the kWh is:
The electrical energy taken from the grid.
The electrical energy fed into the grid.
The energy produced by the PV plant.
The installation of the kWh meter in the system is shown in figure 52. U is the energy produced by the photovoltaic system to the electrical grid, E is the energy consumed from the electrical grid. P refers to the total production of the photovoltaic system while C is the total consumption of the building. During the night or during the cloudy conditions there will not be any energy produced by the photovoltaic system. Therefore, P and U are equal to zero and the consumed energy by the building is equal to the energy bought from the grid. Omar Hamdan | Kingston University London
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Figure 52 kWh meter integration with the system
On the contrary, when the photovoltaic system is producing energy, one of the following situations may occur: -
P > C, in this case the building will be fully fed by electricity from the photovoltaic system and the extra kWh units can be sold to the grid with the feed in tariff stated by the government;
-
P < C, in this case the building will only be fed partially by the photovoltaic system and the rest of the building demand will be supplied by the electrical grid.
5.2.0 Protection and Earthing of the System: When the earthing matter is raised in a photovoltaic system, the earthing concept ought to involve both the uncovered conductive parts, like the module frame and supports, and the live parts, like any photocell. A PV system can be earthed only if it is galvanically separated from the electrical network by means of a transformer. A PV insulated system would seem apparently safer for the people touching a live part. However, as a matter of fact, the insulation resistance to earth of the live parts is not infinite and therefore a person may be passed through by a current returning through such resistance. This current rises when the voltage to earth of the plant and the plant size increase since the insulation resistance to earth decreases. Besides, the physiological decay of the insulators, due to the passage of time and the presence of humidity, reduces the insulation resistance itself. Consequently, in very big plants, the current passing through a person in touch with the live part may cause
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electrocution and therefore the advantage over the earthed systems is present only in case of small plants.
5.3.0 Protection Against Over Current on AC Side: The point of connecting the system with grid, in parallel, is usually designed to have a higher current carrying capacity. The cable connecting the system with the grid should be normally designed to the optimal current of the load, normally less than the connection point to the grid. Therefore, this cable should be protected from any short current supplied by the grid through a protective device positioned near the point of connection with the grid. In this project case, the main circuit breaker (CB) should be enough since the system only has one inverter. Otherwise, in case of multi-inverters, it is mostly much wiser to use a protection circuit breaker for each one to increase the reliability of the system, i.e. in the case of one circuit breaker, the system will be totally off in case of a trip; on the other hand, in case of multi circuit breakers only one part of the system will be out of service in case of fault at that part.
5.4.0 Comparison between Hand Calculation and Simulation The system was designed using the same data source. The hand calculation conducted calculations to find the power output of the system with many iteration attempts. Doing many attempts led to size the system to the current size 57.7 kWp. While on the simulation, the net power output after considering the system losses. The values of both methods were quite different but the when considering the value of the simulation before reducing the power output of losses, it can be seen that the values are close. The annual power production of the hand calculation without considering any losses is 67.6 MWh. The annual power production with near shading losses and AM losses and without system losses is 46.75 MWh. It can be noticed that the near shading is summing around 20% losses of the original estimated power, therefore this last value is expected to be higher than its current value.
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Chapter Six
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6.1.0 Economical Evaluation It is important to evaluate the project economically since the main purpose of the project is to build a system to produce electricity in environmentally friendly methods. Reducing green house gases and gas emission production became an investment in the energy market. To build a model that reduces the energy cost and, in the same time, reduces the impact of producing energy on the environment is a true success. The method to approach the economical evaluation in this project is first to state assumption based on market observers about the cost of production for each kW for PV panels. Then building a model to see if the suggested production is feasible or not. The model will help to take an economical decision when the system is being sized. This is because it is, sometimes, easier to decide, upon engineering prospective, whether the system is optimal to be built under certain conditions or not but it is harder to decide if the project will be economically feasible or not.
6.1.1 Assumptions By looking through many market analysis of photovoltaic system, the records showed that the prices of installing PV panels are decreasing. Since the beginning of 2011 to August of this year 2012, the price index of the solar panels has dropped by 60% (Solar Panel Prices in the UK, 2012). The Feed in Tariff cut by the UK government was the main cause of this decline. The prices is planned to change in the near future, November 2012. The uncertainty of the incentives accompanying the installation of photovoltaic system for households and commercial purposes made the prices in the market to changes continuously. Thus, there is a variation on the cost of kWp installed. A report prepared by the Department of Energy and Climate Change (DECC) generated in May 2012 indicates a drop in the prices and estimating the near future prices. It is estimated for this project to be applied in November 2012, thus the data based on this month has been used in the calculation. The cost of installing one kWp for photovoltaic system is £1275 including planning, panel cost, installing and any
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other expenses. This price for the system between 50 and 150 kW installed on retrofit building. (DECC, 2012) This price is estimated by looking at the figures of the DECC presented from:
Developers and installers of UK systems;
Supply chain parties; and
Anecdotal evidence from DECC and other sources.
The price estimated is an average of all the figures given. Operation and maintenance cost was estimated to be 1% of the total cost yearly. The Feed in Tariff (FIT) value, starting from November 2012, is 11.5 p/kWh. This data is based on the latest update from DECC for photovoltaic systems ranging between 50 kWp and 100 kWp, considering a higher rate value. The saving on the energy bill is found to be 8.5 p/kWh. This value is found according to the tariff rates on the university bills. The tax upon the loan stated is assumed to be 7%.
6.2.0 Sizing the System Based on Data from the Economic Model The model made it possible to see the figures of the cost and cash flow. In addition, it is possible to evaluate whether the system payback period is sufficient or not. The first assumption is to install the maximum possible system size. As suggested before, the second assumption is to produce energy enough to supply 20% of the energy consumption in December. Finally, the power output from the simulation results were applied to the model.
6.2.1 Maximum Power Output When apply the maximum power output size of the system, based on the area available, the capital cost of the project was found to be £318,750 if 250 kWp system is installed. The operation and maintenance cost for the system to be £3,187.5 yearly which will sum for 25 years to be £79,687. Table 11 is a summary of those calculations and shows the cash flow of the project along 25 years. Figure 53 shows the cash flow of the project under those assumptions. It breakeven year is 16.5 years.
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can
be
seen
that
the
86
Table 11 Maximum power output applied on the built economical model (in £)
Year
0
Turnover
0
Initial 318,7 investment 50 O&M EBIT Tax
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
15,8 15,8 15,8 15,8 15,8 15,8 15,8 15,8 15,8 15,8 15,8 15,8 15,8 15,8 15,8 15,8 15,8 15,8 15,8 15,8 15,8 15,8 15,8 15,8 15,8 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
3,18 3,18 3,18 3,18 3,18 3,18 3,18 3,18 3,18 3,18 3,18 3,18 3,18 3,18 3,18 3,18 3,18 3,18 3,18 3,18 3,18 3,18 3,18 3,18 3,18 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8
12,7 12,7 12,7 12,7 12,7 12,7 12,7 12,7 12,7 12,7 12,7 12,7 12,7 12,7 12,7 12,7 12,7 12,7 12,7 12,7 12,7 12,7 12,7 12,7 12,7 318,7 04 04 04 04 04 04 04 04 04 04 04 04 04 04 04 04 04 04 04 04 04 04 04 04 04 50 0
889 889 889 889 889 889 889 889 889 889 889 889 889 889 889 889 889 889 889 889 889 889 889 889 889
11,8 11,8 Net Income 318,7 15 15 50 7,34 7,34 Savings 7,347 7 7 19,1 19,1 Cash Flow 311,4 62 62 03 Net Present 17,9 16,7 311,4 Value 08 37 03
11,8 11,8 11,8 11,8 11,8 11,8 11,8 11,8 11,8 11,8 11,8 11,8 11,8 11,8 11,8 11,8 11,8 11,8 11,8 11,8 11,8 11,8 11,8 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 7,34 7,34 7,34 7,34 7,34 7,34 7,34 7,34 7,34 7,34 7,34 7,34 7,34 7,34 7,34 7,34 7,34 7,34 7,34 7,34 7,34 7,34 7,34 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 19,1 19,1 19,1 19,1 19,1 19,1 19,1 19,1 19,1 19,1 19,1 19,1 19,1 19,1 19,1 19,1 19,1 19,1 19,1 19,1 19,1 19,1 19,1 62 62 62 62 62 62 62 62 62 62 62 62 62 62 62 62 62 62 62 62 62 62 62 15,6 14,6 13,6 12,7 11,9 11,1 10,4 9,74 9,10 8,50 7,95 7,43 6,94 6,49 6,06 5,66 5,29 4,95 4,62 4,32 4,04 3,77 3,53 42 18 62 68 33 52 23 1 4 8 1 1 5 1 6 9 8 2 8 5 2 8 1
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TOTA L 238,3 77 318,7 50 47,81 3 128,1 86 13,33 9 141,5 25 117,5 47 23,97 9 136,8 81
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Cumulative Cash Flow £200,000.00 £100,000.00
£0.00 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 -£100,000.00 -£200,000.00 -£300,000.00 -£400,000.00
Figure 53 Cash Flow when installing 250 kWp as maximum assumption
6.2.2 System Limited by the Minimum Demand of December When applying the model on the system sized at 20% of December demand, the capital cost of the project was found to be £73,567 if 57.7 kWp system is installed. The operation and maintenance cost for the system to be £735.67 yearly which will sum for 25 years to be around £18,391. Table 12 is a summary of those calculations and shows the cash flow of the project along 25 years. Figure 54 shows the cash flow of the project under those assumptions. It
can
be
seen
that
the
breakeven year is 13 years.
6.2.3 Using the Data from Simulation for 20% of December System Size When the system simulated, the power output changed from the results found by hand calculations. This is because in the simulation, the losses were considered while the hand calculation did not consider the losses. The capital cost and the maintenance of the project are the same as in the hand calculation results. The payback for this assumption is found to be 20 years which is higher than the calculation in hand as expected.
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Table 12 20% of December production assumption applied on the built economical model (in £)
Year
0
Turnover
0
Initial investment
73,56 8
O&M
0
EBIT Tax Net Income Savings Cash Flow Net Present Value
73,56 8 0 73,56 8 4,728
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25 TOTAL
1,41 1,41 1,41 1,41 1,41 1,41 1,41 1,41 1,41 1,41 1,41 1,41 1,41 1,41 1,41 1,41 1,41 1,41 1,41 1,41 1,41 1,41 1,41 1,41 1,41 21,21 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 2 73,56 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 8 11,03 736 736 736 736 736 736 736 736 736 736 736 736 736 736 736 736 736 736 736 736 736 736 736 736 736 5 678 678 678 678 678 678 678 678 678 678 678 678 678 678 678 678 678 678 678 678 678 678 678 678 678 63,39 1 47 47 47 47 47 47 47 47 47 47 47 47 47 47 47 47 47 47 47 47 47 47 47 47 47 712 631 631 631 631 631 631 631 631 631 631 631 631 631 631 631 631 631 631 631 631 631 631 631 631 631 64,10 3 4,72 4,72 4,72 4,72 4,72 4,72 4,72 4,72 4,72 4,72 4,72 4,72 4,72 4,72 4,72 4,72 4,72 4,72 4,72 4,72 4,72 4,72 4,72 4,72 4,72 75,64 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 3
5,35 5,35 5,35 5,35 5,35 5,35 5,35 5,35 5,35 5,35 5,35 5,35 5,35 5,35 5,35 5,35 5,35 5,35 5,35 5,35 5,35 5,35 5,35 5,35 5,35 11,53 68,84 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 0 5,00 4,68 4,37 4,08 3,82 3,57 3,33 3,11 2,91 2,72 2,54 2,37 2,22 2,07 1,94 1,81 1,69 1,58 1,48 1,38 1,29 1,21 1,13 1,05 68,84 987 20,03 8 0 4 8 1 1 7 9 5 4 6 9 4 8 2 5 6 5 2 5 4 0 0 6 0 4
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Cumulative Cash Flow £80,000.00 £60,000.00 £40,000.00 £20,000.00 £0.00 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 -£20,000.00 -£40,000.00 -£60,000.00 -£80,000.00
Figure 54 Cash flow of system sized based on 20% of December demand.
Cumulative Cash Flow £30,000.00 £20,000.00 £10,000.00 £0.00 -£10,000.00 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 -£20,000.00 -£30,000.00 -£40,000.00 -£50,000.00 -£60,000.00 -£70,000.00 -£80,000.00
Figure 55 Cash flow of System sized based on 20% of December demand. Simulation results
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90 Table 13 20% of December production assumption applied on the built economical model/ simulation result (in £)
Year
0
Turnover
0
Initial investment
73,56 8
O&M
0
EBIT Tax Net Income Savings Cash Flow Net Present Value
73,56 8 0 73,56 8 3,151 70,41 7 70,41 7
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25 TOTAL
1,15 1,15 1,15 1,15 1,15 1,15 1,15 1,15 1,15 1,15 1,15 1,15 1,15 1,15 1,15 1,15 1,15 1,15 1,15 1,15 1,15 1,15 1,15 1,15 1,15 17,25 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 73,56 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 8 11,03 736 736 736 736 736 736 736 736 736 736 736 736 736 736 736 736 736 736 736 736 736 736 736 736 736 5 414 414 414 414 414 414 414 414 414 414 414 414 414 414 414 414 414 414 414 414 414 414 414 414 414 67,35 3 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 435 385 385 385 385 385 385 385 385 385 385 385 385 385 385 385 385 385 385 385 385 385 385 385 385 385 67,78 8 3,15 3,15 3,15 3,15 3,15 3,15 3,15 3,15 3,15 3,15 3,15 3,15 3,15 3,15 3,15 3,15 3,15 3,15 3,15 3,15 3,15 3,15 3,15 3,15 3,15 50,41 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 3 3,53 3,53 3,53 3,53 3,53 3,53 3,53 3,53 3,53 3,53 3,53 3,53 3,53 3,53 3,53 3,53 3,53 3,53 3,53 3,53 3,53 3,53 3,53 3,53 3,53 17,37 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 5 3,30 3,08 2,88 2,69 2,52 2,35 2,20 2,05 1,92 1,79 1,68 1,57 1,46 1,37 1,28 1,19 1,11 1,04 978 914 854 798 746 697 652 38,21 5 9 7 8 1 6 2 8 3 8 0 0 7 1 2 8 9 6 0
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Looking at the first and the second model it can be seen that the payback period for the first model is around 16.5 years while the second model payback period is 13 years. Upon this it can be decided that it is better to decrease the investment cost and, in the same time, the decrease the risk. The produced kWh in the third model is less than the second model since the losses were calculated in the simulation process. The payback time is less as expected. On the other hand, the calculation in the simulation, occasionally, can be inaccurate. The savings on the energy bill for both models, the first and the second, are shown in figure 56 and figure 57. Figures 58 and 59 shows the demand and the produced kWh in the first and the second model.
Electricity Bill 1500
Electricity bill (£)
1000 500 0 -500
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
New bill
Old bill
-1000
-1500 -2000
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Figure 56 Saving on Electricity bill in first model
Electricity Bill New electricity bill
Old electricity bill
Electricity bill (£)
1000 500 0 Jan Feb Mar Apr May Jun -500
Jul Aug Sep Oct Nov Dec
Month
Figure 57 Saving on Electricity bill in the second model
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Chart Title 30000 25000 20000 15000 10000 5000 0 Jan
Feb
Mar
Apr
May
Jun
Jul
Produced kWh
Aug
Sep
Oct
Nov
Dec
D (kWh)
Figure 58 Demand and Production for the first model
Demand and production New load
Load
12000 10000 8000
kWh
6000 4000 2000 0 -2000
Jan
Feb
Mar
Apr
May
-4000
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Month
Figure 59 Demand and Production for the second model
6.3.0 Analysis It can be seen that there is a huge different between the model when no losses is considered and when the losses is considered. Therefore, the economical evaluation must be done according to the closest power production value.
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Chapter Seven
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7.1.0 Critical Review The approach to design this project was to evaluate the project characteristics by hand calculations and then combining the hand calculations with a simulation. The analysis of the site in terms of demand, solar radiation, useful area available, obstacles and shading and other related issues help to set a methodology to decide the system. London's solar irradiances and the clearness index values were the main dampers of the electrical production the clearness index average value was calculated to be 0.39. This value considers low compared with clearness index values at other locations. The facility demand played a great role of varying the system size since there is a gap between summer's months and winter months. Considering the estimated electrical production in summer is higher than the estimated production in winter whilst the demand of the facility is higher in winter and less in summer. The area assessment was done upon site survey and as built buildings diagrams. Many trouble-shootings were done to estimate the size of the system but the main challenging was the obstacles on the main building roof and the loading withstand of the roof itself. Thus, an erected structure was suggested to overcome this issue. Hand calculation power production value and simulation power value were quite different because in the hand calculation no losses were considered while the simulation program presents realistic values.
7.2.0 Further Work Any further work can be applied is to improve the hand calculation model by adding equations to consider the system loss and attenuation losses. In addition, the system size can be modified using different iterations. Those iterations can be economically evaluated by the model presented in chapter six. Finally, more economical analysis and evaluations can be added to this project since this project was scientific oriented more than economical one.
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Chapter Eight
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7.1.0 Conclusion The paper presents a method to design, size and evaluate photovoltaic system. Many models were built to evaluate the system by means of electrical configuration, structure and economical configuration. Those models were evaluated using hand calculations, simulation of different iterations of the project and an economical model to decide the system size and its entire configuration. The size of the system is first assumed to use the maximum area available for production. This model was modified after looking at both the amount of production, according to hand calculation and simulation, and the economical feasibility. Later, another model was presented by limiting the production to 20% of the demand of the month with the lowest solar electricity production. After evaluating the model by hand calculation, simulation and an economical model presented, it was found that the system size suggested is going to partially achieve the objectives of the project. The system size was decided according to that. Later an electrical design, shade simulation and system configurations were presented for the selected system size. The system size decided to be 57.5 kWp, which is expected to be injecting to either the facility electrical network of the national electrical grid. Number of arrays decided was 13 arrays in parallel accumulating of a current equal to almost 102 A. A twenty four panel is decided to be connected in series and accumulate a voltage of 543 V after considering the wiring voltage drop. Total area used for the system is 858 m2 including only 409 m2 active area. Number of panels decided to be 312 modules and one inverter with rated power of 60 kWp is decided to be installed with the system. Electrical configurations and protection methods were stated. After calculating the capital cost and the operation and maintenance cost, the project is found to payback the capital in 13 years according to data from hand calculations. A longer period is predicted according to power data from the simulation. The payback period found to be 21 years.
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References ABB, (2010), Photovoltaic Plants, user manual, Italy. Baker J. A. (2004),'Development and Global Warming', Public Policy, Melbourne. Benemann J., Chehab O. and Schaar-Gabriel E. (2001), 'Building-integrated PV modules', Solar Energy Materials and Solar Cells, vol. 67, pp. 345-354 [Online]. Available: http://www.sciencedirect.com/science/article/pii/S0927024800003020 Chapman S. J. (2005), Electrical Machinery Fundamental, 4th edn, McGrawHill Department of Energy and Climate Change (2010), Digest of United Kingdom Energy Statistics 2010, London [Online] Available at: http://www.decc.gov.uk/assets/decc/statistics/publications/dukes/348-dukes-2010printed.pdf Department of Energy and Climate Change (2010), Digest of United Kingdom Energy Statistics 2010, London [Online] Available at: http://www.decc.gov.uk/en/content/cms/statistics/energy_stats/source/source.aspx
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Bibliographies Cyril W. Lander, 1994. Power Electronics. 3 Sub Edition. McGraw-Hill Europe. Duffie J. A. and Beckman W. A., 2006. Solar Engineering of Thermal Processes. 3 Edition. Wiley. Robert Hastings, 1999. Solar Air Systems - Built Examples (Solar Air Systems Series). Edition. Routledge
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Appendix A One-hour example of hand calculation. All the data available with the attach CD.
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Appendix B 1- Site diagram, other more detailed diagrams can be found on the attached CD.
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Appendix C PV Data sheet and Inverter
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