PV Array Structure Design, Construction and Installation
Short Description
Solar PV Array Structure Design, Construction and Installation Guidelines...
Description
Amit Nirmal | Shirsh Energy Solutions Pvt Ltd
Sterling Strips Ltd is a multi-disciplined multi-disciplined E.P.C, planning, design and engineering company providing comprehensive services
Boiler Design, Manufacturing & Commissioning
Solar PV Structural EPC Turnkey Projects
Shirsh Energy is a system Integrator for Solar Rooftop and other services on turnkey basis.
Sterling Strips Ltd is a multi-disciplined multi-disciplined E.P.C, planning, design and engineering company providing comprehensive services
Boiler Design, Manufacturing & Commissioning
Solar PV Structural EPC Turnkey Projects
Shirsh Energy is a system Integrator for Solar Rooftop and other services on turnkey basis.
PV array mounting options Engineering variables for designing the mounting system Design methodology for Mounting structures Construction Methodology Installation Overview Q &A
Photovoltaic module mounting systems are one piece of a solar electric project that generally does not receive a lot of attention But a mounting system is an important component that shouldn’t be overlooked. overlooked.
Roof-top Mounting
Ground Mounting
Top-Down Rail System Rack Mounts: Adjustable- & Fixed-Tilt Top-of-Pole Mounts Commercial mounting systems Tracking System
Single Axis
Dual Axis
One of the most common and very popular PV module mounting methods is the “top-down” rail system, since modules attach from their upper side to the rails with specified clamps. This versatile system can be used with almost all roofing types. Top-down rail mounts are popular in both home and business scale
It consist of 4 main component
Feet or posts (also called “footings” or “standoffs”) that are typically secured to the roof’s rafter system; Extruded aluminium rails fastened to the feet or posts and the array; End-clips that secure the ends of the PV array to the rails; Mid-clips that hold the junction of two modules to a mounting rail.
Mounting clips attach PV modules to the rails from the top, allowing quicker installations.
Array is mounted parallel to the roof plane PV modules are attached to the rails from the front side, instead of the back
Rail systems typically result in only 3 to 6 inches of space between the back of the modules and the roof surface.
Rack mounts can be tailored to fit a variety of situations, accommodating both ground mount and roof-mount applications.
Biggest benefit to racks is that they can allow for a variety of specific tilt angles. The PV array can be set at an optimal tilt angle based on the site’s latitude or, if adjustable racks are chosen, repositioned seasonally to optimize energy output. Main Components : legs, beams & Clamps for panels
Since these mounts tilt the array away from the mounting surface, the backs of the modules can usually be conveniently accessed to get to the wiring, junction boxes, and grounding points, making installation and maintenance easier. The increased distance from the mounting surface also facilitates greater airflow along the back of the modules and results in a lower array temperatures compared to the parallel-toroof method.
Same structure can be used for Ground Mounted or Roof mounted in some situations it can be used on side of buildings.
Many designs require ordering a specific rack with mounting hole spacing that matches the PV module’s mounting holes. In roof mounted systems, rack mounts have less layout flexibility than top-down rail systems.
The top-of-pole mounting solution is a favourite among many installers Top-of-pole arrays are viable for locations with enough land space and where possible aesthetic concerns are not an issue.
The footing for the pole is encased in concrete according to manufacturer’s specifications for the array size and the site’s soil and wind-loading conditions.
Components Pole mounting sleeve which slips on top of the pole All necessary bracing and cross members, as well as module mounting hardware. •
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The ability to adjust the array tilt seasonally is a natural function of any top-of-pole mount. In cold climates, top-of-pole mounts are one of the most convenient racking options if snow needs to be periodically cleared from the array. Top of-pole arrays can also be used with tracker systems to help boost PV production even more
Array sits several feet from the ground, allowing for the greatest amount of airflow, top-of-pole mounted arrays operate at lower temperatures than roof- and groundmounted arrays. This reduces the amount o power lost when ambient temperatures are high.
Top-of-pole mounts generally are not viable options in urban or suburban areas due to the yard space required. Additional excavation required to place a pole and trench to the electrical distribution can make top-of-pole mounts more costly in certain situations
These solutions include
Custom designed and fabricated mounting structures, Integrating the PV array into the roofing material, and using a Non penetrating ballast Ballast mounts rely on the weight of the system for flat-roof ballast, modules, and racking rather than applications. fasteners and roof penetrations to secure the array.
The most common type of commercial racking system is the ballast rack, which uses the weight of the modules and rack in conjunction with ballast to securely keep the arrays in place.
Masonry blocks are placed in ballast pans that are located either directly under, or in front of and behind the PV array These racks can add a significant roof load, up to 146.47 Kg per square meter, depending on the . array engineering requirements
Single Axis Tracker system
Dual Axis Tracking system
Trackers are used to minimize the angle of incidence between the incoming light and a photovoltaic panel.
The single-axis method follows the sun’s path from east to west, with the array tilted at a fixed or manually adjustable angle off the horizon. This approach is common in large-scale, commercial installations but can be used in residential applications as well.
Dual-axis trackers adjust the PV array to track the sun’s path from east to west and adjust the array’s tilt to account for the change in the sun’s altitude.
1. 2. 3. 4. 5. 6. 7. 8.
Maximum design wind speed. Snow Load Exposure category. Soil class. Module type and quantity. Desired tilt angle. Ground clearance. Number of modules in a string.
This is the highest wind gust speed probable in 50 years, averaged over a 3-second gust at a height of 10 metre. Refer IS 875 for info. Because wind speeds vary (they are generally higher close to the coast and at high elevations), this is critical information for an engineer Maximum design wind speeds can be found in the IS875 Section 3
deals with wind loads to be considered when designing buildings, structures and components thereof.
Location ( this determines basic wind speed) Calculate design wind speed
Calculate Design Wind Pressure
By Conducting FEA for structures we can
Approximately know the reaction forces which will be responsible for uplift of structure Stresses in each members, that then can be compared with IS 875, IS800 andIS801 for validation Overall displacement and pinpoints exactly where we have focus for optimizing the structure Can be used for studying combinations of Wind, Seismic, Self weight & Snow loads.
A good PV mounting system must be capable of one thing above all: It must stand safely.
Measured in pounds per square foot (or Kg/m2), the weight of snow on a structure can stack up, depending on your location. Snow can be five to more than 15 times heavier than a PV module, and the rack must hold the additional weight. ASCE (American Society of Civil Engineer) Standard 7-10 includes common snow-load values
This is related to wind loading and takes into account the turbulence at the site due to surrounding objects (trees, buildings, etc.). Terrain in which a specific structure stands shall be assessed from IS 875 section 3, typically there are 4 categories of terrain.
This is necessary for determining specifics for anchors, which behave differently in different soils. Soil test report is necessary in determining the anchoring which can Ramming or Piling Soil report typically consists of Safe Bearing Capacity, Moisture Content, Cohesion Value of soil to hold the structure etc.
Acquire a specification sheet for your modules for the rack manufacturer, who will need at least
minimum the number of modules,
plus module depth, height, width, and hole layout, to size the rack correctly.
This will be based on your location’s latitude and the seasonal variation in solar gain The height to the lower edge of the first row of modules (800mm to 1000mm is typical). This basic design decision should be based on site conditions:
potential snow accumulation,
ground covering ( accessibility) aesthetics, etc.
This information can help the rack manufacturer design an efficient layout, with strings contained within a row or sub array for less trenching and conduit.
Preliminary
Sitting: Review property lines, shading, setbacks, right-ofways, or easements; and check for underground utilities. Civil engineering: Will grading, storm water runoff mitigation, or environmental reviews be needed? Check with local permitting, planning, and inspection agencies. Site access: Is the site accessible to heavy construction machinery if needed? Accessibility: Will the array need fencing for security from theft and/or animals, and to comply with Standards ? Be sure there is sufficient space so the fence will not shade the array.
Design
Site-specific info: Catalogue wind speed, snow loads, soil conditions, etc. Electrical interconnection: Determine distance and route to the interconnection point, and placement of electrical equipment including combiner boxes, disconnects, inverters, and other BOS components. Orientation Height Layout Maintenance
Columns : Can be hot rolled or Cold Rolled section Link or Brackets : Preferably Cold rolled as good strength and weight factor
Link can tilting also for having seasonal tilt in zenith
Beams: Preferably Cold rolled as good strength and weight factor Struts & Clamps: For mounting of PV panels
This code applies to general construction in steel The provisions of this code generally .apply to riveted, bolted and welded constructions, using hot rolled steel sections. This code gives only general guidance as regards the various loads to be considered in design , For actual loads to be used reference may be made to IS : 875
This code applies to the design of structural members cold-formed to shape from carbon or low-alloy, sheet or strip steels used for load carrying purposes in buildings. It may also be used for structures, other than building provided appropriate allowances are made for dynamic effects.
Hot dip Galvanized Steel or Aluminum for on grid mounting structures Aluminum / Galvanized Steel or Stainless Steel in Off grid installations. Fasteners : All Stainless Steel preferred Galvanization : Upto 80-90 Microns but will depend upon the soil and Chloride , moisture content of soil & Ph Value of soil.
Surface preparation
Caustic cleaning- A hot alkali solution often is used to remove organic contaminants such as dirt, paint markings, grease and oil from the metal surface. Acid pickling- Scale and rust normally are removed from the steel surface by pickling in a dilute solution of hot sulphuric acid Fluxing- Fluxing removes oxides and prevents further oxides from forming on the surface of the metal prior to galvanizing.
Galvanizing
the material is completely immersed in a bath consisting of a minimum of 98% pure molten zinc. Fabricated items are immersed in the bath until they reach bath temperature.
Inspection
coating thickness and coating appearance
A variety of simple physical and laboratory tests may be performed to determine thickness, uniformity, adherence and appearance.
Structures are modularly constructed into different parts and installed on site using fasteners. Cold Rolling methodology is used in making brackets, beams and struts. Hot rolled or cold rolled can be used in columns.
Marking of Site as per layout for pole mounting Ramming or Piling of Poles / Post or Column Checking Alignment of Poles Mounting of brackets Mounting of Aligner (Tilting link) Mounting of Beams Mounting of Struts Mounting of Panels and supporting it with Clamps
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