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What’s the best way to mount a solar PV array?

#HowTos

This is a question that I've been asked in the field so I wanted to share it with everyone on KnowledgePoint

What are the options for setting up solar arrays on buildings and the ground?

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A: If a small solar photovoltaic (PV) system is to stay in one place for more than a day or two, the modules (panels) need securely mounting to protect them against wind and theft. There are 3 main approaches, the choice of which depends on scale, budget, available skills and materials, and local conditions. The main requirements are for the array to be secure, close to the load, pointing the right way and not shaded between 9am and 3pm. It also helps if the array can be safely cleaned by the users.

Roof mounting This is usually the simplest approach, assuming the load is in a building. The roof offers some height to avoid shade and interference. Preferably find a roof pitch pointing north (southern hemisphere) or south (northern hemisphere). See Knowledge Point Q&A on ‘how to set up PV for best output’ for more advice on orientation and shading. Working on a roof is hazardous. Check the condition and layout of the roof structure before climbing on it. Use boards to spread the load and consider how to get the modules on the roof safely. Modules are best attached to rails – ideally aluminium or galvanised / painted steel, though treated timber will work – using clamps on the frame. The rails can then be attached to the roof substructure – purlins or rafters, not the roofing sheet alone - using long coach screws, J-bolts or stand-off bolts (wood thread one end, machine thread the other, with a roof washer in the middle). Make holes on the ‘hills’ of corrugated roofing and be careful to seal the holes with silicone and rubber washers. If the roof angle is significantly different from the preferred inclination (approximately the site’s angle of latitude), make a sub frame to change the array angle. This is also possible if the roof pitch is east/west to point the panels correctly. Be aware that raising the array above the roof surface may subject it to significant wind loads which may damage the array structure or even the roof itself. Pay attention to sealing if penetrating the roof for the cable entry, or route it off the edge and under the eaves (allow a drip loop). Specialised PV cable is UV resistant but standard PVC insulated electrical cable (and conduit) is not. Polyethylene water pipe provides reasonable protection. To span overhead, add some fencing wire and attach at each end to take the strain.

Pole mounting This is fairly simple for a single module, but becomes more structurally challenging for an array of more than 2 modules. It needs more materials than a roof mounting, typically a pole and framework, and concrete for the foundation. Steel water pipe makes a good pole, 2” for a single module, 3” or 4” for larger arrays. Some welding will probably be needed to mount the array framework to the top. The pole base should have some side struts to embed in concrete and provide a secure anchor. Use armoured cable or polypipe ... (more)

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