Revision history [back]

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 to protect buried power lines (at least 300mm deep, preferably 600mm or more). Poles give more flexibility in siting to avoid shade, and can provide more predictability if turning up to install at a site not previously inspected. They can be a good option for structures with soft roofs – thatched huts, tents, etc. They can also be more secure against theft if reasonably high and mounted with tamper-proof fixings. On the down side, they generally cost more and take longer to set up due the foundations.

Ground mounting Costs and installation time are usually higher than for roof mounting. Concrete foundations and metal framework are required (wood is too vulnerable to rot, termites, fire and theft). An alternative approach mounts the modules on purpose-made plastic buckets that are filled with ballast and placed on flat ground. Fencing is advisable to protect the array from stock and people, but should not shade the modules during peak sun hours (9am – 3pm). Ground mounted arrays are common for water pumping systems with large arrays and no buildings. They can also be more suitable for areas with extreme wind conditions. They are easy to clean, but are more vulnerable to shading from both fixed and growing (shrubs, trees, grass) obstacles.

Theft protection Solar panels are a valuable commodity, and in many parts of the world PV theft is a common problem. No system can be made completely theftproof, but some strategies to reduce the risk include: Engagement: if local people feel a sense of involvement, ownership or benefit from the system, they will be more likely to keep an eye on it. Exclusion: site the array away from casual access, in a compound or behind a fence, high on a pole or roof. Secure: use tamperproof fixings that require specific tools; construct frames so that fixings cannot be accessed with adjustable spanners or hacksaws. Supervison: locate the system where there are always people around.

Summary points Locate array near the load but out of shade. Ensure it is pointing the right way and can be accessed for cleaning. It should be structurally secure to resist high wind and casual theft.