If you PV array needs cleaning why you can see dirt film on the modules and you’ve not had enough rain to wash them off. Plus, module output is down, according to the inverter’s data. What chemicals or detergents can you use to clean the array?
Cleaning modules in large commercial arrays is done based on a cost-benefit analysis that compares cleaning costs with the revenue increase that results from the improved array output. Most residential and small commercial users want their array to perform optimally all the time, and may therefore clean them more often than commercial arrays are cleaned.
Either way, cleaning should be done per manufacturer’s instructions. For example, Quick Guide for Users, states:“Given a sufficient tilt (at least 15°), it is generally not necessary to clean the modules (rainfall will have a self-cleaning effect). In case of heavy soiling, we recommend cleaning the modules using plenty of water (from a hose), without any cleaning agents and using a gentle cleaning implement (a sponge). Dirt must never be scraped or rubbed away when dry, as this may cause micro-scratches.”
Cleaning arrays can be dangerous. Clean the modules with a hose and a soft cloth if you can access them from the ground. Do this only when the modules are cool early morning, on cloudy days, or in the evening after they have cooled. If you need to climb a structure to access the modules, use appropriate safety gear fullbody harnesses adequately secured are OSHA requirements when working more than 6 feet off the ground.
If you have hard water, be sure to squeegee off the rinse water so you don’t leave mineral deposits on the glass. If you have oily or greasy stains on the modules (these can occur if the array is near roads or airports), isopropyl alcohol can be used to spot-clean stained areas. Most manufacturers do not recommend using anything other than water for general cleaning; do not use soaps, solvents, or other cleaning products.
Many people use pressure washers to clean their arrays. Manufacturers that include instructions for using pressure washers indicate that the pressure used should be less than 80 psi. For reaching large arrays and roof-mounted PV modules, lightweight telescopic poles are available with squeegee and other cleaning attachments. Novel cleaning products claim to help keep modules from getting dirty, but with water working for most cleaning and alcohol available for tough stains, additional products are not necessary.
If you are cleaning your modules because of output degradation, it is a good idea to check the electrical connections as well. It’s also a great time to check the mechanical connections.