Dirt built-up over the solar arrays can substantially affect system performance. It is essential to clean the modules regularly to maximize energy output from a solar power plant. However, wrong cleaning practices, bad quality water and use of inappropriate cleaning agent may damage modules and other array components and lower system performance as well. It is also essential to train the cleaning personnel on proper cleaning methods and use of appropriate cleaning tools.
In this article, we are discussing few recommendations for cleaning solar modules in general. Specific cleaning procedures will be based on module manufacturer’s instructions, site condition, quality of water and cleaning mechanism used.
Safety of personnel: Solar modules are connected in series and it generates upto 800V DC. Cracks in modules or damaged cable or joints in a string are extremely dangerous for cleaning person particularly when the modules are wet. Even during low level of sunlight the array will generate lethal voltage and current. Therefore, it is important to inspect modules thoroughly for cracks, damage, and loose connections before cleaning. Cleaning personnel shall wear appropriate electrically insulating Personal Protective Equipment (PPE) during cleaning.
Cleaning time: The recommended time for cleaning modules is during low light conditions when production is lowest. The best time to clean modules is from dusk to dawn when the plant is not in operation and risk of electrical shock hazard is minimum.
Quality of water: De-ionized water should be used to clean the modules. If de-ionized water is not available, rainwater or tap water can be used. Tap water must be of low mineral content with total hardness less than 75ppm. In case mineral content of water used is more than 75ppm but less than 200ppm the water must be squeezed off to prevent scale build up over module surface. Water with mineral content of more than 200ppm should NOT be used. Water must be free from grit and physical contaminants that could damage the panel surface.
Use of cleaning agent: A mild, non-abrasive, non-caustic detergent with deionized water may be used. Abrasive cleaners or de-greasers should not be used. Acid or alkali detergent must not be used.
Removing stubborn marks: To remove stubborn dirt such as birds dropping, dead insects, tar etc., use a soft sponge, micro-fiber cloth or non-abrasive brush. Rinse the module immediately with plenty of water.
Drying: Modules should be dried after rinsing using a chamois or rubber wiper with a plastic frame on an extension pole. Wipe the module surface from top to bottom to remove any residual water from the module.
Water pressure: Water pressure should not exceed 35 bar at the nozzle. Use of high pressure hoses for cleaning may exert excess pressure and damage the modules.
Water temperature: Temperature of water used for cleaning should be same as ambient temperature at the time of cleaning. Cleaning should be carried out when the modules are cool to avoid thermal shock which can potentially cause cracks on the modules.
Dirt built-up due to wrong cleaning practice and poor water quality