How to clean installed solar panels using minimum amounts of water?
For field cleaning of solar modules, I recommend using Liquinox detergent. (See the MSDS and technical bulletin links below). This is a concentrate that would be used at a 1% solution (1.25 oz/gal, or 10 mL/L).
Liquinox is not harmful to discharge onto the ground in an agricultural setting nor will it attack glass or aluminum substrates. I would recommend developing a cleaning procedure that allows you to spray on the 1% Liquinox solution using irrigation water (possibly use a garden sprayer or backpack sprayer), then:
- allow the sprayed on solution to sit for as long as is practical without excessive evaporation,
- do some scrubbing with a light plastic brush to get any really tough spots loosened up,
- rinse thoroughly with irrigation water,
- if practical, do a final rinse and finally squeegee dry.
Water spots occur when tap water or dirty water evaporates and deposits contaminants on the surface; using a squeegee removes the water before it can evaporate and make spots. Whoever is doing the cleaning needs to understand this and learn to work in a way that minimizes evaporation, particularly on the final rinse.
For the Liquinox MSDS, see: http://www.alconox.com/static/msds/msds_liquinox.asp
For the Liquinox Technical Bulletin, see: http://www.alconox.com/downloads/pdf/techbull_alconox.pdf
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For a free sample, visit: http://www.alconox.com/sample15.html