Cleaning PV Arrays [RE-wrenches]

[Joel Davidson]

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Do clean PV arrays operate cooler and produce more power?

The Las Cruces, New Mexico Solar Energy Institute reported a 6% increase in performance after detergent washing a portion of a 17 kW array near El Paso, Texas. A few days later a gentle rain washed the other portion of the array and the difference in output between the two was undetectable. The conclusion was detergent and labor were a waste of money, but also cautioned that dust, dirt and pollutants in other locations may require detergent washing.

Los Angeles air and airborne pollutants are over 3 times worse than the EPA clean air standards (which are set by you know who). In L.A.on a calm, sunny August day, 1:45pm, 920 W/m2 POA, 25.2C ambient temperature, I measured 58C cell temperature and 55.8 VDC array voltage for Siemens SP70 modules. I washed the array with soap, water and a sponge mop, careful not to thermal shock the glass. An hour later after the array temperature stabilized, I measured 850 W/m2 POA, 25.8C ambient temperature, 47C cell temperature and 59.2 DVC.

Agricultural dust and dirt are larger particles and block more sunlight than smaller urban particles, but do rural arrays heat up more from dirt? Are you getting the same voltage improvement? How often do you recommend your local customers clean their arrays?

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