The dirt on my panels after 6+ months...

[Mike90250]

Once the water spots from hard water dry and bake onto the glass, they are very hard to remove, the minerals cement themselves onto paint and glass. So a little extra care like a carwash DI rinse, is a lot easier than to try to de-crust panels with vinegar.

[silversaver]

You missed a spot at the top.

No. The top 2 panels were add on right before the wash, so they still have some kind of wax on them

[SunEagle]

No. The top 2 panels were add on right before the wash, so they still have some kind of wax on them

I was trying to be sarcastic.

[J.P.M.]

Once the water spots from hard water dry and bake onto the glass, they are very hard to remove, the minerals cement themselves onto paint and glass. So a little extra care like a carwash DI rinse, is a lot easier than to try to de-crust panels with vinegar.

I've tried to avoid using vinegar as I've used vinegar to clean aluminum. Works great. So great in fact, I figured that might not be too good for the panel frames, at least any unpainted parts. Just sayin'.

[DanKegel]

Just ran into a couple papers on fouling in desert conditions:

http://link.springer.com/chapter/10.1007/978-3-319-16901-9_11

"Sand Effect on Photovoltaic Array Efficiency in Algerian Desert"
...
"dust accumulation on the PV array surface for a period of several months can significantly reduce the PV array efficiency with an average power loss of about 4.38 %."

http://www.sciencedirect.com/science/article/pii/S0038092X14002928

"Fundamental studies on dust fouling effects on PV module performance" (in Dhahran)
...
"power output has been reduced by 6% after 5 weeks of exposure"

For what it's worth

Probably a lot more of those at scholar.google.com

[justcerfin]

New to this forum. I never even though of how much dust could reduce solar production. All interesting. Thanks for the info!

[max2k]

I've tried to avoid using vinegar as I've used vinegar to clean aluminum. Works great. So great in fact, I figured that might not be too good for the panel frames, at least any unpainted parts. Just sayin'.

What would concern me all these solutions are good ionic conductors and also corrosive: vinegar first but even water after softener has Ca ions replaced with Na, so it basically becomes weak solution of the table salt. Its concentration is proportional to the original water hardness. Usually water softened this way is not recommended for watering plants due to accumulation of Na ions in the soil over time. Not sure if this effect is big enough to affect anything in solar installs as there won't be any accumulation happening.

[J.P.M.]

Some dart throw conclusions from ongoing measurements : 1.) My array fouls at the rate of About 1% per week when it doesn't rain. I believe that rate may become asymptotic at some point but haven't been rain free long enough to see such a trend. 2.) A rain event, depending on both amount and duration, TENDS to reduce the fouling to ABOUT 1/2 to maybe 2/3 of the pre rain fouling, that is, a 4% decrease in output from fouling is reduced to ABOUT 2% or maybe 1+% after a decent rain., but hard to quantify beyond that a good rain helps, but probably doesn't get it all. 3.) I can't measure a difference in improvement between soap/water and tap H2O rinse and soap/ water and D.I. rinse. Basically, maybe in theory, but some water spots make no diff. in output that I can measure. 4.) Given the practical limitations of instrument accuracy, the number of variables involved in the measurements, and the small size of the differences being measured, panel fouling and rates of fouling are at best only estimates. Like all experiment and experimental measurement, what actually amounts to best guesses coming from repeated and consistent measurements, and then looking for trends in the data, adjusting the measurement method as judged appropriate and continuing the measurements that become, at best, educated guesses. The measurements continue.