Underestimated Results of Cleaning Panels

[sensij]

Bottom line: I believe current is affected more by fouling than voltage, and that affects output in a mostly linear fashion, but Voltage is affected by the absorbance of solar energy by the fouling layer and that may increase or decrease the array temp. and thus array Voltage.

Ok, I think we are both at the same bottom line. I had edited my previous response while you were writing, digging in more to the idea of fouling reflectance and just running a sanity check on what the numbers I'm seeing might suggest. Conclusion being, it would be neat if more forum members would do this type of test in different climate zones with different types of fouling, and see if there are conditions that induce a more significant voltage effect. The OP's system, for example, might have been a good one if there had been side-by-side data, since there *appears* to be a larger effect than what I found, but perhaps the fouling there is of a different source and is able to generate a larger thermal impact.

[J.P.M.]

Ok, I think we are both at the same bottom line. I had edited my previous response while you were writing, digging in more to the idea of fouling reflectance and just running a sanity check on what the numbers I'm seeing might suggest. Conclusion being, it would be neat if more forum members would do this type of test in different climate zones with different types of fouling, and see if there are conditions that induce a more significant voltage effect. The OP's system, for example, might have been a good one if there had been side-by-side data, since there *appears* to be a larger effect than what I found, but perhaps the fouling there is of a different source and is able to generate a larger thermal impact.

I think you & I beat this to the point we're the only 2 who are paying any attention to the thread. But, it's a good subject. Maybe more later some time. My interest continues.

Thanx.

[tyab]

Actually JPM, I just follow your basic recommendation. I hose off the array about every 2 weeks in the morning. No scrubbing, no rubbing, no special cleaners, etc. Keep up the good work. Although I do find some small pine needles stuck on some due to sap and crusted bird dropping that don't seem to really come off fully with the hose. For now just leaving them, they seem to go away given a month of heat and bi weekly hosing.

[J.P.M.]

Actually JPM, I just follow your basic recommendation. I hose off the array about every 2 weeks in the morning. No scrubbing, no rubbing, no special cleaners, etc. Keep up the good work. Although I do find some small pine needles stuck on some due to sap and crusted bird dropping that don't seem to really come off fully with the hose. For now just leaving them, they seem to go away given a month of heat and bi weekly hosing.

I've found that the guano usually spalls off w/mummification/desiccation in the sun. Don't know about sap. Pine resins might leave local problems w/ARC coating, but if you find they are H2O soluble, that's more good info.

Thanx for the info.

[sensij]

A couple more weeks of data on my system. I'm still using the daily energy number, the power integration has its own problems I haven't worked around yet.

DailyComparison3.JPG

[J.P.M.]

A couple more weeks of data on my system. I'm still using the daily energy number, the power integration has its own problems I haven't worked around yet.

DailyComparison3.JPG

Thank you.
Q: Any more than usual morning dew at your location after ~~ 10/02 or so ? Dew points here on 10/12,10/13 & 10/14 left measurable precip. in the raingauge of 0.02" per morning. Measured fouling effect seems to have gone down a bit for my array on those dates. Looks like your data may show something similar for those dates ?

[sensij]

Thank you.
Q: Any more than usual morning dew at your location after ~~ 10/02 or so ? Dew points here on 10/12,10/13 & 10/14 left measurable precip. in the raingauge of 0.02" per morning. Measured fouling effect seems to have gone down a bit for my array on those dates. Looks like your data may show something similar for those dates ?

Yes, end of last week I was running wipers on the car in the morning. Not exactly what you are looking for, but might explain some of the noise.

[J.P.M.]

Yes, end of last week I was running wipers on the car in the morning. Not exactly what you are looking for, but might explain some of the noise.

Thank you. Pretty much what I was looking for. This is far from an exact science and anecdotal stuff is always at least noteworthy or more so.

Briefly, I've been playing/looking/thinking on my array's tendency to foul at ~ 0.75 - 1.0% performance loss/week when it doesn't rain, until the performance penalty due to fouling reaches ~ 6%fouled, and then tends to level off in what looks like maybe an asymptotic fashion. One thing that may be happening is that the relatively frequent overnight dew around here (and I suspect by you)acts in some fashion the same as a slight rain would to clean some of the dirt off the panels and maybe, depending on dew point and effective radiant sky temp., either decrease the fouling penalty slightly or slow down the rate of performance decrease from fouling.

Look for wet spots on your roof below your array, or others in your neighborhood. If they are present, moisture was running off your array and may have taken some dirt with it.

Because I've got more time than brains, to that end, and separate from the fouling estimates I do, I've done some calcs. using several empirical correlations of effective sky temps. using dew point temps., and wind speed, dew points and measured array temps. from the Davis to estimate effective radiation heat transfer from the array to the nite sky, see how much condensate that would produce on the array and convert that to measureable precip.

Long story short, there seems to be pretty fair agreement between what I calculate for measureable precip. due to condensation and what the Davis rain gauge shows.

As I've suggested in the past, more/greater rates of precip. generally seems to get the array cleaner. Maybe a few 0.00"'s of condensate might tend to remove some of the fouling or at least slow down the rate of increase of the fouling. Measurements/calcs. continue.

One perhaps practical or at least interesting back pocket factoid I came across while rooting around and under the array at/around sunup on mornings when the sky is and has been clear but the rain gauge shows maybe 0.02 " precip. since midnite, and one that quickly became a no brainer blinding flash of the obvious, is that the underside of the array gets about as wet from condensation as the top side. That made me adjust the top side precip. on the array and reduce it by ~ a factor of 2, and also made me think about how things under and array are not quite as moisture protected as I might have thought. Possible (hoar) frost damage in freezing climates also comes to mind.

[sensij]

As I've suggested in the past, more/greater rates of precip. generally seems to get the array cleaner. Maybe a few 0.00"'s of condensate might tend to remove some of the fouling or at least slow down the rate of increase of the fouling. Measurements/calcs. continue.

We got some rain on Friday, which took another bite out of the difference between the cleaned panel and the untouched panel. Not quite back to parity yet, though.

DailyComparison4.JPG

[J.P.M.]

We got some rain on Friday, which took another bite out of the difference between the cleaned panel and the untouched panel. Not quite back to parity yet, though.

DailyComparison4.JPG

Thank you for the info.

0.01" observed and measured precip. here on 08/20, and 0.01" recorded precip. that was actually dew on 08/21.

Fouling decreased from ~ 0.065 on 08/19 to ~ 0.058-0.060 on 08/21. No 08/20 measurements as sky was not completely cloudless at min. incidence angle time +/- 1/2 hr.

Since I can't/don't claim any better than +/- 0.0075 or so on any one day's fouling estimate, my results for those days and the differences are no better than anecdotal, and I'll not try to make them into something they are not. But, the 11 day running average of fouling continues to show pretty regular and linear increases when there is no moisture, and at this time seems to be running a pretty consistent increase of ~ 0.0011 day, with R^2 = 0.96 for a linear trendline when there is no moisture, with the recent precip./morning dew or 0.01" as recorded by the Davis tending to "maybe" hold the fouling increase to zero or a slight decrease as seems consistent with other light precip. events. That 0.0011/day recsnt running average increase would seem consistent with previous estimates of ~ 0.75 % to 1.0% performance loss/week when it doesn't rain.

It looks like your graphs may tend to show some of the same type of pattern.

Questions:

How often do you clean the "clean" panel. Just a hosing ?, or more involved ?

Any update on your Davis reinstall ?


Thanx again for the info.

[sensij]

Questions:

How often do you clean the "clean" panel. Just a hosing ?, or more involved ?

Any update on your Davis reinstall ?

So far, there has been only one intentional cleaning event, the evening of 9/26, using a hose and (initially) dry swiffer. Since then, we've had a light drizzle on 9/30 and somewhat heavier on 10/20, both of which seemed to affect the relationship between panels, along with heavy dew some mornings. I'm not collecting enough data on this iteration to distinguish between the clean panel getting dirtier or the dirty panel getting cleaned, all I can see is that their output is moving back towards the original equivalent performance after precipitation events.

Davis is still coming, just haven't been able to get up on the roof...

[kingocat]

Hi Steve,
Did you purchase or lease your system?
Im looking for some advice on whether its better to buy or lease. Solar city has a no money down system, I think its called a ppa system. Anyways, I would like your input if you dont mind. Also I only qualify for the 30% tax credit. I usually end up getting back after I do my taxes and I dont understand how that will benefit me.

Thanks

[cebury]

Hi Steve,
Did you purchase or lease your system?
Im looking for some advice on whether its better to buy or lease. Solar city has a no money down system, I think its called a ppa system. Anyways, I would like your input if you dont mind. Also I only qualify for the 30% tax credit. I usually end up getting back after I do my taxes and I dont understand how that will benefit me.

Thanks

Kingocat, go back to Solar Panels for your Home forum and click New Topic button on the top left. We can help determine if you qualify for the deduction if you have your tax return for 2016 handy and if know expectations for your changes in tax status for 2017. You wont get any 30% credit with any lease nor ppa.

[sensij]

It has been about a month since the last update. Lots of cloudy weather, even a little bit of rain a week or two ago, but not much change in the relationship.

Any opinions on what I do with this next? Re-clean panel 1.1.7 and see if I can get it back to the 103% performance level? Clean panel 1.1.10 this time and see if the relationship flips?

DailyComparison5.JPG

[J.P.M.]

It has been about a month since the last update. Lots of cloudy weather, even a little bit of rain a week or two ago, but not much change in the relationship.

Any opinions on what I do with this next? Re-clean panel 1.1.7 and see if I can get it back to the 103% performance level? Clean panel 1.1.10 this time and see if the relationship flips?

DailyComparison5.JPG

Headed out just now. More later/tomorrow. Thanx for the info.