Dramatic YOY Dropoff in Solar Production for April!

[Ian S]

Looks like the 0.18" precip. didn't improve output by reducing the fouling, or perhaps any such effect was lost in the noise of the other variables.

Of course any cleaning effect of the rain could be offset by the increased cloudiness associated with the rain. I haven't been up to clean since last fall and expect to do so this weekend if I can get going early enough to avoid the heat. In reality the closeness of the two years is a fluke. Even with the uniformity of our weather, you'd still expect far more than 0.5 kWh fluctuation. June is coming and then I'll have data for June 2012-2015. Should be interesting but I still think it won't be enough data to see any degradation over the three year period.

[J.P.M.]

Of course any cleaning effect of the rain could be offset by the increased cloudiness associated with the rain. I haven't been up to clean since last fall and expect to do so this weekend if I can get going early enough to avoid the heat. In reality the closeness of the two years is a fluke. Even with the uniformity of our weather, you'd still expect far more than 0.5 kWh fluctuation. June is coming and then I'll have data for June 2012-2015. Should be interesting but I still think it won't be enough data to see any degradation over the three year period.

From keeping about 1/2 an eyeball on system(s) output in my HOA, my mostly anecdotal guess with some observational data from measuring cooperative neighbors output is that most initial panel degradation happens in the first yr. or so and is something like about 1/2 mfg. claims - very ~~ 2% - 3%/yr or so. As for yr/yr degradation beyond initial burn in, my 1/2 step above ignorant SAWG is that the annual degradation is also about 1/2 mfg. claimed spec - ~~ 0.20- 0.40 %/yr. That is, both claims seem to be somewhat conservative across the mfg. board. Time will tell.

[JFinch57]

April, 2014: 1216.12 kWh
April, 2015: 1215.58 kWh

My 38KW system in Pt. Pleasant NJ, Apr 2014 = 5,120 KWh, Apr 2015 = 3,061 KWh. Now that's different!

[cf400]

April, 2014: 1216.12 kWh
April, 2015: 1215.58 kWh

Nice! Funny too!

[J.P.M.]

Of course any cleaning effect of the rain could be offset by the increased cloudiness associated with the rain. I haven't been up to clean since last fall and expect to do so this weekend if I can get going early enough to avoid the heat. In reality the closeness of the two years is a fluke. Even with the uniformity of our weather, you'd still expect far more than 0.5 kWh fluctuation. June is coming and then I'll have data for June 2012-2015. Should be interesting but I still think it won't be enough data to see any degradation over the three year period.

I'm on the same page w/you, and not trying to separate fly crap from pepper, but what if it rained at night ?

[J.P.M.]

My 38KW system in Pt. Pleasant NJ, Apr 2014 = 5,120 KWh, Apr 2015 = 3,061 KWh. Now that's different!

Pretty large but not impossible monthly variation. Highlights that PVWatts is an estimator of long term performance not short term. Was the system operational fore the same amount of each month ?

[JFinch57]

Pretty large but not impossible monthly variation. Highlights that PVWatts is an estimator of long term performance not short term. Was the system operational fore the same amount of each month ?

Yes, no down time. Just entered the April 2015 generation today and noticed it. Has a utility grade digital meter in a meter pan.

[J.P.M.]

Yes, no down time. Just entered the April 2015 generation today and noticed it. Has a utility grade digital meter in a meter pan.

Understood. Thank you.