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  • #46
    Here is the numbers (kWh) -
    Sunday: 113.4 -
    Monday: 113.0
    Tuesday: 112.8
    Wed: 113.6
    Thurs: 123,7 Cleaned in the morning. More high cirrus clouds in the afternoon then the prior days.

    Temps did drop a bit, Thurs was 3F cooler then Wed, and Wed was 7F cooler than Tuesday. Sunday was the hottest day but skies were a tad clearer with minimal high cirrus clouds.

    A tad under 9% (and 3F cooler temps). So I would say that is a worst case of fouling I would ever expect - ash from two large fires combined with about 4 months of dust/pollen/bird droppings/pine needles (minimal) and what looks like very small caked on spots of dried sap. Most of it came off from the simply spray, I'll look at it more closely this weekend in the early morning.

    What this tells me is after this unusual ashy summer it was a good use of time to hose them off, and after future fires it may be worth the time to hit them once the air clears. Previously (prior to the broken water line) I was trying to hit them one or twice every two months but did not sweat it since we were in rainy season.

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    • #47
      Originally posted by tyab View Post
      Here is the numbers (kWh) -
      Sunday: 113.4 -
      Monday: 113.0
      Tuesday: 112.8
      Wed: 113.6
      Thurs: 123,7 Cleaned in the morning. More high cirrus clouds in the afternoon then the prior days.

      Temps did drop a bit, Thurs was 3F cooler then Wed, and Wed was 7F cooler than Tuesday. Sunday was the hottest day but skies were a tad clearer with minimal high cirrus clouds.

      A tad under 9% (and 3F cooler temps). So I would say that is a worst case of fouling I would ever expect - ash from two large fires combined with about 4 months of dust/pollen/bird droppings/pine needles (minimal) and what looks like very small caked on spots of dried sap. Most of it came off from the simply spray, I'll look at it more closely this weekend in the early morning.

      What this tells me is after this unusual ashy summer it was a good use of time to hose them off, and after future fires it may be worth the time to hit them once the air clears. Previously (prior to the broken water line) I was trying to hit them one or twice every two months but did not sweat it since we were in rainy season.
      Thank you. Unless you have more instrumentation, I wouldn't bother getting more involved. Panel efficiency calcs as f(cell temps.) are primarily driven by 3 things, Panel POA irradiance, wind vector and ambient air temp. at the array. Without a pyranometer and ways to estimate wind vector and air temp., the instantaneous efficiencies much less lay long efficiency will be a SAWG. Qualitative conclusions such as you've done are about as good as you can expect and are probably at least good enough for what you want to know which sounds like "when/how often do I want to clean the array, and how involved do I want/need that maintenance to be.

      Respectful suggestion: Hose the array ~ 1X/month or so if it doesn't rain. Get the really big chunks of guano off the array if/as you think necessary and then use ~ 3/4 gal. of H2O per panel. Doing so probably holds my fouling levels to ~ 3% performance penalty. Use it as a guide or something to consider. This is not an exact science.

      Don't bother with D.I. /special rinse/*chemicals. I've measured before/after cleanings a lot, and a good part of those data with/without getting ALL the hard water/mineral spotting off the array. If a benefit exits from getting my array spot free vs. normal (for my situation) hardwater spotting, I've not been able to measure it.

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