Solar PV : Disappointed with new record !

17Aug10

Even with the days shortening we had a super sunshine Sunday and this was backed up by generating the highest total to date since our July installation.  Whilst the daily energy was 25 kWh, I looked at the maximum Wp reading and was surprised to see that the maximum peak was only 3.25 kW.

Head scratching begins to figure out why the peak was down over 18% on less spectacular days.  The inverter was up at 60 oC but this is not an issue.  The panels were rather hot.  I’d hazard from the touch test maybe up nearer 60 oC as well.

Apparently, according to a source on the web …..
Crystalline panels suffer a high voltage DROP when heated by the sun (Crystalline panels lose power, for each degree above 25C). At the 60 C they lose approximately 30% power. Output only 60% to 70% of Wp.
..
.This was from an article pushing different materials.
Other sources 20% loss at 60 oC or 0.5% per degree above the lab 25 oC rating.

So, doing the sums backwards based on losing 0.5% per degree above 25 oC to get the loses the panel temperature should in theory have been 62.5 oC.

I also checked back on an okayish day like today which yields 17 kWh but the wind and lower roof temperatures managed to high full expected peaks of 3.995 kWp

C’est la vie, bummer !

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