The last two days (September 28, 29) we’ve had cloudless skies, so sun all day long. We also had a very good day on September 23, but the temperatures were much cooler (around 17°C), and there was a bit more cloud.
What better way to find out how temperature affects solar PV output!
Though the total on each of the days was around 9kWh, with the peak both yesterday and today at 1.5 kW, but on the 23rd, we had our record output for a 5 minute period of 1.8 kW! So it looks like a warm sunny day will reduce output by about 17%.
The system is 2.1 kWp, and given the sun is pretty much over the equator on the 23rd, we can calculate that at noon on that date, the sun is at 38° (90° – 52°) elevation, and the roof is at 30° elevation, making an angle of incidence of 58°.
Sin(68°) * 2.1 = 1.94, so the panels seemed to be within spec on the 23rd.
Today, the sun was already down to 35° at noon, therefore
Sin(65) * 2.1 = 1.90, so the difference in solar radiation was 2.1%.
Ouch—15% degredation with temperature! I wonder if there’s any way to cool the panels more effectively?
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