last gasp of summer heat, cleaning the solar panels

break-even for cooking with solar

A few days ago it was overcast most of the morning but I plowed ahead with cooking off solar power.

The combination of seasonal solar dropoff and overcast conditions was a tough one. The system made 2.28kHw and bank got to >90% but never hit Vabs. This suggests that, as the numbers suggested, December will not allow such foolishness.

late heat

An increase in ambient temps into the high 70s outside Alamogordo didn’t help harvest (cell temp derating). And it wasn’t fun.

The next few days were forecast to be even hotter so I decided to bail.

up to Cloudcroft, and thence to El Paso

The only relief nearby would be Cloudcroft. It’s actually a bit too high (8500ft-9500ft, depending on the spot) but better too cold than too hot (unless it’s freezing).

So I drove the ~40mins up the hill and found a spot with both data and southern exposure. I’m parked on a hill so the panels are even slightly tilted south-ish.

This spot will hold for a few days until Wednesday the 9th, at which point it will hard freeze overnight. So my plan is to leave for ELP on Wednesday. By that point daytime highs will drop into the 60s in ELP.

cheddar drop biscuits

By the time I got to camp I was quite hungry. The 40min drive would have returned ~20Ah to the bank, so if I was going to cook something “expensive”, energy-wise, this was the day.

I made a batch of cheddar drop biscuits in the sandwich press, clawing back ~6Ah of what I gained on the drive up. Because the press cycles on/off in use actual SoC rose from 80% to 81% during cooking.

cleaning the solar panels

The pic above was taken on my walk back from pre-digging a cat hole. I noticed the panels were unusually filthy. An excellent opportunity for an experiment! I dug out the ladder, put the pushbroom head on the multi-purpose stick, and found a suitable terrycloth hand towel.

I observed yield before cleaning and after each panel was cleaned (dry wiped).

  • 0 panels cleaned - 276w
  • 1 panel cleaned - 284w
  • 2 panels cleaned - 293w
  • 3 panels cleaned (all of them) - 301w

In theory this means the gain was 9.05%. But it took time to clean each panel and to reposition the ladder on uneven ground between each panel. The overall process took about 4.5 minutes, during which harvest was steadily increasing as the sun rose. After the final reading I watched the harvest for another 4.5 minutes and observed a gain of +8w. This suggests the delta between dirty and clean was probably +6.16%. This more closely matches Sandia’s testing where dust removal yielded +5-6%.

+17w was not worth digging out the ladder or the cleaning, IMO. But now I know.


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