Energy Report, March 16-31, 2010

The second half of the month brought us nice spring weather with some cool nights, but we had plenty of sun. We operated the heat recovery ventilator continuously on low speed, and used the wood stoves only a couple of times.


Average daily heating degree-days: 21.2
Average daily heating electricity used: zero!
Average daily other electricity used: 12 kW h = 41,383 BTU
Average daily solar heat collected: 11.4 kW h = 39.069 BTU


In the second half of march we used no electricity for heat or hot water, except for a little bit that was needed to run the pumps. We did use the wood stoves a couple of times on cooler nights, when the heat storage tank temperature got below 120 degrees in the middle of the month.

Here's the heat storage tank temperature graph for the whole month of March. After getting down to a low of 110 degrees in the middle of the month when we had a week of cool, cloudy weather, we had some very sunny days and little heat demand that brought us up to near maximum temperature. Fortunately, the average solar heat gain per day is dropping off, and we collected significantly less solar heat per day than in the first half of month. This is partly due to the changing sun angle on our vertical panels. As the sun gets higher in the sky, our vertical panels collect less heat. That's exactly what we want, now that we are using the heat just for domestic hot water and don't need it for space heating, because otherwise the tank would overheat in the summer. We're also getting less passive solar gain because the overhangs over the south-facing windows are starting to shade them.

This page was updated on Wednesday January 11, 2017