Energy Report, February 2011


Solar electricity produced: 454 kW h (16.2 kW h per day)
Electricity consumed: 386 kW h (13.8 kW h per day)


February brought enough sunshine that we were able to switch off the electric backup heater at the start of the month, so we didn't use any electricity for heating. We kept the house warm mostly with solar heat and only used the wood stoves a few times on colder evenings, more for ambiance than for actual heating needs. We produced 18% more electricity than we consumed this month, and to date we have a 9% electricity surplus over the first 11 months of operation.

The graph below shows the temperatures outside (red) and inside the house (blue), recorded each morning and evening. The warm days toward the middle of the month were offset by some very cold nights in the single digits.

Here's a graph of the heat storage tank temperatures, and you can see that the relatively warm outdoor temperatures toward the middle of the month enabled us to warm the tank up from a low of about 85 degrees to a high of about 115. That 30-degree temperature rise in our 20,000 pounds of water represents 600,000 BTU of stored heat energy. We used up most of that during the very cold weather that followed toward the end of the month. As discussed on the Heat Storage Design page, the heat storage tank was designed for this sort of weather pattern with 3-5 sunny days followed by 3-5 days of cold cloudy weather, and it performed well this month.

Here's a graph showing the solar heat collected over the past 11 months, with the most recent month (February) on the left and last April on the right. This was our highest month to date in terms of solar heat collection with nearly 2 million BTU of heat energy collected. This represents only the active solar collectors that transfer heat into the heat storage tank. Although we can't measure it directly, we also had significant passive solar heat gain through the south-facing windows.


This page was updated on Wednesday January 11, 2017