Energy Report, October 2010


Solar electricity produced: 520 kW h (16.8 kW h per day)
Electricity consumed: 414 kW h (13.4 kW h per day)


Our solar electric production was up 4% from last month but our consumption increased 6%. In the end we produced only 1.25 times what we consumed this month, and we don't expect to do much better as winter approaches. However some of the increased consumption was from running our electric food dryer and canning to preserve some of the fall harvest so at least those should be eliminated next month. In addition we had some increased consumption from the pumps that circulate fluid through the solar heat collectors and the heated floors.

October brought some chilly weather and we started using the solar heat system for heating the house. But the heating needs were modest and we had enough sunny weather to keep the heat storage tank nice and warm. The sharp drops in temperature that you can see in this graph, especially on the blue line that indicates the temperature of the bottom of the tank, indicate periods where the in-floor heating was actively drawing heat from the tank in order to warm the floors.

The graph below shows the temperatures outside (red) and inside the house (blue), recorded each morning and evening. Clearly we're in heating mode now with some nights dipping below freezing, but certainly nothing like winter yet. Indoor temperatures have been very stable and comfortable. As long as we get some sun, the passive solar gains and heat stored in the floor slab are enough to keep the main house warm through the night without drawing from the heat storage tank. The cottage has less south-facing glass and more exposed walls so it generally takes more active heat than the main house even though it has only half the floor area. We still haven't switched on the electric backup heaters for domestic hot water or space heating and we haven't used the wood stoves either so except for our internal heat gains and a little electricity to run the circulation pumps, we're using 100% solar heat.

Here's a graph showing the solar heat collected each month over the past 10 months, as reported by our Heliodyne Delta-T Pro controller that operates the solar heat circulation pump. The first and last bars, November and December respectively, aren't meaningful because they don't represent an entire month. The 10 bars in the middle are in reverse, so the most recent full month (October) is on the left, and you can see that we collected over 1.5 million BTU in October. This shows the effect of orienting the collectors vertically, because the high sun angle in the summer means we collect much less heat energy when we don't need or want it. We're collecting much more heat now that the sun is lower in the sky. Unfortunately the heat collection will drop again in mid-winter, especially in December, because the days are shorter and we tend to have more cloudy weather.


This page was updated on Wednesday January 11, 2017