13 Week Thermal Energy Usage vs. Weather Chart
Chart updated at 11:21:13 PM   Sunday 10-Dec-17 (UTC - 0800)
This charts compares average solar-derived versus average electrically-derived
thermal energy and its relationship to outside temperature and irradiance. To
read an irradiance value from the chart, divide the number on the left axis by
five. Each point on each curve is computed using a 14 sample rolling average
of the daily data.
When the average daily outside temperature exceeds 45° F, the electrically-derived thermal energy is almost all going into the domestic hot water heater. The combination of a tight well-insulated house and a small wood stove keeps the house at about 70° without using the electrically-powered radiant heating system. As the level of solar radiation increases during the spring, solar-powered radiant heating takes over for the wood stove and solar-powered hot water heating takes over for electrical hot water heating.
When the average daily outside temperature exceeds 53° F, the heat produced by the electrically-powered devices in the house (appliances, computers, entertainment equipment) exceeds the heat lost to the outside. The solar-powered radiant heating system is turned off except for the master bathroom which we continue to heat so the floor feels warm to bare feet.