This chart from the DTE Web Site shows my monthly electric bill for heating and cooling our house. The right axis is Heating Degree Days which are a measure of how much (in degrees), and for how long (in days), the outside air temperature was below a certain level. They are commonly used in calculations relating to the energy consumption required to heat buildings. 723 Spring Street has 4,200 square feet of conditioned space on four levels. Since having put in the 8.6 kW solar panel system last fall, we have been near net-zero energy over the five month period. The kWh surplus from the solar panels more than offsets the electrical consumption of the ground source heat pump, but does not totally offset the total electrical consumption of our house load meter (lights, appliances, outlets, etc.).
You can see when comparing the two graphs that our best opportunity for total net-zero energy will be in the “shoulder months” such as September, October, November, April, May. These are the months when we have the least heating or cooling demand combined with generally good solar production.