1) 2:30pm: Sun starts to set (yellow) and the greenhouse has no solar gain and the temperature starts to drop (Orange & green lines)
2) 3:45pm: Temperature goes below 40F (4.5C). Heater is able to turn on/off as it maintains the temp at 40F. Ceiling temp (light green) jumps a bit as the heat rises....
3) 9:15pm: Outside temperature (Red) goes below 20F (-6/7C) and the heater no longer can keep up with the demamd. Temperature slowly declines to around 38F (3.3C). The outside temp is 13.3F (-10.4C)
4) 9:15am: Heater turns off once the sun comes out the next morning. Total run time is roughly 17 hours.
There are 2 electric heaters totaling 2400 watts. After all the fees and taxes, we pay $0.20 per kilowatt:
2400watts & 17 hours = 40.8 kilowatts
40.8kW * 20 cents = $8.16 to keep it heated for the night!
Since we are getting so little sun and it's cold, the lettuce is growing very slowly. There's one tomato plant that I started in the fall still doing OK but needs a lot more light. I had a few cukes growing, but the consistent cold has killed them. I am not generating $8 worth of veggies/day. Perhaps it's time to invest in a propane heater to lessen the heating costs....or just shut it down for the winter..... Jan & Feb will be even colder!