The quartz radiant tubes total 1500 W. The thermostat is set on 45°F. To calculate the power use, I'd have to log how many hours they're on each night, which varies from 1 to 10. But since we have a 4.4 kW PV power system, it's all solar. The PV setup was installed in 2011 and paid itself off two years ago. At this time of year we have banked power and our bill is about $32 per month for line charges.
There are also CFL grow lights on a timer, that I've not used his year, just to see if they make a big difference.
The aim of the design is to render the greenhouse as self-sustaining as possible.
