While I was in the Big Apple teaching a couple of days in the Passivehouse Consultant training, Vineyard Propane came by and took away my propane tank. I had recently sold our last remaining fossil fuel burner, the VT Castings gas heater (the dryer and kitchen range preceded it). I checked when I called them what it would cost for a current delivery - $5.09 per gallon. On a strict BTU basis, that's equal to $0.19/kWh for electricity, about what we pay here on MV. But that's figuring the propane at 100% efficiency. Since we're seeing a pattern when we do energy use assessments here of high summer propane and oil usage with boilers heating DHW, and warm season efficiencies that appear to be as low as 20% or lower, I'm beginning to think that as we design solar hot water systems we should just disconnect the entire DHW system from the boiler and use electricity for the back-up energy.
I'm supposed to get a refund for the propane in the tank, which had about 80 gallons according to the tank gauge. They filled it last fall even though I didn't want it done, and assured me then that I would get refunded for the propane left in the tank. We'll see!