My system has been commissioned for about 10 days now. Today I watched it pretty closely to see what it was doing. The most power it produced was about 8500 watts, at the peak of the day. This is in line with my design goals, so I’m pretty happy about it. I’m expecting closer to 10,000 watts in late June, but even if it is only 9,000 that’s OK with me.

The system is producing about 26.5 kwh per day when it is sunny, and is more than my well and pump require. My wife ran the washer and dryer lots today, so I think we had a slight deficit.

Right now the house is heated with a propane furnace that was installed 10 years ago. It is working fine, but I’d like to convert it to a dual fuel heat pump / propane system, as most of the time the heat pump will do the job (along with the hydronic solar I am adding later this year). I might move the existing furnace over to provide heat for the hangar. Seems better than selling or trading it, it works just fine.

In my research, I have determined that propane is worth about 92,000 BTU per gallon, and electricity is about 3,413 BTU per kwh. The furnaces of the style I need are about 80% efficient or a little less, while the heat pumps are about 200% efficient (heat pumps move heat rather than generating heat). So for, say, a million BTU of heat, it takes about 13.5 gallons of propane or 146 kwh. My current heater is a 100,000 BTU heater, and it seems to run about 15-20% of the time to keep the house warm if I am here; but most of my use is keeping the house warm enough to not freeze, which takes lots less. So let’s say a million BTU will last me 5 days. I’m generating more than 50 kwh a day, so in 5 days I might make 250 kwh, and the heater will use 146 kwh in the same time. Sounds pretty good to me! Of course, if it is overcast, stormy, and cold, then the heat pump and solar won’t work as well, but this is not a big problem in Arizona.

A typical winter will use about 250 gallons of propane, or $800-$900 worth. If I cut that to $100, then I am saving $750 a year, and swapping out the heater will pay for itself in about 7-8 years or so. And of course when I get the hydronics in, it will be even better.

The web box to monitor the system has arrived but is not set up yet. I’ll post a link to look at the actual production when it is installed.