At the end of June we had one full year of operating with the PV and taking energy usage and production data. From July 1st, 2011, through June 30th, 2012 we used 3,755 kWh, which would have cost about $700. This is below the THC target and likely meets the Passivehouse primary energy limit as well. During that period the solar electric system produced 6,779 kWh, meaning that we had a net export of 3,024 kWh – handily achieving zero annual net energy. The surplus could be used to run an electric car over 10,000 miles. It’s important to note that this was an uncommonly warm winter, and I’d expect to use 6-700 kWh more in an average year. It’s also important to note that we are a household of two – add a couple of teens and the energy balance would be different – yet I believe we could still be net zero and meet THC under those circumstances. With the balmy winter, we were actually net zero every month except December and January.
We spent about $26,000 after subsidies to get here. Some of this work was subcontracted and some I did myself. I got some good deals, too. I think another person might have spent $40,000 to have the same work performed. The energy bill of this house when we got it would be in the neighborhood of $3,300 annually, so the simple payback of this effort seems well within the range of reasonable, and we got a more comfortable house with better air quality.