Even with our photovoltaic system offline for 14 days in July, we determined last month that the Unity House can be confidently claimed “Net Zero” — that is, less energy was used to run the house for one year than was produced by the 5.4 kW solar array on its roof.
We did our calculations based on a year of “lived-in” data and use. Mitch’s first read date was October 5, 2008, and I recorded data on October 5, 2009.
October 5, 2008 – October 5, 2009
Production: 6441 kwh (produced by the PV system over one year)
Excess: 5190 kwh (out to grid after immediate use by the house)
In: 5179 kwh (in from grid)
Total Electricity Use: 6430 kwh ((Produced – Excess) + In = Total Use)
Net Energy Use: – 11 kwh
So it was a close one – the system used 11 kwh less than it produced for this time period. The PV system was offline for 14 of our most productive days this summer due to a lightning strike. We’re hopeful that this year will see uninterrupted service from our PV system and demonstrate even greater electricity production.
The Unity House is the on-campus, LEED Platinum residence of Mitchell and Cindy Thomashow. You can find out more about the Unity House by clicking here.