Zero Energy Home: Zero Day, Again

Dan and Karen built a net-zero energy home and blogged about it. Two years later, we checked in with them: How's your home performing for you? This is Dan's report.

It's Zero Day, again.

October 21, 2012 is the second anniversary of the day that Oncor (our electric grid operator) installed our bidirectional electric meter. Last year at this time, we found that we had generated an excess of 484 kWh, but it had been a year of extreme weather. With a more “normal” weather pattern this year, we were interested in seeing what our results would be. On the one hand, it wasn't as hot as the previous year (85 days of 100+ heat) so we wouldn't need as much energy to cool the house, but it was cloudier this year, resulting in less energy generation. The absolute numbers from last year were 5018 (in from the grid) and 5502 (out to the grid).

This year the meter shows values of 9669 (in from the grid) and 10554 (out to the grid). That's 885 kWh excess generation over two years. Subtracting last year's 484 (and checking my basic math skills), we see that we generated an excess 401 kWh this year. That suggests to me that our house is well insulated so the excessive heat last year didn't have a major impact on our energy use. But last year's unrelenting sunshine generated a lot of extra energy that we missed this year.

We don't have any immediate plans for life-style changes, but I've been eying electric cars. I haven't run the numbers, but I would guess that an electric car (over the short distances I drive to work) would use up all (and a bit more) of the excess electricity we're generating. That's an easy sacrifice to make (“free” electricity instead of expensive gas), but I'm finding it hard to justify financially. Even with government incentives, it'll take a lot of cheap miles to make up for the additional expense of going electric (which is a little ironic, since most of the available vehicles have limited range, making it hard to get those miles before running out of juice).

Ignoring my transportation angst, we're happy with our house. It's definitely performing the way we were hoping. When all is said and done, we're generating more electricity than we're using, and it's another successful Zero Day.

See photos of Dan and Karen's net-zero energy home.   Catch up on Dan's blog.