Array milestone: net-zero for dirty electricity

June 23, 2015

Puget Sound Energy began recording data for the solar panel array at my house in mid-October last fall. The race was on: at what point would I be selling the utility clean power from my panels faster than I would be buying carbon-based, “dirty” power from them?

Predictably, through the short, dark days of fall and winter, we needed to buy more power from PSE than we were selling back to them. Round about February, though, as I read the numbers on my meter I began to notice a change.

The number of kilowatt hours returned to the grid was beginning to increase more rapidly than the number of kilowatt hours supplied by the grid.

March and April confirmed the trend: the “returned” measure was chasing down the “supplied” number, slowly but surely.

At last, on Day 250 of having solar panels (June 23), we have achieved net-zero! This means:

  • The dirty power we bought from PSE over the winter has now been offset by an equal amount of clean power our panels have produced and pushed out to the grid.
  • The panels have produced power in excess of what was pushed out to the grid, enabling us to meet our household needs with renewable solar power.

Of course, it is true that the calendar will inexorably move towards a less favorable solar season, again. It is possible that “net zero” is a temporary victory. What will be particularly revealing I think is how the numbers stack up exactly one year in. That will give us an annual baseline measure against which to measure future performance as well.

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