Sunday, September 26, 2010

Solar Power - The Year in Review

For our full story on solar click here.

We installed Solar panels in August 2009, and they were turned on during September. We have now had a whole year of power which is shown below. The time-of-use metering means that we get paid much more for the power we generate in the afternoon than the power we use overnight, so the "zero point" for billing is different than that for power consumption. PG&E recently sent us our annual bill, which was about $500. Added to the monthly bills for basic service this comes to about $700 for the whole year. Our previous electricity bill was about $2000 a year. Since we changed our hot water, clothes dryer and range from propane to electric, we saved over $1000 in propane cost as well. That puts payback at around ten years at todays prices, given the likelihood of increased propane and electricity prices over time, actual payback would be earlier than that.

The panels have got a lot of dust on them (the roof is too high to get at easily to clean them), so aren't running at peak efficiency, the best day we saw was around 28KWh, with a lot of days of 26-27 KWh through the summer. The totals for each month are shown in the screenshots below.

Since we have built a new garage, we now have a lot more roof area. So we are now looking to add another 4KW of panels, and to swap out our propane furnace for a heat pump that will give us heating and cooling (yay - its hot today...) sometime next spring. Then the only use for propane will be the emergency generator. It should also make the garage a bit cooler in the summer by shading half of the roof with panels.