Solar Nemesis: Rain

Yesterday was a rainy one in Seattle, with record amounts falling for nearly the entire day. It provided a good illustration of one of the downsides to solar power: the effects of the weather. Over the course of the day my poor solar panels weren't even able to produce half a kilowatt-hour of energy; their total for the day was just 494 Wh.

Solar PV production from a sunny day (June 11) compared to a very rainy day (October 22)

In comparison, on a sunny summer's day the same system was able to produce that much power in just 11 minutes during the peak period. That same day (June 11) the panels produced a total of 21.4 kWh, more than 43 times as much. Conveniently Seattle City Light has a net-metering program that lets me "store" that excess power from the summer in the form of a credit on my bill, which then reduces the amount I'd pay for power I can't generate on rainy days.

Changing weather throughout the day can also have a significant effect on solar production. The chart below shows the effect of a cloudy start to the day giving way to a sunny afternoon. That day the system generated 17.8 kWh.

Solar PV production on a cloudy day started low, then returned to normal as the weather cleared up in the afternoon.