When the days are short and skies cloudy, the output from my 29 rooftop solar panels drops precipitously.

So far during this gloomy December, my system has produced just over 100 kilowatt hours (kWh) or about one sixth to one seventh of my monthly household usage. December has produced eight days with no solar output and seven with 0-1.5 kWh. In August, the worst day I had was 15.6 kWh and 30-40 kWh a day was common.

With Christmas lights and our two kids home, December is a heavy usage month, often topping 800 kWh.

But overall, the system has performed well and every electric bill from National Grid with whom we are still connected, has been a goose egg since the system was switched on in June. Our best month was August when the system yielded 952 kWh while this fall, October produced 551 and November 540, which roughly equates to an average month’s usage in our household.

So I am eating through the credits built up during the strong months to carry the weak months.

One slight inconvenience is that National Grid does not show a running total of credits. Nor does it show the credits you built up during the monthly billing cycle. All it shows is how much you used from them.

So all I know from my bill is that I used 116 kWh from Nov. 1-29 from National Grid and that solar carried me the rest of the way (I used 712 kWh during last December’s billing cycle). The January bill for the December should be very interesting.

Which is all to say “I wish it was sunny!”

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