Darkest day on UW (Seattle) campus in two years

[BackwoodsEE]

The total sunlight energy falling on the UW campus yesterday was 0.61 megajoules per square meter. This is equivalent to 9.8 minutes of sunshine from directly overhead, e.g., June in Hawaii.

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[bcroe]

Heavy clouds here (norther IL) as well, output for the day was only 10% of capacity. Bruce Roe

[J.P.M.]

Let's see, 0.61 megaJoules = 610,000 joules/3600 sec/hr. = 169 Wh. if that's the daylong total GHI, that's a pretty cloudy day, assuming we're talking GHI here, with a daylong clearness index of something like 0.06 (169 Wh/~ 2,863 Wh extraterrestrial GHI), vs. a monthly average daily clearness index of ~ 0.26 - 0.32 or so for Seattle/Olympia, WA.

Interestingly, there is a PVoutput array in Olympia, WA that put out 0.187 kWh/kW on the same day (11/27/2017), suggesting a POA at that location of probably something like 0.187/.15 = 1.2 - 1.3 kWh/m^2 per day. That array also output 0.106 kWh/day on 11/03/2017, suggesting a daylong POA (or GHI) of something like 0.80 or so kWh/m^2 per day - still a lot higher than the 0.17 kWh/m^2 per day =0.61 megajoules/day you're reporting for 11/27.

(Under cloudy skies as were talking here, GHI and POA are usually within a couple % of one another because most all of the irradiance is diffuse and isotropic.)

Not questioning your veracity or that of the UW, but If I got a 0.17 kWh/day out of my pyranometer, regardless of how cloudy it was, I'd be checking it for errors.