Tuesday, October 13, 2009

Perfect sunny day...

Sometimes you get almost the perfect day.... see the handheld meter - totally sunny in the morning with an unbroken bell curve... and only breaking up a bit in the afternoon with some very late light fluffy clouds, by which time the sun was well round to the west. It intrigues me how the roof picks up power, both by reflection off the clouds, but also by some sort of diffraction - when the sun is clearly round to the west and having no view to the east facing roof, and blue sky above it (nothing to reflect the light), the roof still picks up power and the meter notices when clouds float across.
Of course, if the roof faced south, the bell curve would be symmetrical with a higher zenith. I will photograph the curve at monthly intervals. With the sun low, the bell curve zenith must move to an earlier time of day eg 10am GMT, and in the summer I expect it to move closer to the centre, eg 11am GMT.
For this reading the OfGem meter actually recorded 13.01 kWh for the day, which must be as good as anybody can do for mid October. The handheld meter samples every 30secs and tots up an estimated aggregate, whereas the OfGem meter is always on.

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