Sunday, December 4, 2011

PV, going into the winter

3 Dec 2011: The Sunpath is moving to its winter pattern, which is to be behind Sharp Hill, and for the Sun to rise a whole hour later than it does down in the plains... and to set earlier behind Wilford Hill. The change is seen in the last two winters that we have had, with a massive drop in November (being less than half of October's harvest). There's a miserably dour Dec, Jan and Feb, followed by a colossal rise in March, after which the Sunrise comes from further in the east where it is not behind the hill.
We have to be philosophical about this. We can't move Sharp Hill out of the way, and we can't move or rotate the house. I am just happy that we get what we get. My friend just down the hill a bit from here, with a purely south facing roof has managed more than 3,800 kWh in the last year, whereas I am glad if I can get 3,330 kWh in a year. The chart above shows that the summer of 2011 has been better than that of 2010. It means that the target we have to set for the GSHP is 3,330, not as much as my friend's house.
  This doesn't affect the Sunboxes much, as they take longer to warm up after sunrise and don't really get going in the winter unless the GSHP is demanding heat by driving cold glycol at them. I have increased the Trigger-Delts-T to 6.0 degrees to make sure that it only works if there is a distinct advantage. This reduces the hours of working, but increases the efficiency when it does work.

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