Tuesday, June 22, 2010

Celebrating the Solstice

21 June: It was nice that the last two solstices, Dec 21 and June 21 were both sunny days, so one could compare. In this diagram, the two Poisson curves are at the same time and power scale, and show the difference, impressively comparing the day length and the solar intensity. Other people might go and watch the Sun rising over Stonehenge or Glastonbury Tor.... me? I check the PV meter and the SMA website, measure the time of the sunrise over Sharp Hill etc.... How sad is that! .... :)
   Because we have the high Sharp hill to the south, the winter sunrise is an hour later than on level ground, and the sunset an hour earlier. So in the morning, there is daylight, but not sunlight, hence the tail in and sudden steep rise just after 0930 at the start of the December solstice. By March equinox, the hill has less effect. At this time of year in June, the roof is consistently outperforming all the predictions, and with the sun rising and setting in the north quadrants, the hill has no impact on the performance, because the Sun is rising and setting to the north. We should have up to 2,250 kWh harvested by the end of June (at the present average), and then we have three summer months of July, August and September to bring us to our PV anniversary of October 1.
   We have had no payment from the Feed in Tariff yet, the first one can't be expected until October. I need to chase Good Energy for payment up till the April 1 date, as they are promised to pay some sort of tariff prior to starting the main FiT.


  1. hi David
    I was really pleased with this summer solstice too. And rather than celebrate at Stonehenge, I was hoping for a record PV generation day, since we had no cloud all day on 21st June in Wollaton, Nottingham this year. We managed 10.1KwHrs off a WSW facing 1.72kwp system. The new record production was only tinged with the disappointment that that is the best it will get all year...it's downhill from here to the winter solstice!
    all the best

  2. Well I wonder if the year is so rigidly symmetrical. It's a fair guess that the spring months are better than summer and autumn because of colder air temperatures. If you take our 'harvest' from 21 Dec to 21 June that is 1,697 kWh, and simply doubling it (if the year is symmetrical) would make nearly 3,400 in the year! I guess that the summer months will bring us less than that, but we hope to exceed 3,000 kWh.


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