Tuesday has been the hottest day of the year so far. Temperatures rose into the high 20s, the PV was almost a maximum of over 23 kWh, and even at midnight, the air temperature was 18.9º. The Tubes had their best chance yet to show what they can do, and managed to run for all of 8 hours, gaining a magnificent 6 kWh. The Sunbox ran for 14.5 hours and gained 18 kWh. On days like this, the heat pump is almost totally asleep, so all the thermal gains are retained in the ground. But it has been a good competition, because the morning sunshine was strongly on the east roof.
The weather was so dire in April that the PV capture was a full 100kWh less than in the previous year.
Another bit of plumbing
I added a second airlock preventer to the heat exchanger, so that both circuits should now be reliable. Also, there is too much free running around the circuit when the Heat pump is running, but the Tubes are not. So, although one was fitted originally, there is also a second 22mm check valve, to provide more resistance to the free running. I hope I fitted it the right way round!!
23 May 2012 Postscript : Another hot sunny day, and again, we get 18 kWh from the Sunbox and 6 kWh from the Tubes. I notice that the Tubes kept on working long after dark, because the air temperature was enough to warm the thermal sensor - especially if the roof tiles are warm, and are raising the microclimate above the roof surface above the wider ambient night temperature of 19º. The controller (which has a clock) was flashing a warning sign
24 May Post Postscript: 3 days running of high sunshine, and more to come! Kilowatt-hours from PV has been 23.2, 23.4, 21.0 in consecutive days with the Sunbox at 18, 18 and 20 in the same time. The Tubes have gained 6, 6, and 7 in the same three days. The deep ground temperature is going up nicely again.