Friday, October 8, 2010

Annual capture per square metre

8 Oct '10: Mr A.L. on the Navitron forum attached great priority to the thermal capture per square metre per annum. He went to the extent of counting the bricks on the photos, and working out his own figures.

So I answered: (shortened version) The black collectors are Exactly ONE squ metre each, and there are four of them. The air volume enclosed by the plastic glass is near to One Cubic Metre, in TWO boxes, each 1.75m wide x 1.6m high x 200mm deep, supplemented by 1 sqm of alloy mirror above, and shortly to be supplemented by about the same below.
The black collectors are Polypropylene and flat on both sides, and do not have fins to help exchange heat with the air (Doh! ).  So my next prototype sunbox is using 4 off-the-shelf metal radiators, each precisely one square metre, single panel with a high amount of convecting fins on the back, all sprayed matt black.
   Over 8-12 hour pumping days, we are averaging 0.8-1.5 kW per hour of operating. Best recent day has been 1.75 kW / hour over 8.6 hours in sunny conditions on a coldish October day.

Metered capture so far is 2,160 kWh from 7 months of operating. Heat capture in wintry conditions is doing well (always in double figures if there is a hint of sunshine), so I dont expect us to fall short of the 3,000 by next Mid-March. At an average of over 10kWh a day, I would hazard a guess that we might make 3,300.  On this basis, my boxes' annual capture and bury might be about 825 kWh/m2.

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