Solar Thermal Design and efficiency?

I have finished building and testing my diy solar thermal collector. i decided to paint the outside framework black, will this make a difference? also i was wondering how to work out the efficiency and power it can produce? the temperature difference was 17 deg going in and 29 going out at a flow rate of .36 litres a minute and the solar radiation was 800 watts per m^2. the temp difference might seem low and there a 2 reasons for this. 1)im in ireland and 2)i never bled the radiator so i have a feeling the water only flew across the bottom rather than circulate.


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lemonie7 years ago
PM this guy, he's really into solar-stuff and ought to be able to help you.

rich5007 (author) 7 years ago
thanks it was .53 m^2 bit on the small side that would make it a little over 18% efficient?
No, the other way, you have 1/2 sq metre, which can only intercept 400W, and you've caught 300 of 'em - 75%  Not bad at all. "Suspiciously" not bad ! What were your meaurements made with ? 

rich5007 (author)  steveastrouk7 years ago
for the flow rate i used a simple method of timing a litre in a container, and i used a digital thermostat which could give 2 different readings one for inlet one for outlet but it would be reading off the fittings rather than the water so it might be less accurate.
Couple of things that I thought of last night. How is the water flowing ? You'd benefit from going IN on the lower corner and OUT on the upper one - no air locks that way.

Also, timing a litre rather than a minute will improve your accuracy.

rich5007 (author)  steveastrouk7 years ago
yes I stood the collector vertical so water would come in the bottom and out the top that way it would self bleed.  as for the timing the method you said to do was actually what I did, I actually said it wrong in my above comment. it took around 3 minutes to fill the litre container.
rich5007 (author)  rich50077 years ago
the photo above i painted the outside framework black, was this ok to do?, i felt it would help attract more heat
Sounds like a good idea to me. Did you insulate the back of the box too ? 

rich5007 (author)  steveastrouk7 years ago
yes and the sides on the inside were all insulated
You've gained
12 x 0.36 x 4200 Joules/minute, or 302 joules/second or 302 W.

What was the actual area of your panel ?  If it was 1sq m. you've managed 300/800 or 37% efficiency