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Old 02-19-14, 02:59 PM   #10
Exeric
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Join Date: Aug 2012
Location: California
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Ryland, I'm glad this is moving away from such a p***ing match!. I have never disputed that you can design any solar heat system to match the average BTU requirements for a specific location and size of structure. But the point of this whole thing is the word AVERAGE. We don't live in an average world. When there is high moisture content in the air there is very little heat getting through, sometimes almost none. That is because that moisture, whether it is fog, rain, sleet, or snow, will absorb most of the infrared rays from the sun. That shouldn't be a revelation. There's anecdotal evidence all the time from members on this thread that this happens.

Sometimes there can be long stretches of stormy or foggy weather. The longer the stretch of this weather the more you are screwed with a solar thermal system. You will get almost no heat out of that system for that long stretch. Even if you then get a similarly long stretch of clear blue skies and completely make up for that BTU shortfall you are still screwed. To make things simpler I'll convert a long stretch of BTU representations into unit values of 0 or 1. Not very accurate but you will get the idea. Plus I'm make the similar assumption that you can't store the heat. Again, not that accurate but for month long stretch of similar weather it approximates the truth. Even a thermos bottle will only retain heat or cold for a day or two.

In your location you average 1 BTU each month in December, January, and February. December was a stormy month. In December let's say your BTUs coming in was 0. January was a great month and you got 2 BTUs. February you got the average, 1 BTU. Because a thermal system does not really story heat very well December was a total loss. January had an abundance of BTUs, (2!) but you wasted 1 BTU because it was more than you needed. February came right in on the design spec for the system for the month. Your system worked to specification using the AVERAGE BTUs required for your location. You got 3 BTUs out of your solar thermal system, and averaged 1 BTU for each month. What is there to complain about? Well you might complain that you froze your butt off in December. I would.

On the other hand in a net metered solar PV system, which for simplification I'll assume the same equivalent BTUs in watts, you didn't freeze in December. That's because you designed the size of the array for the whole year's electrical requirements. The grid stored your excess energy when you generated it and returned it when you needed it. It functioned just like a huge perfect battery.

Last edited by Exeric; 02-19-14 at 08:35 PM..
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