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Old 06-08-09, 04:11 AM   #1
Piwoslaw
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Default Increasing efficiency with mirrors

Would adding mirrors to a solar heater increase it's efficiency? Mirrors are cheaper per area unit than solar collectors, but how efficient are they at reflecting heat? Would too much focusing too much (how much?) sun on a collector be harmful?

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Old 06-08-09, 08:28 AM   #2
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There are other things to worry about too. Stagnation temperatures (temps when you are not cycling water because your tank is already as hot as you want it to get) can be a problem without mirrors on the collectors. Add mirrors and you could possibly run the risk of damaging your collector.
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Old 06-08-09, 09:16 AM   #3
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Would mounting mirrors only for the winter months work?
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Old 06-08-09, 04:21 PM   #4
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I still believe stagnation temps are a problem even in winter. A lot of light reflects off of snow on the ground.
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Old 06-09-09, 11:33 AM   #5
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Huge archives of information:
Solar Water Heating Projects and Plans

In one, they used some sort of pressure-release valve to avoid problems.
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Old 06-10-09, 09:45 AM   #6
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If your solar installer does not install a pressure release valve I would not pay them until another installer inspected the system for other safety issues.
I've seen systems boil over in the winter because of the snow reflection when the corner of the panel that had the sensor was shaded for about 3 minutes or less.
So yes, getting more light on to any kind of solar collector will increase your output and void your warranty, you will need more sensors to trigger the pump and higher temp tubing or you will melt some part of it.
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Old 07-02-09, 01:19 PM   #7
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I always assumed that the evacuated glass tube collectors were mirrored on the inside on the 'bottom' so that it would be more efficient.

I also thought by rotating the tube, you could 'tune' the system to better collect for a particular setup.

Maybe they are not that way, as looking into now, I do not see any of them mentioning it.
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Old 07-03-09, 01:54 AM   #8
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Quote:
Originally Posted by ldjessee View Post
I always assumed that the evacuated glass tube collectors were mirrored on the inside on the 'bottom' so that it would be more efficient.
Yes, I've seen evac. tube collectors with parabolic mirrors under them.
Quote:
Originally Posted by ldjessee View Post
I also thought by rotating the tube, you could 'tune' the system to better collect for a particular setup.
I believe only certain types of collectors allow this. The tubes can be rotated a few degrees left or right if the roof isn't exactly facing south. Of course then the parabolic mirrors underneath are more or less worthless (they still may insulate the bottom by reflecting heat which escaped the tube). It would be ideal if the tubes could be rotated automatically during the day, but I haven't seen that.

I spoke to a guy who both researches and installs solar systems and he told me that evacuated glass tubes aren't worth the money. They may be 20% more efficient, but almost twice as expensive, and you'll barely save enough to make up the difference. Well, maybe. But maybe efficiency is more important than money? Which car is better: a cheap SUV or a car that is twice as expensive, but gets twice the milage? It might take long years to make up the difference, but the econocar is still better. At least in my opinion.
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Old 07-03-09, 07:29 AM   #9
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Thanks.

Hmmm...I would think in colder climes (or atleast those of us with below freezing winters) that the extra insulation of the vacuum would make a bigger difference.

Of course, I am not sure why you can't have a panel or flat solar hot water collector in a vacuum.

I wonder which one stands up to hail better?
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Old 07-04-09, 08:39 AM   #10
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I've never heard of complaints of collector damage from anyone who has them. Hail is not uncommon in my state either.

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