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Solar thermal panels: flat plate or evacuated tube?

Posted by Gabriel Wondrausch on 8 October 2010 at 9:08 am

Which type of solar water heating system works best. Watch this video to weigh up the pros and cons of flat panel versus evacuated tubes.

The main difference comes down to the efficiency. With evacuated tubes, the vacuum provides almost perfect insulation. A flat plate panel has insulation at the back and sides, with glass on top, and isn't so efficient per square metre. Flat plate panels are generally slightly cheaper.

During the summer months, there's very little difference in performance between the two. In winter, when we have cold days, and lower light levels, the evacuated tubes will perform slightly better.

We install both systems. They suit different people. The argument often come down to aesthetics versus efficiency. A lot of people prefer the look of the flat plate panels, but if you want the more efficient, then it's evacuated tubes.

About the author: Gabriel Wondrausch is founder and director of SunGift Solar, which installs solar thermal and other renewable energy systems in the South West of England.

If you have a question about anything in the above blog, please ask it in the comments section below.

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2 comments - read them below or add one


nnw49Comment left on: 26 October 2011 at 4:59 pm

I think its likely to be affected by how windy the location is: the more windy, the more wind-chill on the collector - hence tubes will perform better.

 Also (particularly if the collector is mounted on a free-standing frame), a tube collector will have a lower wind loading than panels - as the wind can go through the collector as opposed to having to having to go round it.

 It does depend a little on the design of the tubes' collection element too: there are some that have a flat heat collector that goes across the tube (handy for the installer as they can be angled so that they don't collect heat!); others have wrap around collectors that collect heat from all directions. I suspect these are more effective as they are less particular about the direction of the sun.

 I am told that the theoretical efficiency of panels is 40% and tubes 50% (but I can't lay my hands on the paper that suggests this!)

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Cathy Debenham

Cathy DebenhamComment left on: 18 October 2011 at 3:18 am

The Energy Saving Trust field trial of solar hot water systems published last week confirms that there is little difference in performance between flat plate and evacuated tube systems.

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