Build your own flat panel solar thermal collector

Step 4 Build the frame and assemble the panel

You can use the collector as is. Just lay it out in the sun and pump water through it. However, much more heat can be captured by building an insulated enclosure for it.

1. Cut one 2x3 to two lengths of 22.25" for the ends of the frame. Screw the other 2 2x3s into the ends to make a rectangular frame.

2. Wrap the transparent plastic around this frame and tape in place to make a transparent lid to fit over the collector. In my case this is for test purposes only, since I intend to eventually install the collector underneath transparent roofing material in my attic. The 22" panel width will fit between existing rafters which will provide a ready-made frame.

3. Cut the plywood to 24"x8'.

4. Cut the polystyrene sheet to 7'4" by 3'9" and place it centered on the plywood. This will be the insulation for the back of the panel.

5. Test-fit the collector and drill two holes in the plywood large enough for the hoses to easily fit through (about 1" should be good). Make one of these holes into a slot by drilling another hole right beside it and cutting away the wood between them. This is to allow for thermal expansion of the corrugated plastic sheet. Plastics typically have a high coefficient of thermal expansion. If you restrict the panel from expanding, it may warp and cause a leak.

6. Now stack the whole works together: First the plywood, then polystyrene, then the collector, then the transparent cover.

7. Secure the transparent cover to the plywood back with several clamps (or you can screw it on, but initially you might want to be able to remove it easily for access to the collector)

Comments

[UK_Westy]

Hi, This is great I have been looking at using solar power to heat water for a child's paddling pool. Basically, heat water one day and use the following. I was thinking of using a solar powered pump, but thermo-siphoning costs nothing ! If I used a double glazed unit (I have a couple lying around) instead of the plastic sheeting would this create too much heat and indeed melt the corrugated plastic sheeting ? Also, if the system was plumbed into a supply and as water was drained out, and fresh water replaced by the use of a ball valve, if the whole system was at an angle as you suggested when filling, wouldn't it enable the air to be removed constantly ?

[iwilltry]

If you use double glazing you probably will get too hot for the plastic parts inside. It is possible to design a system that will expel air automatically. You simply need to ensure that at any point in the system there is a path that rises continuously from there to the highest point (highest water level) in the system, and that the highest point is the surface of the water in the storage container which is exposed to the atmosphere. For me that would have meant drilling holes in the side of my cooler (one at the bottom for the exit and one at the top for the inlet). Then air bubbles would simply rise through the system and be released to the atmosphere. I did not want to drill holes in my cooler so I opted to bring the exit and inlet tubes in from the top which introduces the problem of trapping air and makes it necessary to take steps to remove the air in order to get thermo-syphoning to work.