Friday, October 07, 2011

Insulating the flat plate collector

The flat plate collector that I have been using in my comparative tests was constructed as a 1/2" baltic plywood box with 1" polystyrene insulation glued on the outside of the bottom. I did it this way so that I could use staples into the plywood to hold the aluminum absorber plates in place. The construction of my flat plate collector is described here.

Shown above in a bottom view (click to enlarge), you can see also the suspension beam and one of the pivots. The linkage arm sticking up out of the top of the picture normally faces downward and it allows the collector to be rotated to face the sun. One of the fluid inlet/outlet spigots can be seen on the end.

For glazing, I used SUNTUF corrugated polycarbonate glazing made by Palram Americas. Here is a view of the sealed flat plate collector with the Suntuf in place. Suntuf is crystal clear and very tough although the sheet polycarbonate it is made from is quite thin (0.75mm or 0.030") and it seems flippy until it is fastened in place.

You can see the "wings" on both sides. I found the Suntuff hard to cut and did not bother to make the two longitudiunal cuts that I would have had to make to have it fit the collector exactly. The "wings" serve no purpose but they do not affect the function either. It was just easier that way and I was worried about cracking the sheet while cutting.

I was a bit mystified by the plastic horizontal closure strips which I bought to use with the Suntuf. The wooden versions weren't available at the store. With those, I would have simply run a bead of one of the recommended sealants along the length of the top and bottom of the closure strip but these plastic ones are all perforated so that the sealant would just drop through the holes?

I added a subframe (the solid white strip below the brown closure strip) to the top of the flat plate collector and drove cushioned screws through oversize drilled holes in the Suntuf (as they recommend to allow for thermal expansion). The sealant I used was DAP 100% Silicone Rubber Sealant recommended by Suntuf. You can see how I carefully sealed the Suntuf to the top edge of the horizaontal closure strip. I am not sure how the manufacturer intends you to use this product, their literature is silent on the sealing method with the plastic closure strips. But this will do the job.

The insulated flat plate collector is now complete and awaiting further tests.

Index - Comparing concentrator to flat plate solar collector


Anonymous said...

your screws should have been installed on the crests not the valley

George Plhak said...

I see that - thank you. The arrangement did serve the purpose for a short time, your method would last better I think.

Anonymous said...

Hi George,

I'm the Director of Marketing for Palram Americas and stumbled across your post today. It's a cool project. I'd like to thank you for mentioning our product by name. I thought I would chime with a bit of added info for you and your readers:

1. Foam Closures are available, however, many retailers try to minimize inventory, so most do not carry them. Foam closures work great for panel ends when you are trying to seal out weather and infiltration. Here's a link to the closures on Home Depot's web site, in case you'd like to provide a resource:

2. Your reader correctly pointed out that we recommend fastening at the crown instead of the valley. However, in most situations valley fastening will also suffice. The primary rationale for fastening at the crown is to virtually eliminate any chance of leakage.

Hope that helps! If you create any new projects with our products, I hope you'll send me note. We love seeing unique uses for our products.

Stan Schultz
Director of Marketing
Palram Americas