Experiment #2 Heavy Duty Colletor

Polyethylene and PVC can not tolerate temperatures above 180*F so we’ll use high melting point TYVEK as a waterproof underlayment and place a nylon net on top to distribute the water as a thin film. For the absorber plates we’ll use 2 foot wide sheets of aluminum. The idea will be to pass the solar heat from the aluminum absorber plate to the sheet of water below.




First we’ll line the perimeter with silicone caulking, than we’ll install the first sheet. Slide one end over the top of the dribble down pipe and tuck the other end into the PVC gutter. Now caulk the edge of the 24”x 94” absorber plate and slide another one in place.
We’ll need an inner frame to hold the absorber plate; the vertical inner support will be used to press the two sheets of aluminum together. Now we can cover the collector with some fiberglass reinforced glazing material.


The pump comes on and ten minutes later white blotches appear on the glazing… What’s wrong? That’s right we have some leaks through the aluminum absorber plate.
The output temperature of the water reaches 161*F in 30 minutes, but we have leaks to deal with… BUT there is another problem…

Temperature readings are taken from various locations on the absorber plate. These temperatures vary from 140* F to 220* F.





What does this mean?
That’s right, the trickle down water is unevenly distributed under the absorber plate.
Much of the heat is not being collected. They are areas of untapped heat sources. The output water merely represents the average temperature of water in contact with the absorber plate.

We need to build a collector that provides a uniform film of water under the absorber plate and see if we can do something about those leaks. I’d like to use a full 4x8 sheet of Kallwall but the aluminum absorber plate is only 24” wide and the seam in the middle is impossible to make water tight. I was thinking of using Polycarbonate (Suntuf). It’s 26” wide so it should fit nicely over a frame built around a 24”x 94” sheet of aluminum. Instead of a flimsy nylon net we’ll use a nylon screen under the absorber plate. What do you think?

Experiment #1 The Ugly Collector

Scrap wood is used for a frame, and a black plastic bag is used for an absorber plate. Water enters through a PVC pipe at the top of the collector. Small holes distribute water from the top of the collector to a PVC trough at the bottom. A polyethylene film is then used as an exterior glazing. It’s secured to the wooden frame with strips of PVC. Not exactly a glamour collector, but the cost is under $20. Mel holds up the bottom flap of the exterior polyethylene glazing to show the PVC gutter where the trickle-down water is collected. The gutter is simply a PVC pipe with a slit cut into one side.

A bilge pump is used to pump water from a bucket back to the top of the collector. In a half hour the water temperature goes from 60*F to 120*F. I was so pleased with the results of this first MTD experiment that I decided to, unplug the pump and take a brake for lunch and record the results. When I returned to the first experiment I found that the PVC melted and the black plastic absorber wrinkled beyond recognition.

There was plenty of heat but the PVC and polyethylene did not last long without water to moderate temperature. What have we learned and what shall our next experiment be?