Some ambitious and highly-skilled types will surely choose to build their own absorbers. Several good plans have been published lately, and even though they require a lot of picky labor, the final products work pretty well.
One detailed set of instructions is put out by the Brace Research Institute near Montreal, the world-renowned center for studying intermediate technology. Their plans call for a sheet of galvanized corrugated steel roofing riveted to a flat sheet that is slightly larger. The sides of the larger bottom sheet are crimped around the sides of the corrugated top sheet, and the ends are designed to accept short sections of galvanized pipe at either end. These pipes feed and drain the water
Scallop Ends Of Flat Base Plate
Base Plate Turned Up To Close Corrugation
Scallop Ends Of Flat Base Plate
Figure 57. The drawing is taken from plans drawn up by the Brace Research Institute in Canada. The flat sheet is riveted to the corrugated top sheet, and the rivets are then soldered to prevent leaks. The end cuts can be made quite accurately if you make a cardboard pattern and trace it onto the metal before you cut. The problem with this homemade absorber is that water doesn't always flow through it evenly.
channels between the two metal surfaces (Figure 57).
There are several other ways to build absorber plates with corrugated metal to make trickling collectors a la Thomason and Shore. Water can atn either openly in the exposed corrugations or between the sheets (Figure 58).
Both the Florida Energy Committee and the Langley Research Center in Hampton, Virginia have published excellent pamphlets on how to build solar collectors. The one from Florida is called How to Build a Solar Water Heater and costs $3.49. The Langley book, published by the G.S. Department of Commerce, is entitled An Inexpensive Solar Heating System for Homes. Its price is $4.25 (see bibliography).
Each of these helpful booklets describes ways to bend 3/4-inch copper pipe into a series con-
figuration across a copper sheet. The problem immediately apparent here is that bending pipe evenly for almost 180 degrees requires special skills and equipment And bonding it to the copper sheet is a painstaking process that could only be done by someone with plenty of skill and experience. (It also looks like it would take miles of solder.) So it's not something we would recommend to beginners, even though the directions are very complete.
If you're a skilled plumber, and you do choose to make your own absorber plate using a series fluid-channel configuration, double the tubing back and forth across the plate leaving 4 to 6 inches between the runs. The temptation will be to space the channels closer than this to increase the distance fluid must travel through the panel.
But studies show this only creates a bottleneck in the water flow. The absorber will not be more efficient with more closely spaced tubes. That only makes more friction in the pipes (Figure 59).
If you decide to make an absorber plate with a parallel configuration of fluid channels, the spacing between pipes still should be about 5 inches. The parallel riser tubes will want to be 3/8- to 1 /2-inch tubing, while the inlet and outlet manifold pipes may have to be 3/4 inch in diameter to handle the load. (Risers in a thermosyphoning collector should be larger than 1/2 inch.)
The advantage of parallel channels is that less friction is created in the collector. The problem is making leak-proof connections between the risers and the manifolds because they're of different sizes. This either means many expensive fittings if
you use copper, or some exact drilling and welding if you use steel or galvanized pipe. Dissimilar materials cannot be used. If you try, you'll only end up with "galvanic" corrosion at the joints. In any case, a parallel system of tubes should be assembled and thoroughly pressure tested before it's bonded to the plate itself.
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