HOW TO BUILD - AND USE! - A SOLAR STILL

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The still described here uses the same principle, but is a little more complex than simply letting sea water run into a pond to evaporate. By means of a glass-plate collector we will increase the temperature in the still to speed evaporation. The design is borrowed from Dr. Telkes, and has been proved by careful testing over a long period of time. Researchers have shown that it's possible to produce almost a quart and a half of water a day for each square foot of the collector's surface. Thus the unit should have a maximum output of more than one gallon a day. Of course, this figure represents ideal conditions, but it will be interesting to compare your results with the calculated output. The still described here was tested in mid-winter, and produced more than one quart in six hours.

MATERIALS

1 by-4-inch redwood board (8 linear feet)
1/2-inch plywood (one piece, 24 by 24 inches)
Single-weight window glass (one piece, cut to measure)
1/2-inch O.D. copper tubing (4-1/2 feet)
1/2-inch, 90-degree copper elbow (one)
1/2-inch copper pipe cap (one)
Galvanized iron (one piece, 3 by 24 inches)
1/4-inch I.D. copper tube (six inches)
Large tin can (one)
1 /4-by-1-1/2-inch wood screws (approximately 30)
Black terry cloth (approximately two yards . . . one large bath towel)

To begin construction, first assemble all the needed materials (except the glass). Redwood is preferred where possible because it resists rotting, while other woods will deteriorate with constant exposure to water.

At the lumberyard where you buy the 8-foot board (1 by 4 inches) have a groove cut 1/8 inch wide to a depth of 3/8 inch. Locate the cut 1/2 inch from one edge. This is the slot for the glass window. Next cut the 1-by-4 redwood sidepieces to the proper length as shown in Fig. 1.

Drill two holes at each corner of the sidepieces and assemble them with wood screws. The 1/2-inch plywood back may now be put in place and holes drilled for screws. Notice that no screws are put in at the corners, to prevent interference with those which hold the sides together.

Mark the locations for the large holes that will receive the 1/2-inch tubing. Drill a 1/8-inch hole as a guide, and then drill three 5/8inch holes and one 3/4-inch hole, as shown. Be sure the large hole is the proper size for the cap, which we'll solder to the end of the top tube.

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