Pacific island water systems using a combined solar still and rainfall collector

Abstract

The use of simple solar stills for the production of fresh water from sea water, combined with rainfall collection on the top of the solar still is studied in terms of the rainfall patterns on certain of the low islands of the South Pacific. Experimental results have been obtained to show the possible production on these islands from solar distillation. For one particular location it is shown that the probable rainfall collection averages about 2.35 gallons per square foot of collector surface per month. By adding solar distillation the average yield is increased to at least 3.77 gallons per square foot per month. An important feature of these systems is the cistern capacity needed to permit withdrawal of the average monthly production rate. For rainfall only, this amounts to 4.83 gallons per square foot of collector surface and is to be compared with 3.28 for the combined rainfall and solar collector systems. Thus, the combination of rainfall collection and solar distillation will produce about 50 percent more than rainfall only and the cistern storage capacity is decreased effectively to less than half of its volume for a given monthly withdrawal of water. The decision as to whether solar distillation is desirable on a given island should be based on the adequacy of available roofs or other intercepting structures to produce the required water and the cost of cistern capacity.