Performance monitoring is essential in order to conclusively demonstrate the cost effectiveness of a solar heating system. Unfortunately, this “last step” is an aspect which has received little engineering consideration. The monitoring programs in progress typically use instrumentation which is much too expensive and complex for use by individual operators of domestic water heating systems. Hence, few systems are monitored, and the average owner knows little about the performance characteristics of his system. Even malfunctions go undetected. An inexpensive performance monitoring system is described in this paper. It could probably be mass-produced for under 15 dollars or built by the typical homeowner for under 30 dollars. The monitor indicates the instantaneous solar fraction. Overall system performance can be improved with this monitor, since it enables the user to correlate load with the availability of solar heated water. Methodology, performance parameters, and some performance data are presented.

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