A coordinated testing and monitoring program is essential for the reliability of a solar energy system. This paper discusses an approach to testing and monitoring that is applicable to liquid solar systems containing nontracking collectors and a sensible-heat thermal storage tank. The unified approach is based on the use of simple, low-cost meters for the required performance measurements. In this approach, a newly-installed solar system is subjected to a short-duration test to assure that it is operating properly before final, acceptance. Continued use of the meters as part of a preventive maintenance program enables maintenance personnel to detect and diagnose malfunctions of the solar equipment; it also provides valuable data on the system’s performance and reliability for feedback to system designers. Such a unified approach to system testing and monitoring can play a major role in assuring the reliability of the installed solar system and provide the feedback essential for improving the performance and reliability of future designs.