Since the mid-seventies Saudi Arabia has been at the forefront of research and development into solar energy. For example, two major international joint research and development (R&D) programs were funded, in cooperation with the United States of America and the Federal Republic of Germany, aimed at developing renewable energy technology and demonstrating its applications by designing and installing several pilot projects. After more than 20 years of research and development it now becomes essential to evaluate these R&D activities in order to determine their benefits to the scientific community, the country, and society in general. This paper therefore presents an evaluation of a number of research projects in terms of their technical and economical performance and feasibility. The paper also discusses the various lessons that have been learned through the operation and maintenance of these projects, and considers the various reasons underlying either their success or failure.