In order to improve the performance of the solar-assisted and energy-storaged heat pump system, an experimental setup was constructed. In this study, the solar-assisted energy-storaged series heat pump system and other conventional heat pump systems with no energy storage (series and parallel heat pump systems) are experimentally investigated and compared. The experiments were made in July, August, September, October, November, and December in 1990, under the clear-sky conditions for three heat pump systems. The experimentally obtained results are used to calculate the collector efficiency n(k), heat pump COP, and system COP(sys) (coefficient of performance). On the other hand, a dynamic simulation program has been developed for a solar-assisted and energy-storaged heat pump system. The experimental results were compared with the dynamic simulation results.