An objective of the invention is to design and develop an effective method to collect and store heat in a solar collector for delayed release. An embodiment of the invention is directed to an evacuated tube collector, where PCM is placed directly inside the void space of the collector tube, next to the heat pipe. The heat pipe is located with phase change material (PCM) in such a way that its thermal connection with the heat pipe can be switched "ON" to start heat transfer from PCM or "OFF" to keep latent heat stored in PCM for delayed usage. In additional, flow of heat exchange fluid through the manifold can enable release of stored heat of PCM to storage tank. Delayed release of accumulated heat in PCM enables added functionality of on-demand operation of SWH.
STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT
 This invention was made with government support under DOE Phase I STTR Grant No. 87938T12-I awarded by the Department of Energy. The government has certain rights in the invention.