The OTEC is generating electricity by using temperature difference between surface and deep seawater which least max temperature difference is 25 degree Celsius. Then, the OTEC has limited thermal efficiency due to ocean thermal environment. In order to improve the thermal efficiency of OTEC, the increasing of the seawater temperature is required. Off course, the changing of seawater temperature is difficult without adding the other thermal energy. Therefore, a researcher proposed solar heat boost OTEC. The surface seawater can be increased to around 80 degree Celsius by the solar thermal energy which was collected by the solar heat collector. Then the hooter seawater is obtained by the system. However, the system cannot use cloudy, rainy and night times which are without sunshine. Then, any thermal storage method are required to continue operating the OTEC all days. However, the storage of huge thermal energy into the seawater is difficult because need wide sea area and kilo-ton every hour class of huge seawater. Then, the author considered that thermal energy can be stored into the thermal storage medium as a latent heat. And the thermal energy can be extracted from the storage when it is required. In the present study, the author developed new latent heat storage type heat exchanger composed thermal storage medium which is sodium acetate trihydrate. The objective of this investigation is flatting temperature of heat sources using the latent heat storage type heat exchanger was performed. In addition, in order to know the time dependency variation of the solar energy around OTEC site such as southern island area to design of solar collector, the intensity of solar radiation using pyranometer around one year at Kumejima in Okinawa pref. besides of OTEC site. This paper reports the result of the test experiment of latent heat storage type heat exchanger and measurement of solar radiation.