Steady experimental research on a solar energy collection and storage unit with indirect heat exchange

A high temperature energy collecting unit which directly receives and stores solar energy has been developed in this paper. In the unit there is a compound parabolic concentrator which has a very special and novel structure. The concentrator is a type of forward reflected imaging concentrator. When the concentrator traces the sun the emergent light keeps on a fixed direction. So the solar energy receiver doesn’t need to follow the concentrator’s movement. The solar energy received by this new concentrator can be easily transferred to the energy storage oven next to the bottom end of the concentrator. The energy storage oven in the unit is a mental cylinder with a heat preservation layer which is a vacuum sandwich structure. In the inner space of the oven there is a heat transmission channels along the central axis. The space between the channels and vacuum sandwich shell is filled with a kind of phase change material. The phase change temperature of the phase change material is 188℃. Some heat transmission copper tubes are placed in phase change material to enforce heat transmission. A coil tube is set inside the oven (actually merged in phase change material) to export the heat energy to the user by circulating the heat conduction oil in it. The design philosophy and the operation principle of the solar concentrator are introduced in the paper. The simulated experiments for the heat storage and emission performance of the unit have been conducted under the steady condition. The curves of the relations between the heating/emitting process and operation time have been given under the steady condition. The basic analysis for the heating, storage and emission process have been made. The experimental results show that when the provided heat energy is 600W, the temperature inside the oven can reach 200℃ after 9 hours continuously heating. The oven has the features of high efficiency and long time in heat storage. The whole solar collecting and storing unit appears a compact structure. Thanks to the skillfully connection between concentrator and the heat storage oven, the energy transfer through the unit is smooth and efficient. This unit is very suitable for applications in small solar energy system to smooth the fluctuation of the solar energy or to prolong the solar energy use time. It has a good prospect in the practice of solar energy field.