Study on the Performance of a Curved Fresnel Solar Concentrated System with Seasonal Underground Heat Storage for the Greenhouse Application

A solar heating system in greenhouse driven by Fresnel lens concentrator is built in this study. This system uses a soil thermal storage for greenhouse to supply heat in the absence of sunlight, ensuring the safety of the growth of crops. The structure and working principle of the device are introduced in this paper. The underground soil temperature was tested, compared with the indoor and outdoor temperature. The experimental testing result is given. A research shows that when the heating pipe buried 1.65 m underground, the time of heat transfer to the ground is about 5 days. The overall temperature rise of the soil is about 4 °C. In the condition of the coldest weather without additional energy supplement, the greenhouse's temperature is guaranteed above 8 °C, which can ensure the minimum temperature requirements of crop growth. According to the structural parameters of the existing system, the simulation of underground soil heat transfer and heat storage performance was carried out. Then, the temperature curves of different buried depths of the tube are given. The soil temperature steady time in different pipe-buried depths of heat storage temperature is theoretically calculated. It is proved that, to achieve the seasonal thermal storage in this system, the buried depth of the pipe should be over 2.5 m.