Solar concentrator always plays an important role in solar energy collection as it could enhance the energy density effectively. Various structures of solar concentrators have been researched in recent years, among which multi-surface (MS) and multi-element (ME) combinations are the two typical structures. MS concentrator is an improved structure for single surface concentrator. It is usually designed to increase the acceptance angle, enhance the light intercepting efficiency, homogenize the energy distribution, etc. ME concentrator is generally consist of two or more optical elements, in which MS concentrators are usually used as assistant optical components. ME concentrator always has larger tolerance on tracking error so that it is much easier to track the sun. It could be applied in high power concentration. The combination on optical elements of MS and ME solar concentrators was diagramed and theirs advantages and disadvantages were evaluated. Nowadays, solar applications are becoming more and more diverse and concomitantly, the researching methods are also improving. The computer-aided methods including numerical computation and optical simulation are the dominant method in nowadays, which makes it easier to analyze various structures of solar concentrators and their complex applications. Besides, solar applications are not limited in CT and CPV, but in many other fields such as solar daylighting, solar-pumped laser, solar cooling, solar desalination etc. It has been believed that more and more innovative designs on solar concentrator will be proposed in the future. Header of solarlits.com

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.

A multi-surface solar concentrator is proposed in this study. The concentrator is designed by improving the light receiving rate of a parabola when the incident angle changes within 0°~20° by adding involute, shifting the involute up, and changing the shape of the parabolic top. The results show that adding involute can effectively avoid light escaping from the bottom, which improves the light receiving rate under large incident angle. The light receiving rate is improved by increasing the height of involute at incident angle of about 5°~15°. Changing the shape of the top of parabola apparently improves the light receiving rate under high incident angle. Finally, the concentrator was tested experimentally. The experimental efficiency of the concentrator at different incident angles was 0.426. The average light receiving rate of 0.868 was achieved through the optical simulation where different losses include the optical loss, such as the absorption and reflection of the glass cover, the absorption of reflectors, the heat loss, etc. Thus, the concentrator provides a stable and efficient energy source Header of solarlits.com