2 00 7 A closed parabolic trough solar collector

Parabolic trough[1] is the most mature technology for large scale exploitation of solar energy. Several power plants based on this technology have been operational for years, and more are being built. However, the current technology suffers from a too high installation cost. This high cost makes it very hard to compete economically with fossil energy without government subsidies, compromising the perspective of using this technology to solve the problem of CO2 emissions. In this article, we study a design of closed-box parabolic trough concentrated solar collector. By accepting an optical loss of a few percentages due to reflections by the cover, this design offers several advantages over the current open model, in particular a potential of significant cost reduction. In Section 1, we first make a rapid study of the actually dominant open parabolic trough design, to locate its main sources of cost, the problems facing it, and the potential of improvement. The basic design of the closed collector is given in Section 2. It is a hermetic box with a transparent cover and the parabolic reflector forming the back. And the tracking of the sun is done by rotating (swinging) the box around the receiver tube which is fixed with respect to the ground. The advantages include a geometrically rigid structure leading to a considerable simplification of the construction (hence a reduced cost), and the protection of almost all optic surfaces, in particular the reflecting mirror (hence a lower mirror cost without durability problems). Moreover, we can now adopt a tilted installation that reduces the seasonal variation of the output and improves the capacity factor of the whole system. The closed-box model and the subsequent size reduction bring about several technical issues that must be dealt with. The most important one is the receiver tube that absorbs the solar energy and transforms it to heat to be carried out by a fluid. The current permanently sealed Dewar construction is not suitable for the smaller collectors, due to probable high price and high thermal losses that