Experimental facility for a new thermal-solar field configuration: The rotatory Fresnel collector or sundial

Abstract

A very relevant guideline towards commercial competitiveness of Concentrating Solar Power (CSP) is to reduce the complexity of the solar field configuration and to reduce the specific or unitary costs of the elements required for capturing solar radiation. This means to attend to the geometry, the mechanical design and the thermal specifications, avoiding oversize the system by any account. This is particularly applicable to the concentration factor achieved in the receiver, which must not exceed significantly the threshold value for getting a given final temperature in the thermal fluid. In this paper, the experimental facility of the sundial concept is introduced, including very simple embodiments to make and to support the mirrors, which also present a very simple sun tracking. This new configuration is based on circular-cylindrical mirrors, which can easily be made from planar ordinary mirror by applying a bending technique that is also very simple and very cheap. Of course, it is mandatory to analyze in depth the concentration features of circular-cylindrical mirrors when the sun impinges from any direction in relation to the receiver position. In order to have a coherent configuration of the mirrors and the receiver, the full system is fixed on planar platform that rotates as Sun moves, in such a way that the receiver line, which is in the vertical plane of symmetry of the mirror field, keeps a perfect alignment with the Sun. A small-scale prototype has been built in Tecnogetafe campus of UPM, with a very reduced budget and a nominal power over 15 kW with a final temperature above 300 °C, with near 20 m2 of mirrors in 8 stripes.