Concentrating Solar Thermal Energy

3Optics of Concentrating Systems

François HÉNAULT¹, Benjamin GRANGE² and Quentin FALCOZ³

¹IPAG-CNRS, Grenoble, France

²PROMES-CNRS, Font-Romeu-Odeillo-Via, France

³PROMES-CNRS, UPVD, Perpignan, France

3.1. Introduction

Solar concentrating systems are a very original and little-known part of optical sciences. Drawing inspiration from Archimede’s famous “burning mirrors” (see section 3.2), their reflective surfaces are not optical surfaces in the common sense of the term, as their manufacturing cost would be exorbitant. The technologies employed rather rely on industrial glass manufacturing processes, and the implementation of mirrors is often conducted under mechanical constraint. Another particularity is that given the dimensions to be covered, the mirrors are generally composed of hundreds or thousands of individual facets (“segmented”). Finally, the precision of optical surfaces is significantly less restrictive compared to that of classical optical systems, which is measured in fractions of wavelength: here, the manufacturing precision is rather expressed in tenths of millimeters, the imagery capacity being therefore lost. As it will be seen, high-concentration performances can nevertheless be attained, and certain important concepts of classical optics are still applicable (section 3.3). Finally, sections 3.4 and 3.5 offer a more detailed presentation of the two types of the most commonly used concentrating field.

3.2. History

3.2.1. From Archimedes to 19th century ...