Concentrators

Current Practice

Almost all other concentrators use mirrors and/or multiple refractions to redirect the sunlight to the focal region where the HCPV cell is located. Some of these concentrator systems are extremely large mechanically-steered reflection-only concentrator systems and some use transparent glasses and plastics to form various types of lens and hybrid lens-mirror systems. There is also some overlap in technology between Concentrating Photo Voltaic (CPV) systems and Concentrating Solar Thermal (CST) concentrators.

Mirrors may be fabricated from metals like aluminum or silver. They may also be fabricated from multilayer transparent coatings. However, these methods of forming mirrors all suffer from one or more of the problems of high loss, high cost, difficulty in fabrication, and a potential for pealing and cracking from environmental thermal-cycling stresses over many decades of use. Although extremely low-loss and broad-band mirrors can be fabricated, they are very expensive, especially when compared to the superior performance and cost of Total Internal Reflection.

Additionally, most of the lenses used in solar concentration, such as Fresnel lenses, require two refractions and the resulting two separate reflection losses can be quite lossy. This two-surface reflection loss is made even worse by the need to keep costs low and not use anti-reflective coatings.