Limiting efficiency of coupled thermal and photovoltaic converters

This paper presents a general energetic and entropic analysis of ideal photovoltaic and solar-thermal converters. Its purpose is to determine the efficiency limit when both types of converters operate together (hybrid converters). It has been found that, while in practical cases hybrid converters may give very high efficiency (61.7% vs. 40.0% of the solar thermal at 500 K and 40.7% of the photovoltaic at 300 K), in the limiting case of a system formed by an infinite number of band gaps, the efficiency of hybrid converters, 86.8%, is strictly equivalent to photovoltaic or solar thermal converters. Conversely, hybrid systems operating with one gap give an efficiency of 86.7%, very close to the previous one and higher than the top efficiency achievable with a single temperature solar thermal, 85.4%. (C) 1999 Elsevier Science B.V. All rights reserved.