Photovoltaic exploitation of solar energy, the subject of this book, consists of converting directly radiated light (solar or other) into electricity. This transformation of energy is carried out using PV modules or panels made up of solar PV cells (see Chapter 2). Thermal solar energy, on the other hand, functions quite differently, producing heat from the Sun’s infrared radiation to heat water, air or other fluids. This technology is simple compared to PV technology, and therefore less costly. It works by capturing calories through heat absorbing surfaces such as black metal sheets (Figure 1.1). The heat energy collected can be used to heat individual or collective water systems. These are in widespread use in sunny countries to produce hot water for houses and apartments without central heating (Greece, Israel, African countries) and, in the last 10-20 years, partly thanks to financial incentives and subsidies, these systems have also been in use in temperate countries like France and Britain.
Thermodynamic solar energy, however, is the system used in large power stations equipped with solar radiation concentrators in the form of curved mirrors that heat a fluid to a very high temperature (several hundred degrees), which is then used to generate steam by thermal exchange and produce electricity from a steam – driven turbine. Although not widespread and requiring a direct solar flux (countries with little cloud cover), this technology is very spectacular. It is the principle used in the solar power stations of Font-Romeu in southern France and Andasol 1 in central Spain.
These aspects of solar energy are not dealt with in this book, which is strictly limited to PV energy. The term ‘solar collector’ will thus not be used to avoid ambiguity between the different technologies.
Figure 1.1 The different methods of exploiting solar energy
Only thermal panels can be used for solar heating applications. It would be pointless to heat water with electricity generated by PV modules – this would have a very low efficiency and be much more expensive.