1 Introduction

There are two principal ways of solar energy exploitation:

• heat production (for use in the domestic, civil and production fields; in this case, we talk about thermal solar energy);

• electricity production by the direct conversion of energy (photovoltaic solar energy).

Thermal solar technologies are divided into low, medium and high temperature

ones.

The low temperature technology includes systems which, thanks to appropriate devices (solar collectors, see par. 2.2.2.1), are able to heat fluids at temperatures less than 100°C. These systems are generally installed to produce sanitary hot water (for domestic use, collective users, sport centres, etc.), to produce domestic heating and, in general, other room heating, to heat water in swimming pools, to produce heat at a low temperature for industrial utilization (usually to warm the water used to swill machines or to preserve different kinds of fluids at a certain temperature inside tanks, etc.).

The medium temperature technology includes systems, which allow reaching temperatures of more than 100°C and less than 250°C. Currently, medium — temperature solar thermal power systems are not widespread; among their applica­tions, the most common application is the one represented by simple devices which use solar radiation to cook food (the so-called solar ovens, see par. 2.3).

The high temperature technology includes systems which, thanks to appropriate devices that are able to concentrate solar radiation to a thermal receiver (in this case we talk about concentrating solar power (CSP) technology, see par. 2.4), allow heating a fluid at temperatures more than 250°C.

Concentrated solar technology has its application in electricity production (in this case, we talk about ‘solar thermodynamics’ where the heat at a high tempera­ture is exploited in thermodynamic cycles for electricity production) and in the

fulfilment of chemical processes at high temperatures, such as production of hydrogen. [2, 12-15].