3. SOLAR THERMAL SYSTEMS

3.1 Introduction

3.1.1 Background

When we are walking outside on a sunny day we notice that the sun warms us as well as providing light. This simple observation shows the difference between solar thermal and photovoltaic (PV) energy, which converts light directly into electricity.

By using the very simple principle that darker coloured materials absorb more light and consequently get hot, solar thermal technologies use black colored plates as their core heat-collecting device. Solar heating may be either passive or active.

The simplest example of passive solar heating is opening the curtains in winter, which lets the sun heat the room. This type of 'natural' space heating is very important and is an essential part of modern building design, but is not covered here in any detail (see refs 3.1, 9.1). More complex passive systems may require a concentration of solar heat, such as for heating water. Solar water heating systems save money by reducing the energy costs associated with traditional water heating and are also environmentally friendly. Saving electricity or fossil fuel usually means avoiding the types of emissions associated with combustion.

Active solar thermal technologies use a range of simple to complex machinery. Some solar water heating systems are unable to operate on basic water pressure and gravity principles, and require the use of electric or other pumps to move the cold water through the collector. Larger scale solar thermal projects for electricity generation are under development and require the full array of power station technology.