This Digest provides a basic understanding for people who have little or no prior knowledge of solar photovoltaics, and for engineers and architects who wish to know more about the technical details of photovoltaic modules.It includes an introduction to different types of solar photovoltaics, their properties, operating characteristics, annual energy performance, standards and certification. The Digest will also discuss the components of PV systems and their purpose. However, this Digest is not intended to be used as a technical guide for the installation of photovoltaic systems. This is one in a series of four related Digests. Each focuses on a renewable energy technology commonly used in domestic buildings. The technologies also cover wood fuel, heat pumps and solar thermal collectors.