Incident solar radiation is the most fundamental of the sustainable energy sources, being at the origin of all others - wind and wave, biomass and even fossil fuels which represent stored solar energy over a geological time scale. Only nuclear and geothermal sources are non-solar. The direct conversion of incident solar radiation into the most convenient energy vector, electricity, motivates the development of lower cost, higher efficiency and larger area photovoltaic devices and systems. Their history, technology and applications are here reviewed.