Harnessing the energy of the sun is a very attractive approach to meeting our energy needs. There are a range of converter technologies such as solar collectors (for hot water), solar concentrators (for thermal electricity generation) and photovoltaics (PV). PV is an elegant solution, a converter with no moving parts, which is has a long lifetime (25 years + for mono-crystalline silicon) and minimal maintenance burden (dc side of a system). As can be seen in Figure 1 the PV market has been growing significantly over the last few years. It is expected to grow further especially in view of rising fuel prices. However, at present the technology is not competitive if compared with baseload electricity generation. Figure 2 demonstrates the cost of learning to make PV competitive. PV may be applied as either a grid connected or off-grid, standalone system.

Standalone systems are usually employed in developing countries to provide lighting, refrigeration or power for communication systems. PV is competing with diesel generators in these applications which have high maintenance, fuel and supply costs. PV can be shown to have a relatively short payback time when used off-grid, however, all costs are ‘borne up front’ which slows the take up of the technology.

Grid connected PV offers the potential for energy generation at the point of use in urban environments or large scale solar plants in solar resource rich locations such as southern Spain and California. In terms of microgeneration in the built environment, the potential energy yield from PV is perhaps the easiest to predict. Roofs and facades offer large areas at suitable inclinations / orientations. In the UK a South facing sloped roof would be expected to generate ~800 kWh / kWp of PV installed per annum (9m² area with typical silicon wafer cells). Although built environment applications offer the potential for some offsetting of cost through avoided use of materials; most notably cladding in commercial buildings; PV remains an expensive technology. Cost reduction through changes in cell type (lower cost per Wp and / or increase in cell efficiency) is a requirement to enable PV to become a major energy source. Thin film solar cells which use far less semi-conductor material than traditional wafer technology are a key area of development. It is hoped PV will be competitive with peaking electricity generation in countries such as Spain by around 2020, and competitive with baseload generation by 2025-30.

The Sustainable Energy Research Group undertakes research in both areas, standalone systems and grid connected PV. Funding for the work on solar energy has come from the Engineering and Physical Sciences Research Council (EPSRC), the Department for Innovation, Universities & Skills (formerly DTI - Department of Trade & Industry), the Energy Saving Trust, Sainsbury's Supermarkets Ltd, Safeway, Marley Roofing and Powertile Ltd.

Fig. 1 - PV market growth – 30% year on year, but still at a relatively small level.

Fig. 2 - The cost of learning to make PV competitive (0.5 $/Wp). Log Log plot showing a log linear relationship between dollars per Watt ($/W) and cumulative megawatts.