§ Mr. Robathan
To ask the Secretary of State for Trade and Industry what assessment he has made of the(a) short and (b) long-term contributions that photovoltaics could make in reducing carbon emissions in the UK. 
§ Mrs. Liddell
For the short term, photovoltaics (PV) is a relatively expensive technology, and the cost is unlikely to decrease sufficiently for it to make more than a small contribution to carbon emission reductions in the UK over the next decade. In the longer term, however, PV has the potential to make a significant contribution to carbon savings. The DTI has been supporting a programme of research, development and demonstration of the technology in the UK for several years and, together with support from the European Union, a number of major examples of building integrated PV are now operating, such as Northumbria University, Ford Engine Factory, and Doxford Solar Offices.
The annual generating capacity of PV installed in the UK at the moment is around 0.5 gigawatt hours (GWh). A study conducted for my Department in 1998 suggested that, for five key applications, new and refurbished offices, superstores, new housing and prestige public buildings, the maximum potential, disregarding cost, would be around 7 terrawatt hours (TWh) a year in 2010, around 2 per cent. of current electricity consumption. Investment costs were estimated at around £30 billion. The likely market potential for these applications without substantial levels of subsidy, but assuming significant cost and performance improvements and significant levels of carbon and pollution taxes, was estimated at less than 0.2 TWh/yr by 2010. Clearly, all such estimates can only give a broad indication of potential and the figures quoted are not comprehensive, excluding retrofit installation of PV on domestic roofs for example, where costs are currently high but the theoretical potential is large. Nevertheless, I believe that they give a reasonable indication of the possible scale of contribution in the short to medium term.
This compares with a theoretical estimate of around 270 TWh/yr available in 2025 from installing PV on all available walls and roofs for the entire building stock. More realistically, if PV were to be installed on all south-facing roofs and facades this would yield an annual output of around 70 TWh, or a little over 22 per cent. of current electricity consumption, which stands at around 324 TWh/yr. Alternatively, if 50 square miles (about 0.1 per cent. of the UK's total land area) were covered 371W with PV panels, this would have the technical potential to generate about 15 TWh of electricity (about 5 per cent. of current consumption). The extent and rate at which this longer term potential is exploited will depend on a number of factors, principally on the rate at which costs are reduced, itself the subject of much debate.