Energy Policy 28 (2000) 983}988 The viability of solar photovoltaics Tim Jackson*, Mark Oliver Centre for Environmental Strategy, University of Surrey, Guildford, Surrey GU2 5XH, UK Ernst & Young, Broadwalk House, Southernhay West, Exeter, EX1 1LF, UK Received 24 May 2000 Abstract This paper summarises the contributions to a special issue of Energy Policy aiming to assess the viability of solar photovoltaics (PVs) as a mainstream electricity supply technology for the 21st Century. It highlights the complex nature of such an assessment in which technical, economic, environmental, social, institutional and policy questions all play a part. The authors summarise brie#y the individual contributions to the special issue and draw out a number of common themes which emerge from them, for example: the vast physical potential of PVs, the environmental and resource advantages of some PV technologies, and the #uidity of the market. Most of the authors accept that the current high costs will fall substantially in the coming decade as a result of improved technologies, increased integration into building structures and economies of scale in production. In spite of such reassurances, energy policy- makers still respond to the dilemma of PVs with some hesitancy and prefer to leave its evolution mainly in the hands of the market. This paper highlights two clear dangers inherent in this approach: "rstly, that short-term cost convergence may not serve long-term sustainability goals; and secondly, that laggards in the race to develop new energy systems may "nd themselves faced with long-term penalties.  2000 Elsevier Science Ltd. All rights reserved. Keywords: Photovoltaics; Solar cells; Renewable energy; Sustainable energy systems; Clean technology 1. Introduction Solar photovoltaic (PV) cells have attracted increasing attention in recent years as a technology capable of delivering sustainable electricity supplies and reducing the burden of fossil fuels on the environment. Originally developed to provide electrical power for the space programme in the middle of the last century, PVs have subsequently found diverse application in nu- merous o!-grid markets during the last 30}40 years. Still expensive by comparison with conventional generation technologies, grid-connected applications have been slower to emerge; but a recent surge of interest in renew- able energy by policy-makers has led to industry growth rates which averaged 21% per annum between 1982 and 1997, with growth in the latter years as high as 40% per annum (Oliver and Jackson, 1999). A variety of * Corresponding author. Tel.: #44-1483-300800x2181; fax: #44- 1483-259-394. E-mail address: t.jackson@surrey.ac.uk (T. Jackson).  The views expressed in this paper belong solely to the author in his personal capacity and are not the views of Ernst and Young. policy initiatives has set ambitious implementation tar- gets for the installation of building-integrated PVs in grid-connected situations. The "rst such scheme was the German `thousand roofsa programme, which by 1995 had achieved its target of installing small (1}5 kWp) PV systems on the roofs of 1000 domestic residences and small company properties (Weiss et al., 1998). Another early initiative was the Japanese Ministry of International Trade and Industry initiative to subsidise the installation of 70,000 PV roofs by 2005 (Konno, 1998; Luchi, 1998). In 1997, US Presi- dent Bill Clinton announced an even more ambitious programme to install a million solar roofs with the aim of helping to reduce greenhouse gases as part of the climate change programme and supported by funds promoting partnerships with industry. Tax credits, grants and low- interest loans will all be available to help to encourage the deployment of solar technologies (Rannels, 1998). The European Union has recently announced targets to double the renewables contribution to electricity supply from 6 to 15% of total electricity supply by 2010. As part of this aim a target of 1,000,000 roofs has been set, half in the EU and 500,000 in developing countries (Papoutsis, 1998). In addition, signi"cant support has been given to 0301-4215/00/$ - see front matter  2000 Elsevier Science Ltd. All rights reserved. PII: S 0 3 0 1 - 4 2 1 5 ( 0 0 ) 0 0 0 8 5 - 9