Life cycle assessments and external cost estimates of photovoltaics have been often based on old data that do not reflect the extensive technological progress made over the past decade. Our assessment uses current (2004-early 2005) manufacturing data, from twelve European and US photovoltaic companies, and establishes the Energy Payback Times (EPBT), Greenhouse Gas (GHG) emissions and external environmental costs of current commercial PV technologies. Estimates of external costs are about 70% lower than those in recent high-impact publications which were derived from the old data. Copyright # 2006 John Wiley & Sons, Ltd. INTRODUCTIONI t is well understood that production of energy by burning of fossil fuels generates a number of pollutants and carbon dioxide. What is less known is that any anthropogenic means of energy production, including solar, generate pollutants when their entire life cycle is accounted for. A life cycle starts from the mining and processing of materials that comprise solar cells, modules and balance of system, and ends to their final decommissioning, disposal and/or recycling. Costs associated with the environmental, health and societal impacts that are not included in the direct cost of electricity, are called external costs of electricity production. While societal external costs are difficult to quantify, external costs associated with environmental and health protection or damage have been quantified in monetary terms. Perhaps the most well-known effort to quantify environmental and health damages due to electricity production, is the European Union's series of ExternE (External Costs of Energy) projects. The ExternE methodology starts from emissions generated at specific sources and follows their impact to receptors through atmospheric dispersion and dose-response functions. In general, this type of environmental impact assessment is well accepted, although assumptions related to Broader Perspectives the monetary valuation of estimated impacts, especially green-house related impacts, are debateable. 'The ExternE methodology has been applied in a large number of European and national studies to give advice for environmental, energy and transport policies.' 1 Photovoltaic installations in Germany were presented in the latest ExternE report to the European Commission 1 as having 30% higher health impacts than natural gas and GHG emissions of 180 g CO 2 -eq./kWh which would be 10 times higher than those for the nuclear fuel cycle (Figure 1). These results were based on 15-years old PV systems and even older data on module production technology. z Also based on outdated PV technology data a life cycle-based comparison of energy technologies in Australia 2 showed that PV emits about 100 g CO 2 /kWh during its life cycle (Figure 1). The results from these two studies were widely circulated and especially the ExternE publication with its official status is likely to have influenced policy decisions with regard to energy technology. More recent (i.e., 2000) data are included in the Ecoinvent...

Officer and his technical guidance is gratefully acknowledged. John Viren is a private consultant working under contract to Brookhaven National Laboratory. We thank several outside reviewers for their comments. This reportdoes not necessarilyreflect the views and policies of the U.S. Department of Energy nordoes mention of trade names or commercial productsconstituteendorsementor recommendationfor use.

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Title III of the 1990 Clean Air Act Amendments (CAAA) mandated that the U.S. Environmental Protection Agency (EPA) evaluate the need to regulate mercury emissions from electric utilities. In support of this forthcoming regulatory analysis the U.S. DOE, sponsored a risk assessment project at Brookhaven (BNL) to evaluate methylmercury (MeHg) hazards independently. In the U.S. MeHg is the predominant way of exposure to mercury originated in the atmosphere. In the BNL study, health risks to adults resulting from Hg emissions from a hypothetical lo00 MW coal-fEed power plant were estimated using probabilistic risk assessment techniques. This study showed that the effects of emissions of a single power plant may double the background exposures to MeHg resulting from consuming fish obtained from a localized area near the power plant. Even at these more elevated exposure levels, the attributable incidence in mild neurological symptoms @aesthesia) was estimated to be quite small, especially when compared with the estimated background incidence in the population. This research was performed under the auspices of the United States Department of Energy under Contract 7) NO. DE-ACE-76CHWI16

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