**9. Environmental aspects**

Tezuka et al. (2002) proposed a new method for estimating the amount of CO2-emission reduction in the case where the carbon-tax revenue is used as the subsidy to promote PVsystem installations and concluded that the amount of CO2-emission reduction increases by advertising the PV system with subsidy policy even under the same tax-rate and the CO2 payback time of the PV system reduces by half if the GDP is assumed not to change after the introduction of carbon taxation. Krauter et al.(2004) examined a CO2 comprehensive balance within the life-cycle of a photovoltaic energy system and found that the actual effect of the PV system in terms of net reduction of carbon dioxide is the difference between the sum of electrical yield related to the local grid and the value for recycling and the sum of the production requirements and the transport emissions. Fthenakis and Kima (2007) studied solar- and nuclear-electricity-generation technologies' entire lifecycle of energy production; carbon dioxide and other gases emitted during the extraction, processing, and disposal of associated materials and determined the greenhouse gas (GHG) emissions, namely, CO2, CH4, N2O, and chlorofluorocarbons due to materials and energy flows throughout all stages of the life of commercial technologies for solar–electric and nuclear-power generation. Kannan et al. (2006) performed life cycle assessment (LCA) and life cycle cost analysis for a distributed 2.7kWpgrid-connected monocrystalline solar PV system operating in Singapore and provided various energy payback time (EPBT) analyses of the solar PV system with reference to a fuel oil-fired steam turbine and their greenhouse gas (GHG) emissions and costs are also compared revealing that GHG emission from electricity generation from the solar PV system is less than one-fourth that from an oil-fired steam turbine plant and onehalf that from a gas-fired combined cycle plant. Tsoutsos et al. (2005) presented an overview of an Environmental Impact Assessment for central solar systems, to estimate the magnitude of potential environmental impacts and proposed appropriate mitigation measures, can play a significant role to proper project design and to a subsequent project public acceptance.
