Energy viability of photovoltaic systems

Abstract

The energy balance of photovoltaic (PV) energy systems is analysed in order to evaluate the energy pay-back time and the CO 2 emissions of grid-connected PV systems. After an short introduction of energy analysis methodology we discuss the energy requirements for production of solar cell modules based on crystalline silicon and on thin-film technology, as well as for the manufacturing of other system components. Assuming a medium–high irradiation of 1700 kWh/m 2 yr the energy pay-back time was found to be 2.5–3 yr for present-day roof-top installations and almost 4 yr for multi-megawatt, ground-mounted systems. Prospects for improvement of the energy balance of PV systems are discussed and it is found that for future PV technology (in 2020) the energy pay-back time may be less than 1.5 yr for roof-top systems and less than 2 yr for ground-mounted systems (under the same irradiation). The specific CO 2 emission of the roof-top systems was calculated as 50–60 g/kWh now and possibly around 20 g/kWh in the future. This leads to the conclusion that CO 2 emissions of present PV systems are considerably lower than emissions from fossil-fuel power plants, but somewhat higher than for wind and biomass energy. No significant contribution to CO 2 mitigation should be expected from PV technology in the year 2010. In the longer term, however, grid-connected PV systems do have a significant potential for CO 2 mitigation.