Energy requirements and CO2 mitigation potential of PV systems

Abstract

In this paper we investigate the energy requirements of PV modules and systems and calculate the Energy Pay-Back Time for two major PV applications. Based on a review of past energy analysis studies we explain the main sources of differences and establish a "best estimate" for key system components. For present-day c-Si modules the main source of uncertainty is the preparation of silicon feedstock from semiconductor industry scrap. The best estimates of 4200 respectively 6000 MJ (primary energy) per m2 module area are probably representative for near-future, frameless mc-Si and sc-Si modules. For a-Si thin film modules we estimate energy requirements at 1200 MJ/m2 for present technology. Present-day and future energy requirements have also been estimated for the BOS in grid-connected roof-top systems and for Solar Home Systems. The Energy Pay-Back Time of present-day grid-connected systems is estimated at 3-8 years (under 1700 kWh/m2 irradiation) and 1-2 years for future systems. The specific CO2 emission of these systems is 60-150 g/kWh now and 20-30 g/kWh in the future. In Solar Home Systems the battery is the cause for a relatively high EPBT of more than 7 years, with little prospects for future improvements. The CO2 emision is now estimated at 250-400 g/kWh and around 200 g/kWh in the future. This leads to the conclusion that PV systems, especially grid-connected systems, can contribute significantly to the mitigation of CO2 emissions.