Energy pay-back time of photovoltaic energy systems: present status and prospects

Abstract

In this paper we investigate the energy requirements of PV modules and systems and calculate the Energy Pay-Back Time for three 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. Therefore a low and a high estimate are presented for energy requirement of c-Si. The low estimates of 4200 respectively 6000 MJ (primary energy) per m2 module area are probably most 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 array field systems, rooftop systems and Solar Home Systems. The Energy Pay-Back Time of present-day array field and rooftop systems is estimated at 4-8 years (under 1700 kWh/m2 irradiation) and 1.2-2.4 for future systems. 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.