PV Systems: the energy to produce them versus the energy they produce

       

The Energy Payback of Roof Mounted Photovoltaic (PV) Cells

Some studies claim that the manufacturing and material of a PV System consume more energy than will ever be compensated by its energy output. Others calculate that this energy is gained back after a relatively short time of operation. Why is there so little consensus on the Energy Payback of PV Systems? That is what Colin Bankier and Steve Gale tried to figure out in the Energy Bulletin.

Large variations

Their literature study comes up with payback periods ranging from 0.7 up to 25.5 years. Those differences arise mainly from the estimates for the silicon purification and crystallization process, along with some differences in process parameters.

Best estimate

Out of the 16 studies they investigated, Bankier and Gale distilled a best estimate. An energy payback period of about four years was found for both mc-Si and thin film systems. The most difficult major parameters to establish accurately were the energy conversion factors and the energy values of human labour.

Good enough

With an allowance of 100%, the study assumes an energy payback range of 2-8 years for roof mounted PV Systems, which is clearly good enough to call them “sustainable”. Large scale utility PV power stations are generally expected to have a much longer energy payback period.