Sunday, November 15, 2015

Photovoltaics Energy Payback Time

Photovoltaic systems are great in producing clean energy without CO2 emissions. A question that remains however, is the amount of energy invested into production and transport of the materials, cells and panels. To answer this question, we had a look into the annual Photovoltaics Report of the Fraunhofer Society (German: Fraunhofer-Gesellschaft zur F├Ârderung der angewandten Forschung e. V.).

To give a short summary: The energy payback time for current modules is around one to two years. Considering a lifetime of 20 years, this means that photovoltaic systems are quite effective in providing clean energy. The energy payback time depends mainly on three parameters: (i) the  material usage for the system, (ii) the effiency of the cells and panel, and (iii) the irradiation striking onto the panel. Regarding the first aspect, the report shows that material usage for silicon cells went down by a factor of 2.5 over the last ten years due to increased
efficiencies and thinner wafers. Efficiency is improving slower, currently the best multicrystalline modules provide an efficiency of 18.5%, panels with monocrystalline cells a 22.9% and upcoming thin film technologies have a range between 10.9% and 17.5%.

The largest influence for the energy payback time currently is the place where you put your module: In regions with an annual irradiation of around 1000 kWh/m2 - this is basically the value for PV panels installed in Germany, they energy payback time is 2 years, while in sunny areas, the annual irradiation can be double or more, leading to an energy payback time of around 1 year.

Energy payback time for typical PV systems in different regions of Europe

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