Comparison of OPV with other technologiesNieves Espinosa Martinez
In order to compare different energy technologies, a useful parameter to identify possible bottlenecks for massive production is the Energy Pay-Back Time (EPBT). It has been thoroughly investigated for all PV technologies already on the market, and ranges between 4.12 and 0.3 years DOI:10.1016/j.solmat.2010.08.020. These upper and lower limits actually correspond to OPV; the first studies on this regard were performed about laboratory fabrication procedures DOI:10.1002/pip.967, where around 4 years were needed to payback the energy, but progressive improvements have been accomplished up to the current 0.3 years.
It is clear that lower efficiency does imply a larger area for harvesting energy. The efficiency and lifetime of OPV is much lower than other competitors, so key to achieving low values of EPBT reside in a low cumulative energy demand; both the energy attributable to the materials and to the manufacturing of a functional unit which is usually measured in processed area (i.e., per square meter). This is because the energy input (process heat) during manufacture is very low since the technology does not require any high-temperature steps (<<140 °C) as mentioned in the fabrication chapter. Once operational the energy balance of the inputs during the lifespan of an energy must weigh less -or have a lower value- than the energy delivered by the system during its operational phase (i.e., the solar cells, the installation, the decommissioning etc.).
The Carbon footprint, or emission factor, is the other driver parameter useful to compare technologies - the kilograms of CO2 equvilant per generated electricity output. It has been generally confirmed by previous LCA studies that renewable sources of electricity, such as photovoltaic technologies, have low values for the CO2 equivalent emission figures per kWh. For photovoltaic technologies, this footprint ranges between 16 and 60 g per kWhDOI:10.1111/j.1530-9290.2011.00423.x, and thus compares very favorably to coal (900 g), natural gas combined cycle (439 g) and even nuclear energy (40 g), which has been touted as the cleanest technology.