https://www.bnl.gov/pv/files/pdf/PE_Magazine_Fthenakis_2_10_12.pdf[font face=Serif][font size=5]How Long Does it Take for Photovoltaics
To Produce the Energy Used?[/font]
By Vasilis Fthenakis
[font size=3]In the July 2011 PE magazine article “Why We Need Rational Selection of Energy Projects,” the author stated that “photovoltaic electricity generation cannot be an energy source for the future” because photovoltaics require more energy than they produce (during their lifetime), thus their “Energy Return Ratio (ERR) is less than 1:1.” Statements to this effect were not uncommon in the 1980s, based on some early PV prototypes. However, today’s PVs return far more energy than that embodied in the life cycle of a solar system (see Figure 1).
Their energy payback times (EPBT)—the time it takes to produce all the energy used in their life cycles—currently are between six months to two years, depending on the location/solar irradiation and the technology. And with expected life times of 30 years, their ERRs are in the range of 60:1 to 15:1, depending on the location and the technology, thus returning 15 to 60 times more energy than the energy they use. Here is a basic tutorial on the subject.
Life Cycle of PV and
Energy Payback Times
The life cycle of photovoltaics starts from the extraction of raw materials (cradle) and ends with the disposal (grave) or recycling and recovery (cradle) of the PV components (Figure 2). The mining of raw materials such as quartz sand for silicon PVs, and copper, zinc, and aluminum ores for mounting structures and thin-film semiconductors, is followed by separation and purification stages. The silica in the quartz sand is reduced in an arc furnace to metallurgical-grade silicon, which must be purified further into solar-grade silicon (i.e., 99.9999% purity), requiring significant amounts of energy. Metal-grade cadmium and tellurium for CdTe PV is primarily obtained as a byproduct of zinc and copper smelters, respectively, and further purification is required for solar-grade purity. Similarly, metals used in CIGS PV are recovered as byproducts: indium and gallium are byproducts of zinc mining, while selenium is mostly recovered from copper production.
The raw materials include those for encapsulations and balance-of-system components, for example, silica for glass, copper ore for cables, and iron and zinc ores for mounting structures. Significant amounts of energy are required for the production, processing, and purification of all these materials, as well as for the manufacturing of the solar cells, modules, electronics, and structures, and for the installation, sometimes the operation, and eventually the dismantling and recycling or disposal of the system components. Thus, the EPBT is defined as the period required for a renewable energy system to generate the same amount of energy (in terms of primary energy equivalence) that was used to produce the system itself.
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