Sunday, March 9, 2008

Life-Cycle Assessment results in thumbs up for solar!

A new study that measures the life-cycle greenhouse-gas, pollutant and heavy metal emissions of four types of photovoltaic (PV) technologies--multicrystalline silicon, monocrystalline silicon, ribbon silicon, and thin-film cadmium telluride (CdTe)--reveals certain findings that are predictable and others that are surprising.

Simplified process-flow diagrams from mining to system manufacturing stages, namely
cradle-to-gate for (a) mono-, ribbon-, and multi-Si PVs, and (b) thinfilm CdTe PVs. Source: Study

Predictably, the authors of the study concluded that "all PV technologies generate far less life-cycle air emissions per GWh than conventional fossil-fuel-based electricity generation technologies." Despite concerns that the manufacture process of PV panels may be energy intensive, PV technologies harness a clean and ubiquitous source of energy, whereas fossil-fuel or nuclear generate electricity requires capital-intensive (i.e. energy and emissions intensive) plant infrastructure and significant transportation of fuel from its source to the location it is used.

The authors go on to say that at least 89% of emissions can be reduced if electricty from "central PV systems" replaces those from the grid, and that even more emissions can be reduces with decentralized PV systems due to the reduction in energy loss as the need for electricity transmission is reduced.

In an article in Scientific American reviewing this same study, it is suggested that if solar power can be used to start powering the production of PV cells--a so-called "PV breeder cycle"--then the emissions reductions will be even more dramatic.

Among the four PV technologies, CdTe came out tops, against conventional concerns of the toxicity of cadmium (cadmium in its metallic form is a toxic substance that has the tendency to accumulate in ecological food chains). CdTe thin-film PV technologies outperforms silicon-based PV technologies because less energy is required in the manufacture of the former (indeed, the purification of solar-grade silicon is a energy-intensive process), resulting in lower emissions of GHG, criteria pollutants and heavy metals.

Click here if you are interested in other comparative life-cycle studies of PV technologies. by the Columbia University Center for Life Cycle Analysis.


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