Tuesday, September 10, 2013

Storing RE not always sensible

Renewable energy holds the promise of reducing carbon dioxide emissions. But there are times when solar and wind farms generate more electricity than is needed by consumers. Storing that surplus energy in batteries for later use seems like an obvious solution, but a new study from Stanford University suggests that might not always be the case. The costs involved in terms of energy are too high.

Grid-scale batteries make sense for storing surplus solar energy, but not for wind they found. The study, which is supported by GCEP, is published in the online edition of the journal Energy and Environmental Science.

The Stanford team looked at several emerging technologies, including five battery types -- lead-acid, lithium-ion, sodium-sulfur, vanadium-redox and zinc-bromine. Batteries with high energetic cost consume more fossil fuels and therefore release more carbon dioxide over their lifetime. If a battery's energetic cost is too high, its overall contribution to global warming could negate the environmental benefits of the wind or solar farm it was supposed to support.
The researchers compared the energetic cost of curtailing solar and wind power, versus the energetic cost of grid-scale storage. Their calculations were based on a formula known as "energy return on investment" -- the amount of energy produced by a technology, divided by the amount of energy it takes to build and maintain it.

Using that formula, the researchers found that the amount of energy required to create a solar farm is comparable to the energy used to build each of the five battery technologies. The results were quite different for wind farms. The scientists found that curtailing wind power reduces the energy return on investment by 10 percent. But storing surplus wind-generated electricity in batteries results in even greater reductions -- from about 20 percent for lithium-ion batteries to more than 50 percent for lead-acid.

As the team notes, it is important for society to be energy-smart about implementing new technologies.  When plunging into new technologies, policymakers and investors need to consider the energetic cost as well as the financial cost of new technologies.

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