Storing excess energy from wind farms in batteries would use more energy than would be wasted if the excess electricity were not stored. But storing excess power from solar PV makes energy sense, according to a recent study from Stanford University.

Four postdoctoral scholars at Stanford’s Global Climate and Energy Project studied the energy costs of various clean technologies. They measured the amount of energy it takes to create something - such as a wind turbine or solar panel - from mining the materials to maintaining the finished working product and compared that to the energy it generates, saves or stores.

The researchers’ earlier studies found that solar and wind were both “worth it.” Both technologies generate more power than it takes to create them. However, solar requires a much bigger energy investment than wind, according to the researcher’s previous work.

Their most recent study, published in the journal of Energy and Environmental Science, was titled: The Energetic Implications of Curtailing versus Storing Solar and Wind-Generated Electricity.

Solar and wind farms sometimes curtail the amount of power that flows from their projects to the grid because it’s more than the grid needs at the time.

“Curtailment of renewable resources seems wasteful,” lead researcher Charles Bernhart was quoted in a Stanford University news release. “But grid operators routinely curtail wind turbines to avoid a sudden, unexpected surge of electricity that could overload transmission lines and cause blackouts. Curtailment rates in the U.S. will likely increase as renewable energy becomes more prevalent.”

The question researchers asked was, whether there be an energy return on investment if that excess power was stored in one of five different battery technologies.

For solar, the researchers found that storing extra power was a good idea. Because solar panels take more energy to manufacture than wind turbines, wasting the energy they produce is more costly from an energy perspective, according to the release.

The researchers calculated 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.

"Using batteries to store solar power during periods of low demand would, therefore, be energetically favorable," said report co-author Michael Dale.

For wind farms, the battery storage requires 10 to 50 percent more energy to create than it takes to create the wind farm, depending on the technology, making it uneconomical in energy terms to store excess wind power.

It’s a bit like buying a safe, Dale said.

"You wouldn't spend a $100 on a safe to store a $10 watch," he said. "Likewise, it's not sensible to build energetically expensive batteries for an energetically cheap resource like wind, but it does make sense for photovoltaic systems, which require lots of energy to produce."