The total storage capacity of the U.S. grid is less than 1 percent, according to Barnhart. What little capacity there is comes from pumped hydroelectric storage, a clean, renewable technology. Here's how it works: When demand is low, surplus electricity is used to pump water to a reservoir behind a dam. When demand is high, the water is released through turbines that generate electricity.
For the Stanford study, Barnhart and Benson compared the amount of energy required to build a pumped hydro facility with the energetic cost of producing five promising battery technologies: lead-acid, lithium-ion, sodium-sulfur, vanadium-redox and zinc-bromine.
"Our first step was to calculate the cradle-to-gate embodied energy," Barnhart said. "That's the total amount of energy required to build and deliver the technology from the extraction of raw materials, such as lithium and lead, to the manufacture and installation of the finished device."
To determine the amount of energy required to build each of the five battery technologies, Barnhart relied on data collected by Argonne National Laboratory and other sources. The data revealed that all five batteries have high embodied-energy costs compared with pumped hydroelectric storage.
"This is somewhat intuitive, because battery technologies are made out of metals, sometimes rare metals, which take a lot of energy to acquire and purify," Barnhart said. "Whereas a pumped hydro facility is made of air, water and dirt. It's basically a hole in the ground with a reinforced concrete dam."
After determining the embodied energy required to build each storage technology, Barnhart's next step was to calculate the energetic cost of maintaining the technology over a 30-year timescale. "Ideally, an energy storage
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