Grid-scale batteries for storing renewable energy have large carbon footprint

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 technology should last several decades,” he said. “Otherwise, you’ll have to acquire more materials, rebuild the technology and transport it. All of those things cost energy. So the longer it lasts, the less energy it will consume over time as a cost to society.”

To quantify the long-term energetic costs, Barnhart and Benson came up with a new mathematical formula they dubbed ESOI, or energy stored on investment.  “ESOI is the amount of energy that can be stored by a technology, divided by the amount of energy required to build that technology,” Barnhart said. “The higher the ESOI value, the better the storage technology is energetically.”

When Barnhart crunched the numbers, the results were clear. “We determined that a pumped hydro facility has an ESOI value of 210,” he said. “That means it can store 210 times more energy over its lifetime than the amount of energy that was required to build it.”

The five battery technologies fared much worse. Lithium-ion batteries were the best performers, with an ESOI value of 10. Lead-acid batteries had an ESOI value of 2, the lowest in the study. “That means a conventional lead-acid battery can only store twice as much energy as was needed to build it,” Barnhart said. “So using the kind