The Best Grid-Scale Batteries Only Store Six Times the Energy Needed to Create Them

Set against the backdrop of the recent news that the US added a bit over 13 gigawatts of new wind power capacity last year, with 3.3 GW of solar power installations, and efforts to show how New York state could use all renewable energy by 2050, is an interesting new paper looking at how different grid-scale battery technologies compare in terms of carbon footprint—a critical consideration in creating an all-renewable future.

The study, published in the journal Energy & Environmental Science and conducted by scientists from Stanford University's Global Climate and Energy Project, calculates the energy stored for energy invested (ESOI) for a range of battery technologies, comparing them to hydro pumped storage and compressed air energy storage.

The researchers found that pumped storage has an ESOI of 210, meaning that over the lifetime of the project it will store 210 times more energy than was required to build it. Even if was coal used to run the project initially, eventually filling those batteries with renewable power would result in a significant carbon savings over its expected lifetime of 30 years.

Pumped storage projects pump water from lower to higher elevations, then release the water at a later time to turn turbines and generate electricity. It accounts for 99% of all the grid-scale energy storage around the globe today, with 127 GW of storage capacity. In the US less than 1% of total grid capacity can be stored. Pumped storage is comparatively inexpensive to construct, but is constrained by the fact that the number of suitable locations is dropping, with those remaining often being in sensitive environments.

Compressed air energy storage (CAES) has an even better ESOI figure, 240, but there are only two projects in operation today, in Alabama and Germany, and two more expected to be completed over the next few years. A CAES system pumps air under high pressure into a storage area, like a cavern or an aquifer, and then releases it when needed to turn an electrical turbine.

Looking at battery technologies, the ESOI figures pale in comparison. Lithium-ion batteries fared the best, with an ESO1 of 10, sodium-sulphur batteries had an ESOI of six, vanadium redox and zinc bromide batteries came in at three, with lead-acid batteries having an ESOI of just two—storing just twice the energy over their lifetime as was required to manufacture them.

Back to that 30 year lifecycle for pumped storage: The researchers note that the best way to improve the ESOI of all storage technologies is to increase the amount of time they can be charged and discharged. For pumped storage that's a 25,000 charge cycle, while lithium-ion batteries drop to 6,000 charges, and lead acid batteries at 700 charges.

Sally Benson, who co-authored the paper with Charles Barnhart, says, "Most battery research today focuses on improving the storage or power capacity. These qualities are very important for electric vehicles and portable electronics, but not for storing energy on the grid. Based on our ESOI calculations, grid-scale battery research should focus on extending cycle life by a factor of 3 to 10."

As for other constraints on energy storage, beyond the dwindling areas suitable for pumped storage, the report highlights production limits on the materials for lithium-ion and vanadium redox batteries. In comparison, sodium sulphur batteries face lesser constraints, as do CAES systems.

Ultimately, the report concludes, "Energy storage could provide some grid flexibility but its build up will require decades; reducing financial cost is not sufficient for creating a scalable energy storage infrastructure."

Because of these constraints on energy storage, "Increasing grid flexibility as the penetration of renewable power generation increase will require employing several additional techniques including demand-side management, flexible generation from base-load facilities and natural gas firming."

Left out of that conclusion, but included in the chart above showing how New York can go all-renewable, is the hugely important issue of reducing demand for electricity through efficiency or good ole fashioned conservation. Without reducing demand from current and project levels, deploying sufficient energy storage as well as renewable energy capacity, only becomes more of a herculean effort.