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View submission: Ask Anything Wednesday - Engineering, Mathematics, Computer Science
A good resource on technologies being proposed is the agenda for US DOE workshop a year ago[1] which includes links to a bunch of presentations on the particular technologies. This is specifically for long-duration energy storage. Large-scale could also mean high power but short to moderate duration, for which some of the available technologies are ultracapacitors and flywheels.
1: https://www.sandia.gov/ess-ssl/ldes/
The technology categories listed there include thermal storage, gravity storage, chemical storage, and battery storage.
Thermal storage can include storing solar heat at a solar thermal power plant for use to generate electricity when the sun is not out, and it can also include thermal storage located at the end use location. For example, for heating or cooling a building, you can have a simple tank of heated or chilled water, that is heated or cooled when electricity is abundant and cheap and then used when heating or cooling is needed. Other materials including phase-change materials can be used as well.
Gravity storage includes pumped hydro as you mention and we may see expansion of that technology. Also included there are rail systems that haul weight uphill to store energy and roll downhill to generate electricity. Variations on pumped hydro include pumping between underground and surface reservoirs, and systems that rely on air pressure rather than gravity to pressurize the water in the “upper” reservoir. (This is more efficient then simply compressing air because the water pump/turbine is more efficient with water than with air.)
Chemical storage is largely hydrogen, produced by electrolysis, which is an interesting opportunity but has poor round-trip efficiency if you are creating electricity again. However it is useful to consider producing hydrogen by electrolysis when electricity is overabundant and using it in the many current industrial applications of hydrogen to replace hydrogen production from fossil fuels.
Note also that a form of virtual storage is more control over when loads operate. for example, if you have an electric vehicle plugged in to charge overnight, you don't really care whether it charges gradually over the whole night or charges faster during some particular hours overnight when the energy supply otherwise exceeds demand and allowing a utility to control that gives them the same kind of flexibility that they would get having a storage system.
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