While we appear tantalizingly close to having all-electric and extended range electric vehicles (EREVs) on the road very, very soon, thanks to advances in lithium ion batteries, how close are we to having utility scale electrical storage? Since the storage capacity of EV batteries range from 10+ kWh (for EREVs) to 50+ kWh for all electric EVs, clearly there is significant opportunities for EV owners to use their cars as micro-utilities, buying power during off-peak and selling power during peak. In aggregate, along with providing utility scale electrical storage, EVs may eventually eliminate peaks – charging and discharging intelligently and autonomously to smooth demand through daily and weekly cycles – saving their owners money and absorbing all the sudden wind energy the weather has to offer.
A helpful place to get up to speed on utility scale electricity storage is from the website of the Northern California based Electricity Storage Association (ESA) – they have a good survey of electrical storage technologies that deliver solutions at the 1.0+ megawatt-hour scale. From their data and elsewhere, here are some of the technologies that look particularly interesting:
“Pumped storage,” has been used for decades, and consists of two water reservoirs, a lower one and an upper one. When there is excess power on the grid, water is pumped up to the upper reservoir, and when there is demand on the grid, this water is released through hydroelectric turbines to provide electricity. This process is 70-85 percent efficient, meaning that up to 85% of the electricity that is harvested and stored through pumping water uphill can be recovered when the water is later released down through the turbine generators. Probably the most conventional and proven technology for large scale electricity storage, ESA estimates over 90 gigawatts of charge/discharge capacity are in place worldwide. The biggest problem with pumped storage is there are a shortage of useful sites for this technology to work. Ref. ESA’s “Technologies: Pumped Hydro Storage”.
Another very interesting technology is compressed air energy storage (CAES), which has been getting kicked around for years. On a large scale, this technology has been proposed to be used in tandem with a natural gas turbine, greatly improving the efficiency by eliminating the need to compress the air feeding the turbine. According to ESA’s “Technologies: CAES” webpage, the first commercial CAES facility was a 290 MW unit built in Hundorf, Germany in 1978. The second commercial CAES was a 110 MW unit built in McIntosh, Alabama in 1991. But there doesn’t appear to be anything built on a large scale since then.
The third technology that is quite interesting is the “flow battery.” As Wikipedia’s Flow Batteries definition puts it, “A flow battery is a form of rechargable battery in which electrolyte containing one or more dissolved electroactive species flows through a power cell / reactor that converts chemical energy to electricity. Additional electrolyte is stored externally, generally in tanks, and is usually pumped through the cell (or cells) of the reactor, although gravity feed systems are also known. Flow batteries can be rapidly “recharged” by replacing the electrolyte liquid (in a similar way to refilling fuel tanks for internal combustion engines) while simultaneously recovering the spent material for re-energization.”
According to ESA, there are three flow battery technologies, the Polysulfide Bromide Flow Battery, the Vanadium Redox Flow Battery, and the Zinc Bromine Flow Battery. All three of these flow battery technologies are in various stages of development. The apparent leader in Vanadium Redox Flow batteries is VRB Power Systems Technology located in British Colombia. One of their projects (ref. Tapbury / Sorne Hill), a 12 megawatt storage system to buffer a wind farm in Donegal, Ireland. Two leaders in Zinc Bromine Flow technology are Massachusetts based Premium Power, and ZBB Energy Corporation located in Wisconsin. Both of these companies have modular units that deliver up to 100 kilowatt-hours of electricity storage, and are designed to last for decades.
Whether or not our electrical grid shifts to requiring literally gigawatt-hours of electricity storage depends on four interrelated strategic variables that impact all green technology – political, scientific/climate, economic, and technological. For example, the decision to deploy potentially far more expensive electricity storage units on the grid in order to save solar energy harvested during the solar peak to deliver electricity during the demand peak may be a political one, since constructing additional natural gas fired peaking plants would also help meet peak demand for electricity.
Can electricity storage solutions become so inexpensive they can compete with conventional buffering technologies such as quick start natural gas power plants? Probably not. How far electricity storage goes as an industry will depend not just on how storage technology develops, but also to what extent the political decision is made to eliminate dependance on fossil fuel altogether.