Electrochemical energy storage (EES) systems mainly consist of different types of rechargeable batteries. A rechargeable battery comprises one or more electrochemical cells. Rechargeable batteries come in many shapes and sizes, ranging from button cells to megawatt grid systems. Battery systems connected to large solid-state converters have been used to stabilize power distribution networks. Some grid batteries are co-located with renewable energy plants, either to smooth the power supplied by the intermittent wind or solar output, or to shift the power output into other hours of the day when the renewable plant cannot produce power directly. Battery storage technology is typically around 80% to more than 90% efficient for newer lithium-ion devices. Battery systems connected to large solid-state converters have been used to stabilize power distribution networks.
A battery storage power station is a type of energy storage power station that uses a group of batteries to store electrical energy. Battery storage is the fastest responding dispatchable source of power on grids, and it is used to stabilise grids, as battery storage can transition from standby to full power within milliseconds to deal with grid failures. At full rated power, battery storage power stations are generally designed to output for up to a few hours.
Lithium-Ion (Li-I) batteries are the most common type of rechargeable batteries. Sodium-ion batteries are a cheap and sustainable alternative to lithium-ion, because sodium is far more abundant and cheaper than lithium, but it has a lower power density. However, they are still on the early stages of their development. Lead-acid batteries, together with the nickel-cadmium batteries listed below, are among the oldest, best-known and most widely used batteries. Although Li-ion batteries are slowly beginning to displace them from some applications, there are areas where lead and alkaline batteries are irreplaceable. Compared to Li-ion batteries, they excel especially in low temperature resistance, safety and price.
- Lithium-ion batteries. Lithium-ion batteries are also frequently discussed as a potential option for grid energy storage, although they are not yet cost-competitive at scale. Lithium batteries show the largest market growth of all other batteries and have successfully displaced the competing systems. Lithium secondary batteries (lithium-ion batteries) provide multiple reversible transformation of chemical energy into electrical energy, so that these batteries can be often used. Lithium-ion batteries, unlike conventional batteries do not have a memory effect (loss of capacity by not complete loading / unloading) and achieve a high efficiency of up to 95% (ratio of discharge to charge amount). The problem with these batteries is their lifespan, which is typically defined as the number of full charge-discharge cycles to reach a failure threshold in terms of capacity loss or impedance rise. After 500 cycles, the capacity of lithium-ion batteries begins to drop and the capacity is reduced to around 50% after 1200-1500 discharge cycles. One of the largest Li-I storage plants in the world is the 48 MW, 12 MWh Gyeongsan Substation in South Korea, which became operational in January 2016.
- Flow batteries. In rechargeable flow batteries, the liquid electrodes are composed of transition metals in water at room temperature. They can be used as a rapid-response storage medium. Vanadium redox batteries are a type of flow battery. Flow batteries have relatively low energy densities and have long life cycles, which makes them well-suited for supplying continuous power. A 200 MW (800 MWh) flow battery is currently being constructed in Dalian, China.
- Lead-acid batteries. However, they are not popular for grid storage because of their low-energy density and short cycle and calendar life. They were commonly used for electric cars, but have recently been largely replaced with longer-lasting lithium-ion batteries.