A battery storage power station, or battery energy storage system (BESS), 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 electric grids, and it is used to stabilise those grids, as battery storage can transition from standby to full power in under a second to deal with grid contingencies.^[1]

Battery storage power stations are generally designed to be able to output at their full rated power for several hours. Battery storage can be used for short-term peak power^[2] and ancillary services, such as providing operating reserve and frequency control to minimize the chance of power outages. They are often installed at, or close to, other active or disused power stations and may share the same grid connection to reduce costs. Since battery storage plants require no deliveries of fuel, are compact compared to generating stations and have no chimneys or large cooling systems, they can be rapidly installed and placed if necessary within urban areas, close to customer load.

As of 2021, the power and capacity of the largest individual battery storage power plants is an order of magnitude less than that of the largest pumped-storage power plants, the most common form of grid energy storage. For example, the Bath County Pumped Storage Station, the second largest in the world, can store 24GWh of electricity and dispatch 3GW while the first phase of Vistra Energy's Moss Landing Energy Storage Facility can store 1.2GWh and dispatch 300MW.^[3] However, grid batteries do not have to be large, a large number of smaller ones can be widely deployed across a grid for greater redundancy and large overall capacity.

As of 2019, battery power storage is typically cheaper than open cycle gas turbine power for use up to two hours, and there was around 365 GWh of battery storage deployed worldwide, growing rapidly.^[4] Levelized cost of storage (LCOS) has fallen rapidly, halving in two years to reach US$150 per MWh in 2020,^[5][6][7] and further reduced to US$117 by 2023.^[8] Additionally, annualized capital costs varies by which battery chemistry used for storage, but annualized capital costs of $93/kWh could be realized with Lithium iron phosphate by 2020.^{[not verified in body]}

Battery storage power plants and uninterruptible power supplies (UPS) are comparable in technology and function. However, battery storage power plants are larger.

For safety and security, the actual batteries are housed in their own structures, like warehouses or containers. As with a UPS, one concern is that electrochemical energy is stored or emitted in the form of direct current (DC), while electric power networks are usually operated with alternating current (AC). For this reason, additional inverters are needed to connect the battery storage power plants to the high voltage network. This kind of power electronics include GTO thyristors, commonly used in high-voltage direct current (HVDC) transmission.

Various accumulator systems may be used depending on the power-to-energy ratio, the expected lifetime and the costs. In the 1980s, lead-acid batteries were used for the first battery-storage power plants. During the next few decades, nickel–cadmium and sodium–sulfur batteries were increasingly used.^[11] Since 2010, more and more utility-scale battery storage plants rely on lithium-ion batteries, as a result of the fast decrease in the cost of this technology, caused by the electric automotive industry. Lithium-ion batteries are mainly used. A flow battery system has emerged, but lead-acid batteries are still used in small budget applications.^[12]

Some batteries operating at high temperatures (sodium–sulfur battery) or using corrosive components are subject to calendar ageing, or failure even if not used. Other technologies suffer from cycle ageing, or deterioration caused by charge-discharge cycles. This deterioration is generally higher at high charging rates. These two types of aging cause a loss of performance (capacity or voltage decrease), overheating, and may eventually lead to critical failure (electrolyte leaks, fire, explosion).

Examples of the latter include a Tesla Megapack in Geelong which caught fire,^[13][14] the fire and subsequent explosion of a battery farm in Arizona, and the fire at Moss Landing battery farm.^[15] Concerns about possible fire and explosion of a battery module were also raised during residential protests against Cleve Hill solar farm in United Kingdom.^[16] Battery fire in Illinois resulted in "thousands of residents" being evacuated, and there were 23 battery farm fires in South Korea over the period of two years. Battery fires may release a number of dangerous gases, including highly corrosive and toxic hydrogen fluoride.^[17]

Some batteries can be maintained to prevent loss of performance due to aging. For example, non-sealed lead-acid batteries produce hydrogen and oxygen from the aqueous electrolyte when overcharged. The water has to be refilled regularly to avoid damage to the battery; and, the inflammable gases have to be vented out to avoid explosion risks. However, this maintenance has a cost, and recent batteries such as Li-Ion, are designed to have a long lifespan without maintenance. Therefore, most of the current systems are composed of securely sealed battery packs, which are electronically monitored and replaced once their performance falls below a given threshold.

Sometimes battery storage power stations are built with flywheel storage power systems in order to conserve battery power.^[18] Flywheels may handle rapid fluctuations better than older battery plants.^[19]

Since they do not have any mechanical parts, battery storage power plants offer extremely short control times and start times, as little as 10 ms.^{[citation needed]} They can therefore help dampen the fast oscillations that occur when electrical power networks are operated close to their maximum capacity. These instabilities – voltage fluctuations with periods of as much as 30 seconds – can produce peak voltage swings of such amplitude that they can cause regional blackouts. A properly sized battery storage power plant can efficiently counteract these oscillations; therefore, applications are found primarily in those regions where electrical power systems are operated at full capacity, leading to a risk of instability.^{[citation needed]} However, some batteries have insufficient control systems, failing during moderate disruptions they should have tolerated.^[20] Batteries are also commonly used for peak shaving for periods of up to a few hours.^[2]

Battery storage systems may be active on spot markets while providing systems services such as frequency stabilization.^[21] Arbitrage is an attractive way to benefit from the operating characteristics of battery storages.

Storage plants can also be used in combination with an intermittent renewable energy source in stand-alone power systems.

While the market for grid batteries is small compared to the other major form of grid storage, pumped hydroelectricity, it is growing very fast. For example, in the United States, the market for storage power plants in 2015 increased by 243% compared to 2014.^[62] The 2021 price of a 60MW / 240MWh (4-hour) battery installation in the United States was US$379/usable kWh, or US$292/nameplate kWh, a 13% drop from 2020.^[63][64]

In 2010, the United States had 59 MW of battery storage capacity from 7 battery power plants. This increased to 49 plants comprising 351 MW of capacity in 2015. In 2018, the capacity was 869 MW from 125 plants, capable of storing a maximum of 1,236 MWh of generated electricity. By the end of 2020, the battery storage capacity reached 1,756 MW.^[65][66] At the end of 2021, the capacity grew to 4,588 MW.^[67] In 2022, US capacity doubled to 9 GW / 25 GWh.^[68]

As of May 2021, 1.3 GW of battery storage was operating in the United Kingdom, with 16 GW of projects in the pipeline potentially deployable over the next few years.^[69] In 2022, UK capacity grew by 800 MWh, ending at 2.4 GW / 2.6 GWh.^[70] Europe added 1.9 GW, with several more projects planned.^[71]

In 2020, China added 1,557 MW to its battery storage capacity, while storage facilities for photovoltaics projects accounting for 27% of the capacity,^[72] to the total 3,269 MW of electrochemical energy storage capacity.^[73]

There is a lot of movement in the market, for example, some developers are building storage systems from old batteries of electric cars, where costs can probably be halved compared to conventional systems from new batteries.^[74]

• List of energy storage power plants