Grid energy storage
Grid energy storage, also known as large-scale energy storage, is a set of technologies connected to the electrical power grid that store energy for later use. These systems help balance supply and demand by storing excess electricity from variable renewables such as solar and inflexible sources like nuclear power, releasing it when needed. They further provide essential grid services, such as helping to restart the grid after a power outage.
, the largest form of grid storage is pumped-storage hydroelectricity, with utility-scale batteries and behind-the-meter batteries coming second and third. Lithium-ion batteries are well suited for short-duration storage, due to their lower cost and sensitivity to degradation at high states of charge. Flow batteries and compressed air energy storage may provide storage for medium-duration. Two forms of storage are suited for long-duration storage: green hydrogen, produced via electrolysis and thermal energy storage.
Energy storage is one option to making grids more flexible. Another solution is the use of more dispatchable power plants that can change their output rapidly, for instance peaking power plants to fill in supply gaps. Demand response can shift load to other times and interconnections between regions can balance out fluctuations in renewables production.
The price of storage technologies typically goes down with experience. For instance, lithium-ion batteries have been getting some 20% cheaper for each doubling of worldwide capacity. Systems with under 40% variable renewables need only short-term storage. At 80%, medium-duration storage becomes essential and beyond 90%, long-duration storage does too. The economics of long-duration storage is challenging, and alternative flexibility options like demand response may be more economic.
Roles in the power grid
Any electrical power grid must match electricity production to consumption, both of which vary significantly over time. Energy derived from solar and wind sources varies with the weather on time scales ranging from less than a second to weeks or longer. Nuclear power is less flexible than fossil fuels, meaning it cannot easily match the variations in demand. Thus, low-carbon electricity without storage presents special challenges to electric utilities.Electricity storage is one of the three key ways to replace flexibility from fossil fuels in the grid. Other options are demand-side response, in which consumers change when they use electricity or how much they use. For instance, households may have cheaper night tariffs to encourage them to use electricity at night. Industry and commercial consumers can also change their demand to meet supply. Improved network interconnection smooths the variations of renewables production and demand. When there is little wind in one location, another might have a surplus of production. Expansion of transmission lines usually takes a long time.
| Consumption | Network | Generation | |
| Short-term flexibility | Increased use rooftop solar, cost reductions from time-based rates | Congestion relief | Renewables integration |
| Essential grid services | Backup power during outages | Frequency regulation | Black start |
| System reliability and planning | Creation of mini-grids | Savings in transmission and distribution network | Meeting peak demand |
Energy storage has a large set of roles in the electricity grid and can therefore provide many different services. For instance, it can arbitrage by keeping it until the electricity price rises, it can help make the grid more stable, and help reduce investment into transmission infrastructure. The type of service provided by storage depends on who manages the technology, whether the technology is based alongside generation of electricity, within the network, or at the side of consumption.
Providing short-term flexibility is a key role for energy storage. On the generation side, it can help with the integration of variable renewable energy, storing it when there is an oversupply of wind and solar and electricity prices are low. More generally, it can exploit the changes in prices of electricity over time in the wholesale market, charging when electricity is cheap and selling when it is expensive. It can further help with grid congestion. Consumers can use storage to use more of their self-produced electricity.
Storage can also be used to provide essential grid services. On the generation side, storage can smooth out the variations in production, for instance for solar and wind. It can assist in a black start after a power outage. On the network side, these include frequency regulation and frequency response. On the consumption side, storage can improve the quality of the delivered electricity in less stable grids.
Investment in storage may make some investments in the transmission and distribution network unnecessary, or may allow them to be scaled down. Additionally, storage can ensure there is sufficient capacity to meet peak demand within the electricity grid. Finally, in off-grid home systems or mini-grids, electricity storage can help provide energy access in areas that were previously not connected to the electricity grid.
Recent advances in artificial intelligence and machine learning allow for real-time optimization of energy storage assets. Reinforcement learning algorithms are being explored to maximize arbitrage, manage degradation, and respond to market signals, particularly in complex and high-renewable systems.
Forms
Electricity can be stored directly for a short time in capacitors, somewhat longer electrochemically in batteries, and much longer chemically, mechanically or as heat. The first pumped hydroelectricity was constructed at the end of the 19th century around the Alps in Italy, Austria, and Switzerland. The technique rapidly expanded during the 1960s to 1980s nuclear boom, due to nuclear power's inability to quickly adapt to changes in electricity demand. In the 21st century, interest in storage surged due to the rise of sustainable energy sources, which are often weather-dependent. Commercial batteries have been available for over a century. However, their widespread use in the power grid is more recent, with only 1 GW available in 2013.Batteries
Lithium-ion batteries
Lithium-ion batteries are the most commonly used batteries for grid applications, as of 2024, following the application of batteries in electric vehicles. In comparison with EVs, grid batteries require less energy density, meaning that more emphasis can be put on costs, the ability to charge and discharge often and lifespan. This has led to a shift towards lithium iron phosphate batteries, which are cheaper and last longer than traditional lithium-ion batteries.Costs of batteries are declining rapidly; from 2010 to 2023 costs fell by 90%., utility-scale systems account for two thirds of added capacity, and home applications for one third. Lithium-ion batteries are highly suited to short-duration storage due to cost and degradation associated with high states of charge.
Electric vehicles
The electric vehicle fleet has a large overall battery capacity, which can potentially be used for grid energy storage. This could be in the form of vehicle-to-grid, where cars store energy when they are not in use, or by repurposing batteries from cars at the end of the vehicle's life. Car batteries typically range between 33 and 100 kWh; for comparison, a typical upper-middle-class household in Spain might use some 18 kWh in a day. By 2030, batteries in electric vehicles may be able to meet all short-term storage demand globally., there have been more than 100 V2G pilot projects globally. The effect of V2G charging on battery life can be positive or negative. Increased cycling of batteries can lead to faster degradation, but due to better management of the state of charge and gentler charging and discharging, V2G might instead increase the lifetime of batteries. Second-hand batteries may be useable for stationary grid storage for roughly 6 years, when their capacity drops from roughly 80% to 60% of the initial capacity. LFP batteries are particularly suitable for reusing, as they degrade less than other lithium-ion batteries and recycling is less attractive as their materials are not as valuable.
Other battery types
In redox flow batteries, energy is stored in liquids, which are placed in two separate tanks. When charging or discharging, the liquids are pumped into a cell with the electrodes. The amount of energy stored can be adjusted separately from the power output. Flow batteries have the advantages of low capital cost for charge-discharge duration over 4 h, and of long durability. Flow batteries are inferior to lithium-ion batteries in terms of energy efficiency, averaging efficiencies between 60% and 75%. Vanadium redox batteries is most commercially advanced type of flow battery, with roughly 40 companies making them as of 2022.Sodium-ion batteries are a possible alternative to lithium-ion batteries, as they are less flammable, and use cheaper and less critical materials. They have a lower energy density, and possibly a shorter lifespan. If produced at the same scale as lithium-ion batteries, they may become 20% to 30% cheaper. Iron-air batteries may be suitable for even longer duration storage than flow batteries, but the technology is not yet mature.
| Technology | Less than 4h | 4h to 8h | Days | Weeks | Seasons |
| Lithium-ion | |||||
| Sodium-ion | |||||
| Vanadium flow | |||||
| Iron-air |