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Energy Currents
A Blog by Enerdynamics

Batteries May Soon Rival Pumped Hydroelectric In the Electric Storage Market

by Bob Shively, Enerdynamics President and Lead Instructor

Electric energy storage involves amassing and saving electricity for use at a later time. Unlike natural gas, which is easy to store, electricity storage is more complex and until recently has mostly involved pumped hydroelectric storage. The primary focus of energy storage historically has been for utilities to serve peak electricity demand and to save money by avoiding usage of high-cost peaking power plants.

As the grid evolves and new storage technologies are implemented, storage has the potential to provide many grid and customer services including:

  • Customer energy management: tools for controlling bills through trimming peak demand, shifting usage to lower-price time periods, and shifting distributed generation output to higher-price time periods.
  • T&E infrastructure: capacity available on a specific distribution circuit or transmission path that allows the circuit or path to serve peak demand without the need to invest in new facilities such as substations or line capacity, also described as a type of non-wires alternative.
  • Ancillary services: provision of various services required to maintain grid reliability including frequency response, voltage support, fast ramping, spinning reserves, non-spinning reserves, and blackstart.
  • Capacity: supply available to grid operators to reliably meet demand during high-load periods or when other sources of supply are unavailable.
  • Renewables integration: ability to absorb excess supply during times of high renewables output, and to replace renewable supply when renewable availability drops due to weather conditions.
  • Time-shifting supply: ability to absorb supply when supply exceeds demand and return the supply to the grid when demand rises.
  • Price arbitrage: ability to absorb supply when prices are low and return the supply to the grid when prices rise.

There are various types of energy storage systems (ESS). Some discharge stored energy very quickly and some are considered long-duration. 

The technical and cost characteristics of the various types of storage determine which service each is most suited to provide. Three key storage technologies are summarized below:

Pumped hydroelectric storage
The most widely used form of energy storage is pumped hydroelectric power. Pumped hydro involves pumping water from one water reservoir to another reservoir, the second of which is located higher geographically from the first body of water. The pumping is done during off-peak hours when electricity is relatively cheap.

During the peak hours when electricity is expensive, water is sent from the upper reservoir to the lower reservoir and run through a turbine that generates electricity. Thus, the energy in the water that turns the turbine is in effect the storage. Pumped hydro is a mature technology but is typically expensive to build and has very specific geographical requirements.

Typical duration for pumped hydro: Minutes to hours
Typical size for pumped hydro: 10-1500 MW


 Seneca Pumped Storage Station and Kinzua Dam

Thermal energy storage
Thermal energy storage (TES) converts electric energy to thermal energy that can be stored for later use. Examples include ice storage for air conditioners or other cooling loads and heat storage in hot water heaters.

Typical duration for ice storage: Hours
Typical size for ice storage: 10 kW-1 MW
Typical duration for hot water storage: Minutes to hours
Typical size for hot water storage: < 1 kW

Ice storage system for commercial air conditioning units (source:

Battery energy storage systems (BESS) convert electrical energy to chemical energy, which is then converted back to electricity when it is needed. Lithium-ion batteries have undergone rapid development in recent years and are becoming increasingly common on transmission and distribution systems as well as within customer facilities. Multiple other types of batteries are under development and may become commercial in the future.

Typical duration for lithium-ion battery: Seconds - hours
Typical size for lithium-ion battery: 1 kW - 1 MW
Typical duration for zinc air battery: Hours
Typical size for zinc air battery: 100 kW – 1 MW
Typical size of advanced lead acid battery: Minutes – hours
Typical size for advanced lead acid battery: 1 kW – 10 MW

Rabbit Hill Battery Energy Storage Project in Texas

Until recently, pumped storage was the only storage technology that had been implemented in significant volumes with 22,900 MW in the U.S. as of 2018 according to the Energy Information Administration. But battery energy storage is growing rapidly. According to Wood Mackenzie and the U.S. Energy Storage Associate’s latest US Energy Storage Monitor report, capacity in the U.S. is expected to grow from 1,200 MW in 2020 to nearly 7,500 MW in 2025. It now appears likely that in the next decade we will have ubiquitous battery storage throughout the grid rivaling the capacity of the current pumped storage capacity.

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Energy storage , Batteries , Pumped hydroelectric storage , Thermal energy storage ,