Commercialised Energy Storage Technologies

May 11, 2016

Mechanical Storage Technologies

Pumped Hydropower Storage System

pumped hydroThe hydroelectric power plant acts as a generator and a pumping facility. It uses two water reservoirs (upper and lower one) separated vertically. Water is pumped from the lower reservoir to the upper reservoir during off-peak hours. During peak load periods, the water flow is reversed and electricity is generated.

Key features:

  • Fully commercialized, mature technology.
  • High efficiencies 70–80%.
  • Long economic life span – more than 50 years.
  • Storage time between 4–10 hours.
  • Low O&M costs, no cycling degradation.
  • Immediate start-up.
  • Investment cost is usually very high.
  • Requires very specific siting requirements.
  • Provide valuable scheduling and balancing services

Pumped hydro storage is the most used and mature largescale energy storage technology, with 129 GW of installed capacity worldwide.

Source | ECOFYS 2013; Eurelectric 2011; KEMA.

CAES Facility

huntorfCompressed air energy storage (CAES) stores energy by compress air into enclosed volumes – underground caverns or in above-ground storage tanks. The electrical energy is recovered when the stored compressed air is fed into a turbine. There are three different options of CAES available (diabatic, adiabatic and isothermal), depending on the expansion process in the turbine.

Key features:

  • Commercialized technology.
  • Efficiency ranges from 40-75%.
  • Long life span – more than 30 years.
  • 5 to 15 minutes to start up time, ramp up rate of 10%/3 seconds in discharging mode and 20%/minute in charging mode.
  • High investment cost and substantial geology research is required in case of underground storage caverns.
  • Conventional CAES system requires natural gas fuel.

Existing utility-scale CAES plants:

  • Huntorf CAES Power Plant (60MW compressor/321MW generator) built in Germany in 1978;
  • Alabama Electric Cooperative McIntosh plant (50MW compressor/110MW generator) built in US in1991
  • Pacific Gas&Electric is working on a CAES demonstration plant (300MW with 10 hours storage capability).

Source | KEMA & ECOFYS 2013.

Flywheel Plant

flywhellFlywheels store electrical energy by speeding up inertial masses that rest on very low friction bearings. Motor-generator rotor speed ranges from 1800-3600 rpm and the total weight can be around 3000-6000 kg.

Key features:

  • Fully commercialized technology.
  • Efficiencies range 70-80%.
  • Limited life span as continuous cycling operation wear down mechanical components (expected life cycle of 100,000 charge-discharge cycles)
  • Energy storage 0.5-1kWh per module.
  • Capacity ranges from 100kW-20MW
  • Short discharge times from seconds to minutes.
  • Suitable for frequency regulation and power quality applications

Source | ECOFYS 2013; KEMA, Red Electrica and SNL.

Electrochemical Storage Technologies

Advanced Lead-Acid Battery

Solid State Conventional batteries are cells that contain two terminals (cathode and anode) and electrolytes that allow ions to move between the terminals. The electrolyte is ionized during the charging cycle and an oxidation-reduction reaction recovers the energy during discharge. There is a wide range of battery types: lead-acid, nickel-cadmium (NiCd), and lithium-ion.


  • Golden Valley Electric Association BESS energy-storage application commissioned in 2003 uses Ni-Cd batteries (27MW for 15 minutes)
  • 3MW system commissioned in the island of Bonaire (Caribbean Netherlands) in 2010 for stabilizing wind power.

Source | ECOFYS 2013; KEMA and ESA.

Sodium-Sulphur Battery

High energy/temperature batteries are based on reactions that occur at temperatures 300-350°C. Common chemistries are sodium sulphur (NaS), the most common, and sodium nickel chloride. The round trip efficiency of Sodium Sulphur battery systems for stationary applications reaches 90%.


  • More than 270MW of NaS batteries have been installed in Japan (over 190 sites). The largest NaS installation is a 34MW, 245MWh unit for wind stabilization.
  • US utilities deployed 9 MW for peak shaving, backup power, firming wind capacity.

Source | ECOFYS 2013; KEMA and ESA.

 Vanadium Redox Battery

Flow batteries store the electrolyte material in external tanks. The electrolyte is pumped into the cell stack during charging and discharge cycles. There are two types of flow batteries: redox and hybrid. Flow batteries are suited for peaking generators and regulation reserves. Vanadium Redox systems are more mature than Zinc/Bromine batteries. Estimated lifetime of flow batteries is around 20 years. Estimated efficiencies are around 65-75%.

Source | ECOFYS 2013; KEMA and ESA.

Chemical Storage Technologies

Power to Gas

Audi+Gtron+power+to+gasChemical energy storage uses excess electricity to create hydrogen or hydrocarbons, which can be used as fuels (synthetic methane, hydrogen). These projects are still in the demonstration stage, with Germany leading the research.


  • In June 2013 Audi opened 6MW power to gas (SNG) facility to operate 1.500 vehicles. The conversion efficiency of the plant is higher than 50 percent.

 Thermal Storage Technologies

Chilled Thermal Storage

Large-scale chilled thermal storage and small-scale cold thermal storage.

Thermal energy storage refers to storage technologies where instead of storing electric energy, energy is stored as thermal energy.

Thermal energy can be stored as:

  • Sensible heat (as in hot water tanks or ice).
  • Latent heat (the storage medium stores and releases energy by changing phase).
  • Thermochemical heat (thermal energy is absorbed or released via a chemical reaction).

Thermal energy technologies are most effective when used in situations where the end usage is thermal energy (less energy conversions).

Source | KEMA.

Molten Salt Tanks in Gemasolar Power Plant

Thermal Energy Storage Technologies for Concentrated Solar Thermal Power (CSP):

The leading technology involves a two-tank system storing a heat transfer fluid (thermal oil, molten salt). Other technologies like solid media (concrete) and phase-change materials are being developed, improving heat transfer characteristics, controllability, safety, economics, and other aspects.


  • Gemasolar – 19.9MW solar tower commissioned in October 2011.
  • Abengoa’s Solana 280MW solar power station in Arizona with 6 hours of thermal energy storage
  • SolarReserve’s 110MW Crescent Dunes power tower solar thermal plant in Nevada with 10 hours of storage.

Source | ECOFYS 2013; KEMA; Torresol Energy–SENER.

 Electromagnetic Storage Technologies

Metal Enclosed Capacitor Banks

Capacitors help store power over short time horizons. They have very fast response times, very low energy densities, and high cycle lives. Their timeline for market penetration are similar to flywheels.

Source | ECOFYS 2013; KEMA.


Superconducting Magnetic Energy Storage (SMES) store energy in the magnetic field created by the flow of direct current in a superconducting coil. The primary cost components of SMES are the superconductor and the associated cooling system. Up to now, most of the research conceptualized short-duration units for power application. However, some suppliers (such as ABB) are examining a device that could provide significantly higher energy density at lower cost than traditional lead-acid batteries.

Source | ECOFYS 2013; KEMA.