Thermal storage

Thermal storage uses heat to store energy so that when demand peaks, the heat can produce electricity directly by initializing a steam turbine. There are different ways to store this energy. One way is to use large-scale volcanic rocks that can contain a big amount of heat. This solutions is able to hold the energy for up to one week, and is therefore helping with adequacy and sometimes congestion management. Another way is to store heated fluids in insulated tanks. This storage system can respond very quickly, and can provide anything from short term frequency response up to longer cycles over several days. It therefore helps with frequency balancing, adequacy and congestion management. Moreover, district heating and cooling is an energy solution for satisfying urban heat and cooling demand. District energy systems which pipe steam, and hot or cold water, around a district from a central location are being used in a variety of cities worldwide because of their higher energy efficiency which can significantly reduce the greenhouse gas emissions of cooling and heating.

Components & enablers

  • Highly flexible digital control system platforms for virtual power plants that enables to store renewable energy optimally value in electricity markets. It can also provide both adequacy and congestion management.

State of the art in application and research

A pilot plant in Hamburg can store 130 MWh for up to one week, and has a goal of reaching over 1 GWh in the near future. The heat storage facility contains around 1,000 tons of volcanic rock as an energy storage medium. It is fed with electrical energy converted into hot air by means of a resistance heater and a blower that heats the rock to 750°C. EnergyNest are looking at a faster storage solution. The thermal storage unit could be used for thermal power plants by directly being integrated into existing steam cycles, effectively providing a steam storage buffer between the boiler and the turbine. This allows plant operators to run their boiler continuously while boosting or reducing the electric output on demand. Depending on the case, the system reaction time for EnergyNest can be less than 7 seconds. This makes it a solution for providing thermal power plants with the flexibility required to provide primary frequency response. It can be designed to provide a short or long response time, depending on what provides most value in electricity markets. It can also provide both adequacy and congestion management.

In EnergyNest heat at high temperature is transferred to the thermal storage device using a heat transfer fluid (HTF) inside pipes cast into the thermal storage elements. There is no direct contact between the heat transfer fluid and storage material, and the thermal elements with steel piping are compatible with common HTFs such as thermal oil, water/steam or compressed gas etc.

Eco-Stock is a heat storage made from refractory ceramics and works by heating the ceramics directly with hot fumes from the chimney.

E2District is a three year European Commission Horizon 2020 Research and Innovation project formally entitled 'Energy Efficient Optimised District Heating and Cooling (DHC).

Technology Readiness Level

Large-scale volcanic rock: TRL 7 – demonstration:

New 4.0 has a pilot plant in Hamburg that can store 130 MWh for up to one week and the next step is to use its storage technology in commercial projects and scale up the storage capacity and power to reach the goal of over 1 GWh in near future.

Heated fluid in insulated containers: TRL 9 – implementation:

EnergyNest is already commercial.

Current focus of R&D and research gaps

See state of the art.


[1] New 4.0: Simens Gamesa. [Link]

[2] EnergyNest. [Link]

[3] Eco-Stock. [Link]

[4] STORY – pilot 6. [Link]