Storing Energy By Heating Stones To 600 ºc – Could Feed Denmark For Hours

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The excess energy generated by renewable sources requires sustainable storage solutions worldwide. Denmark has started a series of stone trials for district heating systems.

High temperature thermal energy storage.

The Danes are experimenting with stones for high-temperature thermal energy storage, a way to boost renewable energy in the country. Rocks are cheap and environmentally friendly materials.

Renewable energies produce excess energy at certain times that can be used to pump very hot air into a group of stones, where the energy can be stored for several days with little loss.

The process can be reversed by forcing the hot air out of the storage, which in turn creates steam from the water to drive electricity-generating turbines to produce hot water for district heating.

Plant A Ritzau.

The energy company SEAS-NVE and the technical university built a small-scale pilot facility, in collaboration with partners at the Risø Campus, including Aarhus University, Danish Energy, Energy Technology Development and Demonstration Program and Rocwool.

In the facilities they store insulating stones, which can be heated to 600 ºC, driven by the surplus from the wind turbines. After a couple of days, when energy is needed, the heat is passed through a generator to generate electricity and the waste heat feeds the district heating.

In these preliminary studies they are trying to find the right stones and the energy storage model. So far they have applied the bowl shape.

According to the Danish Energy Agency and Storasol, the technical data related to the project for the year 2016 is summarized as follows:

  • Price per kWh stored (electricity): 300 DKK ($46).
  • Volume (amount of energy that can be stored at each site): 1-500 MWh.
  • Possibility of increasing the amount of stored energy: Yes.
  • Energy lost in the storage process (heat): 1-5%, depending on the insulation.
  • Environmental impact: None, except if gas and not electricity are used as the heating source.
  • Geographic location requirements: Better in relation to existing cogeneration plants.

Denmark already has a very complete district heating system, the relative loss in electricity generation from heat has less impact.

This fact helps to ensure a high level of utilization of stored energy, even as the price of chemical battery storage is increasingly competitive.

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