The City of Lappeenranta in Finland is testing an energy storage system at the Selkäharju district heating plant. It is a heat accumulator system whose testing started in 2019 at the Mustola district, Lappeenranta. The testing ended in January 2022, when changes to the district heating network due to the energy crisis meant that Mustola was no longer a suitable test site for the project. The testing will be moved from Mustola to Selkäharju, and at the same time, the storage modules will be changed from a salt-based to a metal-based solution.
The city wants to continue testing the heat accumulator as the challenges for future energy systems are increasing. Energy will be available in excess, but production depends on weather conditions. This leads to an increase in the daily fluctuation of electricity prices. Energy storage solutions are needed to match energy supply and demand better.
Storing energy as heat is cheaper than as electricity. Simultaneously, much of the energy demand is thermal. With the new heat accumulator at Lappeenranta, the profitability of storing electricity directly as heat is tested, as well as the potential for replacing fossil energy with renewable electricity. In Selkäharju, the heat accumulator would replace natural gas. It could reduce carbon dioxide emissions by more than 300 tCO2e, says Miika Alatalo, a Specialist for the city.
“The heat accumulator makes it possible to replace fuels for heat generation, such as natural gas and light fuel oil, with electricity. This reduces carbon dioxide emissions as well as dependence on imported fuels. In Finland, the carbon dioxide nominal value of electricity has decreased rapidly and varies between 0-70 g/kWh, so using electricity instead of fossil fuels is an almost climate-neutral solution. ”
Selkäharju’s heat accumulator will be built, and its testing will start in 2023. The city implements the pilot together with Lappeenrannan Energia Oy, a city-owned energy company. The storage is charged with electricity in high-temperature storage modules, from which the energy is discharged to the use sites as heat. A similar device has already been in use in the industrial sector since 2021, where the heat accumulator has been used to produce process steam. Now, the device is being tested in district heat production.
Elstor Oy, a Lappeenranta-based company, has developed the thermal energy storage technology initially. The company aims to create a cost-effective and practical solution for low-emission and low-cost energy production. The device can also be used as a load for balancing the electricity grid. Testing aims to verify the device's behaviour and to calculate its impact on energy costs and CO2 emission reductions. If the heat accumulator energy storage meets expectations, it will have a large market in Finland and globally.
The heat accumulator experiment is a part of the Towards Carbon Neutral Municipalities and Regions project (Canemure), which belongs to the EU’s six-year Life programme implementing national climate policy.