Efficient Thermal Energy Storage in Lappeenranta

Lappeenranta, the 13th largest city in Finland in population, is located in South Karelia near the Russian border. The 2022 Russian invasion of Ukraine and subsequent closure of the border significantly affected local businesses, while, along with Europe, Lappeenranta faced an energy crisis with rising natural gas and oil prices. However, this challenging context has been accelerating the transition to renewables, which has been seen as a possibility for Lappeenranta. 

The Lappeenranta-Lahti University of Technology (LUT) is internationally recognized for its climate initiatives, ranking 10th globally. The City of Lappeenranta has greatly benefited from its collaboration with LUT University, which plays a key role in providing innovative solutions to support the city's energy transition. 

Heating in Lappeenranta: the road to sustainability 

Heating in Lappeenranta has undergone two major transitions since the 1960s. Initially, the city moved from individual oil heating to a district heat network powered by natural gas. In the 2010s, natural gas was largely replaced with biomass. Currently, a third shift is underway, with electricity becoming a more viable source of heat production. This shift is enabling the City of Lappeenranta to phase out the remaining fossil fuels, including oil, gas, and peat, in its district heating network. 

In 2022, emissions from district heating in Lappeenranta were 52.4 ktCO2e, accounting 15.1% of the city’s total emissions. As the City of Lappeenranta aims to achieve carbon-neutrality by 2030, the use of low-cost and low-emission electricity to charge the thermal energy storage is helping to reach this goal. During the winter of 2023-2024, it produced 600 MWh of district heating, covering 32% of the heat demand in the Selkäharju area, equivalent to heating 100 houses. Over six months, it saved over 800 MWh of natural gas primary energy and reduced CO2 emissions by 160 tons, while achieving 89% electricity-to-heat efficiency.  

Moreover, Lappeenrannan Energia, the local energy company, has reactivated electric boilers and is constructing a large hot water storage facility. In addition, City of Lappeenranta and Lappeenrannan Energia have started piloting demand response of district heating. Together with the thermal energy storage, these innovations help integrate renewable electricity into the district heat system, enhancing both flexibility and sustainability. 

Powering Renewable-based District Heat with Efficient Thermal Energy Storage 

Thermal energy storage replaces fossil fuels in its district heating by utilising low-cost electricity. The charging of this storage is optimised to coincide with the lowest electricity prices throughout the day. An AI-based charging algorithm automatically selects the optimal charging hours by monitoring storage capacity, upcoming electricity prices, and predicted heat demand. Basically, the lower the electricity price is, the higher the share of it is produced with renewables. The stored heat is then used as needed in district heating, reducing reliance on fossil fuels and thus lowering emissions, while also being economically viable. As the cost of district heat production decreases, customer prices can also be reduced. 

The thermal energy storage was developed by Elstor, a company founded in July 2017 as a result of research by a local serial entrepreneur and LUT University’s energy efficiency professor. The project was led by the City of Lappeenranta in collaboration with Elstor Oy, a local startup specializing in thermal energy storage. This partnership enabled the integration of cutting-edge technology into the Mustola district heating network, controlled by Lappeenrannan Energia, showcasing the role of local businesses in driving sustainability. In 2022, Mustola was connected to Lappeenranta’s main district heat network, and the thermal energy storage was no longer needed. As a result, a decision was made to transfer it to the Selkäharju area. 

The first thermal energy storage is successfully operating within the district heat network. Additionally, Elstor Oy has secured eight delivery agreements for thermal energy storages to be used in industrial process heat production. With potential electricity-to-heat efficiency reaching 95%, thermal energy storages can significantly reduce the reliance on fossil fuels as well as enhance energy efficiency in both heat and industrial sectors. 

Reaching everyone with healthy heat 

The thermal energy storage pilot has indirectly addressed the needs of vulnerable populations by focusing on affordability, sustainability, and resilience in heating. These aspects are critical for ensuring equitable access to essential energy services, particularly for households facing economic or energy poverty. In 2024 a closing seminar of CANEMURE project - under which the thermal energy storage pilot was conducted - was held in cooperation with city’s energy advisory services. The seminar focused on energy poverty and featured discussions among stakeholders, including representatives from Lappeenrannan Energia, Lappeenrannan Asuntopalvelu (the Housing Services of Lappeenranta), LUT University and Lappeenrannan Omakotiyhdistys (the local association for detached house owners). 

Where the city is in the heat strategy:

Lappeenranta's Heat Detox

Key Heat Figures

• Emissions related to heating: 52.4 ktCO2 from the district heating system (15% of the city’s total emissions)
• Percentage of renewables in heating system: 65% in 2023
• Other interesting figures: District heating covered 32% of the heat demand in the winter of 2023-2024 

Covenant Figures

• Signatory to the Covenant of Mayors since: 2016
• City Awards: Green Leaf 2021 

Overall CO2 emission reduction target:  

• % GHG emissions reductions by 2030: 100%