Thermal energy storage capacity increased by more than 50%

An energy system combining thermal energy storage, electric boilers and combined heat and power production has been developed at Vaasan Voima’s power plant site in Vaskiluoto, Vaasa. The latest upgrade made it possible to raise the temperature of the thermal energy storage facility to as high as 130°C, increasing its capacity by more than 50% to 17 gigawatt-hours. At the same time, a new electric steam boiler was commissioned. The combination of technologies at the site is unique in Finland and exceptional even by European standards.

Vaasan Sähkö’s Director of District Heating, Markus Tuomala, is pleased with the development of the power plant site.

– The solution improves the reliability of district heating supply and provides flexibility that is essential for the energy system. The energy stored in the storage is enough to heat properties connected to the district heating network for up to 10 days in winter. The system also plays an important role in terms of security of supply.

Thanks to the electric boilers, the system also helps balance excess electricity production on windy days. Solutions like this are therefore one way of enabling a greater share of renewable energy in the energy system.

– The ability to store energy makes it possible to use wind power and other heat sources very efficiently. Energy can be stored and then used when needed. The thermal energy storage can now serve the district heating system even better throughout the year, including during the coldest periods of winter.

In 2025, 22% of the district heating sold by Vaasan Sähkö was based on heat produced with electric boilers.

The solution plays a significant role in reducing carbon dioxide emissions from district heating production in Vaasa.

From the perspective of society and the energy system as a whole, making changes directly to district heating production to reduce carbon dioxide emissions is considerably more cost-effective than making changes to individual properties, Tuomala says.

– In Vaasa, we have been making smart and cost-effective choices for a long time as we move towards district heating production that is not based on combustion.

In 2025, the largest heat sources for the district heating sold by Vaasan Sähkö were non-recyclable municipal waste (59.0%), electricity (22.0%) and biofuels (10.7%). Coal accounted for 0.1% of production.

Vaasan Sähkö is the largest shareholder in Vaasan Voima.