Energy
We produce electricity and heat at the Kymijärvi power plants in Lahti. For industrial customers, we produce, for example, process steam in production facilities customised to their needs.
Heat and electricity from renewable and recycled fuels
We favour renewable and recycled fuels in our production, such as biofuel produced from the side streams of the sawmill and wood industries. Our small-scale plants use biogas and natural gas. We also recover waste heat from, for example, the wastewater treatment process.
As shareholders of EPV Energy Ltd and Suomen Hyötytuuli Oy, we are provided with their electricity produced with wind power, nuclear power and hydropower in an amount corresponding to our shareholding. For industrial customers, we produce, for example, process steam in production facilities customised to their needs.
Kymijärvi II gasification power plant
Kymijärvi II, the world’s first power plant utilising only recycled fuels, was completed in 2012. The gasification power plant produces electricity and district heat in a combined process using the back pressure principle.
The plant’s overall process includes recycled fuel receiving and storage silos, two gasifier and product gas purification lines, a gas boiler, a steam turbine, flue gas cleaning equipment and a chimney. The power plant’s fuel consists of non-recyclable but highly combustible waste, i.e. plastic, paper, cardboard and wood.
The plant’s fuel power is 160 megawatts, with an output of 50 megawatts as electricity and 90 megawatts as district heating. The power plant produces about half of the electric and district heating energy we supply.
Kymijärvi III bioenergy heating plant
The Kymijärvi III bioenergy heating plant completed in 2019 replaced a coal-fired power plant (Kymijärvi I) commissioned in the 1970s. The heating plant reduced carbon dioxide emissions by 600,000 tonnes per year.
Kymijärvi III is responsible for heating the Lahti region together with the Kymijärvi II plant. The district heat output of the bioenergy heating plant is approximately 190 megawatts, with biomass as its main fuel. The sustainable wood fuel is made up of, for example, logging residue chips and sawmill by-products, but it can also include more substantial wood materials unsuitable for further processing. This has been the case as the geopolitical environment has changed. During the coldest time of the year, about 55 truckloads of fuel are consumed per day.
The plant’s circulating fluidised bed boiler makes it possible to use other solid fuels as well, if necessary. At Kymijärvi III, the efficiency of heat production has been maximised with an efficient heat recovery plant. The resulting condensate is treated and the fly ash is recycled for reuse, where applicable.
Unique condensate treatment
A power plant needs water to function. Together with our technology suppliers, we developed a new type of condensate treatment process for the Kymijärvi III heating plant. The system makes the plant nearly self-sufficient in terms of water consumption. The plant needs raw water only for cooling. Process water is obtained from the moisture contained in the fuel, i.e. biomass. Condensate is recycled in the process, which means that the amount of excess condensate generated is very low. The water is discharged into Lake Vesijärvi cleaner than drinking water.
The condensate treatment process developed by Lahti Energy is unique in Finland. The process has been selected as one of the key energy projects of the Ministry of Economic Affairs and Employment (MEAE), and it received key project aid from the Ministry.
Electric boilers
In November 2024, we commissioned Kymijärvi IV electric boiler for district heat production. The 60-megawatt electric boiler strengthens the Lahti region’s security of supply and diversifys emission-free heat production.
The electric boiler produces heat directly with electricity. The heat production system is an independent production unit. The water in the electric boiler will not need to be replaced frequently.
We use the electric boiler all year round as needed. The electric boiler and its auxiliary equipment is placed in the gasifier building of the old, decommissioned Kymijärvi I power plant. For the first time in Lahti’s history, we produced district heating mainly with electricity in summer 2025.
We are building a second 60-megawatt electric boiler at Teivaanmäki power plant site. It is expected to be commissioned by the end of 2026.
District heating heat accumulator at Kymijärvi power plant area
We commisioned a new district heating heat accumulator at the Kymijärvi power plant in 2026. The heat accumulator is a large, heavily insulated water tank used to store thermal energy. Its capacity is about 16,000 cubic meters. When the accumulator is fully charged, it contains 750 MWh of energy, which corresponds to the annual heating demand of approximately one hundred apartment buildings.
We charge the accumulator when needed. When it is fully charged, it can discharge heat into the district heating network for 12 hours. The thermal power output is 60 megawatts, matching the capacity of our electric boiler at the Kymijärvi power plant area.
The heat accumulator is a large facility: its external diameter is 22 meters and its height at the center of the roof is approximately 52 meters. The height is comparable to a roughly 15-storey building.
The heat accumulator enhances the use of our electric boiler. It allows us to store district heating energy produced when electricity prices are low. The accumulator provides flexibility and efficiency for our production. It also improves our ability to utilise waste heat and surplus heat in the district heating network.
The world’s largest sand battery
In 2027, we are commissioning a new thermal energy storage in Vääksy, Asikkala. The sand battery has a heat storage capacity of 250 MWh. Construction began in January 2026.
The objectives of the investment are to improve the profitability of heat production in Vääksy’s district heating network, keep customer prices at a reasonable level, participate in electricity reserve markets, and reduce climate emissions. With the sand battery, fossil emissions from heat production in the Vääksy district heating network will decrease by approximately 60 percent annually. In addition to a significant reduction, around 80 percent, in the use of natural gas, the use of wood fuel will also decrease.
Balancing the electricity grid
The sand battery will be integrated into the electricity grid balancing mark. In the sand battery, ordinary sand is heated to a high temperature using electric resistive heaters, and the stored heat is discharged into the district heating network when needed. The sand battery is charged from the electricity grid during periods of low electricity prices. Towards the district heating network, the sand battery is a flexible and rapidly adjustable form of heat production.
The world’s largest sand battery diameter is about 15 meters, and its’ height is about 14 meters.
Rendering of the sand battery: Polar Night Energy
Ali-Juhakkala heating and cooling plant
An industrial-scale heating and cooling plant has been put into production at Lahti Aqua’s Ali-Juhakkala wastewater treatment plant in 2023. The idea behind the heating and cooling plant is to utilise the waste heat from wastewater for the Lahti district heating network and the needs of the Lahti Aqua wastewater treatment plant. The heat output of the Ali-Juhakkala heating and cooling plant is five megawatts, and approximately 17 gigawatt-hours of heat can be recovered from wastewater every year. The amount of heat corresponds to the annual energy demand of 1,000 detached houses.
The plant consists of seven heat pump units are used to raise the water temperature in phases. The heating and cooling plant is located near the existing discharge pipe for treated wastewater. Wastewater is pumped along a new wastewater line from the wastewater basin to the wastewater heat exchangers. The heat exchangers are used to transfer the energy from the wastewater to the collector circuit of the heat pump, and the cooled wastewater is returned to the Porvoonjoki river. The energy produced by the heating and cooling plant can be fed as it is into the new district heating line.