News / 2.10.2020

Several ongoing studies on alternatives to coal: new research area in the open sea

Heat pump investments are an important part of a carbon-neutral future, and the government’s latest proposals for the amendment of electricity tax also support this development. Helen is now expanding studies on utilising the heat of sea water in district heat production to be carried out around the year and on a large scale.

The smart energy system and the district heating and cooling networks in Helsinki make it possible to combine new technologies and production methods in a flexible way. At Helen, heat pumps are seen as an important part of the future energy system: they are a natural way to utilise new carbon-neutral heat sources in district heat production.

Helen is now studying the utilisation of the heat of sea water in district heat production on a wider scale and throughout the year. In the preparatory study phase, the objective is to study more closely the conditions and currents of the seabed further away from the shore and to find a suitable place to intake sea water and the necessary technical solutions. The intake tunnel for sea water may be up to 15–20 kilometres long, and by diameter it would be so wide that you could drive a lorry through it – in other words, it would be quite a unique solution also on an international scale.

“Heat pumps that utilise sea water are an interesting alternative to replace fossil fuels. The heat contained in sea water is renewable, the source of heat is inexhaustible and, above all, it’s free. The challenge is to obtain sufficiently warm sea water also in the winter, and therefore the study is carried out further in the open sea: when the intake of water takes place deep in the open sea, the heating capacity is in use throughout the winter. In this solution, district heat is therefore produced from sea water with a temperature of +2 degrees,” explains Head of Unit Janne Rauhamäki of Helen.

Currently, a unique heat pump that also utilises the heat of sea water is being built at Helen’s Vuosaari power plant. The heat sources of the pump include sea water sourced from the shore in the summer and the plant’s own circulation of cooling water in the winter. Year-round utilisation of sea water heat, which is currently studied, is clearly a larger project than this, with a scale of up to several hundreds of megawatts. This corresponds to the district heat output of the Salmisaari coal-fired power plant.

Towards carbon-neutral district heat

Helen aims for carbon neutrality by year 2035. Coal use will be phased out already before that date, in 2029 at the latest. In addition to sea water heat, there are also other ongoing studies on replacing fossils fuels, such as the utilisation of excess heat from the process industry in the Kilpilahti area for the use of heating in the Helsinki region, other regional excess heat, and environmental heat, such as geothermal heat.

“This year, Helen has made decisions to invest as much as 350 million euros in carbon neutrality. I think it is important that we study different alternatives extensively to find the best solutions, and seawater heat is an interesting possibility. New, exciting solutions may also emerge through the ongoing Helsinki Energy Challenge,” says Juha-Pekka Weckström, Helen’s President and CEO.


  • Helen will phase out coal by 2029 at the latest, its use is reduced in stages.
  • Solutions to replace heat production at the Hanasaari power plant are already known: some of the solutions are ready now and some are under construction. A bioenergy heating plant is built in Vuosaari, the new Esplanade heating and cooling plant was commissioned in 2018, the Katri Vala heating and cooling plant is expanded with a sixth heat pump, and the efficiency of heat recovery from purified waste water is being improved.
  • Salmisaari will remain an energy production area and coal will be replaced by other solutions. Our aim is to find solutions that are not based on combustion. The Katri Vala heating and cooling plant is expanded with a seventh heat pump.
  • The heat of sea water will be utilised already in the Vuosaari heat pump, which is under construction, where the heat sources are warm sea water in the summer and the plant’s own cooling water circulation in the winter. The Vuosaari seawater heat pump will start production use in 2022.
  • The currently ongoing study on seawater heat is based on year-round use of sea water when the temperature of the sea water needed as a heat source must be at least +2. This requires a seawater intake location further in the open sea, and the length of the required tunnel may be up to 15–20 kilometres.