Cold sea water heats Helsinki homes with a new underwater tunnel
MADRID/HELSINKI (October 18): Helsinki uses an unexpected energy source to heat its home: cold water taken from the depths of the Baltic Sea.
Finland’s capital joins Europe’s rush to find new energy sources and reduce its dependence on imported fossil fuels with a new, carbon-neutral heating system. The city’s electricity company Helen Oy is building a tunnel in cooperation with the Spanish builder Acciona SA and the local infrastructure company YIT Oyj to take water from the deep seabed, where it remains at a constant temperature. By treating water with underground heat pumps, the system could produce enough heat to serve up to 40% of Finland’s capital.
Currently, most of the apartments in Helsinki are heated with a district heating system, where electricity and heat are produced heavily with coal and natural gas. In 2021, fossil fuels accounted for more than 75 percent of the city’s district heating production. The seawater project is to be a key step in the power plant’s transition to renewable energy in order to achieve Helsinki’s goal of carbon neutrality by 2030 – a challenge for a cold-climate city with a high heat demand. Helen uses nuclear power and renewable electricity to run the system’s heat pumps; the company already uses the waste heat of the data centers and the skating rink as an additional heat source.
The 400 million euro ($390 million) investment is in a development phase that will last two years; infrastructure completion will take another five years before the 500 megawatt plant is ready for use. While several smaller cities, such as Juneau, Alaska, and Drammen, Norway, use similar combinations of seawater and heat pumps, Helsinki’s system would be the largest such facility in the world, according to Fernando Vara, Acciona’s head of business development for tunnels and railways.
It’s a “unique project” being developed at “a very sensitive moment,” Vara said in an interview. Russia’s invasion of Ukraine and decision to cut natural gas supplies in retaliation for Western sanctions has led to a sharp rise in fossil fuel prices in Europe, setting the stage for a protracted energy crisis in the European Union.
But the supply of seawater using the Helsinki system will be essentially unlimited and free, Vara said. To build it, Acciona uses a drill to drill a 17-kilometer (10.6-mile) underwater tunnel into the Baltic Sea, which collects water at a temperature of two degrees Celsius (36 degrees Fahrenheit) – even in cold months when the sea surface is frozen.
The water is then treated with underground heat pumps, which Helen plans to build on the site of one of its coal-fired power plants, Jaakko Tiittanen, who manages the power plant’s large projects, said in an e-mailed answer to questions. The coal unit is scheduled to close in 2024.
The heat exchangers remove about 1.5 degrees of heat from the seawater, which is later returned to the sea through another nine-kilometer tunnel. The collected energy is then processed using a heat pump process to a temperature of 80-95 degrees, which is hot enough to use the district heating network, Tiittanen said.
The temperature level at which the pump operates is comparable to existing geothermal systems, but the mass flow of water relative to its volume is so high that similar levels “are not possible even in large geothermal systems,” he said.
In summer, heat pumps can also be used to recover energy from cold seawater to supply the city’s district cooling. The plant is a “very powerful project” that could potentially be expanded further, Accionan Vara said, adding that he thinks there may come a time “when the whole city is heated with this water.”