The City of Helsinki has announced the winners of its million-euro Helsinki Energy Challenge.
An international jury selected four winners out of ten finalists at an awards ceremony that marked the end of the year-long challenge.
The competition attracted 252 proposals from teams based in 35 countries. The winning solutions all focused on the city's district heating system, which accounts for more than half of Helsinki's carbon emissions.
The city has committed to becoming carbon neutral by 2035.
Two of the winning concepts, HIVE and The Hot Heart, would use water from the Baltic sea as a source of carbon-free warmth and energy storage for Helsinki's heating needs.