Finland’s capital city is out to be carbon-neutral by 2035. But one major challenge stands in the way: More than half of the city’s heat is produced by coal. Looking to spark some creative problem-solving, government leaders launched Helsinki Energy Challenge—and dangled a prize of €1 million for “radically new solutions.” Italian design and innovation studio Carlo Ratti Associati (CRA) responded with Hot Heart, an archipelago of basins that will store thermal energy—and serve as an ecofriendly getaway for weary urban denizens.
Located off the coast of Helsinki, it’s being billed as the largest facility of its kind, made up of 10 cylindrical tanks that can collectively hold up to 10 million cubic meters (2.6 billion gallons) of water. The system will operate like a battery: Excess renewable energy will be converted to heat, stored in the basins and rerouted into the city’s heat distribution channels throughout the winter.
“Production of renewable energy is getting cheaper, but storage is still extremely expensive,” says Carlo Ratti, founding partner of CRA in Turin, Italy. “Our idea is to use the giant ‘thermal batteries’ to store energy when prices are at low or even negative levels and extract it when required by the district heating system when demand is high.”
The multidisciplinary team united under a central goal: slash the city’s use of biomass and coal by relying on seawater heat pumps to convert wind, solar and other forms of existing renewable power into heat that could be stored in the system’s reservoirs. Operated by artificial intelligence, Hot Heart is designed to synchronize the production and consumption of thermal energy and help stabilize the national energy grid in relation to changing supply.
The system is slated to be fully operational in Helsinki by 2028 and expected to support all of the city’s heating needs by decade’s end, without any carbon emissions—and at a 10 percent cost reduction compared to conventional methods.
Along with its thermal storage properties, Hot Heart will also serve as a recreational venue and tourist attraction. Four of its 10 basins will be enclosed in transparent domes mimicking tropical ecosystems from the world’s rainforest zones. Powered by LED technology, the “floating forests” will give visitors a place to socialize and enjoy the sunlight, even in the middle of subzero Nordic winters.
“Hot Heart offers a unique experience, bringing the natural and artificial worlds together,” Ratti explains. “It’s inspired by the Finnish concept of jokamiehen oikeudet, which could be translated as ‘every person’s right’: the right to reflect and unwind while peacefully enjoying nature.”
Hot Heart was clearly designed with Helsinki in mind. But project leaders emphasize the model could be replicated by other cities with comparable climatic characteristics—offering a powerful weapon in the battle against climate change.