Finland creates world's largest pit heat storage in Hyvinkaa
The 66-foot-deep reservoir will hold 18,000 megawatt-hours of heat to help stabilise local heating prices.
The Finnish city of Hyvinkaa is filling a former gravel pit with approximately 100 million gallons of tap water to create a massive thermal energy storage facility, according to a Times of India report citing Ecoticias.
Hyvinkään Lämpövoima Oy, the municipal heating company, expects the 66-foot-deep basin to meet nearly a quarter of the local heat demand. The reservoir will be charged using electric boilers and industrial waste heat when electricity costs are low during the summer.
One full charge of the facility holds about 18,000 megawatt-hours of heat. The utility stated this could supply hot tap water to around 20,000 people or warm about 1,000 detached houses for one year.
CEO Sanna Kytömäki said the facility will primarily mean more stable heating prices for residents of Hyvinkaa. The company noted that the network could drop fossil fuels almost entirely with the use of the boilers.
The project costs €33 million, with Finland’s Ministry of Economic Affairs and Employment providing roughly €7.7 million in investment aid. The company projects annual fuel savings of several million euros and a reduction of about 4,400 metric tons of carbon dioxide.
Water began flowing into the Kulomaki gravel pit in early October 2026 and filling is expected to continue until late April 2027. Crews are scheduled to build the permanent cover between April and October 2027.