Vantaan Energia, one of Finland’s larger utilities, will develop a 90 GWh seasonal heat storage facility powered by a mixture of waste heat, solar, and wind, with an underground reservoir of one million cubic meters. This Vantaa Energy Cavern Thermal Energy Storage (VECTES) project will obviate 26,000 tons of natural gas emissions each year by shifting summer heat through to winter, and is nearly ten times the size of other Cavern Thermal Energy Storage (CTES) systems worldwide. Besides being the largest project of its type so far, VECTES is also remarkable for its use geothermal energy, which is a first for Finland. Geothermal energy has not yet been harnessed anywhere in Finland due to unsuitable geology, but the past year…