A seasonal heat storage plant which will have a capacity of about 90GWh looks set to begin construction next year in Vantaa, Finland, with water stored in underground caverns heated to 140°C using renewable energy and waste heat.

City energy company Vantaa Energy said at the beginning of this month that it has selected engineering, design and advisory group AFRY and Finnish urban development and construction company YIT as project partners. Project development begins this summer and construction in autumn next year, with the massive system expected to be online during 2026.

The project, called Vantaa Energy Cavern Thermal Energy Storage (VECTES), will involve caverns around 60 metres underground in bedrock. According to project overview documents produced by Vantaa, situating the water storage that far down means the ground water’s natural pressure will prevent it from evaporating, even at temperatures above its boiling point.

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