Polar Night Energy

Polar Night Energy is a Finnish startup founded in 2018 by Tommi Eronen (CEO) and Markku Ylönen (CTO). The company developed the Sand Battery, a thermal storage system that heats common sand to up to 500°C using excess electricity from renewable sources, and keeps it hot for weeks thanks to the material's excellent insulating properties. When heat is needed, a heat exchange system releases it into the district heating network or industrial processes. The world's first commercial Sand Battery went into operation in Kankaanpää in 2022, at Vatajankoski. The Pornainen plant (1 MW, 100 MWh) is currently the world's largest sand thermal storage system. In 2024-2026 the portfolio expands with the Power-to-Heat-to-Power project at Valkeakoski, a partnership with Lahti Energia for 250 MWh and expansion into Baltic markets. In 2026 the company wins the Breakthrough Award from TEK, Finland's leading engineering association. Polar Night Energy tackles one of the largest and least decarbonized sectors: industrial heat and district heating. Sand — abundant, safe and inexpensive — becomes the energy storage medium for a market where lithium batteries are not designed to operate.