21 °C Electricity to resistive heating coil 650 °C Sand-filled storage vessel 80 °C 400 °C 200 °C Circulating water pipes 100 °C Air/water heat exchange Circulating air ducts 21 °C pere, which began operation during the winter of 2020-2021. The system uses electricity to heat air, which is then circulated through an exchanger that heats water and distributes it to multiple buildings in the city's Hiedanranta district (Figure 1). Inside the system, electrically powered resistive heating elements heat air to more than 600 °C. The hot air is circulated through a network of pipes inside of a sand-filled heat storage vessel. Tech Briefs, June 2024 Electricity to resistive heating coil 80 °C Sand-filled storage vessel 80 °C 200 °C 180 °C Circulating water pipes 80 °C Air/water heat exchange Circulating air ducts Figure 1. A schematic of the components and operating cycle of the Polar Night Energy system. (Image: COMSOL) www.techbriefs.com 19http://www.techbriefs.com