We climbed inside the world’s largest sand battery. Here’s what we found

Pornainen, Finland is using Polar Night Energy’s world-scale sand battery to store cheap electricity as heat for district heating.

The 2,000-tonne sand silo, commissioned in 2025, helps the municipality weather extreme winter electricity-price spikes.

It also cuts oil use, emissions, and woodchip consumption in the local heating system.

The project highlights how low-moving-parts thermal storage can stabilize heating costs and support municipal decarbonization.