From dropping weights down old mine shafts to pumping compressed air into caves, companies are racing to develop inventive new solutions to store renewable energy as European nations try to move away from Russian fossil fuels.
Expanding storage is vital to ensure a consistent supply of electricity as countries shift to using more clean power from wind turbines and solar panels, which do not provide round-the-clock supplies, analysts say.
But today's most broadly used solutions — such as storing power in hydropower reservoirs or in lithium batteries — have drawbacks ranging from environmental impact to limited lifespan, leading to a growing search for alternatives.