In the global race to decarbonize energy systems, attention tends to focus on the headline technologies like hydrogen, carbon capture, electric vehicles, and massive lithium-ion batteries. Yet behind the scenes, a quieter revolution is taking shape. Across Europe and beyond, heat batteries, or thermal energy storage systems, are emerging as one of the most efficient, scalable, and cost-effective ways to balance renewable energy and decarbonize heat. They may not look futuristic. They have no moving parts, produce no dramatic chemical reactions,…