When we talk about energy storage today, lithium-ion batteries tend to dominate the conversation. They are sleek, compact, and have become the default image of the clean energy revolution. Yet behind the headlines, a quieter cast of characters has been doing the heavy lifting. Some of the most effective ways to store energy are not based on exotic chemistry at all, but on gravity, heat, air, and even sand. They are often strange, wonderfully simple, and surprisingly effective. If the world’s energy transition were a movie, lithium-ion batteries…