At a power station in Berlin, Germany, visitors find a shining piece of machinery that looks out of place in the building. Its silver pipes and containers hold a substance that reportedly could become a major ingredient for producing power in the future. Vattenfall, the station’s operator, says this form of energy would not depend on traditional fossil fuels, such as oil or coal. The company, working with a Swedish company called SaltX, is testing the use of salt to store heat. Yet it is not the kind of salt you add to food. Heat-produced energy represents more than the half the power Germany uses. If it works well, the salt-based energy storage system could help solve a problem presented by renewable energy sources, such as wind and the sun’s energy. The problem is that renewable energy sources are not completely dependable. They sometimes make too much, and sometimes too little power.