One hundred years ago, scientists and engineers were actively working on alternative energy, not because they wanted to stop burning fossil fuels but because they believed that the world would soon run out of them. It was known that coal reserves were limited, and the giant oil fields in Saudi Arabia had not yet been discovered. This classic 1931 book reviews the sources of alternative energy that had been proposed at that time. One of the most ambitious proposals was to build a dam across the Strait of Gibraltar and use the inflow to power hydroelectric plants. This was the famous Panropa (Atlantropa) project, which also envisioned much closer ties between Europe with North Africa to create a powerful economic block. The book also discusses wind power (wind towers rather than wind turbines), tidal power, solar power, geothermal power, and even fuel cells. Today, most people are unaware of how much work had been done in the field of alternative energy sources because World War II interrupted this peaceful work.