Scientific American: Near Granada, Spain, more than 28,000 metric tons of salt is now coursing through pipes at the Andasol 1 power plant. That salt will be used to solve a pressing if obvious problem for solar power: What do you do when the sun is not shining and at night? The answer: store sunlight as heat energy for such a rainy day. Part of a so-called parabolic trough solar-thermal power plant, the salts will soon help the facility light up the night–literally. Because most salts only melt at …