The price of solar energy keeps rapidly falling. In May a Dubai project broke the 3 cents per kilowatt-hour record with a 2.99 cents bid. Last month Chile set a 2.91 cents price. Now two companies have offered to build the cheapest solar power plant on record in Abu Dhabi. Their bid: 2.42 cents per kilowatt-hour. By comparison: The average price per kilowatt-hour for power from a coal-fired plant in the U.S. is around 10 cents.