Saudi Arabia produces much of its electricity by burning oil, a practice that most countries abandoned long ago, reasoning that they could use coal and natural gas instead and save oil for transportation, an application for which there is no mainstream alternative. Most of Saudi Arabia’s power plants are colossally inefficient, as are its air conditioners, which consumed 70 percent of the kingdom’s electricity in 2013. Although the kingdom has just 30 million people, it is the world’s sixth-largest consumer of oil.Now, Saudi rulers say, things must change. Their motivation isn’t concern about global warming; the last thing they want is an end to the fossil-fuel era. Quite the contrary: they see investing in solar energy as a way to remain a global oil power. The Saudis burn about a quarter of the oil they produce—and their domestic consumption has been rising at an alarming 7 percent a year, nearly three times the rate of population growth.