A study commissioned by the Financial Times shows that the planet’s 20 largest national economies generated 8% of their electricity from renewable energy — solar, wind, and other green power sources — in 2015, up from 4.6% in 2010. (This does not include hydropower.) There are huge differences among these nations. Overall in 2015, the European Union generated 18% of its 28 nations’ electricity. The United States generated about 8% of its electricity from non-hydro…