Transforming America's energy mix to be fueled by 80 percent clean sources by 2035 will undoubtedly be a significant challenge. How challenging it will be, exactly, depends partly on the way we define "clean energy."
Twenty years ago, Elton B. Sherwin, Jr. plugged a rechargeable flashlight into an outlet. And within a few hours, it was ready to use as soon as the situation called for it. Only somehow, the situation never called for it.