The penetration of renewable energy into the electricity supply mix has been much in the news recently. During the first quarter, Portugal generated three-quarters of its electricity with renewable energy. Meanwhile, in Germany, one-fifth of all electricity was generated with renewables, most of that from new sources of renewable energy, such as wind and solar. And recently, at a conference in San Francisco, attendees heard calls for generating not just 100 percent of electricity supply with renewable energy, but far more — 200 percent to 300 percent of generation — in order to meet the need for heating, cooling, and transportation as well.