Clean energy costs have fallen so rapidly that previously unthinkable scenarios now look like a good deal for the U.S., a new study contends. It will be feasible to power the U.S. on 90 percent clean electricity by 2035 thanks to stunning declines in the costs of renewables, a new study finds. By using updated cost figures for wind, solar and batteries, the researchers found that it will be economically feasible to power a reliable grid by 2035, while only depending on natural gas for 10 percent of annual electricity production.