The election of Donald Trump to the Oval Office set nerves affray in the American clean power field, and with good reason. However, if the president-elect has any ideas about reversing the trend toward a low-carbon economy, it’s going to be a case of locking the barn door after the horses have escaped. The leading U.S. energy company NRG provides a good example of clean energy’s staying power, with a long-term outlook that includes human…