BRUSSELS — NATO is openly backing renewables and other non-fossil fuel sources of energy as key to the alliance’s security, even as its most powerful member actively undermines attempts to shift away from oil and gas.  A NATO-backed study released earlier this year advises the transatlantic military alliance to ramp up use of renewables as a more secure alternative to imported oil and gas — a position likely to deepen tensions with the United States. The center that produced the study, the NATO