Renewable energy like wind power is touted as a great way to reduce our impact on the environment. Tech companies like Google and Tesla, along with cities like San Francisco, understand the need to go green. Still, even renewable sources of energy can have hidden effects on local animal populations. The world's largest solar power plant, in fact, kills thousands of birds annually at its Ivanpah, California site. A new study in Sweden found that the country's wind turbines kill tens of thousands of bats annually -- an average of 10 to 15 bats per turbine. The answer? Halt the spinning of the fans during the summer evenings when wind is low anyway.