Wind turbines generating electricity on top of hill against sky with space for copy. Renewable, sustainable and alternative energy. alternative; clean; copyspace; development; ecology; electric; electricity; energy; environment; environmental; field; generation; generator; global warming; green; green energy; hill; industrial; industry; landscape; mill; nature; plant; power; production; renewable; sky; sustainability; sustainable; technology; turbine; warming; wind; wind turbine; windmill;