DENVER — Renewable energy is gathering steam in several states as voters and governors push electric utilities to generate a set percentage of electricity from clean sources such as wind and solar power. In Washington state, voters approved a measure Nov. 7 mandating that 15% of electrical power come from renewable sources by 2020. That makes 20 states and the District of Columbia with such requirements, according to the Department of Energy. Two others states - Illinois and Vermont - have non-binding goals on using renewable energy sources. More states are forcing utilities toward wind, solar and other renewable energy sources, such as geothermal and biomass, to cut the use of coal and natural gas and spur greater U.S. energy independence. Burning coal produces greenhouse gases such as carbon dioxide that contribute to climate change. Power plants fueled by natural gas pollute the air with sulfur dioxide. Opponents, including some utilities and industries, say the switch will be costly for consumers and businesses. In Senate testimony last year, the National Association of Manufacturers opposed a proposed federal requirement to use renewable energy because it would reduce the flexibility of utilities in choosing fuels and harm businesses […]