FILE - In this April 8, 2013, file photo, an employee of 

FILE - In this April 8, 2013, file photo, an employee of energy company Eon Hanse walks across the premises of the natural gas storage facility in Hamburg-Reitbrook, Germany. Clean Energy refers to energy that pollutes less than coal and oil, the dominant sources of fuel for electricity and transportation. Natural gas is considered by some, including the Obama administration, to be clean because it emits far fewer pollutants than coal or oil. Others consider only renewable energy truly clean. (AP Photo/dpa, Bodo Marks)
Associated Press
FILE - In this April 8, 2013, file photo, an employee of energy company Eon Hanse walks across the premises of the natural gas storage facility in Hamburg-Reitbrook, Germany. Clean Energy refers to energy that pollutes less than coal and oil, the dominant sources of fuel for electricity and transportation. Natural gas is considered by some, including the Obama administration, to be clean because it emits far fewer pollutants than coal or oil. Others consider only renewable energy truly clean. (AP Photo/dpa, Bodo Marks)
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