The efficiency of various heat engines proposed or used today ranges from 3 percent ( 97 percent waste heat using low quality heat ) for the OTEC ocean power proposal through 25 percent for most automotive engines , to 45 percent for a supercritical coal-fired power station , to about 60 percent for a steam-cooled combined cycle gas turbine .
The efficiency of various heat engines proposed or used today ranges from 3 percent ( 97 percent waste heat ) for the OTEC ocean power proposal through 25 percent for most automotive engines , to 45 percent for a supercritical coal plant , to about 60 percent for a steam-cooled combined cycle gas turbine .