wind - energy that will never run out (7), solar - energy that depends on the Sun (7), fossil fuels - an important resource in Alberta, greenhouse gases - prevent heat from escaping into outer space (7), thermal pollution - undesirable effect of thermal energy (7), passive solar heating - solar heating without fans or motors (7), congeneration - technique for using unwanted thermal energy (7), collectors - a means of trapping the sun's energy (7), refrigerant - liquid that easily evaporates at cold temperatures (8), non-renewable resources - fossil fuels are this kind of resource (7), geothermal - energy inside Earth (7),

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