http://www.popularmechanics.com/science/energy/a16045/evaporation-engine/

similar concept to a Stirling Engine, taking advantage of cold & warm air mixing, cooling, and warming,

obviously the inspiration was derived from nature, such as tornadoes, hurricanes, volcanoes ext.
essentially, heat rises, cold falls down. the mixing, is used to spin turbines of some sort, that creates the osolation, which could be used to create electricity, or spin a wheel, or do some other useful work.

hurricanes

volcanoes

windmill, for milling

Hover damn