an open cycle energy conversion system adaptable for use with , inter alia , solar collectors and other sources of available heat for increasing the temperature of a moving gas and employing a substantially vertically positioned gas expanding column comprising an endless arrangement of cups journaled for movement in a closed path in a liquid medium in the column for trapping the heated gas inside a succession of the cups inverted at the bottom of the column and displacing at least a part of the liquid in the cups , thereby providing a buoyancy force on the cups causing them to rise in the column exerting a rotating force on the endless arrangement of cups . the trapped gas is released at the top of the liquid in the column to be exhausted to atmosphere .