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Several studies have combined heat and gravitational energy exchanges tocreate novel heat engines. A common theoretical framework is developed here todescribe thermogravitational cycles which have the same efficiencies as theCarnot, Rankine or Brayton cycles. Considering a working fluid, enclosed in aballoon, inside a column filled with a transporting fluid, the cycle iscomposed of four steps. Starting from the top of the column, the balloon goesdown by gravity, receives heat from a hot source at the bottom, rises anddelivers heat to a cold source at the top. Unlike classic power cycles whichneed external work to operate the compressor, thermogravitational cycles canoperate as "pure power cycle" where no external work is provided to drive thecycle. To illustrate this concept, the prototype of a thermogravitationalelectrical generator is presented. It uses a hot source of low temperature(average temperature near 57{\deg}C) and relies on the gravitational energyexchanges of an organic fluorinated fluid inside a balloon attached to amagnetic marble producing an electromotive force of 50 mV peak to peak by theuse of a linear alternator. This heat engine is well suited to be operatedusing renewable energy sources such as geothermal gradients or focusedsunbeams.

Thermogravitational cycles: theoretical framework and example of an electric thermogravitational generator based on balloon inflation/deflation