Thermal energy system and method

A thermal energy method for converting thermal to mechanical energy, the method comprising:

• circulating liquid and vapor phases of a working fluid in a closed loop comprising a recipient constituting a variable volume within a fixed enclosing volume, arranged at a lower part and a tube system comprising a rising part, a descending part with a condenser section and with a hydrostatic pressure section, wherein the circulating comprises:
• heating the working fluid in the recipient providing working vapor, and compensating for thermal energy loss due to vaporization;
• condensing the working vapor in the condenser section providing condensed liquid phase working fluid, and setting up a pressure differential contributing to lifting the working vapor in the rising part;
• collecting the condensed working fluid in the hydrostatic pressure section providing a hydrostatic pressure head;
• extracting mechanical energy based on the hydrostatic pressure head wherein extracting mechanical energy contributes to expanding the variable volume;
• and
• returning the collected condensed working fluid to the recipient.