A method for operating a plurality of independent, closed cycle power plant modules (5A, 5B, 5C), each having a vaporizer (13A, 13B, 13C), comprising the steps of: a. supplying a medium or low temperature source fluid to a vaporizer of a first plant module, to vaporize motive fluid of said first plant module, and expanding the vaporized motive fluid of said first plant module to produce power; b. supplying the medium or low temperature source fluid exiting the vaporizer of said first plant module to a vaporizer of a second plant module to vaporize motive fluid of said second plant module, and expanding the vaporized motive fluid of said second plant module to produce power; c. delivering the medium or low temperature source fluid to a vaporizer of a terminal plant module, whereby the medium or low temperature source fluid exiting said terminal plant module becomes a heat depleted source fluid, and expanding the vaporized motive fluid of said terminal plant module to produce power; d. providing a primary preheater (19A2, 19B, 19C) for each vaporizer (13A, 13B, 13C); and e. supplying said heat depleted source fluid exiting said terminal plant module to all of said primary preheaters in parallel (19A2, 19B, 19C), characterized in that said method further comprises the steps of: f. supplying the medium or low temperature source fluid exiting the vaporizer of said second plant module to a secondary preheater (19A1) of said first plant module; and g. supplying the medium or low temperature source fluid exiting said secondary preheater (19A1) of said first plant module to the vaporizer of said terminal plant module, wherein the motive fluid of said first plant module is heated by said primary preheater (19A2) of said first plant module, is additionally heated by said secondary preheater (19A1) of said first plant module, and is then vaporized by the vaporizer of said first plant module. a. supplying a medium or low temperature source fluid to a vaporizer of a first plant module, to vaporize motive fluid of said first plant module, and expanding the vaporized motive fluid of said first plant module to produce power; b. supplying the medium or low temperature source fluid exiting the vaporizer of said first plant module to a vaporizer of a second plant module to vaporize motive fluid of said second plant module, and expanding the vaporized motive fluid of said second plant module to produce power; c. delivering the medium or low temperature source fluid to a vaporizer of a terminal plant module, whereby the medium or low temperature source fluid exiting said terminal plant module becomes a heat depleted source fluid, and expanding the vaporized motive fluid of said terminal plant module to produce power; d. providing a primary preheater (19A2, 19B, 19C) for each vaporizer (13A, 13B, 13C); and e. supplying said heat depleted source fluid exiting said terminal plant module to all of said primary preheaters in parallel (19A2, 19B, 19C), f. supplying the medium or low temperature source fluid exiting the vaporizer of said second plant module to a secondary preheater (19A1) of said first plant module; and g. supplying the medium or low temperature source fluid exiting said secondary preheater (19A1) of said first plant module to the vaporizer of said terminal plant module,