System for converting heat energy in electric energy comprising: - a closed main circuit in which flows an organic fluid; - a first heat exchanger thermally coupled to a first energy source through a first circuit; said first heat exchanger being positioned along the main circuit for heating the organic fluid; - an expander comprising at least a first and second suction inlets (6,7) and one discharge outlet; - an electric generator mechanically coupled to an output shaft of the expander; - a condenser positioned along the main circuit and fluidly connected to the discharge outlet of the expander and to a tank, said condenser being configured to condense the organic fluid exiting from the expander; - a first pump positioned along the main circuit between the tank and the first heat exchanger; - a second heat exchanger thermally coupled to a second energy source through a second circuit; said second heat exchanger being positioned along the main circuit between the first heat exchanger and the first suction inlet of the expander for heating the organic fluid; - a branch of the main circuit fluidly connecting a point of the main circuit arranged between the first and second exchangers (3,12) to the second suction inlet of the expander so to bypass the second exchanger; - at least a valve (14,15,16) configured to divert the organic fluid towards the first suction inlet of the expander or towards the second suction inlet of the expander; - a first temperature sensor arranged along the first circuit upstream the first heat exchanger configured to output a first temperature signal; - a second temperature sensor arranged along the first circuit downstream the first heat exchanger configured to output a second temperature signal; - a third temperature sensor arranged along the second circuit upstream the second heat exchanger configured to output a third temperature signal; - a fourth temperature sensor arranged along the second circuit downstream the second heat exchanger configured to output a fourth temperature signal; - a control unit configured to receive said first, second, third and fourth temperature signals (T1,T2,T3,T4) to generate a first pump control signal and a first valve control signal based on said first, second, third and fourth temperature signals (T1,T2,T3,T4) to operate the first pump and the at least a valve (14,15,16); wherein the expander being configured to expand the organic fluid vaporized in said first heat exchanger or in said first and second heat exchangers (3,12) to generate mechanical energy for driving the electric generator. - a closed main circuit in which flows an organic fluid; - a first heat exchanger thermally coupled to a first energy source through a first circuit; said first heat exchanger being positioned along the main circuit for heating the organic fluid; - an expander comprising at least a first and second suction inlets (6,7) and one discharge outlet; - an electric generator mechanically coupled to an output shaft of the expander; - a condenser positioned along the main circuit and fluidly connected to the discharge outlet of the expander and to a tank, said condenser being configured to condense the organic fluid exiting from the expander; - a first pump positioned along the main circuit between the tank and the first heat exchanger; - a second heat exchanger thermally coupled to a second energy source through a second circuit; said second heat exchanger being positioned along the main circuit between the first heat exchanger and the first suction inlet of the expander for heating the organic fluid; - a branch of the main circuit fluidly connecting a point of the main circuit arranged between the first and second exchangers (3,12) to the second suction inlet of the expander so to bypass the second exchanger; - at least a valve (14,15,16) configured to divert the organic fluid towards the first suction inlet of the expander or towards the second suction inlet of the expander; - a first temperature sensor arranged along the first circuit upstream the first heat exchanger configured to output a first temperature signal; - a second temperature sensor arranged along the first circuit downstream the first heat exchanger configured to output a second temperature signal; - a third temperature sensor arranged along the second circuit upstream the second heat exchanger configured to output a third temperature signal; - a fourth temperature sensor arranged along the second circuit downstream the second heat exchanger configured to output a fourth temperature signal; - a control unit configured to receive said first, second, third and fourth temperature signals (T1,T2,T3,T4) to generate a first pump control signal and a first valve control signal based on said first, second, third and fourth temperature signals (T1,T2,T3,T4) to operate the first pump and the at least a valve (14,15,16);