A system for recovering and/or utilizing waste heat energy from a waste heat source, comprising: a first heat engine having a first working fluid, and defining a first circuit for circulation of the first working fluid, wherein the first heat engine is configured and arranged for transfer of heat from the waste heat source to the first working fluid, and a second heat engine, especially an organic Rankine cycle heat engine, having a second working fluid and defining a second circuit for circulation of the second working fluid, wherein the second heat engine is configured and arranged for transfer of heat from the first working fluid to the second working fluid, especially to cool the first working fluid after expansion thereof in a turbine of the first heat engine,wherein the first heat engine comprises a turbine and a first heat exchanger in the first circuit to transfer heat from the waste heat source to the first working fluid and a second heat exchanger in the first circuit for cooling the first working fluid after an expansion thereof in the turbine of the first heat engine, wherein the second heat exchanger is also in the second circuit to transfer heat from the first working fluid to the second working fluid of the second heat engine, wherein the second heat engine includes a second turbine for expansion of the second working fluid at a position in the second circuit downstream of the second heat exchanger, wherein the second heat engine includes a by-pass circuit for by-passing the second turbine, the by-pass circuit including a valve for regulating operation thereof, characterized in that the first working fluid is carbon-dioxide. a first heat engine having a first working fluid, and defining a first circuit for circulation of the first working fluid, wherein the first heat engine is configured and arranged for transfer of heat from the waste heat source to the first working fluid, and a second heat engine, especially an organic Rankine cycle heat engine, having a second working fluid and defining a second circuit for circulation of the second working fluid, wherein the second heat engine is configured and arranged for transfer of heat from the first working fluid to the second working fluid, especially to cool the first working fluid after expansion thereof in a turbine of the first heat engine,wherein the first heat engine comprises a turbine and a first heat exchanger in the first circuit to transfer heat from the waste heat source to the first working fluid and a second heat exchanger in the first circuit for cooling the first working fluid after an expansion thereof in the turbine of the first heat engine, wherein the second heat exchanger is also in the second circuit to transfer heat from the first working fluid to the second working fluid of the second heat engine, wherein the second heat engine includes a second turbine for expansion of the second working fluid at a position in the second circuit downstream of the second heat exchanger, wherein the second heat engine includes a by-pass circuit for by-passing the second turbine, the by-pass circuit including a valve for regulating operation thereof, characterized in that the first working fluid is carbon-dioxide.