A system for recovering and/or utilizing waste heat energy from a waste heat source (S), comprising: a first heat engine (H1) having a first working fluid (F1), and defining a first circuit (A) for circulation of the first working fluid (F1), wherein the first heat engine (H1) is configured and arranged for transfer of heat from the waste heat source (S) to the first working fluid (F1), and a second heat engine (H2), especially an organic Rankine cycle (ORC) heat engine, having a second working fluid (F2) and defining a second circuit (B) for circulation of the second working fluid (F2), wherein the second heat engine (H2) is configured and arranged for transfer of heat from the first working fluid (F1) to the second working fluid (F2), especially to cool the first working fluid (F1) after expansion thereof in a turbine (T1) of the first heat engine (H1),wherein the first heat engine (H1) comprises a turbine (t1) and a first heat exchanger (E1) in the first circuit (A) to transfer heat from the waste heat source (S) to the first working fluid (F1) and a second heat exchanger (E2) in the first circuit (A) for cooling the first working fluid (F1) after an expansion thereof in the turbine (T1) of the first heat engine (H1), wherein the second heat exchanger (E2) is also in the second circuit (B) to transfer heat from the first working fluid (F1) to the second working fluid (F2) of the second heat engine (H2), wherein the second heat engine (H2) includes a second turbine (T2) for expansion of the second working fluid (F2) at a position in the second circuit (B) downstream of the second heat exchanger (E2), wherein the second heat engine (H2) includes a by-pass circuit (BP) for by-passing the second turbine (T2), the by-pass circuit including a valve (V) for regulating operation thereof, characterized in that the first working fluid is carbon-dioxide. a first heat engine (H1) having a first working fluid (F1), and defining a first circuit (A) for circulation of the first working fluid (F1), wherein the first heat engine (H1) is configured and arranged for transfer of heat from the waste heat source (S) to the first working fluid (F1), and a second heat engine (H2), especially an organic Rankine cycle (ORC) heat engine, having a second working fluid (F2) and defining a second circuit (B) for circulation of the second working fluid (F2), wherein the second heat engine (H2) is configured and arranged for transfer of heat from the first working fluid (F1) to the second working fluid (F2), especially to cool the first working fluid (F1) after expansion thereof in a turbine (T1) of the first heat engine (H1),wherein the first heat engine (H1) comprises a turbine (t1) and a first heat exchanger (E1) in the first circuit (A) to transfer heat from the waste heat source (S) to the first working fluid (F1) and a second heat exchanger (E2) in the first circuit (A) for cooling the first working fluid (F1) after an expansion thereof in the turbine (T1) of the first heat engine (H1), wherein the second heat exchanger (E2) is also in the second circuit (B) to transfer heat from the first working fluid (F1) to the second working fluid (F2) of the second heat engine (H2), wherein the second heat engine (H2) includes a second turbine (T2) for expansion of the second working fluid (F2) at a position in the second circuit (B) downstream of the second heat exchanger (E2), wherein the second heat engine (H2) includes a by-pass circuit (BP) for by-passing the second turbine (T2), the by-pass circuit including a valve (V) for regulating operation thereof, characterized in that the first working fluid is carbon-dioxide. <EOS>