  Charge and heat transport in nano-structures is dominated by non-equilibrium
effects which strongly influence their behaviour. These effects are studied in
a setup consisting of three external leads, one of which is considered as a
heat reservoir and is tunnel-coupled to two cold electrodes via two
independently controlled quantum dots. The energy flow from the hot electrode
together with energy filtering provided by quantum dots leads to a voltage bias
between the cold electrodes. The heat and charge currents in the device
effectively flow in mutually perpendicular directions, allowing for their
independent control. The non-equilibrium screening changes the values of the
system parameters needed for its optimal performance but leaves the maximal
output power and efficiency unchanged. Our results are important from the
theoretical point of view as well as for the practical implementation and the
control of the proposed heat engine.
