Method and system for harnessing wind energy using a tethered airfoil

A system for harnessing wind energy using a tethered airfoil, the system comprising:

• an airfoil;
• a tether coupled to the airfoil;
• a tether engine coupled to the tether and configured to allow the tether to extend during a traction phase and to retract the tether during a retraction phase;
• a hydraulic circuit;
• at least one digital hydraulic machine mechanically coupled to the tether engine and hydraulically coupled to the hydraulic circuit, the at least one digital hydraulic machine configured to harness wind energy during the traction phase via extension of the tether from the tether engine, the wind energy being transferred by the at least one digital hydraulic machine to the hydraulic circuit for generating electrical energy, wherein the at least one digital hydraulic machine comprises working chambers having an associated displacement, the working chambers configured to be selectively deactivated;
• wherein the at least one digital hydraulic machine is further configured to receive energy from the hydraulic circuit to actuate the tether engine to retract the tether during the retraction phase;
• and
• a control system communicatively coupled to the at least one digital hydraulic machine, the control system configured to:
• during a traction phase, cause at least some of the harnessed wind energy transferred to the hydraulic circuit to be stored;
• and
• during the traction phase, cause one or more of the working chambers that are active during the traction phase to be deactivated to cause the at least one digital hydraulic machine to have a lower average displacement during the retraction phase than the traction phase;
• cause at least some of the stored wind energy to be transferred via the hydraulic circuit back to the at least one digital hydraulic machine to retract the tether.

A non-transitory computer readable medium having stored thereon computer program code, executable by a processor, and that when executed by the processor causes the processor to perform a method for harnessing wind energy using a tethered airfoil, the method comprising:

• during a traction phase, allowing wind to extend a tether mechanically coupled to at least one digital hydraulic machine operable to harness wind energy for generating electricity;
• storing at least some of the harnessed wind energy during the traction phase;
• and
• during a retraction phase, using at least some of the stored wind energy to cause the at least one digital hydraulic machine to retract the tether;
• wherein the at least one digital hydraulic machine comprises a plurality of working chambers each having an associated displacement, the plurality of working chambers configured to be selectively deactivated and further comprising during the retraction phase, deactivating one or more of the working chambers that are active during the traction phase to cause the at least one digital hydraulic machine to have a lower average displacement during the retraction phase than the traction phase.