An energy extraction device for extracting energy from a renewable energy source, the device comprising a controller and a hydraulic circuit (129, 131, 133, 135), the hydraulic circuit (129, 131, 133, 135) comprising: one or more hydraulic pumps and one or more hydraulic motors, the one or more hydraulic pumps driven by a rotating shaft, the rotating shaft driven by a renewable energy source, the one or more hydraulic motors driving a load, the hydraulic circuit (129, 131, 133, 135) further comprising a low pressure manifold to route working fluid from the one or more hydraulic motors to the one or more hydraulic pumps and a high pressure manifold to route fluid from the one or more hydraulic pumps to the one or more motors, the one or more hydraulic pumps and the one or more hydraulic motors each comprising a plurality of working chambers of cyclically varying volume and a plurality of valves (214, 220) for regulating the net displacement of working fluid between each working chamber and the high and low pressure manifolds (133, 135), at least one valve (214, 220) associated with each working chamber being an electronically controlled valve, said electronically controlled valves being operable by the controller to select the volume of working fluid displaced by each said working chamber on each cycle of working chamber volume and thereby regulate the net rate of displacement of working fluid by the one or more hydraulic pumps and the one or more hydraulic motors, wherein the one or more hydraulic motors are switchable between an active state and a dormant state and at least one of the one or more hydraulic motors is operable to carry out pumping cycles, wherein the controller is configured to cause the said at least one hydraulic motor to carry out motoring cycles to drive the load when the said at least one motor is in the active state, characterised in that the controller is also configured to cause the said at least one hydraulic motor to carry out one or more pumping cycles when the said at least one hydraulic motor is switched from the active state to the dormant state, to thereby use energy from the load to pump working fluid from the low pressure manifold to the high pressure manifold. one or more hydraulic pumps and one or more hydraulic motors, the one or more hydraulic pumps driven by a rotating shaft, the rotating shaft driven by a renewable energy source, the one or more hydraulic motors driving a load, the hydraulic circuit (129, 131, 133, 135) further comprising a low pressure manifold to route working fluid from the one or more hydraulic motors to the one or more hydraulic pumps and a high pressure manifold to route fluid from the one or more hydraulic pumps to the one or more motors, the one or more hydraulic pumps and the one or more hydraulic motors each comprising a plurality of working chambers of cyclically varying volume and a plurality of valves (214, 220) for regulating the net displacement of working fluid between each working chamber and the high and low pressure manifolds (133, 135), at least one valve (214, 220) associated with each working chamber being an electronically controlled valve, said electronically controlled valves being operable by the controller to select the volume of working fluid displaced by each said working chamber on each cycle of working chamber volume and thereby regulate the net rate of displacement of working fluid by the one or more hydraulic pumps and the one or more hydraulic motors,