NOVELTY - The method involves measuring pressure in a high pressure manifold (133). A net rate of displacement of working fluid is selected by a hydraulic pump (129) responsive to the measured pressure to regulate torque applied to a rotating shaft (125). The net rate of displacement of the working fluid is selected by a hydraulic motor (131) to smooth energy flow to a load and to regulate the pressure in the high pressure manifold to remain within an acceptable pressure range.    USE - Method for operating a renewable energy extraction device e.g. turbine such as wind turbine generator (WTG) connected to an alternating current (AC) electricity network, to extract energy from a fluctuating energy flow from a renewable energy source e.g. wind energy source and tidal energy source. Can also be used for a tidal stream generator.    ADVANTAGE - The method enables accumulators at a low state of charge to maximize storage available to accept energy from gusts of wind and to operate the WTG at high rates of fluid flow, thus reducing vibration and noise and increasing lifetime of the WTG. The method enables adjusting low pass filter behavior according to changing wind conditions, so that the hydraulic motor responds quickly to the gust and the pressure does not rise high when energy of the gust increases. The method enables selecting optimum pressure or range of pressures to optimize efficiency of power transmission from the rotating shaft to the load and avoiding damage to the turbine.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) an energy extraction device for extracting energy from a fluctuating energy flow from a renewable energy source    (2) a computer-readable storage medium comprising a set of instructions for extracting energy from a fluctuating energy flow from a renewable energy source.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of a wind turbine generator connected to an electricity network.    Rotating shaft (125)    Hydraulic pump (129)    Hydraulic motor (131)    High pressure manifold (133)    Power amplifiers (180)