The assessment of energy production from a wave energy converter commonly uses a stochastic approach. For short-term evaluations, a sea state can be represented in the frequency domain by an energy density spectrum. If a suitable frequency-dependent transfer function for the device is defined, an estimate of the total energy output for that specific sea state can be made. However, using a spectral averaging of the sea state in this way fails to account for short-term events that may significantly alter the output estimated using the spectral approach.
This paper uses a ‘wave-by-wave’ method to assess the potential energy production of a hypothetical device, using recorded time series of sea surface elevation. The device is modelled as a damped linear oscillator, with the assumption that the device can be rapidly ‘retuned’ to maximise its response to changing wave properties. The method involves calculating the power output for each individual wave in the time series for a range of tuning rates and power transfer function (PTF) bandwidths. The average power output for each time series is then compared with estimates made using the traditional spectral method. The results illustrate the extent to which the estimates of power output differ depending on the rate of tuning and bandwidth of the PTF.