An analysis of oscillating water columns (OWC) at the Mutriku Wave Power Plant to understand their efficiency in transforming ocean energy into electricity. The study aims to estimate the rate of convergence of wave energy flux to kilowatts hour of each OWC and determine whether it is more accurate to estimate for each OWC independently or as part of a system of equations. The dataset includes electricity production data from 7 turbines in the MWPP during 2019, along with ocean measurements such as significant wave height, wave period, wave energy flux, swell direction, and wind direction. All models in the paper have varying coefficients which change with the significant wave height. The methodology includes the use of generalized least squares and local polynomial kernel methodologies for coefficient estimation.