Characterising wind farm yield fluctuations in the Central Mediterranean Sea : a case study in the Maltese Islands

Abstract

Knowledge about the variability in offshore wind farm output is crucial for transmission system operators to determine the level of reserve required over different periods of time. A higher degree of certainty in the expected power output will help minimise the investment risks and operational costs associated with connecting large offshore wind farms to the grid. In this paper 15 months of wind measurements collected from a shore-based 80 metre wind monitoring mast installed at Aħrax Point, located in a coastal area on the Central Mediterranean island of Malta, are used to model the expected variability in power from three hypothetical offshore wind farm arrays in Maltese coastal waters. Measure-Correlate-Predict (MCP) techniques are used in conjunction with a 14 year data set from another onshore wind station to derive the long-term wind statistics for the 80 metre level at Aħrax Point. This data is subsequently used to calibrate a Computational Fluid Dynamics (CFD) software tool that is used to generate wind resources at hub height at the offshore site of interest located between 1.5 and 3 km away from the Aħrax mast. A statistical approach is applied to analyse the fluctuations predicted for each of three wind farm scenarios across the projected 14 year period. The 10 minute, hourly, 3-hourly and 6-hourly fluctuations are henceforth determined. This study reveals how, within the Central Mediterranean climate, higher power outputs are generally experienced between 0700 and 2000 hours (GMT+1). As expected, wind turbines having a larger rotor swept area-to-generator ratio would exhibit marginally higher variability.