A preliminary analysis of wind turbine energy yield

Despite the rapid and extensive growth of wind power, a challenge still faced by wind power operators is the intermittency of wind speed and thus wind power. On different time scales, the stochastic nature of wind speed has impacts on the energy yield from wind turbines. While long term estimates of wind power are ideal for energy mix planning and policy, knowledge of variations in very short-term output is essential for energy grid management, turbine control system and wind power optimization. This study analyzed energy yield from an 800kW operational wind turbine using 15-seconds time-series data averaged into 1, 5, and 15 minutes time steps for cumulative periods of 1 hour, 4 hours and 12 hours respectively. In the three case scenarios explored, theoretical output under-estimated turbine yield within a range of 5% - 48%. The lowest errors recorded were 5%, 14% and - 0.34% for the time series considered although the estimation errors were larger for the higher time intervals generally. Cases of 0 kW turbine output despite wind speed value above the cut-in speed (i.e u > 3m/s) suggest that wind direction may impact turbine yield. The effect of turbine blade momentum was also more evident in some time-steps where yield was sustained despite fall in wind speed to below 3m/s. The results show that the 15 minutes time steps series is more beneficial in short-term energy yield estimations and show the usefulness of short-term yield estimations for wind power operators, grid management and wind power optimization.