Effect of rotor induction and peak shaving on energy performance and cost of stationary unmoored floating offshore wind turbines

Abstract

This paper investigates the effect of rotor induction and peak shaving on energy performance and cost of a stationary unmoored floating offshore wind turbine (SUFOWT). A SUFOWT is a floating offshore wind turbine (FOWT) for which a dynamic positioning (DP) system is used in lieu of a mooring system for station-keeping. It is particularly well suited for deployment in the far-offshore. Previous studies have shown that positive net power production can be achieved with SUFOWTs depending on the number and size of thrusters and on wind turbine characteristics. However, they did not consider the effect of rotor induction or peak shaving. This gap is addressed in the present paper. The study is based on a physical engineering model, the wind turbine rotor design being modelled using the actuator disc theory. Results show that the rotor induction which maximizes net power production (which takes into account the thrusters' power consumption) is smaller than the value of 1/3 which maximizes wind turbine power production. However, the increase in the annual energy production or capacity factor brought by rotor induction optimization is rather small, of the order of a few percent. The effect of peak shaving was also found to be small with respect to energy production and capacity factor. Both rotor induction and peak shaving were found to be able to significantly reduce the power ratio (the ratio of the thrusters' nominal power to the wind turbine rated power), which can be expected to be beneficial for the cost of energy.