Dual-doppler Offshore liDar for optimisAtion of offshore WiNd FArm O&M (DODONA)

The demand for cheaper renewable energy drives wind farm developers to reduce costs and to minimise risks in wind farm planning and operation. A key operations and maintenance cost driver is turbine power loss which can occur due to gradual decreases in performance or unexpected sudden faults. Experience in the wind industry shows that Turbulence Intensity (TI) significantly impacts these two areas, as well as wake losses and power performance.

Higher accuracy TI measurements will allow asset owners to improve the planning process as well as wind farm operation. These improvements range from enhancement of layout designs, risk-based predictive maintenance methods and turbine design loads. Our proposal, centred around dual-Doppler lidar technology, promises to make significant headway in reducing the costs and risks of offshore wind.

Assessment of TI in-situ at offshore wind farms is subject to several major challenges. Meteorological masts for measurement campaigns are expensive. Due to this modern lidar has steadily become a popular measurement alternative over the past two decades.

Profiling lidar are commonly used, however these can only measure the wind conditions at a fixed point directly above the device and have weaknesses when measuring turbulence conditions. Nacelle-mounted lidar devices can measure the inflow conditions upstream, however these devices also have weaknesses when measuring TI. Indeed, these single lidar estimates of hub height wind speed and direction rely on making assumptions of the flow field, such as horizontal flow homogeneity.

In addition, the measurement is limited to the inflow region for a single turbine. Our proposal to use dual-Doppler lidar measurements would lead to significantly higher TI measurement accuracies than nacelle or profiling lidars, due to the greater amount of information on the 3D wind vector at each point. Additionally, the use of dual-Doppler lidar in the wind farm allows for many more points to be scanned and thus the inflow conditions can be measured for multiple turbines.

Additionally, dual-Doppler technology would lead to reduced wind speed measurement uncertainty, improving Energy Yield Assessments.

In this project, for the first time the influence of TI will be assessed by means of dual-Doppler measurements and then applied to augment risk-based predictive maintenance models and methods. Subsequently, owner-operators will be equipped with novel new tools, models and methods for boosting the operational efficiency of their wind farms.