To support the development of wind energy offshore, several different types of floating lidar systems have been developed. These systems measure wind speed and direction at the turbine hub height from the surface, making offshore wind resource prospecting much easier and faster. They are also potentially much less expensive than offshore towers. Floating lidar systems are complex and include communications, energy generation and storage, and various methods to mitigate the effect of the lidar motion on the data obtained by the lidar. These motion mitigation systems (often referred to as motion compensation systems) are a combination of software and hardware, and may reduce the physical motion of the lidar while controlling the lidar or data processing to reduce the effect of motion. Floating lidar systems are considered a TRL 8 at this time as they are currently used widely, but questions remain about their accuracy and long-term performance.
These systems have been used extensively in Europe (particularly in the United Kingdom), the United States, and Asia. At the time of writing, floating lidar systems have been deployed at least 20 times in the United States, and many more times in the United Kingdom and Europe. The first offshore deployments took place in the late 2000s and since then around 10 different lidar and platform designs have been developed.
The type of platform and lidar device are usually optimized for a particular deployment, although at this time the same lidar systems dominate both the offshore and land-based markets. This parallel development stems partly from the fact that offshore lidar users require confidence in the technology that they are deploying, and using an existing and tested design is one way to reduce risk. IEA Wind Task 32 developed a recommended practice for floating lidar systems in 2016 that documents the process of deploying floating lidar systems for offshore wind energy applications (Bischoff et al. 2016).
One major concern about floating lidar systems is the effect of sea conditions and motion on the accuracy and uncertainty of the device. The effect of motion on lidar accuracy was explored in the XPIA experiment (Lundquist et al. 2017). Because the floating lidar system and lidar motion compensation system are limited by the geometry of the system, it can be assumed that there will be some amount or type of motion beyond which the motion compensation system will not be able to function. This performance boundary may impact the accuracy and uncertainty of the floating lidar system when used at two different sites, if the amount of time when the motion exceeds the boundary changes between the sites.
Instrumentation common to Floating Systems