Industry standard compliant offshore wind speed measurements, on floating platform

Introduction

The offshore wind industry growth was based on the experience gained from onshore industry coupled with knowledge from oil and naval industry and state incentives either in the form of direct funding or in the form of higher tariffs. It is however widely accepted that to sustain the growth of the sector, offshore wind has to move towards deep waters and at the same time become more cost competitive.

Approach

One of the most important drivers for reducing the cost of energy is minimizing uncertainty and improving the predictability and availability of wind energy. A small deviation of the wind speed values at the range of 1% may have significant effect at the range of 3% in the wind farm cash flows. Because of this, fixed masts were used in several cases to reveal wind potential in areas where an offshore wind park was planned. However, the cost of a fixed on the seabed wind mast is significant reaching sometimes the range of 10 million Euros. Additionally, as moving to open seas, the use of a fixed wind mast or even a fixed LiDAR is impossible especially during the development stages of the project. Because of this, the use of remote sensing devices like LiDAR’s placed on floating buoys has been developed during the last years. As an alternative to a wind mast, a LiDAR can deliver wind data over the height of modern wind turbines.

Main body of abstract

Placing a LiDAR on a buoy, introduces uncertainties because of the movement of the buoy due to the wave effects. Several approaches of floating LiDARs have been developed over the last 3 years.
Although floating LiDARs is a step forward for the offshore wind industry, wind data measured using LiDARs on a buoy are not compatible with the current industrial standards –IEC 61400-, which require wind masts carrying cup anemometers. Because of this wind data measured by a buoy LiDAR require long approval tests against a fixed mast before going into the market. Additionally the multiple sensors carried by a mast offer a significant advantage in difficult off-shore environments, where maintenance is sometimes impossible.
This gap has been bridged by the seaLIDAR approach. seaLIDAR is a purpose designed and developed floating platform to perform IEC 61400 compatible wind measurements at all sea depths using minor infrastructure with both wind mast and LiDAR. seaLIDAR platform fulfilled last July 2015 satisfactory its proof of concept tests, giving results for the world’s first wind data from a floating platform measured simultaneously by an IEC 61400 compliant wind mast and a LiDAR.
Data collected form the world’s first offshore campaign using both mast and LiDAR measurements show the potential of this method for off-shore wind industry.


Conclusion

As stated by Carbon Trust, it is expected that under ideal conditions and notably during calm sea periods, floating LiDAR device measurement uncertainty could be as low as those of high-quality and well mounted cup anemometers on high quality hub height meteorological masts. This means that only under ideal conditions, solutions of floating buoy LiDARs could have industry standard uncertainties. seaLIDAR on the contrary employs high-quality and well mounted cup anemometers on high quality meteorological mast, together with a “proven technology” LiDAR system, offering the benefits of both technologies to the off-shore wind industry.


Learning objectives
Off-shore wind measurements using both wind mast & Lidar according to existing industry standards are now possible for both shallow and deep waters close or far away from the coast at reasonable cost.