At a seminar held at London’s ExCel during the Offshore Wind Energy 2017 conference in June, industry leaders discussed the pros and cons of LIDAR technology, and it appears to be the consensus of industry leaders that LIDAR is the technology of choice over the older, yet reliable Met masts.
LIDAR, which stands for Light Detection and Ranging, is a remote sensing method that uses light in the form of a pulsed laser to make measurements. In offshore wind projects, the LIDAR laser-based sensor measures the wind speed and direction by tracking the motion of air particles.
A Met mast, or measurement tower, on the other hand, is a free-standing or removed mast that carries meteorological instruments such as thermometers and anemometers. The Met towers have been used for years in developing sites for onshore wind farms in Europe.
Anemometers are mounted on a mast at a range of heights up to the hub height of the proposed wind turbines. They log the wind speed at the varying heights at frequent intervals (like every 10 minutes) for at least a year or more. This information allows wind developers to choose the optimal site for wind turbines.
LIDAR versus Met masts in offshore wind development
Measurement towers can end up being very costly. For example, onshore, a mast can be erected fairly quickly at a cost of about US$50,000. Offshore, a mast typically takes up to a year to get a permit, then around 3 to 6 months to build and the cost can end up being in the neighborhood of US$15 million.
About seven years ago, floating LIDAR devices were introduced to the offshore wind industry – to meet a specific market need. Developers in the growing offshore wind market needed an easy way to gather wind speed data without the huge expense involved using Met masts.
At the seminar, the Beatrice Offshore Wind Farm Ltd (BOWL) was highlighted as an example of the cost-savings in using LIDAR over Met masts. When wind measurements were carried out, BOWL installed two vertical profiler LiDARs and was able to start measurements much earlier and at a greatly reduced cost.
Another offshore wind project developed by RES, choose a single fixed LIDAR, along with two floating LIDARs, positioned across the wind farm zone, over Met masts which would have cost about $12 million. The fixed LIDAR was installed on a lighthouse.
Floating LIDAR’s accuracy tested
To assure the accuracy and dependability of floating LIDAR systems, the Carbon Trust has coordinated a pioneering industry effort to test and validate four floating LiDAR systems. The project was successful in validating the systems and allowing developers to learn about and get hands-on experience in how to use them.
– adjust the yaw angle of the wind turbines
– patrol the wind conditions.
According to Offshore Wind Journal, “the validation trials were conducted on four different floating LiDAR systems, each deployed for a minimum of six months at an existing or prospective wind farm site and independently validated by a third party against existing met masts.”
Founded in 2001 in London, UK, the Carbon Trust’s primary mission is to help organizations and companies to reduce carbon emissions by looking at current and future environmental, economic and societal challenges and then working with governments, corporations, companies, and other innovative projects around the world in developing the technology that will best give us a sustainable future.
With the successful validation of floating LIDAR as a tool in assessing wind measurements for offshore wind projects, we will see a quick transitioning to the system. It is also expected that further reductions in costs will be seen as the systems become more competitive.
