Laser beam buoys assess windfarm viability
Several companies worldwide are working on systems that can measure wind speeds well above sea level in order to find an economic way of assessing the wind patterns for projected wind farms.
These systems are based on LIDAR technology which uses a laser beam to measure winds speeds at different levels of the atmosphere up to around 200m. The laser beam is sensitive enough to measure the speed of particles travelling with the wind and from this it can deduce the speed of the wind at various levels.
The challenge in the development work has been to mount the laser system on a buoy that is moving in waves. This has required the development of stabilisation systems so that the laser beam remains vertical whilst the buoy is moving on the surface of the sea. The power requirements for this require a battery system that can be recharged using both solar and wind energy to enable the buoy to operate in a self sufficient mode for long periods.
AXYS Technologies in Canada is working with the Michigan Alternative and Renewable Energy Centre (MAREC) on the deployment of their first WindSentinel wind resource assessment buoy. This will be used to help conduct a comprehensive wind assessment review on Lake Michigan. The buoy will provide near real-time wind data at six heights up to 150m and allow MAREC to gain a better understanding of offshore wind energy, as well as other physical, biological and environmental conditions on the Great Lakes.
The WindSentinel was constructed at the AXYS facility in Sidney, BC Canada over the last several months. The core sensing technology is Catch the Wind’s Vindicator, which is a second generation laser wind sensor that gathers data on wind speed, wind direction and turbulence at turbine hub-height and across the blade span.
In Norway Fugro has developed their Seawatch buoy system that is equipped with a LIDAR. The prototype readings from this buoy at sea have been validated by comparing them with measurements taken from a fixed land sight close by and these comparisons have shown good accuracy levels from the buoy mounted units.
Dutch company ECOFYS has also developed a similar system that has been used for establishing the wind strengths for projected wind farms of the Dutch coastline. The University of Maine in the USA has also developed a buoy that will be trialled offshore this summer. They are working with Vermont based NRG Systems to build the LIDAR, which will be retrofitted to a buoy 10 feet in diameter. This data will help with the establishment of a 170 unit wind farm in the Gulf of Maine which it is claimed will generate 5 GW of energy
Neal Pettigrew, a professor of physical oceanography at the University claims that the backers of offshore wind farms want hard data about the potential wind conditions before investing in projects and these LIDAR systems will produce that data. The buoy mounted LIDAR units can produce the required data at a viable cost compared with establishing a fixed tower, especially in deeper waters.
The University of Maine system consumes a significant amount of energy so to power the system, a series of six small wind turbines and six solar panels will be attached to charge the battery. With these panels and the small turbines, the buoy can operate unmanned in the ocean for six months to a year with the whole buoy system weighing more than 5,000 pounds. Each unit could be sold for between $1 million and $1.5 million and the University sees considerable business developing in this sector.
By Dag Pike
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