Eye on the Wind: Innovations Designed to “See” and Track Gusts

High-technology company Catch the Wind is commercialising a nacelle-mounted, forward-looking system capable of sensing both wind speed and direction, as well as rapid wind variations. In December 2009, the company released striking trial test results for the innovative lightweight technology, claimed as unique and named the Vindicator Laser Wind Sensor (LWS).

Virginia-based Catch the Wind is a spin-off of US-based Optical Air Data Systems (OADS).  The latter, founded in 1990 near Washington DC, is a leader in fibre-opticpulsed Lidar (Light Detection And Ranging) systems, an optical remote sensing technology.

Building upon 19 years of aerospace research know-how and experience, Catch the Wind, which was founded in September 2008, acquired a technology license from OADS for all its commercial (non-aviation) applications. The Vindicator LWS uses advanced laser technology combined with Doppler radar techniques to analyze air particle movement and determine wind speed and direction. The use of Vindicator LWS is primarily intended for improving the performance of wind turbines, resulting in higher energy production and reduced lifetime maintenance costs.

One major reliability and operational lifetime enhancing factor is a substantially reduced off-axis turbine loading due to optimised rotor alignment to the prevailing, but continuously changing, direction of the wind encountered by the turbine.

The company currently employs eight full-time staff and another 35 experts indirectly via OADS, with full-scale production and shipments of the Vindicator expected soon. In September 2009, Catch the Wind announced that it had entered into a manufacturing services agreement with Ottawa, Canada-based BreconRidge Corporation, a fibre-optics specialist and provider of collaborative design and manufacturing services. Under the terms of the agreement, BreconRidge will also provide technical, engineering, design and other professional services related to the manufacture of the Vindicator.

The fast-track commercialisation efforts also resulted in the successful completion of a full year Vindicator system field-testing programme, conducted as part of different onshore and offshore trial projects in North America.

In a major onshore project, Catch the Wind and Nebraska Public Power District (NPPD) teamed up for a joint trial at NPPD’s Ainsworth Wind Energy Facility located near Ainsworth, Nebraska. This programme involved evaluating how wind speed and direction forward measurement can optimally align wind turbines with the approaching wind.

The latter set up involved a Vestas V82-1.65 MW turbine and a beta Vindicator LWS production unit functionality integrated with the turbine’s control system and mounted upon the nacelle cover.

This particular fixed-speed Active-Stall Vestas model forms part of NPPD’s operating fleet and was originally a former NEG Micon turbine concept. Both fixed speed Classic Stall (fixed blade angle) and Active-Stall (turn-able blade pitch) turbines represent a clear minority compared to more advanced pitch-controlled variable speed turbines now dominating the global wind market.

Phil Rogers, CTW president and CEO explains, ‘A distinct Vindicator LWS product feature, compared to other LIDAR type devices, is the nacelle mounting and the fact that there are no moving parts, therefore requiring little maintenance. Another unique feature is the forward-looking capability to accurately sense and calculate both wind speed and wind direction up to at least 300 metres upfront the rotor.’

Eggbeater Shape Stands Out From the Crowd

The Vindicator LWS ‘Smart turbine control system’ originates from an aerospace product development dedicated to the safety of flight critical applications. Covered by 27 patents, the product’s development track absorbed more than US$70 million in R&D funding. A distinguishing characteristic of the product is the eggbeater-shaped body supplemented by four legs, each with pivotal mounting foot-brackets enabling an uncomplicated nacelle assembly process.

Explaining the Vindicator LWS working principle, which is that the nature of conventional wind turbine control systems is reactive, Rogers says, ‘With today’s wind turbines, both wind speed and wind direction are usually measured at the nacelle rear with the aid of either a conventional rotating anemometer or a stationary device, plus a separate wind direction sensor.’

Rogers continues: ‘This common arrangement implies that the wind control system can only start reacting to a wind gust and/or change in wind direction once the actual event has already occurred. In other words, there is no lead time left for adjusting the pitch angle and/or rotor orientation to the continuously changing wind conditions upfront the rotor.’

In the case of the Vindicator LWS, however, three forward-facing laser beams each reflect off dust particles in the approaching wind, which, in a phenomenon known as the Doppler effect, causes a change in colour. From this sensed colour change, the wind speed and direction are then calculated as a near integral step.

Finally, the Vindicator LWS commands optimal turbine alignment and blade pitch based on this input. ‘Being able to ‘see’ the approaching wind at 300 metres in front of the rotor translates to 20 seconds lead-time at a wind speed of 35 mph (15.6 m/s)’, says Rogers. ‘This lead-time is, in principle, sufficient for all wind turbines and thus independent of a specific wind turbine, but if necessary can be expanded by further extending the range.’

Gust Detection and Smart Alignment Boost Yield

A key finding of the Nebraska trial was that employing a Vindicator on a given wind turbine increases energy yield by 12.3% on average, says Rogers. That positive result in turn can be attributed to both optimized rotor alignment with the oncoming wind, and increased gust detection. He stresses that the increased output was achieved while the Vindicator controlled the turbine for only 56% of the time as specified by the 30-day trial parameters.

‘Excluding statistically insufficient measurement data, the Vindicator improved energy output by more than 18%. The system is also insensitive to specific environmental conditions’, adds Rogers, expanding on the positive trial results.

A Vindicator unit itself is a standard system that can be fitted on all turbine makes and types with an installed cost of about $150,000. ‘This adds about 10% to the current turbine off-factory costs typically in the range of $1.5 million per MW. Based upon incremental cash flows, that in turn translates to a typical two to three year payback period’, says Rogers.

‘Our field trial with Nebraska Power above all validated the Vindicator’s built-in capabilities to improve turbine performance through forward wind speed and direction sensing. By increasing energy output by only 10% for a typical 2.5 MW turbine, for example, we are convinced that wind farm operators can expect to generate a present value of future cash flows in excess of $600,000,’ adds Rogers.

This figure represents an additional $18 million annual revenue for a typical 75 MW wind farm. And as the Vindicator is a standard system, the relative investments costs go down with an increase in wind turbine size, which positively reflects on investment payback period.

Regarding offshore-related developments, in late 2009 field trial tests of a WindSentinel, a wind resource assessment buoy mounted with the Vindicator LWS, were successfully completed in co-operation with Catch the Wind partner AXYS Technologies Inc. of British Columbia, Canada.

AXYS Technologies is an established pioneer specialising in the design, manufacture, distribution and maintenance of remote environmental data acquisition, processing and telemetry systems. The marine consultancy has built and tested over 200 meteorological and oceanographic data buoys of various types, activities sometimes expanded by their long-term upkeep.

The WindSentinel is designed to assist offshore wind farm developers in determining the available wind resource at potential wind farm sites. It is claimed to be the world’s first wind resource assessment buoy capable of accurately measuring wind data at the required hub heights of large conventional offshore wind turbines.

Historically, wind farm developers have had to construct permanent offshore meteorological towers or ‘met masts’ to collect wind speed and direction data. Catch the Wind estimates that such offshore met masts can cost as much as $10 million to build and erect. Rogers aims to eliminate their future need by offering the floating WindSentinel as a less expensive and therefore more economical and easier to employ a solution instead.

The field trials were conducted off Race Rocks Island, in the coastal waters of British Columbia. The main goal was to determine if buoy motions affected wind measurement outcomes. The test set-up compared data collected by the Vindicator LWS on a moving WindSentinel buoy to that collected from a second, stationary Vindicator on Race Rocks Island, 750 meters away.

‘The buoy worked flawlessly during the trials, with wind speeds that reached more than 80 kilometres per hour (22.2 m/s) and wave heights over four meters,’ says Reo Phillips, manager of AXYS product development.

AXYS has been granted a license by Catch the Wind to combine and integrate the Vindicator LWS with custom-made AXYS salt/fresh water fixed and floating platforms, and sell the bundled products worldwide. ‘We are very encouraged by the results of these latest field trials’, adds Rogers, ‘and look forward to bringing the WindSentinel to the market, given the industry’s need to better determine the economic viability of offshore wind energy projects before they are developed.’

Catch the Wind is continuing to conduct further research in collaboration with third parties. These include the Wind Energy Institute of Canada, and Canadian consultancy Helimax Energy, now a group member of Germanischer Lloyd of Germany.

A preliminary field trial with Helimax involved a Vindicator LWS beta version and a meteorological tower at 85 metres above ground level in Quebec. The trial favourably demonstrated the correlation of wind speed and direction data captured by both measuring systems, Rogers concluded.

Eize de Vries is wind technology correspondent of Renewable Energy World magazine. e-mail: rew@pennwell.com

 Danes Hail Lidar Breakthrough in Wind

The world’s largest independent rotor blade manufacturer, LM Glasfiber of Denmark, and two Danish partners are developing a laser-based wind sensing system integrated into a wind turbine’s blades and spinner. They have claimed success for the system in predicting wind direction, gusts and turbulence.

The three-year research project began in 2009 with financial support from the Danish National Advanced Technology Foundation. The R&D is conducted as a joint venture with sustainable energy research organization Risø DTU and sensor specialist NKT Photonics. Among the main project objectives are that the laser-based solution will significantly improve wind turbine load control during operation, improving overall turbine reliability by acting as an efficiency enhancement and operational lifetime-boosting measure.

LM Glasfiber has been working for years on multiple projects aimed at improving rotor blade efficiency as a means to raise wind turbine energy yield. A key objective is developing ‘intelligent’ blades that continuously measure the approaching wind and either adapt to these prevailing wind conditions or supply data to the wind turbine control system, says Lars Fuglsang, LM Glasfiber research director. Integrating Lidar technology into the blades themselves is an extension of LM Glasfiber’s previous blade monitoring technology, he adds.

The partners look to have made rapid progress for their new product development, which has been named ‘wind Lidar’.

Risø DTU claimed during the first half of January 2010 that it had completed the world’s first successful test on a wind turbine with a laser-based anemometer built into the spinner in order to increase electricity generation.

Fuglsang adds, ‘Whereas current blade monitoring technologies measure loads on the blades, integrating Lidars into the blade enables us to measure the exact wind conditions to which these blades are exposed. And instead of realizing afterwards what the force upon a blade has been, we will be able to measure wind real-time and either have the blade or the wind turbine react instantly.’

The combination of Lidar technology integrated into the rotor blades as well as into the spinner is said to further optimize the system’s overall capability to ’see’ the wind well ahead before it hits the blades.

It is claimed that with the new technology incorporated energy yield may increase up to 5% over the wind turbine’s 20 year lifetime, primarily because it will be possible to use longer blades by maintaining the same wind turbine structural stress level. A 5% yield increase would, for a 4 MW class wind turbine, also result in an annual financial gain in the range of $38,000, depending on fossil energy prices and other variables.

LM Glasfiber expects a rotor blade prototype with integrated Lidar technology to be available in 2012, potentially allowing the partners to supply LM’s customers with Lidar-enabled intelligent blades by 2014.

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