DIMETIX USA: Lidar increases wind turbine efficiency

3rd November 2014

Scanning wind before it arrives at a wind turbine can increase generation efficiency, claims Worcestershire-based Zephir Lidar.

Testing was conducted in Boulder, Colorado by a consortium of Zephir, the University of Stuttgart, the US National Renewable Energy Laboratory (NREL), and international energy consultancy DNV GL.

The idea is to use feed-forward control from an up-stream-looking laser wind sensor to control which direction the turbine is pointing (‘yaw’) and the blade pitch, rather than feed-back control from anemometers and wind vanes on top of the nacelle behind the blades.

“Most turbine control systems depend on wind speed and direction measurements from instruments located on the nacelle of a wind turbine. These measurements are usually inaccurate, because they are distorted by the wake of the turbine immediately behind the rotor,” said NREL, which has been testing lidars from several manufacturers. “Lidar-based feed-forward control improves speed regulation compared to the baseline feedback-only control.”

“Lidar feed-forward can give a three, four or five percent increase in efficiency,” Alex Woodward, head of product development at ZephIR, told Electronics Weekly. “The wind turbine can also better handle strong gusts so damage is less likely.”

Zephir’s lidar has a conical beam and looks between 10-300m in front of the turbine. Data is delivered to the turbine control system as the average wind direction and average wind speed within each distance ‘slice’ in the cone.

The lidar is a ZephIR DM, which is a circularly-scanned, continuous-wave coherent Doppler sensor. It generates a measurement every 20ms during each 1Hz circular scan. “Industry research demonstrates that this scan geometry and frequency is well suited to lidar feed-forward turbine control,” said Zephir.

Interruptions by passing blades are automatically muted from the data.

Rotor-equivalent wind speed, hub height horizontal wind speed, vertical wind shear, wind veer, and wind yaw misalignment relative to the turbine axis are amongst the parameters delivered. In addition to control, these can be used to measure the turbine’s power curve and for ‘end of warranty inspections’.

The test lasted for eight months and the lidar worked continuously without intervention through blizzards, low cloud and temperature down to -22°C. Rotor sped was more constant, according to Zephir, with the standard deviation of rotor speed variation dropping by 25% compared with conventional sensing control.

Yaw misalignment was also reduced, said NREL field test engineer Andrew Scholbrock.

Tests were performed on a 600kW 3-bladed research windmill called CART3 (controls advanced research turbine), and now there are plans to extend this a 2MW-class on-shore turbine.

At the moment, the system costs around £80,000-£100,000. “Longer term, price will come down significantly and a system will pay for itself several times within a year,” said Woodward – based on a medium-sized European on-shore upland wind farm.

The firm sees two applications for its products – one is retrofitting a handful of turbines in a wind farm and sharing data around the farm’s turbines in real time, the other is as component fitted to turbines as standard during manufacture.

As Lidar feed-forward can be used to reduce loads on the turbine structure, there are “opportunities to achieve a lower cost of energy for the industry through more optimal turbine design”, said Zephir.

Zephir uses intellectual property developed at QinetiQ when it was a UK government research lab.