Driving across West Texas, it’s impossible to ignore the multitude of wind turbines that dominate the horizon. Those turbines have gone from a few scattered units to thousands that are as much of the landscape of this part of the state as the Llano Estacado escarpment.
But what one might not notice when coming close to the wind turbines is the wake they produce through the air. Unlike an ordinary oscillating fan that produces a compact wake that is easily detectible, the wake of a wind turbine is not as obvious.
However, it is there, and it is significant, so much so that it tends to negatively affect the energy output of other wind turbines downstream. Limiting that waste from effects of the wake is one of the biggest challenges in maintaining the efficiency of wind farms.
A Texas Tech University professor and a company in Israel may be on the verge of changing all that.
Carsten Westergaard, a professor of practice in the Department of Mechanical Engineering and National Wind Institute affiliate, is partnering with Pentalum Technologies of Rehovot, Israel, to use light detection and ranging, or LiDAR, to measure the wake produced by wind turbines with hopes of eventually reducing that wake and making wind farms even more efficient.
Their collaboration is bolstered by a $900,000 grant from the U.S. Department of Energy’s Binational Industrial Research and Development (BIRD) Energy program, which supports the federal government’s efforts to combat climate change through the development of alternative energy sources.
“This is an area where there hasn’t been very much fundamental experimental research done,” Westergaard said. “We want to enhance the results from studies that have already been done and at the same time develop instrumentation to work on the wakes. This is an undiscovered mine of opportunity that has been fairly researched but not to the level of control we can do.”
Scope and scale
With the technology provided by Pentalum, Westergaard’s research will differ both on the scale on which it will be performed and the innovative devices that will be used.
Westergaard will collaborate with the wind and water program at Sandia National Laboratories and utilize the DOE/Sandia National Laboratories’ Scaled Wind Farm Technology (SWiFT) research facility located at Reese Technology Center, which consists of numerous wind turbines specifically designed to study wind farm underperformance attributed to turbine-to-turbine interaction.
The SWiFT site allows researchers to perform cost-efficient testing on a large scale in a relatively short period of time. Westergaard, however, will be taking a longer time period to perform his experiments, between three and six months.
“Wind is never a constant, so a lot of the computations and experimentation done by others is done under controlled conditions or in a very short period of time,” Westergaard said. “What we want to do here is take this and get and array of LiDARs that stays here for three to six months and collects data under all conditions of turbine operations in that time. We want to get a more real-world view of the effects of the wake.”
The time frame is not the only significant difference with Westergaard’s research, and that’s where Pentalum Technologies comes in.
Westergaard was aware of Pentalum through his dealings with other startup companies that attempted to develop LiDAR in the U.S. Pentalum, however, seemed to have success developing the technology, so it became a natural fit to partner with them for this project through the BIRD program, which brings together researchers and technology companies through the Department of Energy and Israel’s Ministry of National Infrastructure, Energy and Water Resources.
What makes Pentalum’s technology a great fit for Westergaard’s project is the LiDAR itself. Most LiDAR, Westergaard said, is based on the Doppler principle, which projects laser beams into the air and dust or other particles in the air reflect them back, giving a specific signature.
Pentalum’s LiDAR operates on the cross correlation method, where a beam is shot into the air and detects an object moving through it. Then, if the object moves through another beam, measurements are taken from the object moving between the beams.
“That’s the correlation principle,” Westergaard said. “You know where it went, and it’s fundamentally different than Doppler. Essentially what it does is breaks down the cost of essential equipment and apparatus, and the cost of the apparatus is much lower than the other ones.”
That lower cost will enable Westergaard to purchase and place multiple LiDAR units in the path of the wake produced by a wind turbine, measuring it in all different directions and speeds, and leave them there for several months to gather data in all types of weather conditions.
Past experiments using LiDAR has focused units from behind the turbine pointed into the path of the wake in order to reduce the wind load coming into the turbine. But research has shown with large wind farms that wind loading downstream is more severe than what was first being detected.
Facing LiDAR units forward is good for studying one turbine, but not for several standing together like is seen on wind farms.
“If we can understand where the wake is statistically and where we can measure from the nacelle on the turbine, then we can start looking at where the wake goes and how to take action to place it where we want it to be rather than waiting for it to go where it goes when the wind takes it. That’s the essence of it.
“There’s an opportunity to reduce the wind load on the turbine from the back, and also the opportunity to take charge of the wake and actually increase energy capture capabilities of the turbines downstream. The end game is to get that turbine downstream to produce more energy or the same as the front one.”
Initially, Westergaard was planning on using five LiDAR units for his research. But with the grant from the BIRD program, he feels he can double that number to 10 to increase the ability to take measurements, and that in turn will help Pentalum develop what will eventually be the instrumentation tool researchers will use in similar projects in the future.
There’s been a lot of effort in looking into this area with computer models, but this is an opportunity to really do some long-term data mining,” Westergaard said.