‘Wake steering’ – the technique of angling turbines fractionally away from the prevailing wind stream – could boost output from projects in low-wind locations by almost 50%, according to a new study from Stanford University.
Tests at a TransAlta Renewables wind farm in Alberta have shown overall power output could be ramped up 47% in lower wind velocities and by 7-13% in average winds, while also trimming the “ebbs and flows” of total power production to the grid.
“To meet global targets for renewable energy generation, we need to find ways to generate a lot more energy from existing wind farms,” said John Dabri, professor of civil, environmental and mechanical engineering at Stanford, and senior author of the paper.
“The traditional focus has been on the performance of individual turbines in a wind farm, but we need to instead start thinking about the farm as a whole, and not just as the sum of its parts.”
By yawing turbines row-by-row throughout a wind farm, the negative impact of so-called turbine wake – the turbulence behind the rotor that can reduce the efficiency of downwind machines by more than 40% – can be turned to help raise overall output, noted Michael Howland, lead author on the study.
“Through wake steering, the front turbine produced less power as we expected. But we found that because of decreased wake effects, the downstream turbines generated significantly more power.”
Wake steering would also help smooth production profiles, particularly from wind farms operating on low-wind sites where complete cut-out is regularly caused by rotors dropping below minimum speeds, with the Stanford study finding the technique reduced short-term variability of power production “by up to 72%”.
The potential of wake steering has long been recognised, but testing computer modelling of the phenomenon in the field has until recently been hindered by finding operators willing to lose production by shutting down normal operations for trials.
Dabri added there might be a added benefit in wake steering for the long-term operation of turbines too.
“The first question that a lot of operators ask us is how this will affect the long-term structural health of their turbines,” he said. “We’re working on pinpointing the exact effects, but so far we have seen that you can actually decrease mechanical fatigue through wake steering.”
The software developed as part of the Stanford research could be a industry-changer for a “very data and computationally intensive” sector such as wind, offers Sanjiva Lele, a professor of aeronautics, astronautics and of mechanical engineering at the university.
“Our model is essentially plug-and-play because it can use the site-specific data on wind farm performance,” said Lele. “Different farm locations will be able to use the model and continuously adjust their turbine angles based on wind conditions.”
Stanford plans to now run full-year field tests using the technique. “If we can get to the point where we can deploy this strategy on a large-scale for long periods of time, we can potentially optimise aerodynamics, power production and even land-use for wind farms everywhere,” said Dabiri.