Wind resource is still poorly understood.
That means a big opportunity for improving performance.
Imagine being the operator of a power plant and no one can answer your simple question, “how much fuel is being fed into the generators right now?” As strange as it sounds, it is actually the fact of life for wind farms. Contrary to all other types of power plants, wind farms struggle to get a precise idea of how much fuel (wind) is available to each turbine to convert into electricity. This is because estimating the wind resource for an array of turbines with any level of accuracy is really complicated. You need to forecast the wind speed, its direction, how it flows, how strong it is at each turbine position, how it interacts with each turbine, and how the turbines impact each other. The industry has been using what amounts to rough guesses for some of the more subtle / harder-to-measure effects. Unfortunately, the lack of accuracy has led to some serious underperformance versus initial expectations at wind farms built during the initial wind boom of the past 15 years.
Recently, there have been two interesting findings which will help advance the science, reduce these estimation errors, and show the industry where to focus efforts in order to significantly improve energy production:
The “blockage effect”
The engineering firm DNV GL published research on this phenomenon recently, about which there was very little prior discussion. In a nutshell, when the wind approaches the front row of a wind farm, it will slow down as it approaches the front wall. This is caused by the turbines themselves – an induction zone is created in the front of each turbine which modifies the wind flow around it.
Source: DNV-GL.
There is an individual blockage effect for every wind turbine position as well as a global effect for an entire wind farm, which is larger than the sum of all of the individual effects. It affects all wind farms large and small, and the magnitude of the effect depends on the density of the turbine layout, turbine size, surface stability (i.e. water for offshore vs land for onshore), wind speed and direction.
DNV-GL concluded that the blockage effect at onshore wind farms slows the wind down by 3.4% on average as it approaches the front row of turbines. This may not sound like much, but keep in mind that the energy content of the wind varies with the cube of the wind speed - e.g. a doubling of wind speed leads to 2^3 = 2 x 2 x 2 = eight times as much energy. So the effect of reducing wind speed is very significant.
Orsted (OTC:DNNGY), one of the largest global wind development companies, acknowledged on their Q3 2019 earnings call that, based on their own studies, they have historically underestimated the blockage effect and are adjusting their production forecasts accordingly.
The “wake effect”
Like a boat traveling through water, the spinning blades of a wind turbine create a wake behind the turbine. Below is a real photo of an Orsted offshore wind project. Very humid air on this day made it possible to see the wind turbulence behind each turbine.
Source: Twistedsifter.com / Christian Steiness
This turbulence can cause material drop-offs in the efficiency of downwind turbines. The impact on total annual energy production has been shown to be on the order of 20% at one offshore wind farm in Europe. Moreover, turbine wakes have been observed to extend 25 miles or more so this doesn’t just affect turbines directly behind others in one wind farm. Wind farms have been built in regional clusters where the wind resource is best, so nearby downwind projects are affected as well.
Unlike the blockage effect, the wake effect has long been known to exist and a focal point of study. Recently, German scientists considered an elegantly simple suggestion: Given that the blades on all turbines have been built to turn clockwise, their modeling suggests that having the upwind turbine blades turn the other way, while the downwind turbine continues to turn clockwise, could increase power output of the downwind turbine by as much as 23% at night. The study is only a computer simulation, but the potential improvement is so great that if even just a fraction of it is realized it could mean very significant increases in wind farm production and revenues. Although you can’t simply switch the direction of blade spin for an operating turbine – the underlying mechanical systems would need to be reconfigured - this line of research could pay huge dividends for the long-term prospects of the industry.
The current state of wind power (and utility-scale renewable energy in general) in most global markets involves very low rates paid for energy, either through arrangements which fix the price of power or low wholesale prices. This means that developers and project owners are scratching and clawing to get every last ounce of value from these assets. Any improvements arising from better understanding of the blockage and wake effects could lead to materially improved economics for everyone involved.
Sources
Orsted Q3 earnings call
DNV-GL
Wind Farm Blockage and the Consequences of Neglecting Its Impact on Energy Production
https://twistedsifter.com/2011/10/picture-of-the-day-amazing-turbine-clouds-in-the-north-sea/
https://www.greentechmedia.com/articles/read/wake-effects-cost-downwind-wind-farm-millions