Where’s the power in ground-level winds?
Harness ground-level winds: the challenges, innovations, and potential of a new perspective on wind energy.
Ground-level wind poses significant challenges for wind energy harvesting, particularly in urban areas. Traditional wind turbines, optimised for steady, high-altitude winds, are unable to capture the highly turbulent, variable winds found near the ground. To harness this untapped resource, we have developed our Wind Panel technology tailored to urban environments. Here, our Founder and CTO, Karthik Velayutham, explores the variability of wind behaviour and the technological challenges and opportunities of exploiting it.
As one of the most significant sources of renewable power worldwide, wind energy growth has increasingly gained momentum. In 2023 alone, 117 gigawatts (GW) of wind capacity across 54 countries were added to the global energy mix and this growth is predicted to continue. Existing wind installations are primarily composed of onshore and offshore turbines, but as net-zero targets move closer, it is becoming more important to investigate new ways to enhance and optimise energy capture from natural resources. At present wind power project winds work to capture higher-altitude laminar winds, but there is significant potential in more challenging wind types, such as ground-level and turbulent winds.
Ground winds behave very differently to higher-altitude laminar flow. Whereas laminar winds have a consistent flow, ground-level winds are by nature turbulent and inconsistent. They undergo changes in speed, direction and orientation changing as frequently as every second. This is often increased by gusts and the presence of obstructions at lower levels. These winds have a high turbulence intensity, which in the context of wind is a measure of the fluctuations in wind speed around its mean value. It quantifies the degree of variability in the wind flow, which is crucial for various applications, particularly in the design and importance of wind technologies, and in site assessment for installations.
The potential for power generation increases exponentially with an increase in wind speed and high turbulence intensity is also linked to higher energy yields. Gust winds can be 60 per cent higher in speed than the mean wind speed. In cities, this increases to 100 per cent. This highlights that the unique characteristics of ground-level and gust winds present opportunities for wind harvesting that at present are being missed.
Unique challenges of ground-level winds
There are some obstacles involved in working with these winds. Much of this is due to the lack of understanding and knowledge around the behaviour of ground winds. As a result, very few technologies exist that are able to work with this unpredictable and inconsistent resource. A novel approach is required to exploit different wind types, and this presents a complex technical challenge.
There are also currently significant limitations to available data on these types of winds, complicating the process of developing and siting new technology. Much of the existing research is reliant on MET data, which measures and publishes average hourly mean near-surface wind speeds at ten metres with minimal obstacles. This data, collected in level, open terrain and based on hourly averages with the highest resolution being ten-minute intervals, fails to account for the high turbulence intensities and rapid changes in wind speed, direction, and orientation that occur at ground level.
The averaging process smooths out peaks in the data where most energy is available, leading to a lower reported average wind speed compared to the more turbulent and energetic real-time environmental wind conditions. Consequently, MET data does not accurately reflect the turbulent nature of gust winds at ground level, posing challenges for energy yield prediction.
A new perspective on wind behaviour
To address these limitations and develop a new system for wind power generation, our team have been gathering our own data to determine the potential of ground-level winds for producing green energy. In partnership with Heriot-Watt University, we have been conducting wind mapping studies across various locations, collecting data at two to three metres above ground level with a higher frequency than the MET data, which is typically recorded at ten metres with minimal obstacles.
While MET data records wind speeds in hourly averages, we have captured over 2.5 million data points per month, allowing for a detailed analysis of gusting effects and higher turbulence intensities, resulting in higher power yields. The studies show that locations with mean wind speeds of four m/s and above have a high potential for significant gusting winds and speed-ups resulting in turbulence intensities, which are not fully captured by the averaging methods used in MET data.
Our data collection, supervised by Dr. Wolf-Gerrit Früh, highlights that typical MET data underestimates turbulence intensities due to its longer averaging intervals. The high-resolution data capture reveals that the Gust Energy Coefficient (GEC), the ratio of the total available energy in the wind over a given period to the assumed available energy, is around 4.57 times the mean average power yield. The Excess Energy Coefficient (EEC), or the extra energy contained within transient fluctuation around the mean wind speed over a given burst period, is 357 per cent higher than expected when using average MET data.
This detailed data collection and analysis underscore the additional energy available in ground-level winds, demonstrating the potential for higher power yields in urban and complex wind conditions.
Informed by the data gathered on wind patterns at lower levels, our team have outlined a list of requirements for a system able to capture highly variable winds. It should smooth turbulent flow as much as possible and have a modular design for flexibility and scalability. The technology crucially must have a high reaction time to instantaneously adapt to changes in wind speeds and effectively operate in highly turbulent environments. Due to their intended small size, ground-level wind energy systems should also be able to dynamically adjust to fluctuating wind conditions to maximise energy yield. Intermediate power storage was also highlighted as essential to capture short bursts of energy from gusts and to be released smoothly, ensuring compatibility with the grid.
We don’t rotate, we oscillate
We developed our Wind Panel to address all of these requirements, with a design adapted to effectively capture an untapped wind resource characterised by more challenging behaviours. Its key features include a hexagonal shape consisting of multiple ducts that smooth turbulent winds and channel and augment airflow. This increases wind speed by up to 50% within the panel through the ducting effect, enhancing energy capture despite the lower wind speeds and energy density typical at ground level compared to higher altitudes. Aerofoils are located in each duct and each aerofoil oscillates independently, allowing it to adapt to varying energy levels caused by high turbulence intensity.
The oscillatory motion of the aerofoils maximises the swept area without disrupting airflow, ensuring high reaction times to fluctuating wind conditions. Designed to generate lift in both directions, the aerofoils facilitate efficient energy capture under oscillatory motion. Additionally, our Wind Panel employs a novel power-train solution for intermediate energy storage, enabling the capture and smoothing of short bursts of energy from turbulent conditions before delivering it to the grid or external supply lines, thereby balancing the power supply effectively.
Limitations of conventional wind technologies
The current standard design for wind turbines is the three-bladed horizontal-axis wind turbine (HAWT). This design consists of a rotor shaft, a generator and a gearbox to convert low-speed rotation into higher speeds suitable for electricity generation. These turbines typically measure around 60 to 120 metres in height. Their design and size mean that they must be installed in remote areas with ample space. They operate most efficiently at 10 metres or more above ground, where the wind flow is more laminar and consistent. For ground-level winds, traditional turbines simply aren’t an option.
The cut-in speed for many wind turbines is between three to five metres per second (m/s), but on average the turbines have an estimated efficiency of only 30 to 45 per cent, which drops to ten to 20 per cent at low wind speeds. They are also not responsive to rapid changes in wind speed and direction, such as gusts, leaving significant wind resources untapped.
Conventional HAWT technology is ineffective at ground level for a number of reasons. These types of wind turbines are designed to operate efficiently in higher, more stable wind conditions and struggle to work effectively at ground level due to the high turbulence component. There is also the potential for the generation of vibrations when not all captured energy can be converted into electricity, imbalances in the system due to each blade experiencing different energy levels in the turbulent wind, and an inability to react quickly to rapid changes in wind speed and direction because of their significant rotational inertia. This makes them unsuitable for harnessing ground-level or gust winds
Testing on the Wind Panel produced promising results in scenarios with wind fluctuations when compared to a HAWT. The standard turbine produces about three per cent of its generator rating but operates more effectively at the mean wind speed, whereas the Wind Panel achieves around ten per cent power capture and reacts to instantaneous changes.
The performance data shows that higher turbulence levels lead to higher power output for the Wind Panel, particularly at lower wind speeds. However, this advantage diminishes at higher wind speeds where larger rotors can better handle short drops in wind. In terms of annual electricity production, our technology can extract economically viable wind energy in areas with annual mean wind speeds from 4 m/s and above, making it well-suited for varied and turbulent wind conditions.
This performance data not only highlights the potential of the Wind Panel as a standalone power generation system in more challenging environments such as built-up or lower altitude areas but also demonstrates its promise as a complementary technology to existing wind installations.
“As long as suitable locations are identified, there is a significant wind resource available which needs a technology to not only extract the power in the mean wind but also the power in the turbulence,” said Dr Wolf-Gerrit Früh. “The Katrick Technologies Wind Panel is designed to do this. It won’t compete with larger standard turbines, but will work alongside them to use the ubiquitous resource near the ground.”
This technology represents a significant advancement in harnessing ground-level wind energy. By effectively capturing the turbulence and variability of untapped lower-altitude winds, the Wind Panel can generate economically viable power in areas where traditional wind turbines fall short. This technology not only expands the potential for renewable energy in urban and complex environments but also complements existing wind farms, optimising energy capture from diverse wind conditions. As we move towards net-zero targets, such advancements are crucial in maximizing our renewable energy resources and achieving sustainable energy solutions.