New theory could maximise wind farm power output

The blades of propellers and wind turbines are designed based on aerodynamics principles that were first described mathematically more than a century ago. However, these formulae don’t work in every situation and, in order to compensate, ‘correction factors’ based on empirical observations are often added.

However, engineers at the US Massachusetts Institute of Technology (MIT) have developed what they claim is the first comprehensive, physics-based model that accurately represents the airflow around wind turbine rotors even under extreme conditions, such as when the blades are operating at high forces and speeds, or are angled in certain directions. The new theory eliminates the need for correction factors, enabling more precise calculations of forces, velocities and power outputs, particularly near the operational limits where previous models failed. The model also suggests that the Betz limit – long considered the maximum efficiency for wind turbines – can be slightly exceeded, suggest the engineers.

The model could not only improve the way rotors themselves are designed, but also the way wind farms are laid out and operated, they say.  

The new findings have been published in the journal Nature Communications.

‘Our theory can directly tell you, without any empirical corrections, for the first time, how you should actually operate a wind turbine to maximise its power,’ comments Michael Howland, the Esther and Harold E Edgerton Assistant Professor of Civil and Environmental Engineering at MIT. ‘This is what we’re so excited about… it has immediate and direct potential for impact across the value chain of wind power.’

The researchers derived their new model, which they call a Unified Momentum Model, based on theoretical analysis, and then validated it using computational fluid dynamics modelling. In follow-up work not yet published, they are doing further validation using wind tunnel and field tests.

Because the fluid flow regimes are similar, the model also applies to propellers, whether for aircraft or ships, and also for hydrokinetic turbines such as tidal or river turbines, say the engineers, although these weren’t the focus of the research.

Do wind turbines have to have blades?

Meanwhile, Spanish company Vortex Bladeless is developing an innovative new wind turbine design based on vibrating energy that does not include blades.

The company says the new design could help reduce interference with migratory routes and nesting seasons, where birds can be killed by collisions with the huge blades when flying near wind turbines. In addition, it may help reduce health problems such as migraines and insomnia that have been reported due to the low-frequency noise produced by conventional turbines when generating electricity.

The new technology is based on a pole made of flexible materials that oscillates when the wind passes through its cylindrical structure. That produces eddies or vortices on either side of the target in what is known as ‘wind-induced vorticity’. This produces oscillations that move a series of coils and magnets, producing direct current that can be stored in batteries or converted into alternating current.  

Vortex Bladeless has unveiled two models: the Vortex Nano, which can generate a few Watts to power sensors and small electronic devices, and the Vortex Tacoma, which is almost three metres tall and powerful enough for LED lights and small off-grid installations. The idea is to install this wind turbine in environments that are not suitable for traditional wind turbines. The company plans to create larger models that could produce 1 kW, enough for individual homes; and perhaps even larger models for more complex installations in the future.  

Unlike a traditional wind turbine, the new design requires no moving parts and its simple shape facilitates production, says Vortex Bladeless. It also requires less maintenance, greatly increasing the lifetime of its components. Although the direct energy conversion efficiency is currently lower that conventional bladed wind turbine designs, the company expects this to ‘improve progressively with each new prototype’. It also adds that the wind speed range before having to shut down the new device to avoid damage is lower than with traditional designs, offering ‘better constancy of electricity supply’.

Windy winner of the ONS Innovation Awards 2024

Finally, congratulations have gone to Siemens Gamesa, which has won the ONS Innovation Award 2024 for its recyclable blade.

Wind turbine blades are designed to be durable by using composite material which, until now, has proven to be difficult to recycle. However, Siemens Gamesa’s recyclable blade uses a novel resin system which fulfils all technical requirements and properties, but with a structure that allows for efficient separation and recycling of materials at the end of its service life.

The ONS judging panel felt the new technology has significant ‘global impact and market potential’. In 2023, nearly 24,000 wind turbines were installed worldwide, while wind power capacity is expected to double between 2022 and 2030, bringing clean energy to more people all over the world.