A reliable power curve has been established for the Vertical Sky® wind turbine based on IEC-compliant measurements. The measured results verified the computational models and show efficiencies for the large 1 Megawatt Vertical Sky® A40 in the range of approximately 40–46 %. This places Vertical Sky® at a performance level comparable to modern, large-scale conventional wind turbines. This finding directly challenges the long-standing skepticism toward vertical-axis wind energy and is attributable to the active real-time pitch control of the individual rotor blades – a system concept that represents a global first in vertical wind turbine technology.
Construction of the A6 test facility in Brütten, Zurich
Skepticism Toward Vertical-Axis Wind Turbines
Vertical-axis wind turbines (VAWTs) have long been regarded as an alternative concept with limited practical relevance. While their geometric advantages – such as omnidirectional wind acceptance – have been acknowledged, their aerodynamic efficiency has consistently fallen short of that of conventional horizontal-axis wind turbines (HAWTs).
This skepticism has not been ideological but technical in nature. Classical VAWT designs operate with fixed blade geometries and passive aerodynamics. As a result, they are unable to maintain optimal angles of attack throughout the rotational cycle, leading to elevated losses, unstable operating behavior, and ultimately almost or non-competitive efficiency levels. These limitations have prevented VAWTs from achieving broad adoption in utility-scale or industrial applications.
Establishing a Reliable Power Curve
In wind energy, the power curve is the central reference for assessing turbine performance, estimating energy yield, and financing. At the A6 test facility, operational data was collected over an extended period and evaluated in accordance with IEC standards. The resulting power curve is reproducible and correlates closely with computational models and CFD simulations, providing a reliable basis for performance assessment.
Measured Efficiency and Its Technical Origin
The measured power curve reveals efficiencies of approximately 40–46 % for the A40 series turbine. These values are comparable to those achieved by modern conventional wind turbines and stand in clear contrast to the historically observed performance of vertical-axis designs. The power curve shows: a level of efficiency that has previously not been demonstrated for vertical-axis wind turbines. This result is directly attributable to the active real-time pitch control of the individual rotor blades.
Through continuous adjustment of blade pitch during operation, Vertical Sky® maintains favorable aerodynamic conditions throughout the rotational cycle and across varying wind speeds. This active control mitigates losses that are intrinsic to passive VAWT designs and enables operation in a performance regime previously considered unattainable for this class of turbines.
A World First in Vertical Wind Technology
To the best of current knowledge, Vertical Sky® is the first vertical-axis wind turbine to demonstrate – based on measured data – that a VAWT can achieve efficiency levels comparable to modern conventional wind turbines through active real-time pitch control of individual rotor blades.
This represents a fundamental shift in the evaluation of vertical-axis wind energy. The measured performance does not rely on theoretical assumptions but is grounded in standardized measurement and empirical validation.
Implications for Deployment and Upscaling
The establishment of a reliable power curve with competitive efficiency marks a critical milestone for Vertical Sky®. It is one of the prerequisites for the transition from prototype development to commercial deployment. At the same time, active pitch control enables the upscaling of vertical-axis wind turbines into large-scale installations capable of producing electricity at low cost and thus economically.
More broadly, it repositions vertical-axis wind technology as a viable option for decentralized and proximity-based applications, particularly where site constraints favor compact designs and low environmental impact.
Key Takeaways
- A reliable, IEC-compliant power curve has been established for Vertical Sky®
- Measured high efficiencies of approximately 40–46 % are comparable to modern conventional wind turbines
- The results directly challenge long-standing skepticism toward vertical-axis wind energy
- Competitive efficiency is achieved through active real-time pitch control of individual rotor blades
- To current knowledge, this represents a world first for vertical-axis wind turbine technology
References:
- IEC 61400-12-1: Wind energy generation systems – Power performance measurements of electricity producing wind turbines.
- Swiss Federal Office of Energy (SFOE): Review and acceptance of the Vertical Sky® A6 performance measurement report.
- Hansen, M. O. L.: Aerodynamics of Wind Turbines, Routledge, 2015.
