rful, especially offshore where 50m blades are now routine and some are even far bigger.
But such horizonally-rotating giants may soon reach their limit. If the axis of the blade is considered, when this blade is horizontal the gravitational force will be perpendicular to it, while when the blade is vertical (upward) the gravitational force will be parallel to the axis and pointing toward the root of the blade. Finally, when the blade is vertical again (downward), the gravitational force will be parallel to the blade axis, but now pointing toward the tip. Some studies claim this oscillating gravitational load limits the size of horizontal axis turbines.
Vertical-axis turbines resolve this problem because as they rotate they experience a constant gravitational force, always in the same direction. Without the stress of holding up 80m metal blades by one end, VAWTs can potentially become much larger.
Research has also shown vertical turbines can be placed closer to each other in a wind farm. So for a given area, more VAWTs can be installed, and more electricity generated than if HAWTs were used, thereby reducing the cost of electricity.
The axis revolution
So now the obvious question arises: why have VAWTs not yet been used if they are so advantageous? The main reason is that it is still a new technology. Although researchers have looked at vertical axes for decades, the technology fell behind due mainly to material and bearing system limitations. Investors still see the known technology as a safe bet and even when looking at deep-sea wind they have been more inclined to support horizontal-axis turbines on floating platforms.
However both governments and forward-thinking companies are now investing in the potential of VAWTs for deep sea offshore wind. The Nova project, funded by the UK government, demonstrated vertical-axis offshore was commercially viable. Sandia National Laboratories, backed by the US energy department, and various EU-backed projects have also supported the technology.
Industrial companies such as the British VertAx Wind or Norway’s Gwind are also following suit through the development of different concepts. The French company Nenuphar is pushing ahead its VAWT design, with plans (pictured at the top of this article) to install the first floating wind farm off the coast of Marseilles.
With increasing demand for energy we are obliged to explore every possible solution. Vertical-axis wind turbines located in the deep sea have strong potential to be one of these solutions.
This article is published in collaboration with The Conversation. Publication does not imply endorsement of views by the World Economic Forum.
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Author: Maurizio Collu is a lecturer at the Offshore Renewable Energy Centre at Cranfield University. Michael Borg is currently carrying out postdoctoral research within the Department of Wind Energy at the Technical University of Denmark on floating vertical axis wind turbine concepts.
Image: An artist’s impression of future wind turbines. INFLOW / Technip / Nenuphar / EDF.