Could 'food processor'-style turbines be the future of wind power?

Windfarm at Soutra <em>Picture: Adam Ward</em>
Windfarm at Soutra Picture: Adam Ward
Earlier this year, a report supported by conservation charity the John Muir Trust (JMT) suggested that windfarms were much less efficient than the industry had claimed.

Research from Stuart Young Consulting claimed that turbines produced less than 10 per cent of their stated capacity for about a third of the time and therefore “cannot be relied upon” to produce significant levels of power generation.

At the time, the wind power industry said it had “no confidence” in the data, arguing that no form of electricity worked at 100 per cent capacity, 100 per cent of the time. In the view of Jenny Hogan, director of policy at Scottish Renewables, the JMT had “commissioned an anti-windfarm campaigner to produce a report about UK onshore wind energy output.”

However, the research does have a point in that wind power is not a consistently reliable source of energy, compared with wave or tidal power. But now, work being carried out in America may help to greatly improve the efficiency of wind turbines. Scientists at the California Institute of Technology (Caltech) may have found a way to squeeze much more power from windfarms.

In a study published in the Journal of Renewable and Sustainable Energy, they show how the flowing movement of shoals of fish is being applied to the understanding of wind turbulence.

The scientists admit that organising the arrangement of wind turbines based on the vortices shed by schooling fish is definitely a new approach. But as Professor John Dabiri, the principal researcher explains, “while the connection between fish schooling and wind farms might seem non-intuitive at first, it is in fact a logical inference from the underlying flow physics.”

In the California desert, a new windfarm has been built to a design that mimics the actions of a school of fish to improve power output. Wind turbines with large propeller blades are effective, but have almost reached their limit of efficiency. When built together in a windfarm, they can’t be positioned close together, otherwise the air passing through them will be disturbed by turbulence from other turbines, limiting the output of the farm.

A test array has been built which adopts a radical new approach. The turbines use a “counter-rotating vertical axis” system that resembles the spinning whisks in a food processor. These are individually less efficient than the traditional turbines, but can use turbulent winds coming from several directions.

Professor Dabiri says the aim is to focus on the design of the windfarm itself, to maximise its energy-collecting efficiency at heights closer to the ground. In his report, he writes that while winds blow far less energetically at, say, 30 feet off the ground than at 100 feet, “the global wind power available 30 feet off the ground is greater than the world’s electricity usage, several times over”. He argues that enough energy can be obtained with smaller, cheaper, less environmentally intrusive turbines – as long as they’re the right turbines, arranged in the right way.

In this new design, closely spaced pairs of counter-rotating turbines funnel air to their neighbours, losing little energy to turbulence. Professor Dabiri points out that the power generated by the paired turbines can actually be greater than that from the turbines working independently. The result is that a windfarm like this could produce around ten times the output of current windfarms.

The design has other benefits, as well. They are likely to be less expensive to produce, while being more robust. The turbines are much smaller and lower than those driven by propellers. This allows them to have environmental benefits such as being less likely to harm passing birds. They are also less intrusive on the landscape and less visible to air traffic control radar.

The team at Caltech admit this is still at the experimental stage. They acknowledge that there are still some problems to be solved, not least how the design would work on a fully fledged windfarm. They haven’t solved the problem of making them both tall and light enough to cope with all the stresses to which they would be exposed.

However, as Professor Dabiri points out, “we have collected additional wind measurements this summer on an array of 18 turbines. The results suggest that the wind flow rates required for enhanced performance relative to horizontal-axis [traditional] wind turbines are regularly attained.”

It may be an experiment a long way from Scotland. But the work being done in California should inspire researchers here to think in different ways. This kind of design may well prove more attractive to those opposed to wind power, including the JMT and some members of the bird lobby. Perhaps we could benefit from the longstanding links between Caltech and Edinburgh University to bring some of the work here to test in a more extreme environment than the California desert.

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