Wind turbines could put the brakes on hurricanes

Wind turbines could provide a front-line defence against cyclones and hurricanes, by slowing damaging winds and reducing storm surges.

New modelling, published in Nature Climate Change, shows large arrays of thousands of wind turbines could theoretically cut wind speeds by nearly 150km per hour and reduce storm surges by 79 per cent.

The study modelled recent US hurricanes – Katrina in 2005 and Sandy in 2012 – and how their impacts might be mitigated by wind turbines. There was a close match between the modelled hurricanes, and wind speeds and storm tracks recorded during the storms.

Peak wind speeds during Hurricane Katrina were reduced by 130-160km/hour when wind turbines were included in the models, while winds during Hurricane Sandy were reduced 130-140km/hour.

Professor Cristina Archer, author on the study from University of Delaware, said the turbine converts the motions of air into the motion of the blades, and then the spinning of the generators.

“This transfer of momentum basically means the air flow is left with less energy and therefore with lower winds,” she said.

Professor Mark Jacobson from Stanford University, who developed the wind turbine model across two decades, said local wind speed reductions reduce wave heights, which reduces friction and, in turn, reduces the redirection of air toward the centre of the hurricane.

“This reduces air spiralling up in the eye wall, which reduces divergence aloft, which increases central pressure, which reduces the pressure gradient in the hurricane, which reduces overall wind speeds in the hurricane,” he explained.

Reducing wind speeds also reduces storm surges — which caused significant damage during Katrina and Sandy. The models found storm surges in Hurricane Katrina could have been reduced up to
79 per cent, while surges during Hurricane Sandy could have been lessened by up to 34 per cent.

The study modelled 543,000 wind turbines off the coast, a number Professor Archer said is, “not practical”, adding further research is needed to find the minimum practical number.

The study modelled lower numbers of turbines and still found a significant reduction in hurricane impacts. Professor Jacobson suggested 20,000-40,000 turbines for moderate to high reductions in wind speed and storm surges. Currently, the largest offshore wind farm is the London Array, consisting of 175 turbines.

The researchers also tested the cost of building wind turbines versus the avoided costs of hurricane damage. At a cost of US9.4c [c.AUD10.56c] per kilowatt per hour, wind turbines avoided up to US0.68c [c.AUD0.76c] per kilowatt per hour of damage in New Orleans, and US0.13c [cAUD0.15c] per kilowatt per hour along the US eastern coast. When other costs were factored in, building extra wind turbines cost US4c [c.AUD4.49c] per kilowatt per hour – cheaper than costs for fossil fuels.

The authors propose wind turbines as a more cost-effective solution than building sea walls, as proposed for defending New Orleans from storm surges following Hurricane Katrina.

Nonetheless, Australian experts have questioned the practicality of building thousands of wind turbines in cyclone-prone areas of Australia.

Australian National University researcher Dr Nigel Martin, who has studied renewable energy in Queensland, said the key is likely to be the speed at which wind turbines can run.

“Turbines need to operate at safe speeds, otherwise – like we saw in Scotland on December 8, 2011 – they will cook the generator wiring. Those speeds were up near 73 miles per second (262km/hour). Cyclone Larry was doing 67 miles per second (241km/hour) when it made landfall in north Queensland and Cyclone Ingrid was doing 62 miles per second (223km/hour) when it made landfall,” Dr Martin said.

The study modelled wind turbines that could handle speed up to 180km/hour. Dr Martin said wind turbines would need more robust generators and blades to handle higher wind speeds.

There would be significant social and political hurdles to cross in building wind turbines off the coast of Queensland.

Dr Martin said concerns about aesthetics, tourism and Indigenous land would be a stumbling block – particularly as modelled turbines were within 100km of the coast.

This article was originally published on The Conversation and the website address at http://theconversation.com/au.