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Evidence is mounting that certain renewable energy technologies can be deployed to defend against floods and storms. This would significantly change the investment case for those renewables.
Modeling by Stanford Professor Mark Jacobsen published in Nature Climate Change suggests that an array of 10,000 offshore wind turbines could cut hurricane wind speeds by up to 90 miles per hour by extracting kinetic energy from the outer winds. This reduces air flow to the hurricane’s centre, eventually slowing the hurricane and causing it to dissipate more rapidly.
Jacobsen modelled the observed storm tracks and peak near-surface wind speeds for hurricanes Katrina, Isaac and Sandy both with and without wind turbines. He found that “offshore wind turbine arrays reduced storm surge by up to 34% for Sandy and 79% for Katrina, mainly owing to the average wind speed decreasing by up to 14% and 58% upwind of New York and New Orleans, respectively”.
Jacobsen still has a way to go before convincing some peers of the results, including Professor Robert Falconer, Director of the Hydro-environmental Research Centre in the Cardiff School of Engineering. “I find it hard to imagine that offshore wind farms would tame hurricanes. I would expect hurricanes to tear the wind farms to pieces”, says Falconer. Jacobsen counters that the paper acknowledges “the potential for turbine damage as an issue”, but the studies found that, “whether it’s in the Gulf Coast or East Coast, the hurricane actually dissipates by the time it reaches the turbines”. He adds that the modelling was based on current wind turbine designs, which cut out at very high wind speeds to prevent damage. However, even with a ‘cut-out speed’ of 34 metres per second (a standard setting), the turbines achieved “significant reductions in both wind speed and storm surge”.
Such modelling, however successful, won’t make a case for investment per se. However, if the cost savings in hurricane avoidance, health and climate damage are taken into account, the investment in offshore wind turbines may compare favourably, for a region at risk of storm damage, with the cost of investment in fossil fuels. Turbines may also prove cheaper than erecting a seawall to protect from storm surge, the study finds, as the turbines pay for themselves through the energy they generate. Moreover, seawalls won’t prevent hurricane damage.
On the other side of the Atlantic, where floods have alerted policy-makers to climate change risk, another development could see tidal lagoons deployed to both generate renewable energy and protect against flooding. Tidal Lagoon Power submitted an application to build the first tidal lagoon in the world in Swansea Bay. Construction could start in 2015, with power generated from 2018, providing power to 120,000 homes for 120 years – with an adaptation plan for likely sea level rise built into the design. Early consultations for further lagoons in Somerset, North Wales and the North West identified strong interest from local communities in the role that energy infrastructure of this kind may play in enhancing flood and coastal defences.
The lagoon works much like a canal lock, keeping the enclosed water out of step with the sea level, and generating renewable energy by allowing water to flow downwards through the turbines. The seawall constructed to hem in the water would act as a barrier against flooding by increasing the hydraulic gradient – or the slope – any sea water would have to overcome to flood the land. During a storm surge, the lagoon operator could also hold water in the bay low while the seawall keeps surge water out.
“Our intention is to supply 10% of the UK’s domestic electricity by building at least five full-scale tidal lagoons in UK waters by 2023, before the UK sees any generation from new nuclear”, said Mark Shorrock, CEO of Tidal Lagoon Power, which is considering optimising subsequent designs for flood defence.
In the future, it’s possible that both offshore wind turbines and tidal lagoons will be staples of the climate change adaptation tool-kit for coastal communities. For now, proof of concept remains the greatest hurdle.
Ibrahim Maiga is a freelance writer on sustainability and entrepreneurship.