Based on a study by Jacobson et al. (2014), offshore wind power has the potential to regionally mitigate high wind and storm surge intensity - in addition to the benefit of reducing greenhouse gas emissions which increase storm frequency and intensity globally. In the article below, we propose conceptual implementations at two scales based on the research of Jacobson’s team [1]. The first proposal outlines an overall strategy for the east and Gulf coasts of North America, while the second focuses on the Gulf coast states centered around Louisiana.

Basic Principles

When the flowing molecules that make up wind collide with the blades of a wind turbine some of their kinetic energy is transferred to the blades while remaining energy propels them downstream at reduced speed. This slowing effect - multiplied by tens of thousands of wind turbines - has been simulated by Jacobson’s team at Stanford University and their modelling predicts that an installed capacity of around 300 GW (e.g. one hundred and twenty thousand 2.5 MW turbines similar in scale to those in the Horns Rev image below) can reduce hurricane surface wind speeds by 56-92 mph and storm surge by 6-79%. The results depend on a number of variables including configuration and proximity to shore (Jacobson et al., 2014). The effect is scalable, nonlinear, and turbines can be distributed over large areas and still be effective, though the best storm surge reduction is obtained by having some percentage close to shore.

Proposed Offshore Wind Turbines Along East Coast, Gulf and Caribbean

Offshore wind turbines proposed for east coast, Gulf of Mexico and Caribbean to reduce hurricane wind and storm surge damage.

For a phased-in North American scanario, wind turbines are shown oriented normal to typical hurricane paths (1980-2005). Approximately 50,000 wind turbines are shown as the first phase. The white curvilinear lines of wind turbines result from conforming to coastlines, bathymetry (avoiding deep water, which is expensive to build in) and aesthetic studies that indicate curved layouts are often easier on the observer’s eye when viewed from the coast, a vessel or aircraft. Other geometries may perform just as well, possibly better (Pasqualetti, Gipe and Richter, 2002: 119). Most wind turbines in this scenario will not be visible from shore, and as illustrated below, can be coordinated with shipping lanes, migratory bird flyways, fisheries, tourism and other industries.

In Phase I, the 50,000 wind turbines would reduce wind and storm surge damage to some extent by locally reducing wind speed. They will have little to no affect on reducing sea level rise - not directly, unless they replace retiring fossil fuel plants, which could be done. The net cost of full deployment of offshore wind power is estimated to be less than seawalls (Jacobson et al., 2014). 50,000 wind turbines could provide approximately 125 GW of power - equivalent to over 230 coal powered electric plants that average 547 MW each (Currently, approximately 572 coal plants operate in the US).

See Jacobson’s paper for more details. IEEE.org offers a summary that doesn’t require a graduate degree in science.

US Gulf Coast Scenario

Proposal to mitigate hurricane damage in Texas, Louisana, Mississippi, Alabama and west Florida with large arrays of offshore wind turbines. Most wind turbines would not be visible from shore and can be coordinated to support and protect industry, urban and rural developments, marine recreation and ecosystems.

In this more detailed, regional scenario, offshore wind turbines are sited along the northern Gulf coast centered off Texas, Louisiana, Mississippi, Alabama and east Florida. In order to preserve a continuous wind break, shipping lanes are accomodated with oblique corridors through wind turbine arrays. To minimize interference with fisheries, offshore wind turbines are aggregated into modules optimized to harvest wind, which are separated by corridors at least 1 or more nautical miles width to permit passage of trawlers (See Petruny-Parker et al., 2015 for more background). Widespread, seasonally variable hypoxia (false color overlay: red [most intense] to blue [least]) will also come into play. Fish further offshore will probably be attracted to the shelter offered by wind turbine foundations - either monopile or floating types (Leonhard et al., 2011). Most of the turbines in the hypoxic areas could be the less costly monopiles due to the shallow depth (< 40m). Bird migratory flyways (transparent blue highlight) might be partially accomodated with angled shipping lane corridors as well, though recent wind turbine technologies that pause turbine rotation when approaching birds are detected would probably be required.

Wind Speed Reduction Illustrated

Wind speed reduction at Horns Rev wind farm in Denmark made visible with nearly saturated marine air and fog.

(Photo credit: Vattenfall, Horns Rev 1. Photographer Christian Steiness).

Air vapor condensation visible just downstream of the turbines at rotor height is due to the pressure drop below the dew point from passing through the turbine blades. This along with the disturbance of the fog just above the water help to make the spiraling, lower velocity wakes visible. The net effect is reduced wind downstream as wind power is transformed into electricity and turbulence. The Horns Rev 1 turbines are 80 m (262 ft) diamter, spaced approximately seven blade diameters apart to allow the wind time to speed up again. While this spacing optimizes for wind energy extraction, the resultant 560m (1837ft) spacing from mast to mast can pose a problem for any trawlers passing through or attempting to fish (Petruny-Parker et al., 2015). Larger wind turbines spaced at seven blade diameters will provide larger corridors, though this introduces other tradeoffs, such as increased visibility from coastlines.

Reduction of Coral Reef Destruction

Florida Keys coral reef destruction from Hurricane Irma 2017.

Video still credit: NOAA National Marine Sanctuaries. <https://floridakeys.noaa.gov/whatsnew/releases/2017/post-hurricane-irma-gallery.html> Accessed 25 November 2018.

While hurricanes temporarily cool the water they pass over (They’re powered by warm rising surface evaporation) and briefly reduce heat stress of coral, they are becoming more intense with global warming and their waves are increasingly destructive (Wilkerson and Souter, 2008). Wind turbines in sufficient numbers can reduce wave loads on coral by reducing the winds that create them. Reefs damaged by storm waves can take years to centuries to regrow, which stresses the species they interact with and support. Other portions not immediately damaged may remain buried in sand where they will eventually die from lack of nutrients and light.