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Hurricane Class Turbines – The US Will Need Them


Areas of the United States' coastal seaboard are prone to hurricanes. These are also good places to site wind arrays because of their high wind speeds. Here we examine the requirements for these turbines.

The offshore wind industry developed around the North Sea. It has the advantages of shallow water, highly-developed infrastructure nearby, and while no-one would say it is the most agreeable place for industrial development, the conditions are relatively clement.

Elsewhere the clamour for renewable energy has resulted in proposed wind farms in zones where hurricanes are a regular occurrence. These include: Northern West Pacific, the U.S. east coast, the US pacific coast, the Caribbean, Hawaii, Japan, China, Taiwan, Korea and the Philippines. The turbines will have to be more robust. Tropical cyclones or hurricanes are classed from 1 to 5 (worst) on the Saffir Simpson Hurricane Wind Scale (SSHWS).


Saffir Simpson Hurricane Wind Scale (SSHWS)


Wind Speeds


33-42 m/s


43-49 m/s


50-57 m/s


58-69 m/s


Greater than 70 m/s


Michael Galea, Underwriter from GCube insurance says,“Hurricanes are common in the US, along with "Nor'easters", macro-scale extratropical cyclones in the western North Atlantic Ocean which typically hit the North East Coast and can cause significant damage. This would be of a specific concern to offshore projects due to be built off the Massachusetts and New York coastlines.”

He continues, “Hurricanes and Nor'easters are commonplace in these areas and, while measures are being taken to 'typhoon-proof' turbines, it remains to be seen how well the technology will withstand such events.”

Investment will be needed for more robust equipment. How should the increased risk be shared amongst the participating companies and local authorities?


Physical characteristics of Turbines Needed


Research shows that tropical cyclone wind conditions exceed the standards for normal wind turbines. In addition other adverse events are possible – shear forces caused by rapid wind direction changes or abrupt variations in cyclone intensity, coupled with grid outages and potential flooding of onshore infrastructure leads to the need for “Hurricane Class” turbines and associated equipment. DNV GL issued a Technical Note “Certification of Wind Turbines for Tropical Cyclone Conditions” in 2013.

An “average” typhoon can sustain wind speeds of between 118–156 kilometers per-hour (km/h), but extreme tropical cyclones can exceed 195km/h. Typhoon Maria which impacted Guam and Taiwan in July of 2018, recorded sustained wind speed of 195 km/h, increasing to 260 km/h for periods of a minute at a time.

Compared to areas like the North Sea, these weather conditions will impose greater loads on all of the turbine's components, but particularly the blades. There will also be significant stresses on the towers, foundations and seabed components, particularly if the ground is geologically unstable. Several manufacturers, including GE, MHI Vestas, and Siemens-Gamesa are constructing turbines to be resistant to the forces that hurricanes produce. Extensive testing and simulation continues to upgrade the designs, although the proof of the pudding will be when some turbines are subjected to hurricanes and survive the experience.


Basis For Certification


It is widely recognised within the industry that OW turbines is hurricane-prone areas need to be specially certified. DNV-GL's Technical Note considers what should be good practice for these turbines, in combination with DNV's existing certification program. The IEC has added a new certification category T (or Typhoon class). Turbines certified to this standard, are rated to withstand a reference wind speed of 57m/s and a 50-year event gust of 79.8m/s, which will cover 90-95% of tropical storms.


Risks and Insurance


Regions that are prone to tropical storms generated additional financial hazards. Turbines may be damaged or put out of commission. Fortunately evidence so far seems to be that wind farms can be quite resilient – there isn't a single point of failure and one turbine being damaged will not paralyse the array, unlike conventional power stations.

Insurers may have difficulty in taking on such large capital risks as billions of dollar investments in offshore plant in regions of natural catastrophe. This is where alternative risk transfer solutions, such as parametric insurance, may provide solutions to plug the gaps and complement traditional indemnity insurance. Parametric insurance has proven to be an efficient instrument to access additional, alternative capital markets outside the insurance world for such peak risks via insurance-linked securities (ILS) and Cat Bonds.

Michael Galea says, “Asset owners will find that insurance capacity for natural catastrophes is limited, and insurers will have limits on the amount of coverage they can provide in these markets, this is particularly important to bear in mind when consulting with Lender Insurance Advisors as whilst full NATCAT limits may be available at the moment this will likely change as more projects are installed and aggregation becomes an issue. It is worth taking this into account in order to future proof financing agreements so that asset owners are not locked into onerous insurance requirements that add substantially to their operating costs.”

Another risk is that storms will disrupt installation, causing heavy financial penalties if projects are delayed. There is a market for weather downtime protection insurance.


In Conclusion


Typhoon Class wind turbines are another technology development for the OW industry. The lessons of relatively safe waters like the North Sea may not be entirely relevant to places that experience natural catastrophes on a fairly regular basis. There will be a learning-curve for the industry, but it has proven adaptable in the past and will take this on board.

The ACE (Alleviating Cyclone and Earthquake challenges) collaboration initiated in late 2019 will undoubtedly bring some new perspectives and analyses to the table.

Interestingly, floating wind designs seem to be considered as more typhoon and earthquake resistant than conventional fixed-bottom designs. This may mean that the first commercial wind farms using this technology will come online in the far east.


Design and Assessment of Wind Turbines under Tropical Cyclone Conditions

DNV-GL: Technical Note on Certification of Wind Turbines for Tropical Cyclone Conditions


The US offshore wind market is probably the most rapidly-developing renewable energy sector in the world. Follow #USOW20 for the latest news and expert opinions.

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By Julian Jackson – writer on technology, arts, blockchain and cryptocurrencies

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