Published on October 7th, 2018 | by Joshua S Hill0
How To Typhoon-Proof Offshore Wind Turbines
October 7th, 2018 by Joshua S Hill
Earlier this month Siemens Gamesa Renewable Energy announced to the world that it would tailor its SG 8.0-167 DD offshore wind turbine variant for Asia Pacific markets in an effort to address what the company subtly described as “local conditions across the region.”
What might have been more helpful and explanatory was to say that its new 8 megawatt (MW) offshore wind turbine variant would be typhoon-proof — or as much as is technically and mechanically feasible, at this juncture.
Siemens Gamesa’s announcement comes hot on the heels of the Taiwan Bureau of Energy’s announcements made earlier this year awarding a total of 5.4 gigawatts (GW) worth of offshore wind capacity to various developers (covered in more detail in May and June). Emerging as the world’s next offshore wind energy hub, Taiwan is already home to a demonstration project — the 120 MW Formosa 1 offshore wind farm — and offshore wind energy companies like MHI Vestas, Siemens Gamesa, and Ørsted have been signing numerous Memorandums of Understanding (MoUs) in order to begin setting up what could potentially be a mammoth regional supply chain.
Taiwan is not the only East Asian country turning its eyes towards offshore wind. In recent months, Japan has begun looking to offshore wind as a potential replacement for its huge nuclear energy sector — a sector which, following the Fukushima Daiichi nuclear disaster of 2011, has become increasingly repellent to a scarred populace. In July, therefore, it was unsurprising to hear that the Tokyo Electric Power Company (TEPCO) would be looking to develop 6 to 7 gigawatts (GW) worth of renewable energy across Japan and overseas, with offshore wind seen as the primary technology.
This was followed up by a September announcement by Japan’s Electric Power Development Co., better known as J-Power, that it had signed a MoU with French multinational electric utility ENGIE to collaborate on power projects, specifically offshore wind and floating offshore wind.
However, as enticing as offshore wind energy is for any country — with technology costs continuing to decline and projects beginning to be awarded with no government subsidies — countries in East Asia (Northwest Pacific) have their particular difficulties that even the turbulent European North Sea offshore wind farms will never have to deal with: typhoons.
“The Northwest Pacific is the most active tropical cyclone basin around the world, which contributes to about a third of the tropical cyclone activity,” explained Aila Aguilar, Meteorological Consultant and Senior Forecaster at Offshore Weather Services in Australia. More specifically, a “typhoon is the strongest of all Tropical Cyclones. The generic term is tropical cyclone and they are classified according to intensity. For NW Pacific (Taiwan-Japan) classification – it will be Tropical Depression, Tropical Storm, and then Typhoon. Once the Typhoon reaches 120kt sustained wind, it is then called Super Typhoon.”
According to Aguilar, Japan and Taiwan have a higher chance of being affected by intense Tropical Cyclones than anywhere else in the world — with Taiwan suffering through an average of 3 to 4 typhoon hits each year, while Japan will encounter 2 to 3 (although, Japan is also susceptible to near-misses from an average of 8 to 10 typhoon passes each year).
An “average” typhoon can sustain wind speeds of between 118–156 kilometers per-hour (km/h), but more violent tropical cyclones can reach as high as in excess of 194 km/h. Typhoon Maria (seen above), which affected Guam and Taiwan in July of 2018, recorded sustained wind of 195 km/h, but increasing to 260 km/h for periods of a minute at a time.
As such, wind turbine manufacturers cannot just stick a traditional wind turbine into the seabed and hope for the best — wind turbines for countries such as Taiwan and Japan need to be decidedly typhoon-proof. “It is not just the wind strength that they have to watch — the sea state will also be a major concern as severe tropical cyclones can cause more than 10-metre significant wave height,” explained Aguilar.
MHI Vestas confirmed in May of 2018 that its 9 MW platform of wind turbines will be typhoon-ready in 2020, in time for the projects it has currently been selected for. “From a technology point of view, we’re proud to announce that our 9 MW turbine platform will be typhoon ready by 2020, putting us in a leading position for the early projects in Taiwan and ensuring that our turbine will be ready for the demanding Taiwanese site conditions,” explained Lars Bondo Krogsgaard, MHI Vestas Co-CEO.
And, as mentioned, this was followed by Siemens Gamesa in the middle of September. Specifically, Siemens Gamesa announced that its new SG 8.0-167 DD offshore wind turbine variant for the Asia-Pacific market is “tailored to meet local codes and standards regarding typhoons, seismic activities, 60 Hertz operation, as well as operation in high and low ambient temperatures.” The company’s typhoon-proof wind turbines will be ready in 2019 in time to be installed by 2020 for its projects awarded in Taiwan.
“Serving the growing Taiwanese offshore wind power market with our new product allows us to provide our customers with a cost-efficient, reliable, and powerful wind turbine which can withstand the challenging local conditions,” explained Andreas Nauen, CEO of the Offshore Business Unit of Siemens Gamesa Renewable Energy. “The market-specific variant of the SG 8.0-167 DD demonstrates our commitment to moving the market forward on a technological front already from 2019.”
Interviews With MHI Vestas & Siemens Gamesa
So what does it take to get a wind turbine ready for installation and operation in the typhoon-prone waters of East Asia? I spoke to both MHI Vestas and Siemens Gamesa to get to the bottom of it.
Exactly what does “typhoon-ready” or “typhoon-proof” mean for an offshore wind turbine that is already meant to be able to withstand heavy wind conditions?
MHI Vestas, Albert Winnemuller, Head of Technical Contracting: Typhoon-ready means that the turbine design is verified against typhoon wind conditions and will be certified accordingly by an accredited certifying body. The typhoon wind conditions are higher than typically seen for the standard heavy wind conditions that a wind turbine would be designed for and therefore very relevant to be taken into account.
Niels Steenberg, Executive General Manager of Siemens Gamesa Offshore for Asia-Pacific: Typhoon/hurricane conditions entail higher extreme wind speeds, compared to the standard IEC class for offshore wind conditions. Certain design modifications are required to cope with these elevated extreme wind speeds.
How do you ‘harden’ such a mammoth piece of technology?
MHI Vestas, AW: MHI Vestas has a rigorous development process, where such typhoon wind conditions are taken into account. The end result is certified by an independent, accredited certifying body, which provides external proof of development quality and product readiness.
Siemens Gamesa, NS: Primarily, minor modifications/reinforcements of key exterior components.
What specific challenges does a typhoon bring that North Sea conditions doesn’t?
MHI Vestas, AW: The wind conditions seen during a typhoon are more extreme than similar wind conditions seen in the North Sea. These more extreme wind conditions need to be taken into account in the design of the wind turbine.
Siemens Gamesa, NS: Increased loads due to higher extreme wind speeds (50 years events).
How do you test a turbine so as to deem it “typhoon-proof”?
MHI Vestas, AW: In the MHI Vestas development process, design and verification are closely linked. As an example, the rotor blades of the wind turbine will be tested according to the expected and calculated loads for the application of the wind turbine. This testing will be for lifetime loading as well as for extreme loading. Next to the various testing taking place, a full documentation package including test reports and extensive calculations needs to be provided. These reports and calculations will be evaluated by the independent accredited certifying body.
Siemens Gamesa, NS: Thorough calculations and CFD (fluid dynamic) simulations secure that every part of the wind turbine is evaluated according to the increased loads.
Taiwan also sits atop the Pacific Ring of Fire which is known for tremendous seismic activity: How do you go about proofing a wind turbine against increased seismic activity?
MHI Vestas, AW: Typically, the seismic parameters will be predicted based on historical data and design standards, and will be included in the design basis for the site.
Siemens Gamesa, NS: Load evaluations and simulations are done for a 475 year event, which is acknowledged to be the applicable design standard in Taiwan. Primarily, structural components, like the foundation and tower, will be evaluated according to the increased seismic loads.
How important is site location and preparation in high-seismic activity regions?
MHI Vestas, AW: Site location and individual positioning of the wind turbines on a site is always an important topic to ensure that the site in the end is suited for generating offshore wind energy in the most economic manner. When there is high-seismic activity in the region, this requires extra considerations in the siting process and in the design process for the foundations and wind turbines.
Siemens Gamesa, NS: Very important. Sub-structures and towers are most often designed based on specific site conditions, so doing thorough site assessments is crucial to ensure a suitable design.
How do you test a turbine so it is prepared for increased seismic activity?
MHI Vestas, AW: As mentioned, seismic activity will be part of the design basis for a certain project site. As such, the seismic loading will be used in the foundation design and turbine suitability assessment. This assessment needs to be provided for evaluation by an independent accredited certifying body. Furthermore, both parent companies of MHI Vestas, MHI and Vestas Wind Systems, have a lot of experience with the placement of onshore wind turbines in seismic regions, and the impact the seismic loading has on the wind turbine itself. This experience is taken forward to the development of new wind turbines, including MHI Vestas products.
Siemens Gamesa, NS: We have experience from our existing track record in Taiwan. Specifically, we have installed 2x G4 turbines as part of the Formosa 1 Phase 1 project. Furthermore, we will install 20x 6MW turbines during 2019 for the Formosa 1 Phase 2 project. On top of that we also do thorough analysis, calculations and load simulations on our latest 8MW wind turbine.
One theoretical solution to seismic activity would be floating wind turbines, but are floating wind turbines untenable given the potential of typhoons?
MHI Vestas, AW: Floating foundations and wind turbines can be made suited for typhoon-prone areas, in our opinion. There is a lot of development work ongoing in relation to floating foundations, and MHI Vestas is monitoring these developments closely. Some developers are considering floating wind opportunities and MHI Vestas is convinced that floating wind will appear in the future at some point in Taiwanese waters, especially at deeper water locations.
Siemens Gamesa, NS: Floating foundations may not be limited by typhoon conditions, so it could be realistic to see floating turbines in typhoon areas in the future. As long as water depths, soil conditions and general site conditions support fixed foundations, this remains the preferred solution. Also, floating foundations are not yet at a cost-competitive level.
Is there a way to develop floating offshore wind turbines that would be able to withstand typhoons?
MHI Vestas, AW: As mentioned, there is a lot of development work ongoing in relation to floating foundations, and MHI Vestas is monitoring these developments closely. Floating concepts will be enablers for further growth of offshore wind, including the expansion into deeper water areas.
Siemens Gamesa, NS: We consider a certain wave height for floating foundations, but we have not evaluated this for typhoon conditions. Currently known sites in the APAC region all support installation on fixed foundations.
Where does MHI Vestas stand in comparison to its competitors (like Siemens Gamesa) in terms of preparing for the typhoon-conditions of Taiwan?
MHI Vestas, Damien Zachlod, Director of Sales APAC: MHI Vestas is one of the global wind turbine suppliers working hard to ensure that our wind turbines are suitable for the typhoon conditions seen in many Asian countries, including Taiwan. These site conditions (that are not present in Europe) mean that the turbine is further developed to meet these specific challenges. Within MHI Vestas, we have already prepared a “Class S” wind turbine to meet these additional challenges. Our 9 MW platform will be typhoon ready by 2020.
Siemens Gamesa, NS: No comment
How important is proving the validity of wind turbines in rough conditions like Taiwan to the overall growth of both MHI Vestas, and the offshore wind industry as a whole?
MHI Vestas, DZ: It is extremely important that customers in new markets like Taiwan can be sure that the wind turbines they install are ready to stand up to the site conditions they will experience. Externally accredited machines allow such certainty that the wind turbine has been designed with these harsh conditions in mind. MHI Vestas believes that the development of typhoon certified turbines will open new markets and help grow the global offshore wind market as customers, financiers and governments all gain confidence that wind turbines can, in fact, withstand typhoons over their lifetime.
Siemens Gamesa, NS: Market evaluation reports suggest a large growth potential in Taiwan and other countries in the APAC region. This is further supported by ambitious targets set by local governments to increase the volume of renewable energy capacity. We are very focused on bringing our products to these markets in order to meet the increased demand.