The future in turbines

By Eize de Vries

Rated capacity in relation to rotor diameter and
drivetrain choice are three key characteristics of any wind turbine. This
article focuses at mainstream commercial offshore turbines and the new roughly
7- 12MW+ superclass being launched and developed in various global markets, popular
configurations, backgrounds and what the future could bring.

Europe was last year again the world’s largest offshore
wind market, and according WindEurope 2018 statistics dominated by only two
suppliers. Siemens Gamesa turbines took a 62.2% majority share with its direct
drive models and MHI Vestas pursuing medium-speed geared accounted for 33.3%. Bankrupt
Senvion pioneered the that period 5MW superclass in 2004 with an offshore-dedicated
high-speed geared turbine. This conventional non-integrated 5M model was uprated
and optimized to 6.2MW in 2009. The original 126-metre rotor size remarkably remained
the world’s largest from 2004 – 2012 in the offshore segment, which conservatism
became finally an Achilles Heel of the once offshore-leading concept. This was
due to the much delayed introduction of a 6.XM152 model with enlarged 152-metre
rotor in 2014. Main competitors Siemens Gamesa and MHI Vestas had two years
earlier already introduced new 6MW respectively 8MW models, which set new (reduced)
head mass standards and together with 154-metre and 164m rotors.

Senvion’s 10MW+ turbine was announced in 2017 but
never realized. It was according well-informed sources a medium-speed concept,
which seamlessly fits into many wind industry statements that there is no
demand for new high-speed gearboxes for offshore above 6MW. One main
contributing reason is (perceived) higher failure rates of the third high-speed
gear stage.

Specific power rating
is the ratio between rated power and rotor swept area expressed in watts per
square metres (W/m2). An optimized ratio contributes to the lowest possible
LCOE of a given turbine configuration under specific wind conditions, but
company strategies differ considerably. The 9.5MW MHI Vestas V164-9.5 MW for
high-wind North Sea application comes for instance with 450W/m2 whereas the V174-9.5
MW successor with enlarged 174-metre rotor for global markets scores 400W/m2.

The successful Siemens Gamesa direct drive commercial
offshore era officially commenced in 2014 with the (Mark I) 6MW SWT-6.0-154 incorporating
an innovative segmented outer-rotor generator. The prototype originates from
2012, but the initial SWT-6.0-120 with 120-metre rotor was introduced in 2011.

The 10MW SG 10.0-193 DD Mark V features 193-metre rotor diameter and the
prototype is planned this year. Product characteristic are a shorter box-type
nacelle and enlarged permanent magnet generator (PMG) compared to the SG
8.0-167 DD Mark IV. Staying technologically ‘close’ to the original concept
allowed a fast development track for entering the market in 2022. The company
explained that its 314W/m2 fits
well into current client wishes for high-wind, and future liberalized market conditions
with high electricity prices during little wind plus high demand combinations.
The SG 8.0-167 DD Mark IV has an about 800-unit confirmed order backlog. Numbers
installed and sold of the 7MW SWT-7.0-154 and SWT-6.0-154 are respectively ±675
and ±500 units.

The SG 10.0-193 DD features
about 94-metre glass & carbon fibre reinforced epoxy composite B94 blades. First
major (conditional) orders are about 140 units for Dutch Hollandse Kust I&2
and 3&4 planned in the Dutch North Sea.

It is further public wind
industry secret that Siemens Gamesa and MHI Vestas each develop a 12MW+ turbine,
but more details are not available.

GE is a relative offshore newcomer with limited track
record in the 6MW class, but the Haliade-X spearheads the emerging 12MW segment,
with the prototype in Rotterdam recently completed. This giant features a
direct drive PMG with ±11-metre diameter and the world’s largest 107-metre
blades. Prototype permitting documents meanwhile indicate 218.2-metre rotor
diameter (officially 220m), and an enhanced 12 – 14MW rating versus the
official 12MW.

First (conditional) 1.2GW US project sales were
announced this September. The most recent news that SSE and Equinor have
selected GE as a preferred supplier for three Dogger Bank sites totalling 3.6GW.
This amounts to 400 units in total based on 12MW rating, which would instantly make
Haliade-X an offshore wind market leader.

China’s new 2018 offshore installations according GWEC
statistics amounted to 40% of the world’s total, with the UK (29%) and Germany (22%)
taking second and third positions. China is a typical low-wind market, but
there are also high-wind parts like off the Chinese south-east coast.

The first offshore turbine installation was perhaps in 2010. The first offshore project commissioned in 2013 is the 201.3MW 80-turbine Jiangsu Rudong demonstration windfarm according the respected Wikipedia ‘Liste der Windparks’ site. It comprises 21x 2.4MW Siemens, 17x 3MW Sinovel, 40x 3MW Goldwind, and 2x 5MW CSIC Haizhuang turbines. Local suppliers have built track record experience with a comprehensive range of 1.5 – 3MW+ offshore-adapted turbines plus a few offshore-dedicated 5 – 5.5MW designs. Many early Chinese turbines were based on foreign third-party designs, through (non-exclusive) license agreements, custom-developed products, or co-development projects. Wind technology providers include aerodyn (e.g. CSIC Haizhuang 2MW, Guodian 1.5MW, MingYang 3MW – 6MW), and AMSC Windtec (e.g. Sinovel 3MW, 5MW, 6MW; and Dongfang 5.5MW). Goldwind initially used licences from German direct drive turbine developer/manufacturer Vensys, and today 70% owner of the company.

Siemens Gamesa has issued multiple turbine licenses to
Shanghai Electric including the 4MW SWT-4.0-130 and most recent for the SG
8.0-167. It according ‘Liste der Windparks’ operates 382 4MW W4000-130 renamed units
in Chinese waters with another 249 under construction.

MingYang introduced
three new offshore turbine models, all three-bladed upwind and featuring a
compact semi-integrated medium-speed geared drivetrain. It installed two 5.5MW
MySE5.5-155 prototypes with 155-metre rotor during 2018, and the 7.25MW
MySE7.25-158 prototype with enhanced 158-metre rotor this February. Both are
certified for high-wind IEC 1B. A 5.5MW MySE5.5-18X sister model for low-wind
is in development. A possible 186m rotor diameter corresponds to only 202W/m2,
compared to 370W/m2 for the MySE7.25-158. All three models comply to typhoon-prone
wind conditions, which could as a strategy could involveletting the rotor turn slowly and continuously redirect it to
continuously changing horizontal wind direction. MingYang’s offshore order
backlog amounted to 3.76GWh this June, mainly MySE5.5-155. A 12MW turbine is in
development.

The overall concept builds at the patented Super
Compact Drive (SCD) technology of German engineering consultancy
aerodyn-engineering. Former SCD-licensee MingYang bought the IP rights in 2016 allowing
free deployment in China as ‘a compact semi-integrated drivetrain solution.’
For international projects, ‘each project will be judged on a case-to-case
basis.’

An ‘original’ offshore-dedicated 6MW two-bladed
downwind MingYang prototype with 140-metre rotor diameter operates in China
since 2014. Such configuration offers according aerodyn-engineering the best
chances of surviving common hurricanes. The hurricane-survival operational
strategy is here minimizing loads by locking the rotor in horizontal position
together with free yawing, which allows the rotor-nacelle assembly to follow
rapid changes in horizontal wind direction. However, the latest wind industry
preference seems to be for three-bladed upwind with a hurricane-survival strategy
as explained above.

Goldwind operates
its direct drive turbines in Chinese waters since at least 2013, with a project
featuring 43 offshore-modified 3.3MW GW140/3300 (214W/m2) units a recent
example. A key model of the offshore-dedicated 6S platform is the 6.45MW GW
171/6.45, of which a low-wind prototype with 171-metre rotor operates since 2017.
Goldwind recently completed an 8MW GW168-8.0MW turbine model for high-wind IEC
1B (361W/m2) sites. The prototype will be installed this year. A GW 184/6.45MW sister
model for low-wind (243W/m2) in development features one of the wind industry’s
current largest 184-metre rotors.

Envision’s smaller
flagship turbine model for both onshore and offshore is the 4.5MW EN148-4.5 MW
with 148-metre rotor diameter. It represents a two-step
evolutionary upgrade of the original EN136-4.0 (2013), and features a conventional high-speed geared
drivetrain with two main bearings (4-point support) and induction generator. The
cumulative offshore track record is at least 219 units.

Dongfang Electric
(DEC) recently presented a 10MW offshore turbine, likely the first in China of
this size and with an in-house developed direct drive PMG. The high-wind design
has 185-metre rotor diameter and commercialization following prototype
installation ‘may still need one to two years.’ DEC’s smaller 5.5MW turbine is
a co-development with AMSC Windtec.

Taiwan has rapidly become a major Asian offshore
market, while Vietnam and India are considered high-potential growth markets too.

Early this century several Korean shipbuilding giants
including Samsung, Hyundai and DSME had planned a fast massive global (offshore)
wind market entry. Today only Doosan has remained active in the offshore
segment, offering a 5.56MW high-speed geared WindDS5500 model with 140-metre
rotor and PMG for IEC 1B. The 2013 prototype in 2017 acquired from Hyundai originates
from AMSC Windtec. Doosan last year commenced developing an 8MW direct drive WinDS8000
turbine, with limited information indicating 90-metre blades and 193m+ rotor
diameter for low-wind deployment.

Three bladed upwind offshore turbine configurations clearly
continue to dominate, including in China where MingYang switched from
two-bladed downwind. 2-B Energy and aerodyn-engineering continue pursuing the
latter concept approach, but both are a niche players. Several Chinese
manufacturers are finally gearing up with new in-house developed turbines in
the 10 – 12MW+ class, most fitted with large trendsetting rotors. At least
several OEM’s are expected to first focus at the local market, but as stepping
stone for global markets entry. International expansion to North Sea and other high-wind
markets will require adaptations of low-wind designs for again achieving LCOE-optimized
solutions. Two common strategy options are increasing the rating, or offering a
smaller rotor with unchanged rating.

Especially leading Chinese suppliers Envision, Goldwind, and MingYang are considered formidable future contenders for western OEM’s, and their international market entrance could become reality sooner than later.

This article was previously published in the Offshore WIND magazine, issue 4, 2019.