Insight report: The 40 most promising wind turbine designs that fell short of expectations – 21-30

Part two in our countdown of 40 key innovative wind turbines developed during the past 30 years that ultimately failed to become a success as a commercial serial product

Senvion's 6.2MW offshore turbine was too slow in development to build on the technological lead established by its 5MW predecessor
Senvion's 6.2MW offshore turbine was too slow in development to build on the technological lead established by its 5MW predecessor

21] Senvion 6.XM/152

The 6.XM/152 was an evolutionary development of the original offshore-dedicated 5MW Repower 5M (2004) and its 6.2MW Repower 6M (2009) successor, later rebranded as the Senvion 6.2M126. The original model was the world’s first 5MW offshore turbine, and its 126-metre rotor remained offshore wind’s largest until 2011. The “far too late” 6.XM152 (prototype 2014) with an enlarged 152m rotor again featured a non-integrated high-speed drivetrain with four-point gearbox support and DFIG. The final 32 6.3M/152 units were commissioned in 2020 after Senvion’s 2019 bankruptcy.  

The first Senvion 6.XM/152 nacelle being installed

22] Genesys 600

The 600kW pitch-controlled variable-speed Genesys 600 prototype (1997), a development led by Friedrich Klinger of the university of applied sciences in Saarbrücken, boasted a 49.5-metre rotor diameter and multiple innovative design features. These included a passive-cooled outer-rotor direct-driven PMG, and a near wear-and-maintenance-free toothed-belt pitch system drive. Series production did not materialise, but its technology heritage is enormous through multiple later Vensys models, which propelled its Chinese licensee Goldwind to a top wind industry position.

23] XEMC Wind Power XE128/5.0MW

This Chinese direct-drive concept builds on the XEMC Darwind XD115/5.0MW and Dutch 2MW Zephyros Z72 technology of 2000-01. XEMC acquired Darwind IP in 2009. The XE128/5.0MW with enlarged 128-metre rotor incorporates a new larger-diameter PMG. The track record includes one onshore prototype and ten operating offshore units (2016) in China. The XE128/5.0MW has a relatively high specific power rating of 398W/m2 for IEC IIB sites, and the successor model is likely to have a lower power rating of 4MW and a rotor diameter of 140 metres. 

24] DSME 7.0MW

South Korea’s Daewoo Shipbuilding & Marine Engineering (DSME) entered the wind industry in 2009 through acquiring German supplier DeWind for a foothold in the fast-growing wind sector. The DSME 7.0MW offshore turbine with 160-metre rotor was announced in 2011, featuring a tube-shape medium-speed drivetrain with flange connections between main-bearing unit, gearbox and PMG, resembling Gamesa G128-4.5 MW and Vestas V164/V174 design choices. But DSME stepped out of wind in 2018 without producing a 7MW prototype.

25] NPS 8.0-175

This 8MW rating and 175-metre rotor specification of US-company Northern Power Systems’ direct-drive turbine concept were highly competitive when unveiled in 2011, especially from a supplier best known for its sub-utility 60-100kW turbines. The NPS 8.0-175’s technology basis was drawn from a 2.3MW turbine with a 93-metre rotor, but this still marked a huge step-up in ambition. A segmented stator was among the innovative features envisaged, but the focus on licensing never bore fruit, no prototype was completed, and NPS folded its US operation in 2019.

26] Sinovel SL6000

The prototype of this 6MW offshore machine was China’s largest turbine when it was installed in 2011. And the future looked promising until untll technology provider/partner US-based AMSC sued the company over alleged software theft. The SL6000 — with a 128-metre rotor diameter built technologically on the SL5000 with a non-integrated high-speed geared drivetrain and DFIG. However, Sinovel was found guilty and has disappeared from the list of leading turbine suppliers with its current status uncertain

27] Aerogenerator-X

UK-based Wind Power introduced a radical 10MW vertical axis turbine concept in 2010, featuring a two-bladed V-shape rotor, 270-metre rotor diameter and double-tip blade winglets for rotor stabilising. The rotor swept area is essentially triangular in shape and modest set against rotor materials input. One could argue that substantial additional area is created between the upward-pointing winglet sections plus a minor area by the downward-pointing winglet sections. The drive system and power electronics are located below the blades’ central mounting area. The project’s status is currently unknown.

28] WinWinD WWD-3 

Finnish company WinWinD was established in 2000, acquiring a MultiBrid license “up to 3MW” from Germany’s Aerodyn consultancy, which had developed and patented the technology in 1996-1997. The 3MW WWD-3 with 100-metre rotor was developed from the fully integrated 5MW MultiBrid M5000 low-speed concept, whereby planetary gearbox, PMG and single rotor bearing are incorporated in a shared load-carrying structural cast housing. Only 20 units were installed (18 offshore) before WinWinD’s bankruptcy in 2013.

29] GE 4.1-113

This discontinued 4.1MW direct-drive offshore turbine with 113-metre rotor was introduced in 2011 with an onshore prototype in Sweden. It was an enhancement of ScanWind’s 3.5MW model with 90.6-metre rotor. GE bought this Norwegian pioneer in 2009, including a 13-turbine heritage at a high-wind coastal site operating since 2007. The GE 4.1-113’s PMG behind the tower concept was claimed to offer “generator design flexibility as well as easy service access and uncomplicated generator exchange without rotor removal”. 

30] WindMaster WM750-E 

The WM750/40 two-bladed prototype with 40.1-metre rotor was among the world’s first 750kW turbines. A 43.4-metre rotor followed in 1995, again fitted with UK-made Aerolaminates (later NEG Micon Rotors) wood-epoxy blades that matched Dutch two-bladed technology preferences. WindMaster Nederland’s 1998 bankruptcy left  only a modest heritage.

Insight report: The 40 most promising wind turbine designs that fell short of expectations – 31-40

Insight report: The 40 most promising wind turbine designs that fell short of expectations – 11-20

Insight report: The 40 most promising wind turbine designs that fell short of expectations – 6-10

Insight report: The 40 most promising wind turbine designs that fell short of expectations – 1-5

How the list was chosen

Success or failure in this context is not limited to how many of the turbines were actually produced or were ever operational.

Products may have been launched as stand-alone models or already envisaged as the basis for a product platform. In some cases, what started as a high-profile product launch, triggering equally high expectations, only made it into the prototype phase, or never even moved past the "paper stage".

The turbines topping the list are considered to rank highest regarding technological and commercial starting expectations, both from the supplier side and expert opinions, set against how it finally worked out. As so often in life, the higher the expectations, the greater the disappointment when these are not met.
The machines nearer the bottom end of the list, in our judgment, are characterised by the highest technical risk and/or the least commercial potential.

It is noticeable that the top 10 contains only "conventional" three-bladed upwind turbines. Of these, nine models incorporate a high-speed or medium-speed geared drivetrain and one a full hydraulic transmission. Direct-drive models are represented lower down the list.

Obviously, all turbines listed had been developed to become a successful serial product, and perhaps a stepping-stone for larger-scale future platform(s). Some of the more radical product developments might,
at the same time, have aimed to transform current wind industry practice, convinced that "state-of-the-art three-bladed upwind technology would ultimately prove a dead-end track".

The risk for radical concept is, by definition, always highest because, as well as having to gain entry to the market, the developer must bear the full costs and risk of the product development and industrialisation and build a new supply chain.

Ever since the start of the modern wind era in the late 1970s, there have been many examples of well-designed commercially successful turbine models, and these often turned into continuously enhanced product platforms. Such success stories include the high-speed geared Vestas 2MW platform introduced in 2000, and the direct-drive Enercon E-66 (1995) that developed into the E-70 E4 (2003) and further models.

Several years earlier, the 300-410kW Kenetech KVS 33M-VS became (one of) the most hyped turbines of that period, but unfortunately came with a "litany of design failures", Windpower Monthly reported in 1997. This innovative, lightweight US-made turbine was developed between 1989 and 1993, already incorporating many features that were far from common at the time but are now semi-standard, such as pitch-controlled variable-speed operation and a flexible power rating. Touted a technological breakthrough, the Wall Street Journal wrote in September 1991: "Energy experts say this new "five-cent machine [0.05$/kWh] could do for wind energy what Henry Ford did for the car."

KVS 33M-VS commercial deliveries commenced in late 1993, but due to a combination of technical failures and other contributing reasons, Kenetech filed for Chapter-11 bankruptcy three years later.

The global wind industry has matured a lot since the Kenetech failure, but things can still work out very differently from initial expectations. This could be for many possible reasons, such as technology and/or product-market related risks, impacts of insufficient company size set against higher than initially expected cost and risks, or the outcome of mergers and acquisitions. And maybe sometimes, the world just isn't ready.

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