Success or failure in this context is not limited to how many of the turbines were actually produced or were ever operational. Eize de Vries explains the criteria for the selection and describes numbers 31-40 in the first part of this special report
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.
31| XEMC Darwind XD115/MW
The prototype of the 5MW XD115/5.0MW is installed at the Dutch Zephyros Z72 development.Main characteristics include a small nacelle, PMG, 115-metre rotor and unusually high 108m/s rated tip speed. Darwind IP was sold to XEMC Windpower of China in 2009. Two onshore prototypes were built in the Netherlands (2011) and China (2012).
32| Bard 6.5
This 6.5MW turbine (below) with an unchanged 122-metre rotor diameter was intended as the successor to Bard’s 5MW offshore machine, and a first scaling step towards a 7MW-plus vision. The drivetrain comprised a Winergy Multi-Duored distributed gearbox and two PMGs fitted inside existing Bard 5.0 nacelles. Two onshore prototypes were built in 2011, but development ceased with Bard’s 2013 bankruptcy.
33| Condor 5
This radical, lightweight 5MW medium-speed offshore concept with two-bladed 122-metre upwind rotor was introduced in 2011. It built on 1.5MW Gamma research turbine experiences during the 1990’s in Italy. Unique features included a flexible teeter hub, blades with fixed pitch angle, “active yaw” output control, and very high 127m/s rated tip speed. Condor was discontinued without a prototype.
34| 10MW AMSC SeaTitan
US-based technology provider AMSC issues third-party licenses. This 10MW offshore concept “in an advanced development stage” is perhaps the world’s first with a compact direct-driven superconductor generator. The original SeaTitan featured a 164-metre rotor diameter until 2010, since enhanced to 190 metres. Head mass is around 500 tonnes, though, which is achievable by conventional turbines such as the MHI Vestas V174-9.5MW.
35| NedWind NW53/NW55
The pioneering fixed-speed active-stall controlled NW53 with two-bladed rotor and 52.6-metre rotor was the earliest commercial 1MW turbine at its launch in 1993. The rotor was later enhanced to 55 metres. It featured an unusual distributed gearbox with four generators mounted in the nacelle rear. NEG Micon acquired NedWind in 1998, leaving behind only a modest NW53/NW55 heritage.
36| 2B Energy 2B6
The 6.2MW 2B6 with 140.6-metre rotor (399W/m2) is a radical two-bladed downwind offshore turbine with a claimed design life of 40 years. The turbine is mounted on a wide-base lattice-type truss tower that extends to the seabed. The nacelle has a self-aligning “soft jaw” system. The non-integrated high-speed geared drivetrain incorporates a main shaft with two bearings, gearbox and DFIG. A prototype has been operating since 2015.
37| SWAY ST10
This striking 10MW direct-drive concept with a 164-metre rotor featured an “open” 25-metre spoked PMG. The blade pitch bearings were positioned around 15 metres off rotor centre, allowing shorter blades and direct coupling between the blade support structures for short optimised load path. The company filed for bankruptcy in 2014, with no prototype built.
38| VertAx 10MW
The UK-based VertAx 10MW announced in 2009 is a concept for a high-wind vertical-axis offshore turbine with H-shaped Darrieus rotor, 140-metre rotor-diameter and 110-metre blade length. Innovative features include modular-design “foldable” blades with skeletal load-carrying structures and aerodynamic cladding, plus two PMGs at the tubular upper tower section. No prototype has been built.
39| Vortex V3500
New Zealand’s Vortec Energy announced a 3.5MW diffusor-augmented turbine in 2000, targeting a 20% LCoE reduction against similar-rated free-flow equivalents. Diffusor technology allows more air drawn through given size blades. The V3500’s 54-metre rotor in a duct was mounted at a lattice-steel support structure with a ground-based yaw system. Vortec filed for bankruptcy some years later.
40| AirGenesys 11MW
The pitch-controlled 11MW Airgenesys concept unveiled in 2012 featured two three-bladed 103-metre rotors at opposite nacelle sides with 30-degree blade offset. Each drives a single-stage planetary gearbox and their coupled output shafts power a step-up bevel gear. The vertical output shaft drives 12 generators at a rotating flywheel circle in the tower base. The project status is unknown.