Vestas takes 2MW platform to next level

DENMARK: Three years after launching the V110-2.0MW turbine, Vestas has further extended its 2MW platform with new models aimed at low wind markets. Windpower Monthly was given exclusive access to the new models.

Vestas' new V116 and V120 2MW turbines are its fifth upgrade on the platform
Vestas' new V116 and V120 2MW turbines are its fifth upgrade on the platform

Vestas is planning to install prototypes of the new V116-2.0MW and V120-2.0MW in late 2017 and early 2018 respectively, with the first deliveries following later in 2018.

Vestas' current 2MW flagship, the V110-2.0MW has a competitive specific power rating of 210W/m2, but that has been comfortably surpassed by the new V116 and V120 models, according to 2MW product manager Mads Hovmøller Mortensen.

"The V116-2.0MW for IEC IIB features 189W/m2 and will complement the V110 at better low- and medium-wind sites," he said.

"The V120-2.0MW offers a record-low 177W/m2 for IEC IIIB and focuses specifically on low and ultra-low wind speed markets and regions in the US, India and China," he added.

"Our overall product-market strategy is to maximise annual energy production and minimise the levelised cost of energy at wind-farm level."

This is being achieved by keeping down cost increases and Opex, the Capex-related fitment of new, larger rotors, retaining the main structural dimensions, and to continue building on proven technology and supply-chain principles.

Goals also included keeping product changes to the absolute minimum and reducing complexity whenever feasible.

Big seller

There are more than 18,000 Vestas 2MW turbines operating in 45 countries, making it one of the most widely sold turbine platforms ever.

Last year, Vestas took an order for 1,000 units from one customer alone when MidAmerican selected the V110 model for its six-site 2GW Wind Xl project cluster in Iowa.

The success story started in 2000 with the launch of the pitch-controlled variable-speed V80-2.0MW, which was developed and refined from the semi-variable speed V66-1.65MW turbine introduced in 1997.

The 39-metre blades of the now discontinued V80-2.0MW (398W/m2 specific power rating) were at the time considered about the maximum length the industry could deliver as a series product.

And because IEC wind classes were only introduced in 2001, these turbines were applied at a wide variety of sites, from high-wind offshore (Horns Rev 1) to typical low-wind regions such as inland Germany.

Enlarged 90-metre rotors were introduced to the 2MW platform in 2004, followed by 100-metre rotors five years later.

In 2014 Vestas upgraded the V100-2.0MW for IEC IIB sites and introduced the V110-2.0MW aimed at IEC IIIA and IEC S.

From the start, the 2MW series machines were fitted with doubly fed induction generators (DFIG), apart from a short period from 2011 when Vestas switched to permanent magnet generators (PMG) for the Gridstreamer models incorporating a new ZF gearbox, manufactured in a new purpose-built facility in the US.

But Vestas switched back to DFIG in 2012, and this proven generator type is incorporated in the new V116-2.0MW and V120-2.0MW, together with a matching converter offering improved grid capabilities.

"You need volume to attract large suppliers like ZF and Winergy, but there are benefits in significantly reduced costs, plus simultaneous product quality and efficiency boosts," said Mortensen.

"In 2010, there were still challenges regarding the gearboxes, but the successful collaboration led to a steep learning curve."

The exchange of ideas also contributed to developing in-house capabilities such as performing dedicated up-tower gearbox repairs. Evaluating the entire electric-power conversion-system value chain further showed that a DFIG with partial converter was a highly efficient and economical solution.

Vestas has retained the proven 2MW platform gearbox design — consisting of one planetary gear stage and two helical parallel gear stages — for the V116 and V120, considering it a more economical solution than the two planetary and one helical gear stage alternative.

"Perhaps most important, we can still fully meet 20-year gearbox design life," said Mortensen.

Another important product development was keeping the dimensions and mass of the nacelle and hub unchanged, and mounting the full drivetrain in the nacelle for easier and cheaper transport.

"Unchanged nacelle dimensions, and staying within the 70-tonne maximum nacelle mass with the drivetrain mounted, enables standard, rather inexpensive road and rail transportation in main market US," added Mortensen.

"A second benefit is that each complete nacelle can be tested and pre-commissioned before leaving the assembly plants."

Enhanced control

The Vestas design team also wanted to retain the standardised blade-root diameter, despite the inevitably higher loading with the longer V116 and V120 blades.

This enabled the hub's outer dimensions to remain unchanged, again easing road, rail and sea transport in the US and China.

The multiple technical challenges were tackled in different, complementary ways. "The first measure was switching from four-point ball-type pitch bearings to three-roller-type units, offering higher load capacity and elongated bearing life," Mortensen said.

"This is essential due to the use of 'classic' independent blade control (IPC), which involves continuously re-adjusting individual blade pitch angles during each rotation, and inevitably leads to higher pitch-action frequency. In parallel, the capacity of the hydraulic pitch system was increased for enhanced control capabilities of the longer blades."

A second measure involved opting for a slender structural-shell-type blade design with carbon incorporated in the shells and a simplified central single-web structure (internal reinforcement beam).

The aerofoils are now more rounded for higher structural stability without compromising aerodynamic performance. The result, according to Mortensen, is the mass of the V120 blade is only 500-600kg greater than the five-metre shorter V110 unit, while further work has helped reduce manufacturing costs.

The rotor-swept area of the V120 is more than double that of the old V80, offering up to 40% higher AEP, with the maximum gain at the least favourable IEC III wind sites. Set against the V110, swept area has increased by 19% resulting in about 7% higher AEP at 7.5m/s wind speeds, while Capex and Opex have been kept low.

"Major efforts in achieving platform-product synergies and overall business-case optimisation across the value chain have added together to offer a substantial positive impact on LCOE," said Mortensen.

"The V120-2.0MW reaches rated power at 10.5m/s, which makes it a winner under specific environmental-economic circumstances, such as those in the Los Angeles area, when little wind coincides with high energy prices."

Swept-area benefits

Regarding the benefits of larger rotors over a higher rating, and focusing on sites constrained by capacity, Mortensen quoted an interesting example.

He compared the V120-2.0MW model with a hypothetical V110-2.4MW turbine, each producing about 10GWh under given mean wind speed conditions.

A site with a maximum capacity of 200MW could be equipped with either 83 V110-2.4MW machines or 100 V120-2.0MW models. The lower-rated turbines would generate a 19% higher AEP across the project, due to the larger cumulative rotor-swept area.

"A larger rotor with unchanged power rating creates huge benefits in offering more stable production at lower wind speeds. Set against the daily wind distribution at a typical site, it means a faster power-curve response, less variability, and higher certainty in turbine performance and output," explained Mortensen.

Low and ultra-low wind sites in the US, India and China will also greatly benefit from the availability of matching high towers to supplement the large rotors.

"If at ultra-low wind sites the wind speed at hub height could be raised by 1m/s, this will have a huge impact on AEP and the overall business case," says Hovmøller Mortensen.

"We are currently evaluating several tower options for these specific markets, and we will offer a wide range of hub heights.

"This varies from 80 metres at sites in the US where the 500-foot rule applies [equivalent to a tip height of 152 metres], to 137 metres and beyond in other markets."

Vestas globalised the platform strategy in 2012, industrialising integral parts of the supply chain while ramping up in-house and external overall capabilities.

"Key aspects of industrialisation are working on standardisation and modularisation within and across platforms," he said.

"It further requires great flexibility in addressing new challenges like the auction systems being introduced in Germany, Brazil and Spain, and translate different market demands in the right products.

"Time to market is thereby essential, and, equally important, how quick can we scale products as well as ramp-up production capacity?"

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