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Senvion, or Repower Systems as it was initially called, was established in 2001 through the merger of three small German wind companies: engineering consultancy Pro + Pro, and wind turbine suppliers BWU and Jacobs Energie.

Within a few years it had built a strong reputation for technical competence and advanced products.

Industry analysts were soon rating it alongside Enercon and Siemens Wind Power as a top player in the fast-growing German market.

The foundations for success were laid in the second half of the 1990s when Pro + Pro developed the advanced 1.5MW high-speed geared MD70/77 series as a commercial product.

Its combination of pitch control and variable speed is commonplace today, but at the time was pursued only by a few pioneers, notably Enercon and Lagerwey.

The use of a doubly-fed induction generator (DFIG) was also unusual. The dominantly Danish industry focused on fixed-speed technology during this period, only switching to pitch-controlled variable speed in the early 2000s.

The MD70 prototype was built in 1997 by licensee Jacobs and was initially met with scepticism by the industry.

But the MD70 and its sister model with an enlarged 77-metre rotor proved a remarkable commercial success.

This included licence sales to suppliers including HSW, BWU and Fuhrländer — all now defunct or swallowed up by competitors — and "the biggest fish", Nordex.

Scaling up

The 2MW MM-series launched in 2002 built on the lessons learned from the MD70/77, retaining a non-integrated drivetrain with three-point gearbox support and DFIG.

It became the company’s sole product series with more than 5,000 units operational. It started production with a 70-metre rotor but this was soon supplemented by the MM82 in 2003 and the MM92 in 2005. The MM100 followed in 2011.

The MM100 has faced increasing competition in the low-wind sector in the past few years from more recent product developments with superior specifications, such as the Vestas V120-2.2MW and the Siemens Gamesa SG 2.1-122.

Senvion’s response — uprating to 2.3MW and a 130-metre rotor — brought it fully in line with the competiton, but a prototype was installed only last May in India.

Since August, the first of a new modular 2.XM series has been offered by Senvion India, now operating as an independent business unit.

Senvion became a genuine trendsetter in the 3MW-plus onshore class with the installation of the 3.4MW 3.4M104 prototype in late 2008, the first of its new 3.XM series.

The family has grown with multiple variants produced, most recently the 3.6M140 EBC and 3.7M144 EBC.

The 3.XM series formed the mechanical design basis for the 4.XM class, the key products of which are the 4.2M140 (prototype installed in 2018) and the 4.2M148.

Offshore plunge

Remarkably, Senvion had leapfrogged the 3MW class by starting development of a 5MW offshore-dedicated turbine shortly after the company was formed in January 2001.

This "giant" would also boast the world’s biggest rotor at the time of 126 metres.

This was a bold initiative — propelling the company into the forefront of multi-megawatt turbine design, despite its small (10-12 strong) development team, the overall lack of wind-industry experience of large-scale offshore turbines, and the high-risk conditions associated with an unestablished market.

The 5M series features a conventional non-integrated high-speed drivetrain with a hollow, mass-saving, cast-iron main shaft suported by two bearings, a three-stage gearbox and six-pole DFIG.

The envisaged benefits of this four-point support were an uncomplicated gearbox exchange without having to dismantle the rotor, and optimised gearbox protection against rotor-induced bending moments.

The first prototype was installed onshore during the second half of 2004, months ahead of the Aerodyn-designed 5MW Multibrid offshore turbine.

Equally impressive was the installation of two turbines at the Beatrice project off the Scottish coast in 2006-07 under demanding conditions and record 44-metre water depths.

The 61.5-metre blades were developed by LM Wind Power, and the 5M’s 126-metre rotor diameter retained the offshore size record until 2012.

An upgrade to 6.15MW with an unchanged rotor diameter followed in 2009 with the 6.2M126, which enjoyed some commercial success. But the lack of a much-needed larger rotor in the face of strong new competition in the 6MW segment started gradually eroding the turbine’s business fortunes.

A 6.2M152 prototype with a 152-metre rotor was installed in 2014, but it came too late to turn the tide because by then it was having to compete with the Siemens (now Siemens Gamesa) SWT-7.0-154 and the MHI Vestas V164-8.0MW.

Plans for a 10MW successor in the offshore class were announced in 2017, but the company’s growing financial problems stalled development.

Suzlon takeover

Indian OEM Suzlon took a controlling stake in the company in June 2007, in what was chairman Tulsi Tanti’s most-valued acquistion in a bid to make his company a true global wind industry player.

Suzlon paid about €1.8 billion when the acquistion was completed, selling Hansen Transmission to ZF to ease its huge debt burden.

But the Suzlon group’s financial difficulties had a negative impact on its new German subsidiary’s product development and market expansion opportunities.

Matters weren’t helped by the departure of several prominent wind industry figures, notably R&D head Peter Quell in 2011, and CTO Matthias Schubert in 2013, the year before the company name was changed from Repower to Senvion.

Suzlon sold Senvion to US-based private equity firm Centerbridge Partners in April 2015.

In an accompanying statement, Centerbridge said: "Senvion is a company with impressive technology and leading market positions.

"The global market environment for renewable energies is promising for a wind turbine manufacturer, particularly for one of the most experienced players in the industry with onshore and offshore capacity."

Sadly, the reality turned out differently.