Driving marine machines

Mammoth offshore wind turbines and energy-generating ships could be among the technologies to solve the world’s looming energy crisis. These impressive designs are part of a new class of radical machines created to harness much-needed energy from our oceans waves, winds and currents.

While innovative marine technologies are gaining popularity, the more conservative supply chain has been trailing behind. This, however, could soon be about to change. Investment in the sector is increasing and component manufacturers are getting ready to grab a slice of the market.

Since 2010, for instance, £3bn worth of private-sector investment has been pumped into renewable energy in the UK. Offshore wind alone is expected to become a £78bn global industry by 2020. The overall marine energy industry is forecast to be worth £6.1bn to the UK economy by 2035, creating nearly 20,000 jobs.

The machines that promise to generate this revenue are breaking new ground and drives, motor and gear suppliers are now doing the same. ‘The pace of innovation is perhaps quicker than it has ever been,’ said Felix End, Rockwell’s European product manager for low-voltage drives. ‘Equivalent drives are now half the size that they were even just 10 years ago, meaning more and more is possible.’

One area where this has become particularly clear is in offshore wind. Traditional wind turbines use a gearbox between their rotor and the standard generator. But over the past few years, a different technology that eliminates the gearbox has been gaining popularity. Instead it uses a low-speed, permanent magnet generator that manufacturers claim reduces failures and cuts cost.
Siemens and GE were the first to replace the traditional gearboxes and high-speed generators with direct drives and bigger low-speed generators. ‘Starting as early as 2020, we will offer our customers technologies that allow offshore wind power to be produced for less than €0.10 per kilowatt hour,’ said Siemens Wind Power chief technology officer Henrik Stiesdal at a conference
in November.

Installing these wind turbines is an impressive feat. By their very nature, offshore energy systems are placed in some of the most extreme locations. Components will face crushing waves, powerful winds and freezing temperatures. Attempting to repair a broken drive, gear or motor is a difficult task offshore and could jeopardise the entire project.

Component manufacturers are turning to unique solutions to test new products. Last year, the National Renewable Energy Centre (Narec) unveiled a facility that it claims will reduce the risk for engineers and help increase investment in the sector. Dubbed ‘Project Nautilus’, Narec has developed the world’s first drive-train test area dedicated to the marine renewables sector.

The 3MW drive system allows engineers to perform faster lifetime testing of new tidal power generation. It is capable of testing the complete drive train and electrical generation, as well as control and support systems. ‘We can replicate, on demand, about six months of tidal conditions that you would otherwise have to wait a couple of years to occur within the actual environment,’ said Tony Quinn, operations director at Narec.

‘We can run tidal turbines, for instance, through some very demanding simulated operating environments in a relatively controlled, benign environment,’ he added. ‘It’s about robust testing but it’s also about the team of engineers here that is able to analyse and help that innovation and design… projects of this nature are rare; they are one-off in terms of scale and technicalities.’

Rather than test separate components, Nautilus is able to test complete systems including the turbine, generator and power converter. For instance, a 20:1 reduction gear box develops output shaft torque and rpm characteristics that represent the ranges typically experienced by tidal stream drive-train systems. Meanwhile a 3,256kW motor, weighing almost 60 tonnes, can deliver high torque similar to that found in offshore energy systems.

Nautilus will be crucial for more radical concepts of generating power from the seas. One particular project that could benefit is a concept for a ship that is powered by the ocean’s waves. Not only does this drive the vessel, but the energy generated can also be stored and sent back to shore to supply the grid without the need for subsea cables. 

Created by Boston University and the Fraunhofer Centre for Manufacturing Innovation, the proposed ship would be 50m long.
It is designed to harvest wave energy through a number of buoys hanging from the side of the ship. The buoys move up and down with the movement of the waves and cause the pivoting arms to drive a generator creating 1MW of electrical power an hour. The power is stored in an onboard battery with a capacity of 20MW. A 20-hour journey gives the ship’s battery a full charge.

But while this might reduce the cost of getting wave power back to shore, ships such as this come with their own unique challenges for component manufacturers. ‘The three major challenges for marine propulsion remain those of vibration, temperature and space. Modern drives that meet and exceed low vibration certification are helping with the first of these issues, but they also need to be reliable in high temperatures,’ said End.

While Rockwell’s drives are not used in the Boston wave-energy ship, End claims that challenges of technologies such as this will drive innovation. ‘The internet capability of increasing numbers of components is an exciting trend,’ he said. ‘It’s often referred to as the ‘internet of things”, particularly outside of the industrial sector and is something we observe throughout industry as a very exciting and essentially limitless source of innovation. In the marine environment, linking the drive to the control system is just the start.’

Innovative testing, design and connectivity could drive real change in the market and bring in much-needed investment. The inner mechanics of marine energy systems are some of the most advanced available. It now remains up to the component manufacturers to work together to get deeper and further into the most powerful reaches of the world’s oceans.