The wind turbines of the 21st century are quite different. Tall, white and sleek, nearly always three-bladed, made of a complex mixture of fibreglass, carbon, wood and steel, it might seem to a casual observer that wind turbines everywhere, from Sweden to Spain, look pretty much the same these days.
Yet although this may be close to the truth for onshore wind energy, anyone who keeps half an eye on the latest news from the industry will be familiar with the rapidity at which new offshore technology is developed and tested. Perhaps this is why, despite near unanimity from the industry on the likely development of onshore technology in the next ten years, the voices diverge on what offshore wind energy will look like.
“The offshore sector is going to change enormously by 2020”, says Nicolas Fichaux, Head of Policy Analysis at EWEA. “But the shift in onshore technology will be more subtle – the turbines will look similar but be more efficient. It’s like cars – ten years ago, cars looked like they do now, but their motors were much less fuel-efficient. Now you’ve got a similar looking machine that’s much safer and more fuel-efficient.”
Onshore machines may increase slightly in size to around 3-4 MW, is the general consensus, but further growth would be hampered by the problems of transporting them. “What’s happened in the onshore sector is similar to what happened in the aircraft industry in the 1970s”, explains Peter Jamieson from Garrad Hassan. “Basically planes got bigger and bigger and then around 1975-6, thegrowth slowed. It was the same for wind turbines, which grew in size and capacity up to 2003, when we reached a plateau. I think some wind turbines larger than at present will appear but further growth in unit turbine size will slow down a lot or even stop in the next ten years.”
The motto of the offshore sector, on the hand, sometimes really does seem to be “the sky’s the limit”. “Ten years ago when we started working on the Lillgrund offshore wind farm in Sweden, we put in 1.5 MW turbines and we couldn’t imagine anything bigger”, recalls Goran Loman from Vattenfall. “If we were to build it today, we would be using 3.5 or even 5 MW turbines.”
This rapid offshore turbine development is likely to continue, although where we will be in 2020 is up in the air (figuratively and, given the growing height of offshore turbines, pretty literally as well). Estimates range from those sceptical about anything over 7 MW to enthusiasts for 10 and even 20 MW offshore turbines in the next decade.
“The difficulty with offshore turbine growth isn’t the logistical issue we have onshore, but a physical problem”, explains Henrik Stiesdal from Siemens Wind Power. “It all boils down to the square cube rule, which means that as the surface area of an object is squared, its volume is cubed. For example, while small birds fly easily, larger ones need a run-up, because their weight is proportionally much greater. So if an offshore turbine doubles in size, its blades will be four times longer but its weight is cubed.”
If there is at least agreement on all sides that offshore turbines will get substantially bigger still by 2020, if not by how much, it is less clear how far out to sea the industry can go by then. Floating platforms, which would open up deeper waters for development, are currently being tested, although several different models are currently available.
“I can see floating platforms beginning to take off around 2020”, says Jason Jonkman of the US National Wind Technology Center. “At the moment the prototypes are all very expensive, but by 2020 they should be cost-effective.” While Stiesdal sees commercial projects with floating turbines beginning in around five years, Loman is less sure.
“Although there are full-scale prototypes being worked on, we still have a long way to go”, he says, and also mentions the possibility of concrete foundations, which would be far cheaper than steel. There is a similar range of views on the feasibility of two-bladed offshore wind turbines, which in theory are much simpler and lighter than three-bladed ones, with higher tip speeds, but whose use onshore is restricted because they make more noise. “Two-bladed turbines don’t make sense – they are too complicated to build, due above all to the higher tip speed and the unbalanced forces in the rotor hub”, believes Jens Gösswein of RePower. “The perfect wind turbine has three blades.”
One of the most complex issues surrounding offshore wind development at the moment is operations and maintenance, which is estimated to cost on average €16 per MWh, and is dependent on weather conditions and the availability of repair vessels and cranes. Jamieson is cautiously optimistic. “In the mid-1990s, we had onshore wind turbine designers being restricted in the components they were creating because economically available cranes had a limit on the weight they could carry for the installation. Ten years later, the crane companies were making cranes to suit wind farm installation. The same sort of change can take place in technology for installation and access to offshore wind farms.”
Jonathan Wheals and Giles Hundleby from engineering company Ricardo mention the possible development of intelligent monitoring systems in the next ten years. “The idea is that the system can identify a likely failure early and predict the time to failure, so repairs can be much better planned and costs are brought down”, explains Hundleby. “It would even allow you to manage the operation of the turbines so that three or four turbines could be repaired at once”, adds Wheals.
One of the components that most often presents maintenance issues is the gearbox. Currently, the main manufacturer of turbines without a gearbox is Enercon, although these are only used onshore. Fichaux believes that in 2020 both types will still be in circulation.
“Turbines with gearboxes will become more reliable and compact, with some of the problems ironed out. For turbines without gearboxes, the generator will get smaller”. Stiesdal is convinced there will be no more gearboxes in new offshore wind turbines by 2020, whereas Wheals and Hundleby argue that there will be, because “reliability problems are being overcome with better design tools and with a gearbox you will have the lowest tower top mass, which is important as turbine sizes increase”.
Many issues surrounding wind energy technology in 2020 and beyond remain surrounded by debate. It is a sign of the offshore sector’s relatively rude health that all these possibilities are open to discussion, and it is only to be expected that, as with any quickly maturing technology, there are diverging opinions on which possibilities will be realised. Two goals that most industry players are unanimous in striving to achieve however are greater efficiency and better reliability. It seems a commonly held conviction that component development through R&D – the rotor blade design, the control system, the pitch system –will certainly lead to improvements in both areas.
If offshore R&D is essential for greater efficiency and bringing costs down, financing is essential for offshore R&D. Via the European Commission’s Strategic Energy Technology Plan, the wind energy sector is proposing a €6 billion long-term research, development and demonstration programme for wind energy, called the European Wind Initiative (EWI). The sector has a list of key areas the EWI and European R&D must focus on to bring the costs of both onshore and offshore wind farms down. These include optimised wind farm design, increased turbine reliability and offshore substructures.
Ten years ago, in 1999, the first offshore wind farm – at Vindeby in Denmark – was just eight years old. Horns Rev I, the first farm to be built more than a few kilometres out to sea, was still two years away. Today, there are nearly 1.5 GW of installed capacity in Europe. The sector has evolved enormously in a decade and provided it gets enough R&D financing, and that this is spent in the right areas, it will certainly evolve further in the next one.