Thanet windfarm

Offshore wind targets need more than optimism

Mark Venables warns that the offshore wind industry’s rosy image glosses over some areas of serious concern.

When the great and the good of offshore wind energy congregated in Amsterdam in November for the EWEA Offshore 2011 conference it was hard not to ride the wave of optimism sweeping through the assembled throng. Yet despite the positive messages emanating from the industry’s proponents, it is clear that there are some significant hurdles to overcome before the technology’s true potential can be realised.The EU has set itself a target of providing 20 per cent of energy consumption from renewable sources, within which the UK’s individual target is 15 per cent. To have any hope of achieving this there must be a big expansion in wind energy, but it will not be easy.

The vast majority of new installations are planned offshore in the unforgiving North Sea where – aside from the inhospitable conditions – water depth and distance from shore are considerable challenges. New designs are required for both foundations and turbines, a shortage of suitable installation vessels will hamper construction and, even without those hurdles, an undersea grid is needed to get the power back to shore.

Even if the giant Round Two and Three wind farms overcome these obstacles and move from the drawing board to construction and operation, the logistics of maintenance and accessibility have still to be surmounted.

Listening to the evangelical rhetoric in Amsterdam it was difficult to maintain a pessimistic demeanour, but there are lingering, nagging doubts.

On the face of it the facts make compelling reading. According to the European Wind Energy Association (EWEA) more than 141GW of offshore wind energy capacity has been built, is under construction, consented, or planned in Europe: enough to power 130 million average EU households. These wind farms would provide 13.1 per cent of Europe’s electricity production.

But there lies the first real disconnect between the talk and reality. Only 4GW, less than 3 per cent of the promised capacity, is operating and generating electricity – leaving 137GW still to come online. Much of that admittedly impressive total has yet to move from the drawing board, stalled by planning, financial or technological shortcomings.

EWEA estimates that by 2020, 40GW of offshore wind capacity will produce 148TWh annually, meeting over 4 per cent of the EU’s total electricity demand and avoiding 87 million tonnes of CO2 emissions. Between 2020 and 2030 a further 110GW of offshore wind capacity is expected to be added in European waters. 150GW of wind power would produce 562TWh a year, enough to cover 14 per cent of the EU’s 2030 electricity demand and avoid 315 million tonnes of CO2 emissions.

The principal cheerleader was Arthouros Zervos, president of EWEA. “There is huge developer interest in offshore wind energy across Europe”, he declared. “Developers, governments and investors realise that offshore wind energy offers the growth and jobs that Europe desperately needs.”

He pointed to the economic benefits – citing 169,000 jobs in the EU offshore wind energy sector that are expected to be created by 2020, going up to 300,000 by 2030.

Zervos highlighted what he called “several areas for growth”, though the more level-headed observer might regard these as significant hurdles that the industry needs to overcome. The key areas include turbine and turbine component manufacturing as well as substructures, vessels, electrical infrastructure including high voltage subsea cables, ports and, above all, connections.

But not surprisingly, given the current economic climate, the largest hurdle is seen as financing. Zervos warned that if the offshore wind energy sector’s potential is to be fulfilled in Europe, it is imperative that sufficient levels of financing are brought in by investors. Quite where that will come from is unclear, given the reluctance of financial institutions to fund anything less than a cast iron investment, while national governments are scrambling to cut expenditure. Almost certainly the brunt of the cash will have to come from the power sector, but that will require a firm political commitment guaranteed for the life of the investment. Given the recent debacle over solar power feed-in tariffs, that would seem to be wishful thinking in the extreme.

Over the coming two decades, offshore wind will need to move rapidly from an emerging, immature technology if it wants to be a key component of the EU’s energy mix. Going hand in hand with that maturity, competition across the supply chain will need to increase through an influx of significant new entrants if costs are to be reduced to a manageable level.

On that front at least, the portents are promising. The industry, having invested heavily in the sector, is responding with an impressive and growing list of manufacturers developing new wind turbines specifically for offshore installation. It is estimated that the supply of turbines will meet and exceed demand for the next decade, leading to healthy levels of competition within Europe and the potential for export to emerging markets.

Looking at turbine technology it is readily apparent that for offshore applications size matters. The majority of the turbines in operation at present are below 4MW. The largest offshore wind farm is Thanet, which boasts 100 Vestas V90 turbines that can each generate 3MW. Other manufacturers are pushing the boundaries – Enercon for example has the E126 that is rated at 6MW – but that is not expected to be enough.

The EU-funded UpWind project, which was completed in 2011, looked at the design limits on upscaling and evaluated the feasibility of a 20MW turbine. Despite some key weaknesses it provided a significant amount of positive feedback. One area of investigation for the extrapolated virtual 20MW design was the weight on top of the tower, the corresponding loads on the entire structure and the aerodynamic rotor blade control.

The conclusion was that by reducing fatigue loading, longer and lighter blades could be built. The aerodynamic and aeroelastic qualities of the models were significantly improved by integrating the shear effect over large rotors. Advanced blade designs could alleviate loads by 10 per cent, by using more flexible materials and fore-bending the blades.

However, even after reducing fatigue loads and using materials with a lower mass-to-strength ratio, a third essential step will be needed: the application of distributed aerodynamic blade control, requiring advanced blade concepts with integrated control features and aerodynamic devices.

Various devices can be used to achieve the reduced fatigue loads, such as trailing edge flaps, (continuous) camber control, synthetic jets, micro tabs, or flexible, controllable blade root coupling.

Given that sites for new projects are moving further from shore and into deeper waters, the key incentive is to develop offerings that are tailored specifically for offshore. To offset the costs involved in such challenging projects, there is a clear trend towards reducing the cost of energy through lessons learnt, improved reliability and structural efficiency. Design trends are driving the supply chain towards specialisation – partially decoupling it from the onshore wind industry and developing specific offshore solutions.

The move into deeper waters will see space-frame structures – that is, wind turbine substructures which use several piles to keep the turbine stable – having an increased market share, with new fixed and floating structures in the longer term. Nevertheless, improved fabrication and installation procedures could also enhance the depths at which monopiles are used.

But one critical bottleneck is subsea cables. There is a limited range of suppliers for high voltage (HV) submarine cables due to high investment costs and long lead times for new capacity, and without increased capacity in manufacturing, cable shortages are likely.

Other equipment is generally drawn from much larger transmission and distribution (T&D) industries which are relatively unconstrained, with the exception of HV transformers, where delivery times are set by general world demand.

Those challenges aside, the time is ripe for wind’s big push given the global disdain for nuclear power since the accident at the Fukishima plant in Japan, allied with the continued aversion to traditional fossil fuel generation. But the sense is that the window of opportunity is closing. And the jury is still out regarding the industry’s ability to live up to its hype.

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