TODAY’S STUDY: BIG, BIGGER AND BIGGEST WIND TURBINES

The astonishing thing about the report highlighted below is how absolutely boring and tedious it is.

In a writing style that could only be from an engineer, the study finds the building of a TWENTY MEGAWATT wind turbine entirely feasible. That would be a single windmill FOUR TIMES as big as the biggest in service today, a single machine capable of providing enough electricity for 4,800 U.S. HOMES.

The report doesn’t waste hyperbole on this remarkable conclusion but is entirely matter-of-fact: “No significant problems have been found when upscaling wind turbines to that scale,” it reports, “provided some key innovations are developed and integrated. These innovations come with extra cost, and the cost / benefit ratio depends on a complex set of parameters.”

The wind industry continues to be an inspiration for the community of people fighting to redeem this world from those who would, as Jackson Browne said, “forge its beauty into power.”

The industry has, for the last three decades, steadily expanded its capacity to turn the restless winds of this ever-changing world into the power that lights the night and cools the day.

It has stumbled. Among its earliest utility-scale undertakings was one of the most poorly sited projects ever built. But it learned from its mistakes and did not repeat them.

Despite the best efforts of its enemies to mischaracterize its accomplishments, the wind industry goes on building and fighting back against discredited claims with cold hard facts.

Birds: 1 in 10,000 bird deaths are due to wind turbines. House cats are more threatening.

Emissions: Introducing wind dramatically reduces overall climate change-inducing greenhouse gases.

Cost: Wind is so cheap it is probably irresponsible of utilities not to buy and build it.

Subsidies: Because it does not have a century or more of subsidies from U.S. taxpayers behind it like its fossil fuel competition and a half-century of subsidies like its nuclear competition, wind does get larger per-megawatt year-by-year federal support today. All governments always support their best energy bets as a matter of national security. Wind’s competition is just going to have to get used to being out of favor.

Health: Claims of “wind turbine syndrome” have been discredited by blue ribbon medical panels in the U.S. and Canada

Hazards: Turbines have been safely integrated into every kind of landscape around the world without increased incidence of fire, altered ambient climate or pollution.

Noise and shadow-flicker: With appropriately sited turbines, there are no such impacts.

Property values: Studies show appropriately sited turbines do not affect real estate prices.

Aesthetics: While there is no arguing against those who find turbines unappealing, surveys show people generally find them an acceptable or even elegant and exciting addition to the horizon in developed areas.

Since it began gathering momentum around 2005-06, the wind industry has provided more than a third of all new electricity generating capacity built in the U.S. and more than the coal and nuclear industries combined.

The industry’s goal, which the U.S. Department of Energy during the Bush administration found entirely feasible, is to provide 20 percent of the nation’s power by 2030.

Meanwhile, wind’s visionaries are thinking about unprecedentedly powerful turbines that will live far offshore, away from human objection, where recent studies show they will benefit ocean life.

Wind’s master builders will do it in their usual matter-of-fact way, but not without commitment or satisfaction. They already know what Walt Disney, King of the Imagineers, once noted: “It's kind of fun to do the impossible.”

UpWind; Design limits and solutions for very large wind turbines – A 20 MW turbine is feasible
March 2011 (European Wind Energy Association)

Summary – A 20 MW turbine is feasible

The need for the UpWind project: exploring the design limits of upscaling

The key objective of the European wind industry‘s research and development strategy for the next ten years is to become the most competitive energy source by 2020 onshore and offshore by 2030 1, without accounting for external costs.

In October 2009, the European Commission published its Communication “Investing in the Development of Low Carbon Technologies (SET-Plan)”, stating that wind power would be “capable of contributing up to 20% of EU electricity by 2020 and as much as 33% by 2030” were the industry‘s research needs fully met. The wind industry agrees with the Commission‘s assessment. Significant additional research efforts in wind energy are needed to bridge the gap between the 5% of the European electricity demand which is currently covered by wind energy, and one-fifth of electricity demand in 2020, one-third in 2030 and half by 2050.

Meeting the European Commission‘s ambitions for wind energy would require meeting EWEA‘s high scenario of 265 GW of wind power capacity, including 55 GW of offshore wind by 2020. The Commission‘s 2030 target of 33% of EU power from wind energy can be reached by meeting EWEA‘s 2030 installed capacity target of 400 GW wind, 150 GW of which would be offshore. Up to 2050 a total of 600 GW of wind energy capacity would be envisaged, 250 GW would be onshore and 350 GW offshore. Assuming a total electricity demand of 4,000 TWh in 2050 this amount of installed wind power could produce about 2,000 TWh and hence meet 50% of the EU‘s electricity demand.

Thus a significant part of the required future installed wind power will be located offshore. For offshore application new technologies and know how are needed beyond the existing knowledge base, which is mainly focused on onshore applications. Going offshore implies not only new technologies but also upscaling of wind turbine dimensions, wind farm capacities and required – not yet existing – electrical infrastructure. The need for upscaling found its origin in the cost structure of offshore installations and is the “motor” of modern wind energy research. The results will not be applicable to offshore wind energy technology only, but will also lead to more cost effective onshore installations.

Ultimately, all research activities, aside from other implementation measures, are focused on reductions to the cost of energy. The industry is taking two pathways towards cost reductions in parallel:

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Incremental innovation: cost reductions through economies of scale resulting from increased market volumes of mainstream products, with a continuous improvement of the manufacturing and installation methods and products;

Breakthrough innovation: creation of innovative products, including significantly upscaled dedicated (offshore) turbines, to be considered as new products. The UpWind project explores both innovation pathways. In formulating the UpWind project the initiators realized that wind energy technology disciplines were rather fragmented (no integrated verified design methods were available), that essential knowledge was still missing in high priority areas (e.g. external loads), measuring equipment was still not accurate or fast enough, and external factors were not taken into consideration in minimising cost of energy (grid connection, foundations, wind farm interaction).

In order to be able to address all shortcomings in an effective way a comprehensive matrix project structure was designed, where disciplinary, scientific integration and technology integration were included (see page 18). A key issue for integrating various research results was developing an overall engineering cost model.

This unique UpWind approach quantifies the contribution of the different types of innovation resulting from the project. Not only are upscaling parameters incorporated, but also innovation effects are defined as a separate independent parameter. At the time of writing the full results of the integration process through cost modelling was not yet available, but will be published in 2011. However, some early conclusions may already be drawn, such as the benefits of distributed aerodynamic blade control.

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The question often arises whether there is one single “optimum” technology. UpWind did not seek to define one unique optimum technology but rather explored various high-potential solutions and integrated them with respect to the potential reduction of cost of energy. An optimised wind turbine is the outcome of a complex function combining requirements in terms of efficiency (electricity production), reliability, access, transport and storage, installation, visibility, support to the electricity network, noise emission, cost, and so on.

UpWind‘s focus was the wind turbine as the essential component of a wind electricity plant. Thus external conditions were only investigated if the results were needed to optimise the turbine configuration (e.g. grid connection options) and the other way around (control options for wind turbines) in order to optimise wind farms.

UpWind did not seek the optimal wind turbine size, but investigated the limits of upscaling, up to, approximately, 20 MW / 250 m rotor diameter. Looking at very large designs, attention is focused on physical phenomena or model behaviour that are relevant for large-scale structures but have negligible effects at lower scales.

For instance, the development of control methods for very large rotors requires the full wind behaviour, including wind shear and turbulence, to be taken into account. This in turn means the anemometer values must be corrected based on the rotor effects and therefore advanced wind measurement technologies need to be used. UpWind therefore developed and validated the measurement devices and models able to provide such measurements (LIDAR).

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UpWind also developed the tools and specified the methods to enable large designs. These tools and methods are available to optimise today‘s designs, and are used to improve the reliability and efficiency of current products, such as drive trains. UpWind demonstrates that a 20 MW design is feasible.

No significant problems have been found when upscaling wind turbines to that scale, provided some key innovations are developed and integrated. These innovations come with extra cost, and the cost / benefit ratio depends on a complex set of parameters. The project resulted for instance in the specification of mass /strength ratios for future very large blades securing the same load levels as the present generation wind turbines. Thus in principle, future large rotors and other turbine components could be realised without cost increases, assuming the new materials are within certain set cost limits.

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UpWind methodology – a lighthouse approach

For its assessment of the differences between the parameters of the upscaled wind turbine, UpWind adopted a reference 5 MW wind turbine. This reference was based on the IEA reference turbine developed by the National Renewable Energy Laboratory's (NREL). As a first step, this reference design was extrapolated (“upscaled”) to 10 MW. The 20 MW goal emerged progressively during the project, while the industry in the meantime worked on larger machines. The largest concepts which are now on the drawing board measure close to 150 m rotor diameter and have an installed power capacity of 10 MW. While a 10 MW concept progressively took shape, UpWind set its mind to a larger wind turbine, a turbine of about 250 m rotor diameter and a rated power of 20 MW. Also the idea of the lighthouse concept was adopted to present the many
results of UpWind in one image.

The lighthouse concept is a virtual concept design of a wind turbine in which promising innovations, either mature or embryonic, are incorporated. The lighthouse is not a pre-design of a wind turbine actually to be realised, but a concept from which ideas can be drawn for the industry’s own product development. One of the innovations, for example, is a blade made from thermoplastic materials, incorporating distributed blade control, including a control system, the input of which is partly fed by LIDARs.

The 20 MW concept provides values and behaviour used as model entries for optimisation. It is a virtual 20 MW turbine, which could be designed with the existing tools, without including the UpWind innovations. This extrapolated virtual 20 MW design was unanimously assessed as almost impossible to manufacture, and uneconomic. The extrapolated 20 MW design would weigh 880 tonnes on top of a tower making it impossible to store today at a standard dockside, or install offshore with the current installation vessels and cranes.

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The support structures able to carry such mass placed at 153 m height are not possible to mass manufacture today. The blade length would exceed 120 m, making it the world‘s largest ever manufactured composite element, which cannot be produced as a single piece with today‘s technologies. The blade wall thickness would exceed 30 cm, which puts constraints on the heating of inner material core during the manufacturing process.

The blade length would also require new types of fibres to resist the loads.

However, the UpWind project developed innovations to enable this basic design to be significantly improved, and therefore enable a potentially economically sound design.

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UpWind: 20 MW innovative turbine

Key weaknesses of the extrapolated virtual 20 MW design are the weight on top of the tower, the corresponding loads on the entire structure and the aerodynamic rotor blade control. The future large-scale wind turbine system drawn up by the UpWind project, however, is smart, reliable, accessible, efficient and lightweight.

A part of UpWind (WP3) 3 analysed wind turbine materials. This enabled the micro-structure of the blade materials to be studied and optimised in order to develop stronger and lighter blades. However, this would not be sufficient unless fatigue loading is also reduced.

Reducing fatigue loading means longer and lighter blades can be built. The aerodynamic and aeroelastic qualities of the models were significantly improved within the UpWind project, for example by integrating the shear effect over large rotors WP2. Significant knowledge was gained on load mitigation and noise modelling.

UpWind demonstrated that advanced blade designs could alleviate loads by 10%, by using more flexible materials and fore-bending the blades (WP2).

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After reducing fatigue loads and applying materials with a lower mass to strength ratio, a third essential step is needed. The application of distributed aerodynamic blade control, requiring advanced blade concepts with integrated control features and aerodynamic devices.

Fatigue loads could be reduced 20-40% (WP2). Various devices can be utilised to achieve this, such as trailing edge flaps, (continuous) camber control, synthetic jets, micro tabs, or flexible, controllable blade root coupling.

Within UpWind, prototypes of adapting trailing edges, based on piezo electrically deformable materials and SMA (shape memory alloys) were demonstrated (WP1B.3). However, the control system only works if both hardware and software are incorporated in the blade design. Thus advanced modelling and control algorithms need to be developed and applied. This was investigated in WP1B3.

Further reducing the loads requires advanced rotor control strategies (WP5) for “smart” turbines. These control strategies should be taken into account in the design of offshore support structures (WP4). The UpWind project demonstrated that individual pitching of the blades could lower fatigue loads by 20-30%. Dual pitch as the first step towards a more continuous distributed blade control (pitching the blade in two sections) could lead to load reductions of 15%. In addition, the future smart turbine will use advanced features to perform site adaptation of its controller in order to adapt to local conditions (WP5).

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Advanced control strategies are particularly relevant for large offshore arrays, where UpWind demonstrated that 20% of the power output can be lost due to wake effects between turbines.

Optimised wind farm layouts were proposed, and innovative control strategies were developed, for instance lowering the power output of the first row (thus making these wind turbines a bit more transparent for the air flow), facing the undisturbed wind, allowing for higher overall wind farm efficiency (WP8).

Control and maintenance strategies require load sensors, which were adapted and tested within UpWind.

To avoid sensor failures causing too much loss of energy output, loss of sensor signals was incorporated into the control strategies (WP5) and a strategy was developed to reduce the number of sensors. The fatigue loading on individual wind turbines can be estimated from one heavily instrumented turbine in a wind farm if the relationship of fatigue loading between wind turbines inside a wind farm is known. The so-called Flight Leader Concept 4 was developed in WP7.

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Those load sensors can be Bragg sensors, which were tested and validated within the project (WP7). UpWind demonstrated the efficiency and reliability of such sensors, and assessed the possibility of including optic fibres within the blade material without damaging the structure (WP3).

However, using sensors implies the rotor is only reacting to the actual loading phenomenon. As a result of the system inertia, the load will be partly absorbed.

A step further is to develop preventative load alleviation strategies by detecting and evaluating the upcoming gust or vortex before it arrives at the turbine. A nacelle mounted LIDAR is able to do this (WP6), and can be used as an input signal for the individual blade pitching, or in distributed blade control strategies (WP5).

In recent years, UpWind has been a focal point for LIDAR development, and has considerably helped the market penetration of LIDAR technologies. Although LIDARs are still considerably more expensive than SODARs for instance, their technical performance, and thus potential, is substantial. UpWind demonstrated that LIDARs are sufficiently accurate for wind energy applications. (WP1A2). LIDARs can be used for the power curve estimation of large turbines, for control systems, for resource assessment in fl at terrain, including offshore and soon in complex terrains (WP1A2 and WP6), and for measuring the wind shear over the entire rotor area.

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UpWind demonstrated the need to take the wind shear into account for large rotors (WP6 and WP2). The 20 MW rotor is so large that the wind infl ow needs to be treated as an inhomogeneous phenomenon. One point measurement, as recommended by IEC standards, is not representative anymore. A correction method was developed and demonstrated within UpWind.

The smart control strategies and high resolution modeling described above require a highly accurate wind measurement, since a small deviation can have a significant impact on reliability. In the metrology domain, UpWind considerably improved knowledge on wind measurement accuracy within the MEASNET 5 community. Cup anemometers, LIDARs, SODARs and sonic anemometers (WP1A.2 and WP6) were tested, demonstrated and improved. UpWind‘s WP1A.2 had access to almost all existing wind measurement databases.

The advanced control strategies of smart blades using smart sensors enable loads to be lowered considerably, so lighter structures can be developed. The improved modelling capability means the design safety factors can be less conservative, paving the way to lighter structures (WP1A1). UpWind investigated this path, developing accurate integral design tools that took into account transport, installation, and operation and maintenance (O&M). Onshore, the transport of large blades is a particular challenge, and UpWind developed innovative blade concepts (WP1B1) enabling a component to be transported in two sections without endangering its structural safety or aerodynamic efficiency.

Integral design tools were also developed to improve the reliability of the entire drive train (WP1B.2), and to investigate the possibility of developing proportionally lighter generators for large wind turbine designs. UpWind investigated ten different generator configurations and found promising potential weight reductions for permanent magnet transversal flux generators.

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The UpWind project worked on ensuring the reliability of large turbines, in particular for far offshore applications.

UpWind focused on condition monitoring technologies (WP7) and fault prediction systems. Such advanced systems enable fault detection and preventative maintenance to be carried out, with a large potential for cutting O&M costs. The reliability of the future large blades can be assessed using probabilistic blade failure simulation tools (WP3).

Reducing the loads and the nacelle weight enables the offshore substructure design to be optimised (WP4). UpWind developed integrated wind turbine/substructure design tools and investigated optimal offshore substructure configurations according to the type of turbine, type of soil and water depth. Future deeper water locations were investigated and innovative cost-effective designs were analysed.

Progress was made on deep water foundation analysis, including the development of advanced modeling techniques and enhancements of current design standards which for example become very important for floating designs.

With the improved intelligence of wind turbines, wind farms are operated more and more as power plants, providing services to the electricity system, such as flexibility and controllability of active and reactive power, frequency and voltage, fault-ride-through or black start capabilities (WP9). Those capabilities will allow for substantially increased penetration of wind power in the grid in the near future. The future large offshore wind farms, far from shore, will be connected to HVDC VSC, forming the backbone of an integrated European offshore grid, and supporting the emergence of a single electricity market.

It will be challenging for the wind energy sector to attract and train the required number of engineers, postgraduates and PhD students to fulfil its needs. UpWind focused on training and education (WP1A3), and developed free of charge advanced training modules on wind energy, including the latest innovations in the field. This content is distributed through the REnKnow database 6.

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UpWind: rooted in history

UpWind is the largest-ever EU-funded research and development project on wind energy. In terms of scope, content and volume, the project can be compared to typical national R&D programmes carried out in countries like Denmark, Spain, the Netherlands and the USA. The UpWind project was made up of 48 partners, all leaders in their field, half from the private sector, and half from the research and academic sector. This makes UpWind the largest public/private partnership ever designed for the wind energy sector.

The story of the UpWind project starts in 2001. At that time, the 2001 renewable electricity directive (2001/77/EC) was facilitating the rapid growth of wind energy in Europe. By the end of 2000, the installed wind capacity in Europe was 13 GW. Growth was based on 1 to 2 MW wind turbines, the work horses of that time, and demonstrators of 4 to 5 MW were under development, showing the potential for upscaling and innovation.

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Large cost reductions were envisaged. However, the wind energy sector needed to considerably accelerate its innovation rate if the energy objectives were to be achieved.

An innovation accelerator was required that could set clear pathways for future development and rapidly transfer technological advances to the market. In order to shape such a vehicle, the wind industry created what was known as a ‘ Wind Energy Thematic Network ’ (WEN), an initiative supported as a project by the European Commission. Through an extended consultation process, WEN identified the key innovation areas and put forward recommendations to address the declining public R&D funding in the wind energy sector. The WEN placed wind energy innovation in the context of the newly adopted Lisbon strategy for the first time 7 : wind energy was identified as being able to improve European competitiveness.

In 2005 WEN published a roadmap for innovation, which was the first Strategic Research Agenda for the wind energy sector. This document was used as a basis for the European Wind Energy Technology Platform. TPWind updated the Strategic Research Agenda and developed an industry-led master plan with a total R&D budget of €6 billion up to 2020: the European Wind Industrial Initiative (EWI). The recently created European Energy Research Alliance (EERA) reinforces this trend by putting more emphasis on long-term research. The UpWind proposal and consortium, financed by the European Commission under the sixth Framework Programme (FP6), was developed in parallel with the creation of the Technology Platform by the sector involving individual key institutions and companies with the European Academy of Wind Energy (EAWE) and the European Wind Energy Association (EWEA) as essential catalysers. Building on UpWind‘s achievements, EERA and EWI together cover the main road of designing the European wind energy technology of the future and helping to meet the EU‘s 2020 renewable energy targets, and beyond.

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UpWind: continuous innovation

UpWind is one of the few integrated projects launched under FP6. Integrated projects were designed to cover the whole research spectrum. Due to the broad range of innovation challenges to be covered in a single field, such projects required a high level of coordination and consistency. Due to their size and complexity, high demands were put on the management. An innovative management concept was designed, enabling research to be carried out on specific issues, both scientific and technological ones, while at the same time integration of the results was guaranteed.

These considerations led to a matrix structure shown below. In this structure, scientific and technical disciplines are dealt with within horizontal work packages (WP‘s), and integration through vertical activities. The vertical activities are themselves grouped into scientific and technology integration work WP‘s respectively. The earlier mentioned lighthouse approach 8 forms the focus of the WP1A.1 Integrated Design Approach and Standards and WP1B.4 Upscaling. All other WPs provide inputs.

In addition to defining a clear way forward for wind energy technology, UpWind had the responsibility of accelerating innovation within the sector. This required strong involvement from the private sector. The involvement in UpWind of leading wind turbine and component manufacturers, as well as software providers, technical consultants and energy companies, demonstrated the sector‘s high level of maturity. Handling Intellectual Property within large EU-funded projects was secured by IP agreements and was dealt with inside the WP concerned. This proved to be a very effective model.

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The strategy followed by UpWind was to focus on innovation with a long-term aim: exploring the design limits of very large-scale wind turbines, in the 10-20 MW range.

UpWind used upscaling as a driver for innovation, and moved away from the competitive arena. Along the way, the challenges dealt with in UpWind became a reality, with the demonstration of 5 MW turbines, the current testing of 7 MW machines, and the development of 10 MW designs. The innovation developed within the project helped solve day-to-day challenges, such as was the case in the field of WP1B.2 Transmission and Conversion. UpWind had an international impact, through the IEA Wind Implementing agreement, where the UpWind results are included in several international task activities. Partnerships, especially in the field of material research (WP3), were developed with India, Ukraine and China.

In terms of project financing, UpWind shows the way forward for public-private partnership instruments. The scale of today‘s challenges, and the scarcity of resources require developing innovative funding instruments able to create a leverage effect. Those should combine funding from the Framework Programmes, other Community programmes and Member States, private capital, and European Investment Bank instruments.

The future FP8 instruments are likely to be fl exible, with less red tape, and their structure is likely to be shaped by the time-to-market of innovation, and able to combine those various sources of funding in a coordinated manner. Although UpWind was financed under the FP6, some specific WP activities were co-financed by Member State programmes beyond the financial scope of UpWind. One outstanding example is the development of LIDAR remote sensing techniques (WP6). This made UpWind the first project within the European Wind Initiative priorities that complemented support from the Framework Programmes with coordinated calls for proposals from committed countries. Within EWI, UpWind is used as a reference case for such instruments.