Wind Power Technology Development By IEA

No single element of onshore wind turbine design is likely to dramatically reduce cost of energy in the years ahead, but there are many areas where design can be improved, which, taken together, could considerably reduce the life cycle cost of wind energy. Notably, this road mapping exercise concluded that greater potential remains for technology breakthrough in the offshore sector than in the land-based wind sector.

Three technology areas specific to wind energy require particular attention and apply to both onshore and offshore wind. These areas include wind energy resource assessment, including characterisation and forecasting methods; wind turbine technology and design; and supply chain issues. In the light of continually evolving technology and to ensure high reliability, standards and certification procedures will be crucial to the successful deployment of new wind power technologies.

Metrics for quantifying technology improvements

One way to quantify efficiency improvements in wind energy extraction is by measuring the increase in electricity production while holding the rated power of the turbine and the quality of the wind resource constant. In other words, for the same installed capacity, in the same place, the additional energy produced (via, for example, operation over a wider range of wind speeds, or reduced losses) represents the increased efficiency gained, for example, by implementing a new technology.

The capacity factor is a measure of energy production, and represents the ratio of the actual output of a power plant over a period of time and its output if it had continuously operated at full capacity over that same period. For wind generation it is typically used to express the quality of wind resources in different locations.

However, it can also be used as a metric to measure improvements in energy extraction as described above. An advantage of using the capacity factor metric to measure efficiency improvements is that it is used for all electricity generating technologies, and so enables comparisons to be made across a large scope of technologies. The US DOE has developed a summary of wind turbine performance improvements expressed in terms of capacity factors.

Set standards for resource assessment

There is a need for standardised methods for computer modelling of the resource, data gathering and onsite measurement of wind resources. Resource data are particularly sparse in developing countries as well as for wind at heights above 80 metres. Standardised data collection and analyses near demand centres and existing transmission infrastructure are of particular value in the near-term.

A computer model of the wind resource alone is insufficient basis for building a wind farm. Modelled data must be compared against real data gathered in the field. Anemometry masts, which measure the wind speed at a certain height, are the usual method, but are costly, particularly offshore. Remote sensing using SODAR or LIDAR technologies, and computational fluid dynamics (CFD) techniques to model air flow, have the potential to provide a reliable alternative in time.

These technologies are already available but need to be refined and validated to be a realistic alternative to mast anemometry. Models are needed to accurately depict wind patterns in different types of land features such as ground cover, coastlines and hills, which greatly complicate the way wind behaves. In 1982, the IEA Wind Implementing Agreement coordinated an important field experiment that examined the effect of low hills on the flow of wind.

The Askervein Hill Project in the Outer Hebrides, off Scotland, comprised 50 measurement masts and yielded data that remained the basis for modelling for the next 25 years. Japanese research is ongoing to develop wind models for complex terrains, based on analysis of meteorological data at more than 300 locations, and the use of remote sensing in mountainous terrain.

Data are also needed on wake effects, the influence of one turbine on the air flow incident on another turbine. This phenomenon can have serious implications for energy capture, which can be reduced by as much as 10% within a wind power plant. Wake effects are particularly persistent offshore, and can influence energy capture among neighbouring wind plants. This is likely to become a more serious factor by 2030 as larger numbers of offshore wind plants are installed in greater proximity to each other.

Share wind resource data

A shared database of information on the availability of wind resources in all countries with significant deployment potential would greatly facilitate the development of new projects. The compilation of wind characteristics over large areas – greater than a 200 km radius – could also significantly increase understanding of the extent to which distance can smooth the aggregated output profile of widely dispersed plants.

Commercial sensitivity concerns need to be addressed by the industry to establish which data can realistically be included. The database should include details of wind variability, average speeds and extreme speeds, and link to other databases of the solar resource, site topography, air temperature, lightning strikes, and seismic activity.

Improve wind forecasting accuracy

Improving the predictability of wind resources will increase the economic value of wind-generated electricity in the power market by helping producers meet delivery commitments. Discrepancy between the volume of electricity scheduled for delivery to the market and the amount actually delivered results in a supply imbalance that must be offset by flexible plants and other resources, and which in some cases incurs a penalty to the producer.

The most flexible, rapidly dispatching plants, such as open cycle gas turbines (OCGT), have expensive fuel requirements. More accurate, longer term output forecasts would increase the extent to which plants with less rapid dispatch times but cheaper fuel requirements, such as coal and combined cycle gas turbines, can be scheduled to balance fluctuating wind output on the system.

Advanced forecasting models should be developed that use meteorological data, online data from operating wind plants, and remote sensing technology. Once validated, it is important that such models are implemented by power system operators.

Improved wind turbines

Develop stronger, lighter materials to enable larger rotors, lighter nacelles, and to reduce dependence on steel for towers; develop super-conductor technology for lighter, more electrically efficient generators; deepen understanding of behaviour of very large, more flexible rotors. Ongoing. Continue over 2010-2050 time period.

Build shared database of offshore operating experiences, taking into account commercial sensitivity issues; target increase of availability of offshore turbines to current best-in-class of 95%. Complete by 2015.

Develop competitive, alternative foundation types for use in water depths up to 40 m. Ongoing. Complete by 2015.

Fundamentally design new generation of turbines for offshore application, with minimum O&M requirement. Commercial scale prototypes by 2020.

Develop deep-water foundations/sub-surface structures for use in depths up to 200 m. Ongoing. Complete by 2025.

Accelerate reduction of turbine cost

Onshore wind turbine development is now characterised by incremental reductions in the cost of energy, rather than by single, disruptive technology leaps. Deeper understanding of the conditions to which a wind power plant will be subjected over its lifetime will facilitate the development of improved turbine designs with the ability to extract more energy from the wind, more of the time, over a longer lifetime, and in specific operating environments (e.g., areas of higher typhoon activity or extreme cold).

Energy capture in the rotor holds the greatest potential for long-term reduction of the cost of wind energy. The larger the area through which the turbine can extract that energy (the swept area of the rotor), and the higher the rotor can be installed (to take advantage of more rapidly moving air), the more power that can be captured. However, a larger swept area typically means a heavier rotor, which is needed to cope with increased loading during high wind events, and increased costs. This factor has effectively set an economically optimum rotor size, based on cost-effective materials available today.

Advanced materials with higher strength to mass ratios, such as carbon fibre and titanium, could enable larger area rotors to be cost-effective, but their usage has yet to be made commercially feasible. Additional cost reductions could be achieved through lighter generators and other drive train components, which would reduce tower head mass. New materials could also encourage a transition away from industry’s current dependence on steel for taller towers.

As rotors become larger with longer, more flexible blades, a fuller understanding of their behavior during operation is required to inform new designs. Notable rotor-research areas include advanced computational fluid dynamics models; methods to reduce loads or suppress their transmission to other parts of the turbine, such as the gearbox or tower head; innovative aerofoil design; nanotechnology to reduce icing and dirt build-up; and lower aerodynamic noise emission.

Additional cost savings can be achieved through technology developments that reduce electrical losses in the generator and attendant electrical/electronic components. Enabling technologies include innovative power electronics, use of permanent magnet generators, and super conductor technology.

Improve offshore turbine performance

Greater reliability of all components, such as gear boxes and generators, is an important objective in the offshore context. High access costs and often narrow weather windows mean that a new balance needs to be struck between upfront investment costs and subsequent O&M costs – a balance that places a higher premium on reliability. Reliability and other operational improvements would be accelerated through a greater sharing of operating experience among industry actors, including experiences related to other marine technologies such as wave and ocean current technologies.

Unlike the early stages of the offshore oil and gas industry, to date there is little evidence of information sharing among entities in the offshore wind industry; however a database of operating experiences is currently under development at the German Institute for Wind Energy Research and System Integration (IWES), which could represent a potential nucleus for wider, international research cooperation.

Again, commercial sensitivities will be important, but a way should be sought to make operational data available through a shared database, possibly facilitated by government actors, to accelerate learning industry-wide. Current “best in class” operating availability of 95% should be adopted as a target for the offshore sector as a whole.

Design dedicated offshore turbines

Although a number of companies are field testing turbines purpose-built for the offshore environment, most offshore wind turbines today resemble “marinised” onshore wind turbines. Because the real requirements of wind technology in offshore conditions remain insufficiently understood, conservative design practices have been adopted from other offshore industries for use in turbine design. These persisting uncertainties need to be resolved so design processes can build in more appropriate (potentially lower) safety margins.

A new generation of more robust turbines should be developed that are designed from the very beginning for the offshore environment. The design of “dedicated” offshore turbines would be based on specific offshore operating conditions. The combined effects of different loads on all parts of the wind turbine and foundations, as the marine atmosphere interacts with sea waves and currents, is worthy of particular focus.

One possible development pathway could be a turbine with two blades rotating downwind of the tower, with a direct-drive generator (no gearbox), and simplified power electronics. Turbine capacity could be as much as 10 MW, with a rotor 150 m in diameter. It should require minimal onsite O&M.

To achieve this, it could be equipped with system redundancy and remote, advanced condition monitoring and self-diagnostic systems, which would reduce the duration and frequency of on-site repairs. Such approaches would also help prevent the escalation of minor faults into serious failures that result from delayed access to the site owing to poor weather conditions.

Design new deep-water foundations

The foundations of most offshore projects to date consist of a single pile driven into the seabed, called a monopile. Current monopile designs make up about 25% of the total investment and installation costs.

New types of foundations, developed with improved knowledge of the subsurface environment, may present significant potential for cost reduction. At this time, apart from the experimental offshore turbines off the Scottish coast (at 44 m), no offshore wind farms are known to be operating in depths greater than 30 m which is where some of the best offshore wind resources are found. Other designs using tripod, lattice, gravity-based and suction bucket technologies should be developed for use in water depths up to around 40 m.

For deeper water, new floating designs will need to be demonstrated and readied for commercial deployment. Again there may be opportunity for technology transfer from the offshore oil and gas industry. Development of new designs has already begun. In December 2007, a floating platform prototype was deployed off Sicily, while another prototype is scheduled for deployment off the Norwegian coast in 2009.

Supply chains

Develop internationally standard education and training strategies for the complete range of skills needed, from design to deployment. Complete by 2015.

Accelerate automated, localised, large-scale manufacturing for economies of scale, with an increased number of recyclable components. Ongoing. Continue over 2010-2050 period.

For offshore deployment, make available sufficient purpose-designed vessels; improve installation strategies to minimise work at sea; make available sufficient and suitably equipped large harbour space. Sufficient capacity by 2015.

As a result of successful growth and policy support, wind energy has grown tremendously over the past decades. However, this has given rise to bottlenecks in supply of key components, including labour. These must be resolved if the hundreds of thousands of new turbines necessary to meet this roadmap’s vision are to be made a reality. Strong supply chains will provide stability and predictability for investors. The roadmap has identified several areas where the industry and public partners can make significant progress.

Develop wind workforce

To achieve the vision of this roadmap, a large, skilled workforce will be needed to develop new designs, establish new manufacturing plants in new locations, develop installation technologies, and to build, operate and maintain the resulting wind power plants.

However, trained personnel are in short supply. For example, in the United States, the number of engineers graduating from power engineering programmes today is one-quarter of its level in the 1980s. The US national Science and Technology Council currently predicts that the number of graduates in science and engineering degrees will continue to fall for the next 40 years.

This reflects a trend that is occurring in a number of other industries and will need to be reversed. Strong governmental support can help the establishment of education and training activities to create the needed workforce. For example, in June this year the US Department of Labor announced the designation of USD 500 million (EUR 340 million) for clean energy job training.

In Europe, a number of training programmes are provided, with centres of excellence located at specific universities. The European Academy of Wind Energy hub links the key institutions. However, the wind industry needs a more concerted and coherent training framework that offers comparable qualifications from a wide range of institutions and regions.

Make stronger supply chains

Pathways to increase manufacturing efficiency include improvements in serial production and automation of manufacturing as well the location of factories nearer to installation sites. These strategies reduce transport costs and import taxes and provide for more efficient means of turbine delivery. Serial production can in some cases hinder technology development since large-scale, automated manufacturing can be an impediment to quick implementation of recent innovations.

A balance needs to be struck between expanded production and technology innovation. Supply chain pressures are severe in the offshore market segment. At present, the offshore market is closely linked to the land market; i.e., demand for more land turbines restricts the supply of offshore turbines. At least one major manufacturer has reserved part of its manufacturing capacity for offshore production. Governments should consider supporting testing, manufacturing and assembly processes located in specially designed harbours in the vicinity of resource rich areas.

International Energy Agency