Machine sizes have been increasing for many years, one of the most important factors in driving down the cost of wind energy. In 2011 the average wind turbine installed in Germany was 2.24MW, almost 10% higher than the average in 2010. Today's turbines have twice the power rating of those just a decade ago. The rate of increase in machine size steepened significantly last year, partly due to many early, smaller machines being decommissioned.
Larger machines deliver lower costs of energy for a number of reasons. They are taller and so intercept the higher wind speeds found at greater heights. They also make more efficient use of materials, particularly in the tower and foundations. The tower of a 100-metre-diameter machine is not double the weight of that of a 50-metre machine, which is important because towers typically account for 30% of the cost of a wind turbine.
There are other reasons why larger machines drive lifecycle costs down. If there are 100 machines of 5MW in an array, rather than 200 machines of 2.5MW, that means less maintenance and hence lower costs. Also, losses from wake in the 100-machine array will be less.
Economies of scale
Building bigger arrays can be another route to lowering costs. Large projects spread the costs of site investigations, for example, including wind measurements; for a 30MW site, a typical cost would be EUR30/kW, compared to only EUR2/kW for a 1GW site. There are also savings in cable connection to shore, and use of specialist transport and installation equipment is also more effective for larger sites. More efficient operation-and-maintenance strategies can also be used andbanking and legal fees should be lower per kilowatt.
Improvements to the basic technology of wind turbines are expected to deliver a number of small improvements in several areas. Direct-drive machines are increasingly common and these are usually variable speed; this delivers limited extra amounts of energy compared with fixed-speed types of similar size. Control systems are important as they enable blade pitch and rotor yaw to track the wind in magnitude and direction. Siemens has a $4 million contract from the US Department of Energy to investigate the use of passive aerodynamic control technologies capable of significantly improving the aerodynamic performance of blades.
The prospects for two-blade machines - especially for offshore use - have been debated for some years and some manufacturers are investigating the possibilities (see page 11). Such machines would be lighter, but the dynamics of two-blade rotors are more complex and they are slightly less efficient, so there is a trade-off.
Being a newer area of interest, the prospects for offshore cost reductions are possibly greater than for onshore. There is much interest in floating turbines because, while wind speeds generally increase with distance from shore, so does water depth. There is a rough consensus that fixed foundations may be usable up to a depth of 30-40 metres, but beyond that floating designs may be more cost-effective. Data is needed to substantiate this hypothesis.
An important contribution to lowering costs is simply experience. In any technology, increased manufacturing activity generally leads to lower costs from improved methods of manufacture. Before steep increases in material costs around 2006-08 upset prices, several studies had indicated that every time production doubled, it led to an 8-15% reduction in wind-turbine costs. With material prices now more stable, there are indications that this trend is re-emerging.
Q: IN YOUR SPECIALIST FIELD, WHAT TECHNOLOGICAL IMPROVEMENT WOULD MAKE THE BIGGEST CONTRIBUTION IN THE NEAR FUTURE TO CUTTING WIND ENERGY COSTS? BELOW ARE SOME INDUSTRY RESPONSES
TURBINE SIZE AND ROTOR DIAMETER
Norbert Giese Vice-president of offshore wind development, Repower Systems
Turbine size and rotor diameter are likely to make the biggest contribution to reducing the cost of offshore wind energy. Bigger turbines will mean higher yields and therefore more efficient wind farms. In essence, the more kWh per turbine, the lower the cost of energy.
As the industry ventures further from shore, where the wind conditions are more favourable, the 6MW-plus class turbines will come into their own.
Design and technological improvements can help reduce material costs - Repower cut the material costs of its MM92 turbine by 25% in the past four years. Component costs will fall as makers start producing high-volume, standardised parts. Currently many component parts are made to order, which is inefficient but inevitable in early stages of development.
Industrial partnerships will also lower costs. At present tower, foundations and the interface between them are developed independently. By encouraging collaboration at design, production and installation stages, we can produce highly efficient turbines that are cheaper to build.
Jyrki Virtanen Senior vicepresident technology, Moventas
Combine the wind-turbine gear with the generator to cut costs in turbine construction. Reduce the complexity of the system to increase reliability which, on a drive-train level, will lead to the integration of independent equipment to hybrid systems. On a gear level, this means a smaller number of components.
Design concepts are based on load-sharing techniques. Minimal total mass is achieved with optimised and verified load sharing between the components that transmit the load. Lower weight and smaller size of direct drives enables savings in transport and assembly, as well as producing a much shorter drive train than a conventional one.
BETTER ELECTRICITY INFRASTRUCTURE
Jim Platts Lecturer, Cambridge University manufacturing department
The task for this decade should be to improve the public debate on strategic development of the electricity infrastructure. There is no public understanding of the geographically particular nature of the wind-energy resource or its individualistic, minute-by-minute, hour-by-hour, day-by-day time distribution.
There are glaring examples of low-capacity wind farms close to the existing grid and of potentially good wind farms that are still unconnected, as in China. We need to discuss the resource, its nature and the whole technical system of the infrastructure that is involved in tapping it effectively.
We should be aiming for turbines with a lifecycle of 40 years - elements of infrastructure with a life of only 20 years are little more than toys.
Then we must get to grips with mass production of wind farms offshore. Leanness is a key concept in design for manufacture, and rhythm and flow are central to cost-effective manufacture itself.
Heavy, materials-intensive foundations offshore miss the point. Fortunately, there may be some progress towards lighter, guyed towers, as Finland has figured that there is way to cut through all this mess. Add composites, and you have a route to really light weight and seriously long fatigue life.
Christoph Mertens Managing director, Dong Energy
The biggest potential to bring down energy cost in the wind industry will be provided by logistics. There will be new logistical concepts on how to overcome the challenge of building large wind farms more cost-effectively.
Also important is the design of new foundations that are lighter and more easy to install than the traditional monopile. These will tie in effectively with future logistical and installation concepts.
Marie Hartis Management consultant, Parker Hannifin
Power conversion for wind turbines is only as good as the grid available to receive it and dispense (or store) the energy as needed. Energy conversion and storage solutions are emerging that will need to be packaged into convenient containers at the source, for easy tie-in to the energy grid. Visionary integrators are working to deliver these solutions, which can not only harvest energy, but also store it in virtual silos for proper distribution when needed, at an affordable cost and with minimal energy waste.
DESIGN PHASE COLLABORATION
Luc Themelin Chief executive officer, Mersen
To reduce production costs, numerous turbine manufacturers are still tending to choose the cheapest solutions, even for critical components. And yet opting for an apparently less costly solution often impairs performance and can give rise to high maintenance costs.
As manufacturers now offer their customers long-term maintenance contracts, they need to consider the total cost of ownership of a wind turbine over its entire lifetime rather than merely its production cost.
It is vital to involve suppliers of critical components from the design phase of a turbine model, in order to develop a technical solution to extend the service life of the components or implement predictive maintenance via remote monitoring. For example, an optimised design of carbon brushes can more than double their service life. Maintenance costs are reduced immediately.
Re-engineering solutions for such components in wind turbines in operation are already available, and can pay for themselves in less than 18 months. Wind farm operators should work more closely with suppliers of critical components so that together they can develop technical solutions to deliver more efficient and thus less costly wind energy.
LONG-LASTING BATTERY ALTERNATIVE
Nick Cataldo Senior vice-president of sales and marketing, Ioxus
The adoption of ultracapacitors in wind turbine systems can lower the total cost of ownership and drive down the cost of wind energy generation.
High reliability is required for a cost-effective operation, and typically, the maintenance cost of the energy storage system in a wind turbine outweighs the cost of a replacement system - especially offshore.
Current ultracapacitors last more than ten years as opposed to battery life of two to four years. They require little maintenance, and perform well under a wide range of temperatures.
Use of ultracapacitors can save on both cost and the potential danger associated with wind-turbine maintenance.
TIMELY FAULT DETECTION
Manfred Mauntz Managing director, CMC Instruments
Large wind turbine roller bearings frequently suffer early failures before the nominal end of life of the bearing is reached. Cracks develop from friction-induced vibrational peak loading.
Implementing a continuously working online oil sensor can identify potential damage to mechanisms and detect early wear to allow timely maintenance and control of the running conditions below tolerance levels. Early corrective action will reduce downtime and maintenance costs.
BETTER MAINTENANCE PLANNING
Peter Tavner President, European Academy of Wind Energy
We need to pay more attention to the performance of offshore wind turbines and manage the costly logistics of servicing them. Offshore plants are huge, distributed, remotely controlled power stations so we must take lessons from the nuclear, coal and gas industries, where maintenance and operational performance is carefully planned for maximum performance. Among these lessons are that maintenance must be planned to coincide with fair weather; and when technicians are dispatched to site they must be equipped with the tools and spares to ensure that they can realistically resolve any fault.
As an industry we still seem to try to address each problem as it arises on an ad hoc basis. This just won't do; it is costly and counterproductive. Let us use high-quality project management, operations research and straightforward asset-management skills to cut costs.
THE RIPPLE EFFECT
Mikael Jakobsson Chief operating officer, 2-B Energy
There is no golden nugget in offshore wind power that alone provides substantially lower cost of energy. An offshore wind turbine must be designed as an integrated part of the whole power plant, where choices are carefully weighed between risk and the ripple effect on all the various aspects of the wind farm. An integrated approach allows tailored designs and interfaces for optimal cumulative affect, achieving more cost-of-energy savings.
Examples of new designs choices where early consideration of the ripple effect resulted in innovation and savings, as well as reduction of risk, include: simpler blade and rotor design to offer safer access and lower costs; full helicopter operations and landing access to avoid wave-height and fuel restrictions, reduce personnel needs and improve safety and availability; and new machine head installation leading to fewer lifts and possible operation in higher wind-speed conditions.
These examples are doable today, with proven designs to a great extent, without the need for exaggerated risk or design innovation. The key is for leading companies with established design teams to step out of their comfort zones and seek integrated, project-wide solutions to develop lower cost products for future wind farms.