Wind power energy is one of the beacons of hope among the various sources of renewable energy. But exactly how "ecological" are wind turbines in reality when taking into account every relevant aspect over their entire life-cycle?
These include the energy necessary to manufacture, produce and transport the materials from which they are made all the way through to the energy used in their installation, operation and dismantling. In a scientific article in Environmental Science & Technology, a research group from the ETH Zurich, Empa and Radboud University, Nijmegen (Holland) has provided a new perspective on this topic. They conclude that the larger the wind generation plant, the greener is the electricity that it produces.
According to the main author of the study, Marloes Caduff, this effect is due to a combination of plant size and the lessons learned by manufacturers as their experience increases over time. Doubling the performance of a wind turbine does not automatically mean that twice as much energy and materials are necessary to construct it. In fact it requires only slightly more energy to build wind energy plants on a large scale than it does for small ones. Caduff adds that of the main reasons why electric power produced by large-scale plants is greener is because the manufacturers are gaining experience and learning from each other, thus accelerating progress in the design and construction of these systems. This has meant for example that the shape of the rotor blade could be quickly optimized, allowing better exploitation of the available wind power without the necessity of increasing the size of the turbine tower or generator head.
Wind turbine manufacturers now have about 30 years of development experience under their belts. In 1980 the average rotor diameter was about 15 meters; today plants exist whose rotor diameters are up to 10 times larger, for example those in the «Alstom Haliade 150» offshore installation off the French coast. Scientists working on methodologies for ecobalance life-cycle analyses have also been able to take advantage of these three decades of technological development. A team of Empa researchers headed by Hans-Joerg Althaus is investigating if the development of wind turbine plants is following the same defined set of rules as any other "new" technology. After all, they too must follow the path from drawing board to prototype to pilot plant to become a reality. The results of the continuous further development and up-scaling of wind turbine plants are now feeding into the methodology of life cycle analyses, making it possible to take into account new technologies in a meaningful way when appropriate.
Reliability is the key attribute of a turbine today, particularly offshore. There are many other important measures of wind turbine performance, notably the cost per unit of electricity generated, but they count for little if a turbine breaks down. And how do you investigate reliability? Test, test some more – and then test again.
Besides reliability, wind turbine testing proves a new design’s validity and shows how well a sub-system — or the complete turbine — actually performs in practice. Testing component-level performance and reliability is also vital: accurately predicting the lifespan of critical elements like main bearings or generators allows operators to plan servicing and replacement throughout a turbine’s lifetime.
Manufacturers have long had their own test facilities, but there are significant innovations at independent third-party sites. The borders can often blur: centres such as the Fraunhofer Institute frequently work on long-term research projects with businesses and their investors, while Sandia’s new test site at Lubbock, Texas features both academic and commercial partners.
Independent centres can offer very large or very specialised equipment. And they can also be seen as impartial — which is crucial for project developers, increasingly focused on the reliability of the equipment that underpins years-long, multi-million-dollar investments. ‘There is a huge expansion of wind power and a recognition that to put the next generation of turbines offshore, you need to prove them first,’ says Jim Tuten, project manager for the Wind Turbine Drivetrain Test Facility at North Carolina’s Restoration Institute. ‘The capital backers of these projects also want some assurances. Testing allows you to exercise the unit to its capacity in controlled conditions and without being at the mercy of the wind.’
To complement laboratory work, Spain’s CENER hosts many other testing, design and analysis services, and also runs a test wind farm offering high-speed winds that can take turbines up to 6 MW (CENER)
As well as services ranging from design assistance to electrical testing, these facilities have three main offerings: blade and drivetrain testing — and longer-term turbine trials at outdoor sites that offer grid connections — monitoring equipment and meteorological masts.
Blades are delicate composite structures but face extreme cyclic loads over 25 years or more. Their failure can have severe repercussions in safety, downtime and public image. If many turbines need to be retrofitted, significant costs arise. So validating a blade’s design, its manufacturing process and reliability over time are essential to the success of manufacturers, developers and the industry as a whole.