Despite continuing challenging conditions for the wind industry in Europe, the mood of visitors to the exhibition floor at EWEA 2014 in Barcelona in March was upbeat. While the area occupied by the exhibition was compact, activities were lively.
UK-based Magnomatics, a green-technology company specialising in advanced magnet transmission systems, and its partner, renewables and technology consultancy and certification specialist DNV GL, presented a new and innovative drivetrain solution, described as a "front-mounted magnetically-geared pseudo direct-drive generator". Instead of gears interconnecting with each other, torque is transferred through a magnet force, claimed to increase efficiency and near-eliminate wear by avoiding direct metal-to-metal contact. The partners in this research project have analysed the design for a 2.5MW onshore turbine with a 120-metre rotor diameter, and say the concept is scalable to a 12.5MW offshore turbine with a 225-metre rotor.
Several turbine suppliers presented incremental product optimisations and other system improvements. French manufacturer Alstom and US firm GE both raised the power rating of their low-wind flagship models without changing the rotor diameter and both aim to optimise yield for the windiest IEC class III sites. Both companies also introduced new high tower concepts to go with their model upgrade.
Alstom's 3MW ECO 122 succeeds the 2.7MW model of the same name, claiming a 6% higher annual yield potential, measured at the maximum 7.5 meters per second average wind speed for IEC class III. The company introduced a new 119-metre concrete tower for the ECO 122, developed with French civil-engineering specialist Freyssinet. The design comprises 11 concrete sections and has a 7.2-metre base diameter. A novel installation method using bridge-building techniques allows new sections to be added at the bottom rather than on top. Three sections plus the nacelle are installed on site first and then, using an Eolift, they are lifted, allowing up to eight further sections to be installed underneath.
GE introduced the 2.75-120 model, an upgrade to 2.75MW of the 2.5-120, introduced last year. The new model is claimed to give a 5% higher yield, again measured at 7.5m/s wind speeds. The turbine will become available with GE's new bolted space-frame tower (see page 45) offering 139-metre hub height, a measurement similar to the current hybrid concrete-steel tower supplied by German specialist Max Bogl.
GE also revealed more details about its internal energy storage option, with the main operating benefits being its ability to stabilise short-term power fluctuations and frequency control. The maximum installed battery capacity is 200kW per turbine. GE offers a choice between lithium-type and sodium-sulphur batteries, both offering a high energy density, and the company is clearly still considering the benefits of both. Only a proportion of the energy generated is temporarily stored, and the storage-cycle efficiency is said to be 87-95%.
Siemens Wind Power introduced a power-rating upgrade platform from the initial 3MW class, introduced in 2009, to 3.2MW. The direct-drive model now includes stronger magnets that deliver the higher generator torque with the same stator dimensions. The SWT-3.2 will be available from the end of 2014 with 101-metre and 108-metre rotor diameters for IEC class IA, and 113 metres for IEC class IIA sites. An IEC class III sister version with enlarged rotor seems a likely future addition. Siemens claims about 4% extra annual yield at 7.5m/s average wind speed for the SWT-3.2-113 compared with the 3MW version. The 3MW models will remain available for project sites with lower wind speeds.
An ongoing debate in the wind industry is whether popular doubly fed induction generators (DFIGs) will be capable of meeting wind-turbine grid-integration demands in 2016 as laid down in the new European Network of Transmission System Operators for Electricity (ENTSO-E) network codes. Some experts believe that this will be difficult for DFIG and predict a switch to either induction generators or classic synchronous-type. Others point at possible revisions or flexibility that may yet be added to the ENTSO-E codes, and another group of experts believe that DFIG technology still has much potential left and expect that solutions, together with ongoing converter technology, will be delivered in time.
Blades with variable lengths
Blade manufacturer LM Wind Power and Dutch partners, including the University of Twente and the energy research centre ECN, announced a development that may become a key trend in the wind industry. The partners have developed a blade production and design concept that allows variable lengths to be produced in one large order of rotor blades. They claim that this could reduce the cost of energy by 8-10% on a wind farm. The background to the research project is that output of individual wind turbines at a wind farm depend on location variables, including wind-flow disturbances such as wake effects. The research baseline is an existing lightweight composite blade with variable tip lengths, with the innovative part being an assembly process that enables the permanent joining of the two blade parts while adding minimal mass.
Acciona already manufactures the blades for its 3MW AW116/3000 and AW125/3000 models in a functionally comparable manner. Each blade comprises a similar structural inner blade section and interchangeable tip sections of different length.