OTERO Alejandro Daniel
capítulos de libros
Innovative Concepts in Wind-Power Generation: The VGOT Darrieus
Wind Turbines
Año: 2011; p. 137 - 162
Over the last 30 years, there has been a spontaneous tendency in the wind-turbine industry to increase the size of the state-of-the-art machine. This tendency is driven by economies-of-scale factors that substantially reduce the cost of wind energy. Starting from the typical 50 kW machine of the early 1980s, output power of the state-of-the-art wind turbines is now in the range of 3.6 to 6 MW, with rotor diameters up to 127 meters. Commercial models within this range are available from several manufacturers like GE, RE-Power, Enercon, Vestas, and Siemens. In recent years industry insiders have been talking about a next-generation of giant offshore turbines of 7.5 to 12 MW with rotor diameters up to 200 meters. If this generation of superturbines is successfully developed, wind-energy costs would be reduced substantially.There is still a wide margin for improvement within the current horizontal-axis wind-turbine technology (HAWT), which looks as the most effective way to go in the short- to medium-term future. The development of adaptive-blades with aeroelastic tailoring the flexo-torsional modes of the blade structure to reduce aerodynamic loads, the introduction of a modular-concept blade that could be split into easy-to-handle segments, and the use of advanced materials and manufacturing techniques in blades and other components are only some examples of how to improve the economics of design, manufacturing, transport-logistics, and operation of HAWTs. But the HAWT technology would ultimately reach its limits in the long-term future. As sizes increase, a number of related problems would appear in rotor design, transport and assembly. Ultimately, the low rotational speed associated with huge radii would complicate the coupling with the electrical generator to the point that the size and weight of the drive train required would become impractical.On the other hand, there are geographical regions around the world (e.g. Alaska, British Columbia, Labrador, Patagonia) characterized by vast wind resources. Mean speeds in some areas almost double those recorded at the typical locations for which commercially-available wind turbines were designed. Those regions, classified as outstanding and superb, offer an enormous potential in terms of energy resource where, in the future, it might even be possible to produce hydrogen as a substitute fuel in competitive terms, helping to close the gap between global fuel needs and the maximum amount of biofuel that may be produced sustainably. Hence, it is worthwhile to explore innovative concepts in extra-large wind-power plants to be able to exploit the renewable energetic potential that those regions offer.In this chapter we are going to explore an innovative concept that, by going beyond the classical evolutive-design process based on the HAWT concept, may help address those challenges in the long-term future of wind-turbine technology. The Variable-Geometry Oval-Trajectory (VGOT) is an innovative type of wind turbine based on the Darrieus-type rotor which has been introduced by Ponta & Luna Pont (1998). In a traditional Darrieus, the blades rotate around a central vertical axis. In the VGOT, instead, each blade slides over rails mounted on a wagon formed by a reticulated structure supported by standard train bogies. Each wagon contains its own electrical generation system coupled to the power-wheels and the electricity is collected by a classical third rail system. With the VGOT design, if we keep constant the velocity of the wagons (i.e. the tangential speed of the blades), we can increase the area swept by the blades (and hence the rated power of the plant) without the low-rotational-speed problems associated with a classical Darrieus rotor of large diameter.