First commercial offshore wind farm in the United States (1 October 2016)
Henrik Stiesdal
Honorary Professor Technical University of Denmark
Department of Wind Energy
Risù Campus
Frederiksborgvej 399, Building 118 Denmark
hsties@dtu.dk www.vindenergi.dtu.dk
Airborne Wind Energy – Challenges and Opportunities Based on Experiences from
the Conventional Wind Industry
Henrik Stiesdal
Department of Wind Energy, Technical University of Denmark
Airborne Wind Energy Systems (AWES) have significant potential to expand the field of wind power by capturing energy at altitudes that can not be reached with ground-based wind turbines, thereby benefiting from higher and more persistent winds. However, while the potential ad-vantages of AWES are clear, the full range of challenges may not be equally clear. Based on experiences from the development, expansion and maturing of the conven-tional wind industry, the challenges facing the AWES in-dustry are of such magnitude that it cannot be stated with certainty that this industry will be commercially viable. The operational challenges vary considerably as a func-tion of the airborne wind energy system (AWES) concept. Still, for all concepts, the requirements for operational reliability and robustness under conditions of long ser-vice intervals are high, much higher than known from other, apparently similar industries. The conventional wind industry has had to learn the hard way that experi-ences could not readily be transferred from other indus-tries due to the much higher equipment demands posed by wind industry application. The same will apply to the AWES industry, but aggravated by the requirements for low weight.
The environmental challenges are considerable for all types of wind turbines, and in tendency, most will be more severe for AWES. Wind does not always behave in accordance with the textbooks’ descriptions of smooth logarithmic wind shears and well-defined turbulence spectra. In addition to normal turbulence, large wind
turbines often experience high and uneven shear condi-tions, pronounced veer, and gust front passages. Due to the larger areas swept by AWES and the significant al-titude variations, these phenomena are likely to affect AWES even more than conventional wind turbines. Fur-thermore, wind turbines experience other environmental conditions having a detrimental effect on performance: rain, snow, hail and icing, and insect fouling. Finally, all large wind turbines are at some point hit by lightning and also AWES must be able to handle lightning.
The regulatory challenges for AWES comprise a combina-tion of challenges shared by the convencombina-tional wind indus-try and challenges particular to the AWES indusindus-try. Expe-rience shows that radar interference, noise emission, and visual impact are limiting factors for onshore wind power deployment. In addition to these challenges, AWES have particular challenges regarding aviation and on-ground safety. The scaling challenges are of particular concern regarding AWES. Experience shows that the conventional wind industry needed megawatt-scale turbines to reach grid parity. However, the square-cube law will severely limit the size potentials for AWES, and new thinking will be required to reach competitive infrastructure cost lev-els. In the face of all these challenges, it is perhaps dif-ficult not to lose heart. However, the AWES opportuni-ties remain unaffected ś subject to the above challenges, the potential to change the game by exploiting hitherto inaccessible wind resources, using lightweight, low-cost equipment.
