Experimental launch setup of Delft University of Technology (23 August 2012). 94
Stephan Schnez Senior Scientist
ABB Switzerland Ltd Corporate Research Applied Physics (RD-E4)
Segelhofstrasse 1K 5405 Baden-Dättwil
Switzerland stephan.schnez@ch.abb.com
www.abb.com
The Take-Off of an Airborne Wind Energy System Based on Rigid Wings
Lorenzo Fagiano, Stephan Schnez ABB Switzerland Ltd Corporate Research
The term airborne wind energy (AWE) refers to wind power generators that use tethered aircraft to convert wind energy into electricity [1–3]. Lower construction and maintenance costs and the possibility to reach higher al-titudes, where faster and steadier winds blow, are two main advantages compared to conventional wind power. AWE systems with aerodynamic lift can be classified by the placement of the electrical generators: on-board of the aircraft or on the ground. For systems with ground-based generators, a further distinction can be made be-tween concepts employing rigid-wing aircraft and con-cepts with flexible wings like kites. Small-scale proto-types (10–50 kW of rated power) of all concepts have suc-cessfully demonstrated power generation.
Autonomous take-off from a compact ground area has been achieved with AWE systems with on-board genera-tion [4] and kite-based systems with ground generagenera-tion [5]. The same functionality for systems with rigid wings and ground-level generators is still lacking. Indeed, au-tonomous take-off of this class of generators was demon-strated by using a rather conventional winch launch that requires a large ground area [6]. However, if a large area is required for the deployment of an AWE system, this will compromise some of the advantages of AWE mentioned above. The only study in the literature concerned with the launch phase of ground-based AWE systems with rigid wings studies a rotational start-up [7]. There, the focus is on the control and optimisation aspects instead of eco-nomic viability and the comparison with other possible methods.
Here, we will present an analysis of several conceivable
launching schemes for a rigid-wing AWE system. More specifically, we will compare a vertical lift approach with vertical-axis propellers, a linear launch technique com-bined with on-board propellers, and a rotational start-up like the one considered in [7]. The comparison will be based on performance criteria which we will introduce. A deeper study of the concept that is deemed to be the most viable one, i.e. the linear launch manoeuvre com-bined with small on-board propellers, will be performed. In particular, we derive a dynamical model of the system that includes realistic aerodynamic coefficients, as well as friction and inertia. We use the model to refine the ini-tial analysis in terms of power and land usage required for take-off. Finally, we will present first steps towards the ex-perimental verification of our approach.
References:
[1] Loyd M. L.: Crosswind Kite Power. Journal of Energy, Vol. 4, No. 3, pp. 106–111 (1980)
[2] Ahrens U., Diehl M., Schmehl R. (Eds.): Airborne Wind Energy. Springer (2013)
[3] Fagiano L., Milanese M.: Airborne wind energy: an overview. In: American Control Conference 2012, pp. 3132–3143 (2012) [4] Vander Lind D.: Analysis and Flight Test Validation of High Perfor-mance Airborne Wind Turbines. In: Airborne Wind Energy. Springer (2013)
[5] Fritz F.: Application of an Automated Kite System for Ship Propul-sion and Power Generation. In: Airborne Wind Energy. Springer (2013)
[6] Ampyx Power: http://www.ampyxpower.com/. Accessed 3 June 2015
[7] Zanon M., Gros S., Diehl M.: Rotational Start-up of Tethered Air-craft Based on Nonlinear MPC and MHE. In: European Control Con-ference, pp. 1023–1028 (2013)
