Effect of Mass on Airborne Wind Energy Performance

Tim Brodrick Aerodynamics Engineer

KPS Ltd 103 West Regent Street

Glasgow G2 2DQ United Kingdom tim.brodrick@kps.energy

www.kps.energy

Effect of Mass on Airborne Wind Energy Performance

KPS Ltd This study explores the impact of airborne device mass on system performance and yield in an airborne wind energy system. This is studied using a quasi-steady-state time-stepped model. The baseline system is a utility scale, yo-yo, system flying circular trajectories and operating at constant line tension during generation.

The effect of the airborne device mass on the system power output depends on the wind speed (Figure 1). At nominal rated wind speed there is a small impact (doubling the airborne mass reduces the power output by 12%). During lighter wind conditions the airborne device mass has a larger effect on the system power output (at 75% of rated wind speed doubling the airborne mass reduces the power by 26%).

Varying the airborne device mass significantly impacts the winch requirements. Changes in gravitational potential energy during the generation phase produce a sine-like wave in the power output (Figure 2), and hence also in line speed. A heavier airborne device gives a larger amplitude of variation. This is a tougher requirement for the winch and therefore will have cost implications. The effect of the airborne mass upon the system’s annual yield was also analysed. It was found that doubling the mass reduces the yield by 15%, and halving the mass increases the yield by 6%.

Figure 1: Power curves for a kite system at 5 different airborne masses normalised by the baseline system.

Figure 2: Variation in instantaneous power during a single circular flight trajectory for 5 different airborne masses at the nominal rated wind speed.