Vertical Airborne Wind Energy Farms with High Power Density per Ground Area based on Multi-Aircraft Systems

Abstract: This paper proposes and simulates vertical airborne wind energy (AWE) farms based on multi-aircraft systems with high power density (PD) per ground area. These farms consist of many independently ground located systems that are flying at the same inclination angle, but with different tether lengths, such that all aircraft fly in a large planar elliptical area that is vertical to the tethers. The individual systems are assigned non-overlapping flight cylinders depending on the wind direction. Detailed calculations that take into account Betz' limit, assuming a cubically averaged wind power density of 7 m/s, give a potential yearly average PD of 43 MW/km$^2$. A conventional wind farm with typical packing density would yield a PD of 2.4 MW/km$^2$ in the same wind field. More refined simulations using optimal control result in a more modest PD of 6 MW/km$^2$ for practically recommended flight trajectories. This PD can already be achieved with small-scale aircraft with a wing span of 5.5 m. The simulations additionally show that the achievable PD is more than an order of magnitude higher than for a single-aircraft AWE system with the same wing span.