In this topic, the power to space use ratio is assumed to be in MW / km³.
And the power to land use ratio is like the power density of farms of wind turbines, in MW / km², not forgetting to count the length of the tethers passing above the land of use, which can pose problems for secondary use, while the part of the tethers above and outside the perimeter of the land of use increases the area of implementation (thus the land use) and therefore reduces the power density, which is rarely or not fully taken into account in analyses, including the interesting analysis (on which I will dwell a little), and although their vertical arrangement of unities lead to shorter tethers (see Fig.1) at the periphery, leading to drastically limit the loss of power density.
Vertical Airborne Wind Energy Farms with High Power Density per Ground Area based on Multi-Aircraft Systems (Jochem De Schutter, Jakob Harzer, Moritz Diehl), DOI:10.1016/j.ejcon.2023.100867:
https://www.sciencedirect.com/science/article/abs/pii/S0947358023000924?via%3Dihub
Highlights
Vertical airborne wind energy farms dramatically increase ground area power density.
Farm optimization is a trade-off between ground area and wing area needed.
Optimization of single-aircraft based farms result in no power density improvement.
Dual-aircraft systems are Pareto dominant for both small- and medium-scale wings.
In the introduction:
Airborne wind energy (AWE) is a renewable energy technology which aims at harvesting the steady and strong high-altitude winds that cannot be reached by conventional wind technology, at only a fraction of the resources. AWE developers mainly consider single-aircraft AWE systems (S-AWES), which are based on the principle of one tethered aircraft flying fast crosswind maneuvres. However, S-AWES are subject to several limitations that impede the technology to increase PD with respect to conventional wind.
First, S-AWES are characterized by high tether drag dissipation losses. These losses are inversely proportional to the aircraft size, which is why large and heavy (and thus, costly) aircraft are needed to achieve the efficiency needed for a high PD. Second, since the maximum tether length is limited due to the drag losses, S-AWES in farms would all operate at similar altitudes, leading to wake interaction between systems. Detailed wind field simulations of utility-scale S-AWES in farms suggest that these wake losses are comparable to those observed in conventional wind farms [7]. Therefore, a similar system spacing is required, resulting in ultimately the same achievable PD.
To overcome these limitations, this work proposes and simulates the concept of “vertical” AWE farms based on multi-aircraft AWE systems (M-AWES), as depicted in Fig 1. In M-AWES, previously investigated in [5], [8], [11], [16] two or more aircraft fly very tight loops around a shared, quasi-stationary main tether. Because of the low tether drag, M-AWES are very efficient even for small aircraft size while using airspace more effectively, resulting in a lower trajectory footprint on the ground. The proposed vertical farm layout additionally exploits the fact that M-AWES can fly at arbitrarily high locations above the ground, so that they can operate at distinct locations in the sky, thereby avoiding wake interaction. A somewhat similar idea based on networked rotary AWE systems was proposed but not simulated in [13], with a focus on overall flight stability rather than power density.
PDF available on:
This study is interesting because it tends to provide conceptual tools to increase the power density and the power to space use. But unities are very close to each other. What happens when the winds change? Even with very sophisticated controls, over time, tangles have every risk of occurrence.