What is the Right Size for an AWE System?

Andy Stough presenting Windlift’s 4.5 m2_{prototype (13 September 2019)}

Andy Stough

Chief Technology Officer Windlift LLC 10410 Globe Rd suite 116 Morrisville, NC 27560 USA andy@windlift.com www.windlift.com

What is the Right Size for an AWE System?

Andy Stough, Mark Aull, Robert Creighton

Windlift LLC

The cost-optimal scale for an airborne wind energy sys-tem (AWES) is a question that defies simple analysis. Many participants in the AWE industry propose that multi-MW systems are required to compete with tradi-tional wind, while others argue that square-cube scal-ing renders systems of this size impossible. Windlift will present the results of a study that further explores these questions.

The levelized cost of energy (LCOE) for any energy gener-ation system can be calculated from capital expenditure (including financing, installation, and logistics costs), op-erations and maintenance costs, system lifetime, and ca-pacity factor. The assumptions involved are many and performing a sensitivity analysis with so many unknown factors risks missing more fundamental drivers of cost. In order to simplify the analysis, Windlift has utilized the specific energy of the flying system as a proxy for system fitness. Specific energy is defined as net system energy output per unit mass (flying). If one assumes that O&M costs are not a strong function of system size and that sys-tem weight is a reasonable proxy for capital expenditures,

the analysis can inform optimal sizing of a system. Windlift has utilized a proprietary design tool called Air-borne Wind Energy System Optimization (AWESOPT) to conduct the study. AWESOPT is a lumped parameter con-strained optimization tool that produces an optimal net power output given a set of inputs. Typically, vehicle de-sign and trajectory parameters are fixed inputs and/or constraints and AWESOPT determines maximal power closed cycles by optimizing flight speeds and drag/thrust at each point in the cycle. Importantly, AWESOPT accu-rately models the effects of mass on power output, which is both difficult to model and critical to the sizing discus-sion.

Windlift will present estimates for specific energy as a function of scale, considering sensitivities to mass scal-ing coefficient, wind shear, and select vehicle design pa-rameters. The presentation will conclude with a brief dis-cussion of the effect of scale on logistics, installation, and O&M costs and a comparison to existing renewable en-ergy technologies.