Airborne wind energy systems use tethered flying devices to harvest wind energy beyond the height range accessible to tower-based wind turbines. Current commercial prototypes have reached power ratings of up to several hundred kilowatts, and companies are aiming at long-term operation in relevant environments. As consequence, system reliability, operational robustness, and safety have become crucially important aspects of system development. In this study, we analyze the reliability and safety of a 100-kW technology development platform with the objective of achieving continuous automatic operation. We first outline the different components of the kite power system and its operational modes. In the next step, we identify failure modes, their causes, and effects by means of failure mode and effects analysis (FMEA) and fault tree analysis (FTA). Potentially hazardous situations and mechanisms which can render the system nonoperational are identified, and mitigation measures are proposed. We find that the majority of these measures can be performed by a failure detection, isolation, and recovery (FDIR) system for which we present a hierarchical architecture adapted from space industry. KEYWORDS airborne wind energy, fault detection, fault isolation, fault recovery, FDIR, FMEA, FTA, health monitoring, kite power, reliability, safety INTRODUCTIONThe increasing need for renewable energy has led to a widespread deployment of wind turbines: initially, only on-shore, but for more than a decade, also off-shore. 1 The trend goes to ever larger turbines with increasing capacity factors because the wind power density generally increases with the distance from the ground, as a result of the wind shear. 2 On the other hand, the cost of larger structures scales unfavorably with a square-cube law and modern wind turbines are approaching an economically feasible size limit. 3 Airborne wind energy (AWE) systems, on the other hand, use tethered flying devices to harvest wind energy beyond the height range accessible to tower-based turbines. 4,5 The use of a tether allows the harvesting height to be adjusted continuously to optimize the availability of the wind resource. Compared with harvesting at the fixed hub height of wind turbines, the wind power that is available 95% of the time increases roughly by a factor of two. 6 Of particular interest are deep-sea applications because a tower is in principle not needed for the operation of the system. The tether attaches to the ground station at sea level, which substantially reduces the structural loads and thus also the required material. 7,8 The lower material effort, the increased capacity factor, and the access to a so far unused wind resource render AWE a potential cornerstone in a future low-carbon energy economy.However, the technology is operationally more complex than conventional wind turbines. Most implemented concepts rely on aerodynamic lift, and the tethered flying devices can thus not be stopped immediately when unexpected wind conditions or system failures occur. Exact...

Safety is a major factor in the permitting process for airborne wind energy systems. To successfully commercialize the technologies, safety and reliability have to be ensured by the design methodology and have to meet accepted standards. Current prototypes operate with special temporary permits, usually issued by local aviation authorities and based on ad-hoc assessments of safety. Neither at national nor at international level there is yet a common view on regulation. In this chapter, we investigate the role of airborne wind energy systems in the airspace and possible aviation-related risks. Within this scope, current operation permit details for several prototypes are presented. Even though these prototypes operate with local permits, the commercial end-products are expected to fully comply with international airspace regulations. We share the insights obtained by Ampyx Power as one of the early movers in this area. Current and expected international airspace regulations are reviewed that can be used to find a starting point to evidence the safety of airborne wind energy systems. In our view, certification is not an unnecessary burden but provides both a prudent and a necessary approach to large-scale commercial deployment near populated areas.

Airborne wind energy (AWE) systems use tethered flying devices to harvest wind energy beyond the height range accessible to tower-based turbines. AWE systems can produce the electric energy with a lower cost by operating in high altitudes where the wind regime is more stable and stronger. For the commercialization of AWE, system reliability and safety have become crucially important. To reach required availability and safety levels, we adapted an fault detection, isolation and recovery (FDIR) architecture from space industry. This work focuses on, “flight anomaly detection” layer of the FDIR. Tests verifies that proposed architecture is capable of detecting flight anomalies without generating false alarms.

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