Airborne wind energy (AWE) is a novel concept aiming to substantially reduce the material demand and environmental impact of wind energy generation. AWE systems can also access steadier and stronger wind at higher altitudes, which is inaccessible to conventional wind turbines. The lower material effort, the increased capacity factor, and the access to so-far unused wind resources render AWE a potential cornerstone in a future low-carbon energy economy. The new conversion concept is currently being demonstrated by several start-up companies using different technical implementations at different maturity levels. The unifying challenge for commercialization is the operational robustness of the technology. For a successful market acceptance, the introduced aviation and ground-related safety risks need to be mitigated.

The present work aims to bring AWE closer to commercial success through two main contributions. As a first contribution, well-established practices of reliability engineering are used to measure and then systematically improve the safety and reliability of AWES systems. Experience from other safety-critical domains such as aviation, space, automotive, and medical are used to achieve this objective. A fault tree analysis (FTA) and failure mode and effects analysis (FMEA) are applied to an existing demonstrator system. A common practice in the safety-critical domain is automatically monitoring the system's health and taking action in case of faults. In this regard, a systematic fault detection isolation and recovery (FDIR) model is proposed for AWES. This architecture is generally applicable and flexible and can be applied to different AWE systems.

After reaching the required reliability and safety levels, formalization by the certification authorities is required. As a second contribution, the current regulatory framework is reviewed, the relevant authorities identified and a roadmap for aviation certification is presented. The ``Specific Operations Risk Assessment'' (SORA) by the Joint Authorities for Rulemaking on Unmanned Systems (JARUS) is a comprehensive and well-structured framework. Therefore, following the SORA is considered the best way forward to get the flying permit for AWES, claiming the ``specific'' category from the European Union Aviation Safety Agency (EASA) regulation. This permit is applicable for commercial operations in Europe. Other civil aviation authorities may also recognize the EASA's flying permit. In this respect, the SORA is applied to a hypothetical commercial operation scenario, and requirements for the flying permit are discussed.@en

Integrating the operation of airborne wind energy systems safely into the airspace requires a systematic qualification process. It seems likely that the European Union Aviation Safety Agency will approve commercial systems as unmanned aircraft systems within the “specific” category, requiring risk-based operational authorization. In this paper, we interpret the risk assessment methodology for airborne wind energy systems, going through the ten required steps of the recommended procedure and discussing the particularities of tethered energy-harvesting systems. Although the described process applies to the entire field of airborne wind energy, we detail it for a commercial flexible-wing airborne wind energy system. We find that the air risk mitigations improve the consolidated specific assurance and integrity level by a factor of two. It is expected that the framework will increase the safety level of commercial airborne wind energy systems and ultimately lead to operation approval.@en

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.

@en

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.

@en

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.

@en

Due to the emerging interest in Airborne Wind Energy, a considerable number of prototype installations is approaching a commercial stage. As a consequence, operational safety and system reliability are becoming crucial factors for technology credibility and public acceptance. In our case study, we investigated the reliability and safety level of the current 20 kW technology demonstrator of Delft University of Technology, which is also the starting base of the EU Horizon 2020 project REACH. The objective of the REACH consortium is to develop a commercial 100 kW version of the demonstrator. The project team systematically improves the system’s reliability and robustness with the aim of demonstrating 24 hours of continuous automatic operation without any pilot intervention. To achieve this goal, reliability and the safety level of the system are analyzed using two traditional methods, FMEA (Failure Mode and Effects Analysis) and FTA (Fault Tree Analysis). From the conducted analyses, hazardous situations and the mechanisms that lead to unoperational or hazardous states are defined. Consequently, mitigations are offered to prevent these mechanisms. It is found that a majority of the proposed mitigations can be performedby a FaultDetection, Isolation and Recovery (FDIR) software component. Development process improvements are offered for the components for which it is impossible to decrease the risk using the FDIR. In this talk, author will present the key points and the important results of the reliability analyses. In addition, proposed FDIR architecture will be discussed. @en

As an increasing number of Airborne Wind Energy Systems (AWES) is reaching early commercialization operational safety and system reliability become important aspects. This presentation will provide an overview of existing and expected rules and standards for ensuring safe operation of rigid wing AWES. The objective is to systematically determine the relevant authorities and their points of view from the top down to the national levels and provide an overview of relevant system standards independent of the specific AWES concept. This overview will be supplemented by the current specific legislation for rigid wing concepts and the relevant upcoming changes of the European airspace law.@en