**1. Introduction**

Sustainability and reducing emissions are significant challenges for airports. Frankfurt airport will reduce CO2 emissions by around 65% until 2030 and operate in 2045 without any CO2 emissions. A total of 34% of the vehicles in the airport in Frankfurt are hybrid-electric or hydrogen-based. With this advantage, it was possible to reduce the CO2 emissions on this German airport by around 35% since 2010 [1]. Aircraft manufacturers such as Airbus plan to introduce hydrogen planes by 2035. With the code ZEROe (short for zero emissions), Airbus plans three types of passenger planes that rely on liquid hydrogen (LH2) as fuel [2]. Aircraft manufacturers have already initiated a transition to sustainable aviation, which the airports strive to follow. However, there are enormous challenges, such as the generation of hydrogen or electricity from renewable energies, to decarbonising the industry entirely. The electrification of aircraft systems raises the question of whether airports will be among the largest electricity consumers in our infrastructure in the future. At the small Corisco International Airport, Source [3] proposes the renewable energy generation of 307.42 MWh/year with an energy surplus of 41.30% by integrating wind turbines (WTs), photovoltaics and diesel generators. This integration will reduce annual greenhouse gas emissions on the island by 98.50% [4]. The Soekarno-Hatta Airport Railink Project is one of the projects the Indonesian government prioritizes to ensure reliable mass transport to and from Soekarno-Hatta International Airport [5,6]. In this study, the electricity demand for the operation of the Soekarno-Hatta airport railway is discussed and compared with the demand for the existing substation. The results of this study show that

**Citation:** Meindl, M.; de Ruiter, C.; Marciello, V.; Stasio, M.D.; Hilpert, F.; Ruocco, M.; Nicolosi, F.; Thonemann, N.; Saavedra-Rubio, K.; Locqueville, L.; et al. Decarbonised Future Regional Airport Infrastructure. *Aerospace* **2023**, *10*, 283. https:// doi.org/10.3390/aerospace10030283

Academic Editor: Jordi Pons-Prats

Received: 23 February 2023 Revised: 9 March 2023 Accepted: 10 March 2023 Published: 13 March 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

the substations will require a small amount of additional capacity. However, overall, the existing substations will remain reliable even though additional capacity will be required in 2030 to maintain the reliability of the electricity supply for two different services. According to the calculations, the cost of the additional capacity is USD 4.3 million. Electricity costs are estimated at USD 85,000 to 100,000/month for the first year, with 89 trips per day [6]. These examples show that both small and very large airports are currently investing heavily in electrification to drive the electrification of the entire aviation industry. The first simulations of energy supply technologies for a regional airport show that the energy demand of a regional airport with 13 gates will increase from 6 GWh to 22.53 GWh by operating 49 hybrid-electric aircraft per day [7]. As part of the Clean Sky 2 ENhanced electrical energy MAnagement (ENIGMA) project, a centralised smart supervisory control (CSS) with enhanced electrical energy management (E2-EM) capability was developed for an Iron Bird electrical power generation and distribution system (EPGDS) [8]. These projects show that this is a very current and important research topic.

The Rotterdam The Haque Airport (RTHA) is a subcontracting partner of the Clean Sky 2 GENESIS project (Gauging the ENvironmEntal Sustainability of electrIc and hybrid aircraft Systems) and seeks to change its infrastructure to adopt hybrid-electric aircraft (HEA). To accomplish this, RTHA plans to electrify around 70% of its aircraft traction fleet from 2030 onwards and aims to replace the remaining 30% with hydrogen-powered aircraft by 2050 [9]. Therefore, they must develop and adapt their ground power supply strategies to meet the demand for HEA (Hybrid-Electric-Aircraft) traffic. The study aims to determine the energy requirements for a regional airport's operation and the expected emissions. This paper is framed in the context of GENESIS, which corresponds to the EU theme JTI-CS2-2020-CFP11-THT-13 under the Clean Sky 2 programme for Horizon 2020 and presents a forward-looking view focusing on the assessment of appropriate energy supply technologies for ground energy storage, grid connection and power transmission to aircraft. Based on these technologies, a flight plan and the design of a 50 PAX HEA developed in the project, the energy requirements for operations at a regional airport can be estimated [10]. The fuel types for HEA change depending on the time horizon. The energy demand of the developed HEA was used to classify the energy demand of a conventional aircraft (ATR 42 with a Pratt and Whitney PW127 engine). In the short-term (2025–2035) and medium-term (2035–2045), a direct comparison between kerosene and a mixture of kerosene and sustainable aviation fuels (SAF) can be made. This study also assumes that LH2 and a battery in the medium-term can power HEA. In the long-term (2045–2055+) horizon, hybrid-liquid–hydrogen aircraft are assumed exclusively. Based on the energy requirements of the aircraft, which were provided by two partners of the consortium UniNa (Università degli Studi di Napoli Federico II) and SmartUp Engineering, the flight plan and the number of take-offs and landings, the emissions can be estimated. In addition, a flight plan is being developed to replace conventional aircraft with HEA and thus enable more environmentally friendly air traffic. Table 1 provides the key figures of the conventional aircraft and HEA designed with GENESIS, with information on the amounts of fuel (kerosene, SAF and LH2) and battery energy consumed per kilometre. Results are presented in this table for two separate missions: a 600 nmi mission, which was used to size both conventional aircraft and HEA concepts, and a shorter 200 nmi mission, more representative of the typical mission for a regional turboprop aircraft.


**Table 1.** Overview of fuel and battery energy consumptions per km based on calculations performed by UNINA and SmartUp.

(ref)\*: Reference aircraft with conventional gas turbine engines as power plant technology. (1)\*: Nautical mile. (2)\*: Internal Combustion Engine. (3)\*: Polymer Electrolyte Membrane Fuel Cell. (4)\*: Sustainable Aviation Fuel.
