Why Hybrid-Electric is a Key Solution for Decarbonizing Aviation

October 3, 2024

By Thibault Baldivia, CTO of Ascendance

The aviation sector, urged by ambitious U.S. goals to achieve net-zero aviation emissions by 2050, is poised for transformation. CO² is responsible for most anthropogenic greenhouse effects, representing 76 percent of GHG emissions according to the IPCC. CO² emissions are compounded by contrails - the white trails left by aircraft from kerosene combustion. Experts do not expect these emissions to decrease in the coming years, as projections show that global air traffic will triple by 2050.

In this context, the race to improve aviation efficiency is in full swing, with hybrid-electric alternatives emerging as a promising technology for the short, medium, and long term. Recognizing the economic stakes, the U.S. government has taken significant steps to bring alternative fuel sources forward, including the Department of Energy’s Sustainable Aviation Fuel Grand Challenge, aiming to produce 3 billion gallons of sustainable aviation fuel per year by 2030. Additionally, the FAA has introduced the FAST-SAF program, providing $245 million to advance the deployment of sustainable aviation fuels.

Hybrid-Electric: The Most Relevant Solution Today

Similar to the automotive sector, many small aircraft initially pursued all-electric solutions. However, aviation quickly faced range and infrastructure challenges, causing a pivot towards hybrid technology. Other alternatives to all-electric have undergone testing, such as 100 percent SAF (Sustainable Aviation Fuel). This option is already a technical reality for aircraft manufacturers such as ATR and Airbus, who demonstrated in 2022 a reduction of about 80 percent in CO² emissions during flights with aircraft and helicopters. However, the current lack of globally available biomass resources makes it difficult or impossible to produce biofuels in massive quantities at an affordable price.

But SAF is still facing a prominent issue: the production is nowhere near the level that would be needed to meet the demand.

To bridge this gap, technology must accompany the deployment of SAF to reduce fuel consumption at the source - directly at aircraft level. This is hybrid-electric technology. Based on a propulsion system using both electricity and fuel combustion, hybrid-electric can reduce fuel consumption by up to 50 percent on both existing and new aircraft. By reducing consumption, it allows for less fuel use, hence an acceleration of SAF adoption. Half the fuel consumption means twice the number of aircraft decarbonized! This is an attractive alternative, as it requires no modification to existing aircraft engines or airport infrastructure.

It’s worth noting that the use of biofuels is already a common practice in the sector. Today, all aircraft flying worldwide are certified to use 50 percent SAF. The transition to 100 percent SAF is currently underway, with certification announced for 2025.

A Deeper Look at Hybrid Electric Aircraft

Hybrid electric aircraft combine two energy sources - fuel and battery. The aircraft engine is modified to fit the power required in cruise while batteries are used to provide an instantaneous, high power, electrical boost during take-off and climb - the two most power-demanding phases of a flight.

Hybrid solutions are often a set of bundled technologies and components for aircraft and rotorcraft OEMs to make them more sustainable. As a result, it works for new developments as well as retrofitting existing aircraft and takes several shapes depending on the manufacturers’ aircraft and the program objectives, from turboprops to regional planes. As aircraft are often in use 20-30 years, meeting our 2050 objectives require us to make plans about the existing fleet, hence the benefit of hybrid.

A combination of different energy sources and algorithms ensures optimal performance inflight and on the ground. Hybrid-electric aircraft have similar performances than conventional airplanes while drastically reducing their environmental impact to smooth their adoption by the industry. This technology is available today, without betting on any technological breakthrough making it a very suitable candidate for the decarbonization of Aviation.

However, piling up electrical motors, batteries and fuel engines is far from sufficient to make a hybrid system - especially in Aviation. Specific algorithms to control the energy flows in the aircraft, embedded intelligence to erase the complexity of the system for the pilot to simplify her operations and safe and powerful electrical distribution systems are mandatory to make Hybrid-electric Aviation a reality. This is Ascendance core expertise and offer.

Ascendance’s hybrid is not a basic system but 2.0, evolved version: a plug-in hybrid. Thanks to unique and patented algorithms and systems, aircraft batteries can be recharged both in flight or on the ground, leading to lighter batteries. A virtuous circle as lightweight reduces drag, reduced drag reduces fuel consumption hence CO² emissions while smaller batteries also means lighter recyclability impact and less mineral resources used.

Which Aircraft, for Which Uses?

While there is no one size fits all solution, building the decarbonized aviation of tomorrow involves developing a technology with the capability to address the larger airplanes existing today. While technology is still restricting the size of aircraft that can be fully decarbonized, Hybrid-electric systems presents themselves as a sustainable solution for 2050. Indeed, hybridization applies to both sustainable aviation fuel and hydrogen power. However, when discussing all-electric or all-hydrogen, it is a question of use cases and timing.

The hybrid-electric solution, due to its adaptability to infrastructure and opportunities for fuel diversification (JET A-1, SAF, or Hydrogen), is the best option. Hybridization will enable the emergence of hybrid-electric aircraft for regional mobility under different configurations, from conventional takeoff (cTOL) to vertical takeoff (VTOL) and short takeoff and landing (STOL). This solution will be used for regional connectivity and medical and emergency transport and is applicable to multiple long range uses.

In contrast, all-electric solutions, due to their specific characteristics, will only be used for very short distances or cargo drones. Ultimately, hybridization is ideal for both conventional aircraft applications and vertical takeoff and landing aircraft, the latter also offering flexibility of use.

Hybridization is a major asset, scalable and applicable in the short term. The technology allows for the incorporation of alternative energy sources such as electricity and hydrogen as it reduces overall consumption. Finally, hybridization also offers the possibility of optimal configurations ranging from vertical takeoff and landing aircraft to optimized conventional aircraft.

Transformation is an extraordinary challenge for the aeronautical and the energy industries, and the outcome will have a long-term impact. The stakes are high for climate, social and economic advancements, and as an industry, the way we face this challenge will determine the future. The good news is sustainable, efficient solutions are available now.

This article was written by Thibault Baldivia, CTO, Ascendance (Toulouse, France). For more information, visit www.ascendance-ft.com .