How the Energy Mix Impacts Hydrogen’s Sustainability for Aviation
The value of hydrogen as a sustainable aviation fuel depends on the weight of renewables in the electric grid. Using Chicago’s O’Hare International Airport as a case study, research highlights several developments needed to integrate electrolyzed hydrogen with no emissions in the production life cycle.
Hydrogen is often hailed as a renewable fuel source for aviation, emitting only water vapor rather than carbon dioxide and other pollutants. Still, the methods used to produce hydrogen entail significant emissions, meaning its true carbon footprint is much greater across the production life cycle.
5H2FLY, a subsidiary of California-based Joby Aviation, recently demonstrated a world-first piloted flight of a liquid hydrogen-powered electric aircraft. Image used courtesy of Joby Aviation
Most of the world’s hydrogen is made from fossil fuels today. Per the International Energy Agency, natural gas supplied 70% of global energy demand for hydrogen production in 2022, followed by coal (around 30%). Low-emission hydrogen, which is produced via electrolysis, claimed a tiny 1% share.
This trend will likely continue until the electric grid is entirely renewable, according to a study analyzing the impact of the grid mix on hydrogen-based aviation at Chicago’s O’Hare International Airport. Land requirements and water use were also considered to forecast the airport’s energy demands.
The study was published in Aerospace Research Central and authored by Phillip Ansell, an associate professor in aerospace engineering at the University of Illinois Urbana-Champaign (UIUC). Ansell modeled the life cycle carbon dioxide-equivalent emissions of liquid hydrogen production based on U.S. grid forecasts. His research found that based on the grid mix in 2020, hydrogen production would represent 2.5 times the global warming potential as directly using fossil-derived jet fuels.
Energy Mix’s Impact on Grid-Sourced Electrolytic Hydrogen
Renewable energy accounted for 13% of the U.S.’s primary energy consumption in 2022, according to the Energy Information Administration (EIA). It also represented about 13% of primary energy production, trumped by fossil fuels’ 81% share. Wind, hydropower, solar, and other renewable energy sources currently claim 21.5% of utility-scale electricity generation.
Ansell’s analysis found that even incremental strides in renewable energy deployment aren’t enough to make electrolytic hydrogen an environmentally sustainable solution. However, a fully renewable electric grid in the U.S. by 2035 would change that dynamic.
Ansell analyzed EIA data and two forecasts from the National Renewable Energy Laboratory (NREL) to project the U.S.’s trajectory for a 100% renewable grid by 2035. The UIUC mentioned that the study assumed the grid would be heavily weighted toward solar, wind, and other clean energy sources. Ansell then determined the amount of land required to produce electricity for hydrogen production through water electrolysis, for the hydrogen liquefaction process, and for shipping it to the O’Hare airport.
Ansell also considered other factors playing into hydrogen’s ultimate sustainability for aviation applications. He estimated the physical land needed to produce energy by combining solar installations and wind turbines. This is relevant in green hydrogen production, which uses electrolysis powered by renewables instead of natural gas or coal.
Required land area use for a fully renewable energy grid based on the O’Hare International Airport’s needs. Image used courtesy of the University of Illinois Urbana-Champaign
Water use is another factor engineers and planners consider in gauging infrastructure needs. The O’Hare airport’s proximity to Lake Michigan offers freshwater resources for hydrogen production. Plus, O’Hare could receive the water without desalinating it first, thus avoiding even more emissions.
Hydrogen in the Aviation Sector
Worldwide, interest is building around using hydrogen as a sustainable fuel source and propulsion mechanism in aircraft and other aviation applications.
Engineers at industry-leading Airbus are working to determine the best methods to combine hydrogen propulsion and synthetic fuel technologies by 2025. The company is one of 150 members of the Hydrogen Council, a group that facilitates collaboration between multinational companies across transportation, energy, manufacturing, and other sectors.
Other companies, such as California-based Joby Aviation, are advancing hydrogen-electric fuel cell propulsion systems that run on liquid hydrogen. Joby’s subsidiary, H2FLY, recently completed the world’s first piloted flight of HY4, a liquid hydrogen-powered electric aircraft demonstrator.
Such innovations mark a critical step in demonstrating hydrogen-based aviation technologies, but they generally address operating emissions rather than the output of the entire life cycle. Joby Aviation’s 2022 Environmental, Social, and Governance (ESG) report includes a note from the CEO stressing that designing electric aircraft with no operating emissions isn’t enough for climate-neutral aviation. Broader emissions-reduction measures would be needed across its business, as both a manufacturer and operator, such as sustainable manufacturing, sourcing renewable electricity, and managing water use.