While there are many unknowns related to the advanced air mobility (AAM) sector to come, we do know that charging these aircraft are going to need a lot of electricity — even at the start of vertiport operation within the next two or three years.
Indeed, it’s expected that as the industry moves forward after introduction, electricity will be a major limiting factor in AAM scale-up in the U.S. and globally.
The National Renewable Energy Laboratory (NREL) recently analyzed this issue for the Federal Aviation Administration (FAA) and released results of its study in March. The team surveyed aircraft manufacturers, spoke to stakeholders at planned vertiport sites, analyzed probable air service routes, and — using several publicly-available NREL tools — evaluated charging demand, costs, emissions, hazards, regulations and technical requirements for electrified vertiport infrastructure.
It’s no surprise they found that potential eVTOL charging demand could “considerably” impact grid infrastructure and operation. But there are solutions in their report as well.
On-site electricity
The NREL team point to on-site electricity generation (microgrids) and storage solutions at vertiports as important concepts to consider to improve power operability and integration.
NREL researcher Bharat Solanki first explained that at a reasonable rate of use, vertiports are projected to require multiple charging stations, rated for 300 kilowatts or more. Ali Ilyas, head of electrification at U.K.-based Skyports Infrastructure, put the requirement higher, in excess of 500kW per stand for fast charging. That means a typical vertiport will require roughly 1.5 to two megawatts of power (the same amount that’s used by roughly 700 to 2,000 homes, depending on their location, occupancy level, etc.).
Looking at charging itself, Solanki noted that power demand for charging eVTOLs will be intermittent and spiky, which can cause power quality issues like voltage dips. It can also affect power distribution to nearby areas fed by the same substation.
Battery banks at vertiports, able to discharge during the charging peaks, will help smooth overall charging demand. Indeed, Solanki said that without both on-site power storage and generation at vertiports, “local utilities may need to upgrade their infrastructure, such as adding voltage regulators, transformers and overhead or underground lines.”
However, he added that “vertiport operators and eVTOL manufacturers could use other tools to reduce energy impacts, including managed charging, coordinated operations or other operational techniques.”
Optimum operations
Ilyas explained that to minimize the cost, space requirements, and potential power quality disturbance, optimizing operability of power systems is key. In its models to predict this, Skyports includes several factors such as demand calculations and simulated battery charging profiles.
Ilyas also explained that it’s important that a battery’s “state of charge” — its remaining capacity at a given time and in relation to its age-related performance issues — be carefully moderated based on AAM mission profiles to maximize battery life.
“This approach, combined with pre-determined high-throughput flight schedules, allows for forecasting of charging schedules,” he said. “This enables the smart power system to prepare and program the power infrastructure for daily power consumption needs with a highly-efficient and optimized incorporation of microgrid solutions and energy management systems.”
Location
Microgrids and power management aside, the placement of vertiports is also critical in terms of power availability and more.
Ilyas pointed out that having vertiports near areas abundant in large grid and network substations are preferable, where there’s spare power capacity readily available (peak power usage is not happening all of the time), or where spare power capacity can be easily reinforced.
Solanki agreed that integrating the “intermittent electrical load” that characterizes eVTOL charging would pose less disruption if vertiports are located in areas with existing larger peak load capacities. An eVTOL charging system could access unused capacity at various times of day when it’s not needed for other loads.
These areas tend to be urban, but while Ilyas noted that suburban and rural areas generally entail major network reinforcements and longer lead times to deliver equivalent power levels to those of urban areas, “these locations are more favorable for securing the footprint necessary to establish green energy on-site generation and storage solutions. There is a real balancing act when assessing potential locations, so we take a macro network view as opposed to a site-by-site view.”
In addition, Solanki pointed out there are multiple communities in the more remote areas of the U.S. that subsidize commercial aviation service through the U.S. Department of Transportation’s Essential Air Service program.
And while an analysis specifically for eVTOLs has not yet been done, NREL has evaluated the like-for-like replacement of nine-seat conventionally-powered aircraft for similar electric fixed-wing aircraft on such essential routes. That team “found that operating costs could be significantly reduced with this approach,” Solanki said. “What’s more, if electric aircraft were used in a manner similar to current schedules, infrastructure demands at remote airports would be lower.”
Advice for moving forward
Asked for the best guidance for those who need to secure power at vertiports, the NREL team stressed the importance of acting now. “In this study, we highlight the need for vertiports to engage early with utilities to discuss potential upgrades to distribution systems and any implications on tariffs or rates,” Solanki said.
He added that to effectively engage with utilities, vertiport planners need to work closely with aircraft manufacturers to be clear on charging needs per aircraft, and also have a good handle on what future overall charging demand will likely look like.
Ilyas said vertiport planners will need to adapt to differing baseline parameters for each site, including power availability, spatial limitations, structural constraints, and site intricacies. These parameters apply to all aspects of electrification, from grid supply to microgrid components.
Cabling routes, ground support equipment placement, and equipment lead times are other immense challenges that require careful design and planning, he said. The potential range of climate conditions at a particular vertiport and all regulatory requirements must be addressed as well.
Hydrogen and more
With the very real and substantial challenges involved in managing and increasing electricity capacity for the AAM industry, other sources of power need to be examined.
To that end, NREL is currently working with the FAA on an energy analysis for AAM hydrogen infrastructure. “In that ongoing study, we are exploring various applications of hydrogen-fueled aircraft and their fueling infrastructure, including an economic analysis,” Solanki said.
However, he stressed that NREL is supporting the investigation of a wide range of aviation fuels besides hydrogen and electricity, including sustainable aviation fuel, and electrofuels, also known as e-fuels — synthetic fuels made using captured CO2 or CO and sustainably-produced hydrogen.
“We would hesitate to embrace the opinion that there is one solution or one opportunity that will overshadow another,” Solanki explained. “Our approach mirrors how multiple energy pathways are being pursued in other transportation sectors.”
For its part, Skyports is also actively collaborating with others “to explore emerging green energy technologies like hydrogen fuel cells and microreactors,” Ilyas said.