When eVTOL aircraft begin commercial service, will the existing power grid be able to handle it? That was a question explored by an expert panel, including engineers from the U.S. National Renewable Energy Laboratory (NREL), during last week’s advanced air mobility infrastructure workshop organized by the Vertical Flight Society (VFS).
Research engineer Jesse Bennett said eVTOL aircraft and all-electric fixed-wing commuter aircraft will undoubtedly stress the existing grid, but while there could be alternate solutions to expensive infrastructure upgrades, these might be expensive and complex.
“When you are dealing with recharging a large number of vehicles, the considerations really cascade back to the grid,” he explained. “The peak power demand is going to result in the need to upgrade a series of equipment on the grid: distribution transformer upgrades, primary lines, substations, near side branch circuit and wiring conduit installations, service panel upgrades, and main circuit breakers and protection.” Bennett added that large-scale customers may also need to add equipment such as distribution transformers.
The NREL team has studied the impact of installing all-electric commuter aircraft service at Denver International Airport (DIA). The study used the nine-passenger, fixed-wing Eviation Alice as the representative vehicle. Conventional aircraft of similar capacity, namely Pilatus PC-12s, are already operated at DIA by Boutique Air, an airline that provides regional passenger service from essential air service communities to hub airports.
According to the NREL research, at any given time, three to four of these aircraft are on the ground at DIA. Assuming these are now all-electric aircraft with 30-minute flight turn times, and that at any given moment two would need charging, it would require a 4 MW boost in electric capacity at the airport. Bennett called this “a really significant new load to the grid.”
Adding further aircraft to the mix could ratchet up the power requirement by anywhere from 5 to 20 MW, the NREL study found. “Just to provide that kind of capacity from the grid is going to be an expansion project on the order of magnitude of millions of dollars,” Bennett maintained. “It’s tough to estimate precisely [how much] because every grid is different, but it is really expensive to prepare the grid just to provide the power that you need.”
However, Bennett stressed that based on experience with electric car charging facilities, there are alternative solutions to expanding grid capacity, such as managed charging. This approach prevents transformer overload by monitoring power and local voltage and responding to load peaks by reducing power output and voltage quality.
In fact, NREL installed such a system at its own facility, which expanded the number of electric vehicle charging stations from 36 to 108. The system there manages charge times based on when an individual vehicle arrives, how long it stays inactive, and when it departs, as well as on energy demand. “It saved us a lot of money,” Bennett said. “Reducing the need for a grid upgrade is tied to reducing peak demand and leveraging onsite generation.”
Leveraging power storage can also minimize the need for grid upgrades and that is where hydrogen can play a role, said Mike Peters, an NREL engineer specializing in hydrogen and related infrastructure. “Measured in kilowatt-hours per kilogram, you get a lot of efficiency out of hydrogen,” he told the VFS workshop.
Peters explained how an on-site electrolyzer, a system that uses electricity and water to produce oxygen and hydrogen gas via electrolysis, could be used to augment power generation, store electricity, minimize grid disturbances, and improve grid reliability. Hydrogen would then be stored on-site and called upon to augment power generation as needed, either as a primary electric turbine fuel or as part of a mix with natural gas.
“We see a path to cost-competitive, renewable hydrogen,” said Peters. “The way we get there is by prying down the capital cost of equipment and by finding opportunities to free up low-cost electrons.” Peters said the best way to do that is to use electricity from wind and solar to power the electrolyzer system. “We do see a path to low-cost, renewable hydrogen in the future,” he said.
Nonetheless, it remains to be seen how the emerging advanced air mobility sector will fund the additional power capacity and management capability that operators of electric aircraft will need at airports and vertiports. Experts anticipate further debate over the case for possibly using public funds to invest in these facilities, whether they are at existing airports or in new urban locations.
“There are political ramifications if we start investing money in things that don’t benefit the current taxpayers,” Peters suggested. “How do we generate more revenue to support new things without compromising existing funding streams and not alienating our current stakeholders, who may not ever fly an electric aircraft?” he asked.