November 11, 2022, ©. Leeham News: We have spent some 50 articles going through the new air transport category, eVTOL, or electrically propelled Vertical TakeOff and Landing vehicles.
They promise to replace the helicopter for local air transport above congested cities and highways.
The question is now: How do eVTOLs fit in sustainable air transport? Are they a green way of starting a flight journey, and how does it compare to alternative transports?
eVTOL OEMs push the green credentials of their products. But how green is this mode of transport? Some proponents say it can compete with chauffeur-driven cars like Uber transport.
We have the typical energy consumption per mile or km for our eVTOLS. We consumed 50kWh for a 25nm leg from the city center to the local airport. It was with four passengers and the pilot. It also included takeoff and landing procedures that does not count for distance.
If we reduce the load factor to the level Joby assumes in their calculations, 2.3 passengers on average, we get a lighter eVTOL and end up with a consumption of 42kWh for the trip. It means we consume 18.3 kWh per passenger to move them 25nm, or 0.73kWh/nm, 0.39kWh/km, or 0.63kWh/mile.
We use Wikipedia to get the values of energy used per passenger km traveled.
If the passenger takes an airport shuttle train, the consumption is about 0.10kWh/km or four times lower per passenger km than an eVTOL. This value is for “Urban rail,” which contains a lot of stops and goes. An airport shuttle that uses a more direct run might have a lower value, closer to a local train of 0.05kWh/km.
A turboprop like an ATR 72-600 with a 75% load factor has the same energy consumption per passenger and km (0.10kWh/km) on its typical feeder routes of 300nm. The intercity Boeing 737 MAX or Airbus A320neo would consume 0.15kWh per passenger and km. You pay for the higher speed with higher energy consumption.
The gasoline-powered car is an energy hog, as discussed before. It consumes about 50% more energy than the eVTOL at 0.60 kWh/km and transported person, but if we instead use an electric car, we are at 0.15 kWh/km or 2.6 times lower than if the passenger is flown in an eVTOL. This is when we count, on average, 1.4 people in the car during daily use.
Figure 1 shows the energy consumption by type over the last 200 years. Over the last 50 years, our energy consumption has exploded, and the main sources of energy are carbon-based; coal, oil, and natural gas. If a transport system uses electric energy for its consumption today and tomorrow, we can’t say this electricity was produced by the tiny green sources we have. Thus we have an energy consumption problem and not enough green sources to replace the carbon-based ones running the world right now.
That a transport uses electric energy as the storage and propulsion source doesn’t qualify it as green. It simplifies the switch to green energy but doesn’t change the label. The source of the energy does.
If we add a new transportation concept that consumes 2.6 to four times more energy than an electric car or a shuttle train, should it be called a sustainable way of transporting people? Just because its energy consumption is based on electric energy? In the large scheme of things, we need to lower our energy consumption per person, not increase it.
I, therefore, think that part of the eVTOL pitch shall be declared invalid.
eVTOLs will be a more convenient way in certain large cities to get to an airport and replace helicopter services, but that’s for the privileged few or business travelers using such transports today. It’s certainly not a means to lower our energy consumption. The average Joe, with his family, will continue to take the airport train at a four times lower energy consumption.