Mobility 3 – Energy

Energy versus Emissions

Is your electric car lowering emissions? Maybe not, unless it’s largely charged by solar panels or other zero carbon sources. Most electric cars consume electricity generated in a power station far away. In the U.K. or Germany over 40% of electricity is generated by burning fossil fuels like coal and gas. In the U.S. it’s nearer 60%. McKinsey forecasts that most of the world’s electricity will be non-renewable until at least 2035.2018 UK Energy (left) and Electricity (right) consumption by fuel type

U.K. total Energy (left) and Electricity (right) primary energy source

This blog started off cheering for flying taxis in 2018. Environmental consciousness was also swelling behind the scenes, and peaked in 2019. The U.K. made it law to have net zero emissions by 2050, extinction rebellion ran amok, and “flight shaming” in Scandinavia pushing demand for air travel down by 3%.

Flying comes under a lot of scrutiny for polluting the world, but many insiders feel aviation is a scapegoat. Is it simplistic to say that flying vehicles are bad for the planet? Maybe, depending on their size. Large airplanes are by far the most practical approach for some long journeys. This article looks at the numbers for smaller vehicles like flying taxis and E-VTOL concepts.

Energy versus Emissions

First, some physics. Getting around doesn’t just emit CO2. It consumes energy. Whether you’re burning off a cake to go for a run, or burning diesel to move a lorry, you’re using energy that came from somewhere.

Aside from nuclear energy, all energy on earth comes from the sun (and little bit from the moon – tidal). The sun’s energy can come as an instant peppering onto solar panels, and it can heave wind through turbines. But today, 80% of global energy consumption is still from fossil fuels: these are super-concentrated stores of solar energy in the form of long-dead plants and animals (or recently deceased ones, in the form of food…).

Rather than just looking at CO2 emissions, this article will look at how much energy different modes of transportation consume. Why? It allows us to compare the cost of motion for anything before specifying its fuel.  It encourages less consumption, period. It also doesn’t let things like solar off the hook: solar panels need land and they need to be replaced every 20 years. Wind farms and biofuel can compete with agricultural land, and a lot of countries don’t have enough land to sustain their food needs.

Complex chart, suggest you see the source: Alexander et. Al 2016. Basically if the whole world wanted the French diet there would not be enough land to feed us.

If we want to be real about sustainability, we can’t just consume less fossil fuels. We need to consume less energy in total. We also can’t ignore society needing fast ambulances, or that productive adults will want to cross the country with more urgency than backpacking teenagers. So, we need options for speed and comfort. But are flying cars an energy efficient addition to today’s options?

Flying Cars – Revisited

In 2018 I was excited at the possibility that flying cars would solve the world’s traffic woes. We wouldn’t feel overpopulation because we could build neighborhoods sparser and further apart. Alas, it’s not that simple. Aside from the challenges I have already reviewed like capacity and air traffic management, I had not really appreciated the amount of energy (and arguably, land) it would need.

The flying car craze that swept the world in 2019 is led by companies promising to be “emission free” and “sustainable” by using electric vehicles. Chances are they won’t be. They’ll want to maximize flying time and minimize charging time to be profitable, so they’ll need to speed charge. They’ll probably need public grids for that, and we said earlier that those grids will be up to 60% fossil fuel powered for the next 15 years.

But that’s still not bad if they’re more energy efficient than the alternatives for similar journeys. The problem is, physics makes it very difficult. To move on planet Earth, there are three energy costs: you need overcome inertia, friction and gravity. The latter is what puts flying things at such a disadvantage to trains and cars, particularly on short routes.

The Numbers

The table below shows the total energy in kiloJoules per passenger per kilometer for a typical journey in each mode. I start with how much energy it would take to move (a person or helicopter), and then how efficient it is at converting its fuel (in today’s world) to motion.


For example, it’s estimated that humans need to burn around 3kJ of food to get 1kJ of motion because of entropy and heat. We need to send 115kJ of electricity from the station to get 100kJ into a train’s wheel motors, because of transmission and conversion losses.

Message me and I’ll send you the full list of assumptions and calculations. I would love to have people check and validate my method. Assuming I’m generally correct, we can deduce:

  • For the same commute, a flying electric car will consume nearly 4 times more energy per passenger than a normal electric car. (Although it will be nearly 3 times faster).
  • High-density, high-efficiency electric trains are the most efficient form of mass transport, consuming between a third and a tenth energy per person per km of today’s flying solutions.
  • Cycling is extremely energy efficient and happens to make you healthy and happy.
  • We could shave around 50% of the domestic flying fuel bill in Europe if we banned jet aircraft on routes under 1,000km and replaced them with turboprops – people would just need to live with slightly longer journeys.
  • Helicopters perform very poorly, which is why the two best funded electric car concepts are tilt-rotors, below

What this means for Urban Air Mobility

Monstrosity or Masterpiece

In the last 18 months,  nearly a billion in VC dollars have poured into urban air mobility startups. Believing that VCs have smart people, I am sure they’ve identified markets where energy efficiency isn’t assumed to be a regulatory problem. There are hundreds of concept vehicles out there, but these are probably the front runners:

Joby Aviation (+ Uber)Tilt-wing concept with several embedded fans (revision 1)($700M+ raised from investors like Jet Blue and Toyota),
LilliumTilt-wing concept with several embedded electric fans($100M+ raised from investors including Skype ex Founder)
VolocopterVTOL Helicopter with several electric fans instead of a turboshaft rotor($50M+ raised from investors like Intel)

Without giving too much away, Uber intends to pilot its service in Dallas and Los Angeles, and Lillium’s homepage animation shows a beautiful machine zipping around New York. The question is: will flying cars start in luxury niches then become mainstream, or stay in luxury niches forever? Here’s my guess;

Europe, Japan and California

In regulated and eco-friendly markets like Japan, Europe and California, I think physics will soon become a major challenge to anything flying. This is especially as high-speed rail is a well-developed form of travel in the first two, and cycling routes are proliferating within major cities.

So far, the states who have signed up to a net zero CO2 target for 2050 contain about 1 Billion people, or 14% of the world’s population. Many are in low population growth or even decline, meaning their citizens could number closer to 10% in the coming decades.

However, they are also where most of the world’s wealthiest people live, and where the transportation infrastructure is generally good. As such I can only see flying taxis become luxury niche market here, replacing helicopters and maybe developing into a premium route.

In terms of mainstream flying within Europe, I am struggling to see the basis for long term growth if net zero carbon targets are taken seriously. On routes under 1,000km turboprops may become mandated over jets, and on even shorter routes, flying altogether banned if there are suitable train connections.

Rest of the USA

I sat with a friend who ran a future product strategy project for a major American aerospace company. The view there is: flying is the best way to get between cities, and energy isn’t a worry. The GDP and scale of the U.S. coupled with the lack of high-speed rail options creates a necessity for flying; the U.S. is the world’s dominant private and general aviation market.

Guess Lillium’s Launch Market

Electric tiltrotors promise to be cheaper, more reliable and faster than helicopters and private aircraft, So there could be large market here, possibly even becoming mainstream in places. Uber intends to trial its pilot air taxi service in Dallas and Los Angeles. It is also likely the U.S. will also make its own equipment, from vehicles to service infrastructure.

India and China

Flying in general is in its early days in China and India – only 10% of their populations have ever flown, despite having 40% of the world’s population. They are also where most of the forecast growth in passengers is expected, with nearly half of the growth in demand to 2035. Neither country has made serious CO2 commitments, although they are net energy importers. 

I’m honestly not sure what the flying car market will be in either country but suspect it will remain a luxury for the foreseeable future. China for example has the world’s longest fast train network which may make inter-urban flying unnecessary.

But both are so big that even their niches could be substantial. Combined, I think the combined market in India and China will be somewhere between Europe’s and America’s.

Bottom Line

With the world’s population and consumption growth, pressure on energy and land, increasing low-carbon policies and the many existing alternatives like high speed rail, I can’t see flying taxis becoming a mainstream transport method anywhere outside the USA. The high net-worth niche is likely to be a sizeable market in China and possibly India. But in Europe it’ll probably be an amusement ride, although emergency vehicle and VIP transport could be justified use cases.

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