Why Big Electric Planes Won’t Take Off: The Stark Physics Behind Aviation’s Energy Dilemma
Exploring the daunting energy barriers and engineering realities that restrict large-scale electric flight in commercial aviation.
Can electric propulsion replace fossil-fuel-powered jet engines for commercial passenger planes? Amid growing climate concerns and innovation in battery technology, many hope so. But the reality is much grimmer for long-haul aviation: the basic physics of energy storage severely restricts how far and how efficiently electric planes can fly compared to traditional kerosene-fueled jets.
Introduction: The Dream and the Challenge
The sight of prototype electric aircraft and grand announcements at international air shows suggest a bold future for green aviation. Companies have showcased small, battery-powered planes and made claims about imminent revolutions in transport. Yet, underlying these ambitious visions is a set of inescapable physical and technical limits on what batteries and electric propulsion can actually deliver at scale.
- Prototype electric aircraft (like Eviation’s Alice): Only nine seats, not operational as initially claimed, struggles with design and range.
- Small certified electric planes: Pipistrel Velis Electro is EU-certified for just two passengers, flies for about an hour.
The Energy Density Gap: Kerosene vs. Batteries
The heart of the issue is energy density—in simple terms, how much energy can be stored per kilogram of fuel or battery. Jet fuel’s energy storage is fundamentally superior, and this discrepancy grows dramatically when applied to large commercial aircraft.
| Energy Carrier | Energy Density (Wh/kg) |
|---|---|
| Aviation Kerosene (Jet Fuel) | ~12,000 |
| Commercial Li-ion Battery (2020s) | ~250–300 |
Implications:
- Jet fuel stores about 40 times more energy per kilogram than today’s best batteries.
- Accounting for the higher efficiency of electric motors, the effective gap still remains about 20 times.
- This gap is so vast that foreseeable advances in battery technology won’t bridge it for decades, if ever.
Batteries: Progress and Limits
- Battery energy density tripled since the 1990s. For reference, Li-ion cells in the early 1990s delivered less than 100 Wh/kg; now best commercial cells reach 250–300 Wh/kg.
- Even aggressive improvement projections (1,000 Wh/kg by 2050) leave batteries far behind jet fuel. Wide-body planes would remain infeasible for long-haul flight on batteries alone.
Comparing Aircraft: Electric vs. Traditional
Small electric planes are possible, but only for short flights and very limited payloads. The numbers tell a stark story:
- Pipistrel Velis Electro: 2 passengers, 100 km range.
- Boeing 787-10 Dreamliner: 336 passengers, 11,750 km range—a payload and distance 20,000 times greater than the electric plane.
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Physics and Practicality: Why Size and Distance Matter
Why Can’t We Just Make Bigger Batteries?
Making batteries larger or adding more packs isn’t a solution for aviation:
- Weight: Battery weight scales linearly with stored energy. Unlike fuel (which is consumed during flight), batteries are carried the entire time, a critical penalty for aircraft.
- Volume: Batteries are bulkier than fuel, challenging cabin designs and aerodynamics.
- Efficiency: Even if batteries achieved wild energy density increases, logistics and safety constraints (thermal runaway, fire risk) remain severe issues.
The Efficiency Argument
Electric motors are far more efficient at converting energy to propulsion than turbines—sometimes nearly twice as good. Yet, due to the low energy density of batteries, this efficiency gain only partially offsets the overwhelming storage disadvantage. The result: electric planes will never bridge the range and payload gap necessary for large-scale, long-haul flights.
The Growth of Air Travel: Why Small Increments Don’t Matter
Even if short-haul electric planes proliferated, their impact would be minuscule compared to global air travel’s total footprint:
- Passenger-kilometers flown has doubled over the last decade, with jet airliners forming the backbone of travel.
- Electrified short-haul flights would amount to a rounding error in both passenger numbers and carbon emissions.
Larger Context: Energy Transitions and Power Density
Smil’s Energy Insights
Vaclav Smil, one of the world’s leading thinkers on energy transitions, frames this challenge starkly: society has always moved from weak to powerful energy sources—wood to coal to oil. Now, renewables like batteries and biofuels ask us to accept much lower power density than fossil fuels, reversing centuries of progress.
- Fossil fuels: High power density, compact, and fuel modern society efficiently.
- Renewables: Low density, requiring far more infrastructure, land, and resources for the same energy output.
This retreat from concentrated energy particularly hinders transportation modes—like aviation—where weight and volume must be minimized for efficiency.
Carbon Emissions: The Big Picture
If aviation is to seriously address its carbon footprint, battery-electric planes cannot be the answer for most of its emissions:
- Short electric flights: Minimal emissions savings due to small payload and low range.
- Long-haul jets: Remain irreplaceable, and are responsible for the lion’s share of CO2 emissions and fuel consumption.
Alternative Strategies
- Sustainable aviation fuels: Biofuels or synthetic fuels could burn cleaner than kerosene but face their own daunting scalability, sustainability, and production challenges.
- Hybrid concepts: Limited potential for niche improvements; hybrids cannot overcome the fundamental energy density challenge for big jets.
- Efficiency improvements: Optimizing aerodynamic designs and engine performance incrementally lowers emissions, but doesn’t electrify flight.
Frequently Asked Questions
Q: Why can’t batteries simply be made lighter?
A: Battery chemistry determines energy density. Even theoretical maximums for current battery types fall far short of jet fuel, meaning the weight penalty remains overwhelming for large aircraft.
Q: Aren’t electric planes more efficient?
A: Electric motors are indeed more efficient than combustion engines. However, the major problem is not efficiency, but energy density – batteries simply carry far less energy per kilogram than fuel, making them unsuitable for large passenger planes.
Q: Will new battery technology change the situation?
A: Battery energy density has improved, but only tripled in 30 years. Futuristic targets (like 1,000 Wh/kg) would still be dwarfed by jet fuel, and are decades away if achievable at all.
Q: What about hydrogen or other fuels?
A: Hydrogen has higher energy per kilogram but is difficult to handle and store; it takes up much more space due to low volumetric density, and infrastructure for hydrogen aircraft is not yet available.
Q: What will replace kerosene for big planes?
A: For the foreseeable future, only kerosene and related high-density fuels can sustain long-distance, high-capacity aviation. Synthetic or bio-based versions may supplement, but complete electrification is not viable for large planes.
Conclusion: The Unyielding Physics of Commercial Aviation
While electric aviation for short-haul, low-passenger operations can and will expand, the dream of electrifying large jetliners is fundamentally blocked by the physics of energy density, battery weight, and aviation logistics. Wide-body, long-distance flights will remain powered by kerosene for decades, if not longer. The move to electric propulsion in aviation is not a matter of ambition, investment, or technological optimism; it is constrained by the very nature of how energy can be stored and used in flight.
- Electric planes: Feasible for commuting and small-scale, short-range uses.
- Kerosene jets: Remain essential for mass transport and long-haul flights.
- Carbon emissions: True reductions will depend on new fuels or dramatic efficiency, not battery power.
Only by understanding these limits can aviation innovation focus realistically on sustainability and emissions reductions, rather than chasing technically unfeasible dreams.
References
- https://vaclavsmil.com/wp-content/uploads/2021/12/ELFLIGHT.pdf
- https://www.science.org/content/article/meet-vaclav-smil-man-who-has-quietly-shaped-how-world-thinks-about-energy
- https://techratchet.com/2020/05/06/book-summary-energy-transitions-by-vaclav-smil/
- https://www.gatesnotes.com/books/society/reader/how-to-feed-the-world
- https://vaclavsmil.com/wp-content/uploads/2010/02/2016-ERSS-Debating-Energy-Transitions-1.pdf
- https://www.nateliason.com/notes/energy-and-civilization-by-vaclav-smil
- https://syllabus.pirate.care/library/Vaclav%20Smil/Energy%20Transitions_%20Global%20and%20National%20Perspectives,%202nd%20Edition%20(67)/Energy%20Transitions_%20Global%20and%20National%20Pe%20-%20Vaclav%20Smil.pdf
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