Can large airplanes ever run on batteries?
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For all the talk about electric aviation, the industry is yet to figure out how to overcome a fairly hard problem – let’s call it the 40:1 problem
Batteries – even the best of them – have gravimetric (mass-based) energy densities of only about 300 Wh per Kg. The energy density of aviation fuel is about 12000 Wh/Kg, about 40 times that of batteries.
A 200 ton (empty weight) Boeing 747 today carries around 120 tons of fuel for a long distance flight (though it has a capacity of about 200 tons). I have not been able to get precise estimates for fuel to useful energy efficiencies but I reckon it should be in the 30-35% range as we are talking gas turbines for large aircraft. Electric motors are far more efficient, about 85%. If I consider all the above, if that long haul Boeing were to run fully on batteries at 300 Wh/Kg, it needs to carry about 2000 tons of batteries.
It will never fly – figuratively and in this case, literally!
Is it possible for battery energy densities to increase significantly?
During our many studies related to batteries for e-mobility, I have not seen any company close to commercilization envision densities higher than 600 Wh/Kg for Li-ion batteries – this would still mean 1000 tons of batteries – no fly!
A related challenge is the volumetric energy density (energy/unit volume). Here too, batteries do pretty badly – the best Li-ion battery today has only 1/20th the volumetric energy density as jet fuel. Implying that we may need a battery space that is 20 times than currently required for liquid fuel.
No fly again!
It appears that battery propelled aircraft are destined for small aircraft, short haul routes for the foreseeable future.
See my LinkedIn post on this topic.