bl0rq t1_is3y16g wrote on October 13, 2022 at 2:58 AM

Reply to comment by RandomlyMethodical in NASA has invented a new type of high-performance battery that researchers claim could be used to power fully electric airplanes. by phife_is_a_dawg

For further comparision: jet fuel is about 12,000 Wh/kg.

MegaHashes t1_is52tat wrote on October 13, 2022 at 11:13 AM

I think this is a little bit misleading. While Jet fuel is incredibly energy dense, jet engine designs convert only 30-50% of the energy stored in jet fuel into mechanical effort.

I’m not certain what the power efficiency of an equivalent electric based propulsion device would be, but I believe the losses within electromagnetic motor designs are much lower.

That doesn’t exactly close the gap between energy densities, but it does narrow it a lot.

pantsonhead t1_is5v651 wrote on October 13, 2022 at 3:01 PM

You are forgetting that a dead battery weighs as much as a full one, whereas burned fuel doesn’t weigh anything. Any gains in power efficiency in the context of an airplane is likely to be offset by carrying extra battery weight all the time.

hucktard t1_is6cfu7 wrote on October 13, 2022 at 4:55 PM

You just have to launch the spent batteries out of the back of the airplane.

MegaHashes t1_is9zkrl wrote on October 14, 2022 at 11:48 AM

We need r/TheyDidTheMath on the case to prove that.

Commercial airliners never fly on empty, and you can’t gain more jet fuel by covering planes with solar panels they way you can with electricity.

The technology isn’t there yet, and I’m not suggesting it is. My suggestion was only that the energy density numbers don’t tell the full story because of inherent losses when using that energy source.

BioClone t1_iskfo6y wrote on October 16, 2022 at 5:33 PM

well the environmental hit, and ways to reverse it also needs to appear on the maths by the same reason.

pantsonhead t1_islavry wrote on October 16, 2022 at 8:50 PM

I guess the point is, some green energy source other than batteries is probably the solution for airplanes i.e. hydrogen/biofuels.

beatthestupidout t1_is4v1i0 wrote on October 13, 2022 at 9:33 AM

It is, but it requires pumps, heavier engines, etc. to run, and only convert their energy into motive power with around a 30% efficiency compared to the >90% of an electric motor. The batteries are catching up in real terms faster than a simple comparison of densities would suggest.

bl0rq t1_is67xjc wrote on October 13, 2022 at 4:26 PM

Modern jet engines are closer to 50%. And yes fuel pumps and whatnot have mass too. But so do the supporting things for the electric version. A electric motor about equal to a 787 engine output weighs at least as much. And both it and the battery would need cooling.

> The batteries are catching up in real terms faster than a simple comparison of densities would suggest

They are not. They are dense enough for many things (commuter cars) but not airplanes.