Originally Posted by
pattern_is_full
Bottom line - an electric aircraft is always going to need knife-edge efficiency. No power will be diverted for anything other than "go" and "payload" - so no pressurization. Thus the practical limit on altitude will be 12500 feet or so, regardless of the physics at higher altitudes.
I'll go out on a limb and say that the optimum altitude for an electric aircraft will be "as low as possible" for the forseeable future. Think "Piper Cub."
Pattern, that's simply nonsense. It takes energy to pressurize the aircraft - regardless of the fuel source - but the lower the altitude the higher the drag and the more thrust required. The reason we normally cruise at 30k and above is simple - the reduction in drag means less fuel (energy) is required to fly a given distance, overwhelming the relatively small amount of extra fuel (energy) needed to warm and pressurize the aircraft. That is simple physics - going to electric propulsion doesn't change the physics.
Now, the early generation electrical aircraft will be relatively short range given the weight and energy density of current batteries. Shorter range means lower cruise altitudes simply because the additional energy needed to get to higher altitude is not justified by the smaller amount of energy saved due to short time at cruise.