[Enthalpy]

Zinc-air fuel cells are well alive! Also called "mechanically recharged", they store zinc powder separately from the cell that converts it into electricity. For instance that Canadian company
  zinc8energy
markets electricity storage, about home-size but scalable, with a "zinc regenerator", a "storage tank" and a "fuel power stack".

This is perfect for wind energy. But if sunlight provides the energy, covering km² with expensive solar cells to lose 80% in the conversion is plain bad. We must obviously use the sol-zinc process to produce efficiently metallic Zn from a cheap concentrator area. If this process hasn't progressed, it must receive much moneys, work, ambition, vision - more so because zinc-to-electricity has progressed.

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By the way, many people find alternatives to lithium for utility-scale storage. Iron-air batteries make big demos
  innovationorigins
10MW 1GWh, wow.

A Chinese maker markets a car with a sodium battery.

Anybody still caring about the availability of lithium and cobalt?

[Enthalpy]

Fast electric machines use carbon fibres, typically to hold the magnets at the rotor against the centrifugal force. But meanwhile PBO fibres like Zylon outperform carbon and would increase the rotation speed or reduce the gap on the magnetic path, very nice.
  wikipedia - toyobo.co.jp
A report of superior performance to reinforce 80T magnetic coils, a use nearly identical to fast electric machines:
  Huang et al, Mechanical properties of Zylon/epoxy composite

Huang coiled impregnated fibres in-situ with pre-tension and obtained from the composite nearly the fibres' strength. I believe it's simpler than the separate sleeve of carbon fibres.

PBO fibres isolate, carbon fibres don't. This shouldn't change much. Nd magnets conduct anyway.

Huang obtained 2.9GPa tensile strength from a composite and even more with increased pre-tension. Waaah !

Marc Schaefer, aka Enthalpy

[Enthalpy]

Ever more projects and companies do what I had described. I proposed among others to retrofit existing airplanes with hydrogen nacelles integrating propellers, electric motors, fuel cells and liquid hydrogen tanks, much smaller than the opponents claim
 Piaggio 180 -
Atr72 - Dornier 328 -
Boeing 737 - Dhc615 water bomber
This company does offer a conversion kit, notably for the Atr72, but it delivers the liquid hydrogen in tanks ready to load in the adapted aircraft, so the airports need no adaptation
  Universal Hydrogen - Get orders
Interesting idea! But I'd put the tanks in the nacelles, not in the hold.