Solar/ Fuel Cell H2/He Airship

This first occurred to me in the context of working out how much lift gas one needs to carry a certain type of fuel, and which fuels were the most energy dense (joules/ gram). This is why electric blimps, and other electric aircraft, have not generally been feasible to date, because the fuel storage (batteries) is far, far less energy dense than a tank of avgas, and conventional solar panels are also quite heavy for a given power output.

So the idea struck me, why not use a fuel source which has negative mass? IE is bouyant in air. The first and most obvious choice being hydrogen.

I believe this one is in the process of being baked somewhere, but I thought I'd put it up as some friends and I were discussing it some months before I saw a report that R&D is actually underway.

Basically the envelope of the balloon is contructed of a "very special polymer". Now I am aware that the properties of fictional polymers can approach the stupendous power of genetic WIBNIs, but these properties exist, just not AFAIK in the same polymer. I have a Plan B for the eventuality that the VSP is totally unfeasible.

Firstly, it is photovoltaic. Secondly,it has microscopic channels through it for transporting water. Thirdly, it is a catalytic membrane for a fuel cell.

During sunlight hours, the balloon absorbs photons which create electrical current. This current is used to crack hydrogen from water, and dump the H2 on the inside of the envelope, and the O2 on the outside. The entire envelope - or a part of it - is a giant, low-pressure hydrogen fuel tank.

The drive motors of the airship would be electric, and driven directly from the PV during sunlight.

During darkness, the fuel cell membrane operates in reverse, generating electricity through the H2/O2 reaction and creating water. This water is then collected in a holding tank at the base of the craft for re-use. In the meantime, it acts as ballast.

Now as buddha_pest points out, this creates a problem where the bouyancy of the whole craft changes over time. There's a number of possible solutions to that.

The fuel gas (H2) need not be the only lift gas in the craft. The object of the exercise was to make a solar- electric airship feasible by reversing the energy density problem, rather than to rely on the H2 as the only source of lift. So the hydrogen storage could simply be an inner bladder, surrounded by the main lift gas, helium.

This would reduce the chances of catastrophic explosion by separating the H2 storage from the atmosphere. You get around the biggest problem of storing H2 - the heavy tanks - by keeping it in an unpressurised bladder.

A reversible pump could transfer gasses between different chambers, to raise or lower their pressure and thus bouyancy.

Now for Plan B. It may well prove impossible/too expensive to have all the polymer properties in one substance, *and* make it strong enough to hang paying customers from. Photovoltaic polymers are already on their way to market, so we stick with the idea of making/ coating the envelope with PV polymer, and using solar power to run the engines and create H2, but separate all the fancy-schmancy fuel cell stuff out into a proven, reliable conventional fuel cell carried in the gondola.

If - and as always with these ideas, it's a big if - the sums all work, this could allow near-continuous operation without refuelling.