Vehicle: Aircraft: Airship: Solar
Solar/ Fuel Cell H2/He Airship   (+6, -3)  [vote for, against]
Using unpressurised H2 as a self-bouyant fuel store, replenished by cracking H2O, powered by sunlight on a PV polymer envelope.

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.
-- BunsenHoneydew, Jul 02 2003

Kinda 1/2baked elsewhere
Canadian study on airships for remote cargo - find "hydrogen" [BunsenHoneydew, Oct 04 2004, last modified Oct 05 2004]

Photocatalysis links
Pretty inefficient to date. [BunsenHoneydew, Oct 04 2004, last modified Oct 05 2004]

Partial bakeage http://en.wikipedia...hips#The_Golden_Age
"... Interestingly, the Graf Zeppelin burned un-pressurised blau gas, similar to propane, as fuel. Since its density was similar to that of air, it avoided the weight change when fuel was used." [BunsenHoneydew, Nov 03 2005]

LTA wing
this also uses H2 for lift and fuel. [the great unknown, Jun 25 2007]

French Students Make Solar Blimp
More baking [BunsenHoneydew, Aug 26 2009]

Turtle Airships
Proudly in the half-oven since 1987. Can haz 1/2$bn venture capital plz? [BunsenHoneydew, Aug 26 2009]

Néphélion http://www.gizmag.c...olar-airship/12454/
More progress on the French blimp above [BunsenHoneydew, Mar 28 2010]

Cloud camping http://www.lowtechm...pelin-baseship.html
Uses drive fanblades as wind generators when parked. [BunsenHoneydew, Jan 13 2014]

The lift gas isn't being burned to heat itself, it is being burned to drive engines to move the airship around. But yes, your objection is valid and I've tried to tackle it in the longer description.
-- BunsenHoneydew, Jul 03 2003

Purty good. I bet that VSP ain't gonna work, but Plan B jes'bout fixes it.

On another note, why not just charge batteries instead of converting to H2? You skip the whole fuel cell bit; you said in Plan B that the main lift gas is He anyway.

-- galukalock, Jul 03 2003

Why throw away all that fine fine O2? Keep it aboard for fuel!
-- bungston, Jul 03 2003

You save energy by using solar energy to power the engines directly. You might do better converting to H2 than charging conventional batteries, but I'm no physicist.

As far as ballast is concerned, I think blimps today use good old fresh air. A balloon inside the balloon is pumped full of air, compressing the helium in the outer balloon, and increasing the overall weight...
-- dbsousa, Jul 04 2003

// why not just charge batteries instead of converting to H2? // [galukalock]

Because batteries are extremely heavy, fuel cells are much more efficient, and unpressurised hydrogen has negative weight in air.

As stated in the original posting.

Dbousa: yes, the intention is to use solar power to directly drive the electric motors as much as possible, but to design in excess generating capacity to provide energy stored as H2 for later use.

Bungston: O2 is freely available from the outside air. It makes sense for complexity, weight and safety reasons not to attempt to store the O2 onboard, unless you are building a craft for extremely high altitude experiments.
-- BunsenHoneydew, Jul 08 2003

Safety will be a big concern if you're involving hydrogen and lots of electricity around the exterior surface of the ship. It was an electrostatic buildup on the surface of the Hindenburg which caused it to blow.

If you extract any energy from any self-contained fuel at all, you'll have to refuel sometime, simply because of thermodynamic law. But I'd be interested in the efficiency, if it could ever be worked out.

Lots of effort went into this one. +
-- RayfordSteele, Jul 08 2003

As an extra feature of this design, you'll be able to use the oxygen to support your crew (if you have one) when flying at high altitude.
-- Worldgineer, Jul 08 2003

Except that pure oxygen is very bad for you.
-- RayfordSteele, Jul 08 2003

I see no issue there. You can reuse nitrogen and CO2 would be abundant.
-- Worldgineer, Jul 09 2003

Worldgineer: good call on the oxygen.

RayfordSteele: the "refuelling" comes from sunlight. Any water lost from the system could possibly be topped up with rain or dew.

I've attempted to tackle the safety factor by surrounding the H2 bag with an outer envelope of He.
-- BunsenHoneydew, Jul 09 2003

Drat. This is exactly what happened to my Blood Glucose Indicator Tattoos. You halfbake a decent idea and someone somewhere puts it into practise. Sheesh.

[see second link]
-- BunsenHoneydew, Jul 28 2003

The more time I spend here the more I realize that everything good is baked if you're a talented enough googleer.
-- Worldgineer, Jul 28 2003

This all sounds horribly expensive. Current technology in fuel cells needs a form of platinum as a catalyst. Along with the proposed method of storage for the hydrogen, you would see your multi-billion dollar aircraft rain horrible fiery death on the landscape below when some hunter's mis-aimed shot comes your way.
-- zindog1282, Aug 08 2003

//multi-billion dollar// hardly, a lot of the things he mentions in "plan B" are "off the shelf" items that car companies are currently field testing. Sure, the hydrogen fuel cell / propulsion system / containment system would cost millions of dollars, but certainly not BILLIONS <pinky to edge of smile>
-- thejini, Aug 08 2003

Course, if we wanted to spend some serious money, we could possibly do away with the PV stage altogether, and use direct photocatalytic hydrogen cracking. No doubt with some horrendously expensive catalyst.
-- BunsenHoneydew, Feb 28 2004

-- finflazo, May 24 2004

Surprisingly, it seems the famous Graf von Zepellin had similar ideas about bouyant fuels. see [link]
-- BunsenHoneydew, Nov 03 2005

Why not use flexible photvoltaics to directly power electric motors, saving the fuel burning motors for flying through clouds and flying at night. Saves lots of fuel, no storage issues and avoids the problem with liquid fuel burning - of increasing bouyancy as fuel weight decreases. And we don't have to wait for the fuel cell sciece to be perfected/costs to come down.
-- Akhenaten, Jul 30 2006

That's exactly what I envision. You design in excess PV generation capacity to both direct drive the motors and crack H2 during the day, and reverse the fuel cell to provide current for night flying.

And if the single layer VSP is out of the question, it may be possible with composite layers of existing polymers, with some weight penalty.
-- BunsenHoneydew, Sep 06 2006

I did an idea like this, my LTA wing. One of the problems is that you need to balance the H2 cracking & the engine fuel consumption so that there's enough gas to keep the whole thing up. Most engines produce excess heat, so that could be used to give the gas extra lift. The balloon can be shaped to give it maximum top surface for the photocells.
-- the great unknown, Jun 25 2007

How about a giant hydrogen fuel cell powered airship for transporting energy and clean water? Instead of transporting water in its liquid form, it would be transported in the form of hydrogen which lifts the ship, powers fuel cells to produce electricity for propulsion(electric ducted fans) and then at the point of destination is also used to produce power and in the process also producing clean water.
-- SemisapientSuggestionBox, Dec 27 2007

Well, whaddaya know? [linkage]
-- BunsenHoneydew, Aug 26 2009

// you would see your multi-billion dollar aircraft rain horrible fiery death on the landscape below when some hunter's mis-aimed shot comes your way//

No you wouldn't. Bullets lose a lot of energy as they fly upward and typically won't get high enough unless you use a sniper rifle. If you are trying to kill birds you would use a shotgun with a fairly low exit velocity. If a bullet did hit, it wouldn't make a big fireball anyway, just a couple of pinholes. Airships were used as bombers in the first world war and they were quite hard to kill. A hunter would not down one by accident
-- Bad Jim, Mar 31 2010

random, halfbakery