h a l f b a k e r y
A riddle wrapped in a mystery inside a rich, flaky crust
add, search, annotate, link, view, overview, recent, by name, random
news, help, about, links, report a problem
or get an account
Solar/ Fuel Cell H2/He Airship
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,
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
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
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
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
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
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
A reversible pump could transfer
gasses between different chambers,
to raise or lower their pressure and
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.
Kinda 1/2baked elsewhere
Canadian study on airships for remote cargo - find "hydrogen" [BunsenHoneydew, Oct 04 2004, last modified Oct 05 2004]
Pretty inefficient to date. [BunsenHoneydew, Oct 04 2004, last modified Oct 05 2004]
"... 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]
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]
Proudly in the half-oven since 1987. Can haz 1/2$bn venture capital plz? [BunsenHoneydew, Aug 26 2009]
More progress on the French blimp above [BunsenHoneydew, Mar 28 2010]
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
||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.
||Why throw away all that fine fine O2? Keep it aboard for fuel!
||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...
||// 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.
||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. +
||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.
||Except that pure oxygen is very bad for you.
||I see no issue there. You can reuse nitrogen and CO2 would be abundant.
||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.
||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.
||The more time I spend here the more I realize that everything good is baked if you're a talented enough googleer.
||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.
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>
||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
||Surprisingly, it seems the famous
Graf von Zepellin had similar ideas
about bouyant fuels. see [link]
||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.
||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
||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.
||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.
||Well, whaddaya know? [linkage]
||// 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