I did once consider a similar question regarding hydrogen fuel celled
vehicles and thier associated systems: solar shingles, electrolysis of
water to hydrogen at home, storage in a gasbag in the attic or in a low
pressure balloon tethered up the chimney, etc.

It seemed to me that high pressure H2 tanks were self defeating because
of thier weight; if a low pressure tank, or balloon were employed in
lieu, a large enough tank would make it unneccessary to drive on roads,
as the gasbag could carry the vehicle, with some unexpected
consequences. An H2, or any blimp would allow the vehicle to climb and
accellerate without expenditure of energy, but would require energy
expenditure to descend, if bouyancy was controlled and reduced by
compressing some of the H2 in the lifting gasbag into a higher pressure
bouyancy compensating bladder, like fish employ. If the vehicle was
tethered to a runner on a bridle between journey end points, bouyancy
would accellerate the vehicle and approaching the other end being
pulled back to earth by running along the tether would assist in
deccellerating it. It seemed that the vehicle could also employ sails
if the wind were favourable and the tether acted as a keel preventing
leeway, like the rails on a wind train.

It seems an equally interesting in not practical idea, if not mainly
because of the weight of the tether. Of course, if it were a tube
bouyed up by H2, eliminating that weight limitation might make it work,
not to mention the free flight option.

Terry K