electrolysis is only 35% efficient, if you are using it to store energy
you are wasting a large part of the power- - better of to just use a flywheel (90% efficient but dangerous), compressed air (maybe 60%) or pump water uphill (like they do in Raccoon Lake).

as far as solar so far the most efficient seems to be the solar concentrator types to heat up stirling engines (in California) Ithink 35-40% efficient.

right now (the cheapest way) we get most hydrogenis through steam reforming of natural gas but there are ghgases as byproduct.

one answer to transporting hydrogen long distances is (from a recent SCI American article) to build large superconducting pipes for long distance electricity transmission - since the pipe is a bundle of wires which is cooled for superconductivity there is no loss of power through resistance. ANd the cooling is done by pumping compressed hydrogen gas into the pipes. NOw this would be a huge project but they already are working on an experimental one in the NOrth east US.

Theoretically this could be used as a way of storing and transporting hydrogen as well as using the hydrogen as needed for electricity generation. And presumably, surplus power generated from wind, tidal and solar could go into such storage and this would provide a hydrogen infrastructure.

I dont see hydrogen fuelcell powered cars happening simply because the cost of platinum vs lithium. Battery technology has been steadily improving and cars like the GM volt show promise.

google 'the energy blog' for interesting articles.