A review of the industry will reveal many approaches to the production of hydrogen. Biological processes, chemical processes, and solar powered methods for producing hydrogen are being explored. Wind to H2 using electrolysis, and really any existing means of producing electricity can be used to convert water into a H2 fuel supply. This has the benefit of relatively easy energy storage which is very difficult with electricity. This issue of storage has long been a problem for the alternative energy crowd; as well as for mainstream energy producers. Many lakes have been built to act as energy storage units for dams that have too much power. The water is pumped up hill to a lake an then re-released to pass through the dam. The efficiency of this process is in the dirt.
Next, you can put that H2 right into your car. Experts claim that any car can be modified - easily for most typical cars - to burn H2 rather than hydrocarbon based fuels. This includes trains, planes, and industry. No other energy option to my knowledge has the benefit of practical and immediate application to trains, planes, and large industrial machinery.
Hydrogen burns almost completely cleanly [I am thinking 99.5% but it may be 95%]. Some oxides of nitrogen can be produced, but this can be improved with lower operating temps. Still, the exhaust is mostly water. Some gurus of this technology claim that it is so safe that you can condense and drink your exhaust.
Finally, there have been some indications that a primordial layer of hydrogen lies deep in the earth. One expert estimated that enough H2 may be stored to power the planet, based on current estimates, for 500 years. If this hydrogen supply is trapped in rock and waiting for harvest, it will require clever new technologies to get at it. I believe this layer was estimated as being about 50 Km straight down; all over the planet.