I pose the question with respect to the much predicted "hydrogen economy." In Iceland it may become a reality because the country has abundant, cheap geothermal power. You can practically drill a hole anywhere on the island and get geothermal energy. That means the the power needed to make hydrogen from water is nonpolluting and inexpensive. The combination will be hard to come by in most places on earth. And, even if Iceland could produce hydrogen for export, it would be difficult and costly to get across the ocean.
The main problem with hydrogen is that it is an energy carrier not an energy source. It currently takes much more energy to get hydrogen out of water, by electrolysis, for example, than the hydrogen yields. That means burning coal or natural gas to create electricity to extract hydrogen from water would be huge energy loser. It would be much better, for example, just to burn the natural gas in vehicles directly.
Naturally, if someone figures out how to get more energy out of hydrogen than it takes to extract it, the problem will be solved. Or if someone invents or discovers an incredibly cheap, nonpolluting energy source that it is possible to use in most places on earth, hydrogen could become a success. Windmills might work in some locales. Solar might work in others. But, the efficiencies are not yet there, and the scale of the new energy infrastructure would require astronomically huge investments using existing energy sources such as oil, coal and gas. If we're going to do it, we better start now.
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