Wind and solar are interesting, but I think the real play is in fuel cells. I think this will all be solved in a decade or so. The pdf below is on the internet and is public information (apparently, through the Freedom of Information Act), so I'm not violating any confidences by posting the link.
www.ostp.gov/PCAST/agenda_9_20_05_files/Sridhar_IonAmerica_PCAST_20Sep05.pdf
Investors with vision in the private sector are pumping big money into alternative energy solutions, even if the government is still in denial of the problem. John Doerr, the well known venture capitalist, is on record as saying that alternative energy will make the internet revolution look teeny in comparison, as far as the amounts of money that will be made...
Hydrogen and all related types of fuel cells are just another way of building a battery. You still need some source of energy to separate the hydrogen from the water or natural gas or whatever it is bound to. I think this particular problem will eventually be solved by capacitors that are much improved from the current state of the art (one company, EEStor, claims to have solved that today and is attracting some VC money, but I'm always skeptical of such a large efficiency jump in something that has been incremental for a while)
Hydrogen will go nowhere, the only problem it solves is reducing emissions from the tailpipe of automobiles. We still need energy to get that hydrogen, and transport it around. So we either still burn oil to do that, or we use solar or wind to generate some of that power. But hydrogen has very limited energy storage, good batteries are already better. Once capacitors are better, hydrogen is dead as a practical solution. Leave it to a government run by oilmen to propose a "hydrogen economy" that would still have oil at its center, or lame stuff like corn or switchgrass ethanol that's got a very low yield per acre. You find me a place in the lower 48 that can grow sugar cane, then we are talking. Algae is even better, it would be a great way to find a use for all that swampland in Louisana and Florida instead of draining it and trying to build stuff there that the next hurricane will just flood out and cost us tax dollars to bail out the idiots who live there.
Really there are only 3 or 4 forms of energy we know of and can make use of here on earth:
nuclear
tidal - stealing gravitational potential energy from the moon and sun
geothermal - using the earth's heat, which according to some theories may actually be nuclear if the earth has a uranium core at its very center as some believe
solar - which covers PV, wind, oil, coal, biodiesel, ethanol, etc.
I wish people weren't so afraid of nuclear power as a big boogyman. We free more uranium into the environment burning coal to generate X megawatts than we do using nuclear power to generate X megawatts. Its just that the nuclear waste is more concentrated, but we should be looking at that as an advantage, not a disadvantage.
If we used breeder reactors to reprocess spent fuel we could use our existing nuclear waste for all our energy needs for the next several thousand years. Yes, we end up with a small amount of horribly radioactive waste, but because it is highly radioactive it also has a very short half life so we only need to worry about what to do with it for about 100 years, instead of the 10,000+ years we are worried about with our current nuclear waste. We can glassify it and store it on site since the amount would be so small (and therefore much easier to keep track of)