Obviously, renewable energy and/or fission can meet all our energy needs. The question is whether they are able to do so at the current price. I think that's an open question.
So essentially there's a double pinch. First, power generation becomes a lot more expensive, and then transport costs become doubly expensive, because the energy can't be stored efficiently.
Hydrogen is not (or at least is not clearly) a solution to this. Hydrogen production generally requires a lot of energy, and a lot of fossil fuels; the alternative methods require even more energy, and a variety of (increasingly) expensive catalytic elements. The hydrogen then has to be used as a fuel, in an extremely inefficient process. Hydrogen fuel cell technology is currently LESS efficient than the normal battery technology in cars, which is itself highly inefficient. Well-to-wheel, electric cars are at least three times as efficient as hydrogen cars... Not to mention that through the production process, hydrogen cars use more fossil fuels than petrol cars!
What's more, the entire idea of widespread hydrogen fuel cell us is founded purely on hope: with all known methods to date, it will be impossible to produce enough of the rare materials required at prices low enough to enable mass adoption of the technology. [Platinum is catalyst of choice...].
Oh, and the fuel cells themselves are made of complicated polymers, which are created from fossil fuels via an energy-intensive process.
Of course, I'm not saying we WON'T develop sufficiently efficient energy-storage technologies. Just that it is far from clear that we will.
As for fusion... that's planned for early in the next century, which I think is quite reasonable. It MIGHT be available earlier - but then it might not even be possible, so I don't think giving it another century is too wild.
As a general point, people underestimate how much we rely on rare elements for our modern technology. For instance, Torco suggests solar power. Well, even the plain old inefficient solar cells use silicon. The flashy modern cells use cadmium, tellurium, gallium, arsenic, indium, selenium, and ruthenium! Oh, and they all need silver. A lot of silver. To produce 5% of global energy requirements, we would have to use 30% of global silver production purely for solar cells. And that's a silver production level that is already unsustainable.
Even computers and the internet are not immune. Modern computers (and mobile phones) and so on require rare earth elements. 97% of rare earth supply is from China, and China's reserves are projected to have been used up within twenty years. And even plain old silicon - in the last boom, the cost doubled in only five years - it then dipped in the credit crunch due to lack of demand, and has now doubled again in the last two years. That's just the rarity issue (yes, silicon is commonplace, but usably pure silicon isn't). In the future, the energy costs of silicon will have to be borne in mind. Making a ton of metalic silicon requires at present 1.4 tons of coal and 2.4 tons of wood: and that's not including the fossil fuels we use to supply the electricity for the process. And as that electricity has to heat the coal and silicon to 2200 degrees, that's quite a lot of energy. And then you've got to turn the metalic silicon into usable silicon, and then you have to process that into the finished article... it's a hugely expensive process, and will become even more expensive as energy costs increase.
But the river tripped on her by and by, lapping
as though her heart was brook: Why, why, why! Weh, O weh
I'se so silly to be flowing but I no canna stay!