[ars]

Why does everyone obsess over fuel for transportations? It's the most difficult thing of all to make from renewables.

Just plant some switch-grass and shovel it - as is - into a coal plant. No ethanol or anything else. Take the resulting ash (mostly potassium, i.e. potash), and use it as fertilizer, then and do it again.

[dredmorbius]

Because transportation accounts for about 1/3 of all energy use, and oil accounts for 95%+ of all transportation energy.

Because good transportation fuels are hard to find. If you're on a fixed track (rail, trolly), you can electrify. If you're not going too far and can keep your vehicle weight low, batteries become an option. If you've got a big enough structure, you can consider solid fuels (ships). For overland untracked transport (trucks), you might be able to use steam power (allowing solid fuels) at considerable losses of convenience and increase in mechanical complexity.

For heavier-than air craft you're pretty much SOL.

Transportation isn't just moving people around, but everything: food, raw materials, finished goods, and more.

And liquid fuels are also convenient for powering other equipment, especially for mobile, temporary, or remote locations.

Finding a replacement for liquid fossil-fuel based hydrocarbons is the holy grail.

Coal and oil fundamentally changed human existence in ways that are very, very difficult to convey. They've made possible not only all of modern technology, but even the world of 1850, primitive as we would consider it, would be impossible without fossil fuels. Take them away and you're going back before that time, but with 14x the population. Trust me, that's the sort of thing that keeps me up nights.

Though he's rather much the cornucopian, Daniel Yergin's The Prize, both a book and TV series, really impress how much the world changed with the discovery of petroleum in 1859. I highly recommend it:

http://fixyt.com/watch?v=Qspu35JG59Q

http://www.powells.com/biblio/1-9781439110126-2

[ars]

So lets save the expensive oil for transportation and stop burning it in fixed installations.

The are plenty of electrical plants that burn oil.

[dredmorbius]

The are plenty of electrical plants that burn oil.

Relatively few. On a cost basis, oil's been more expensive than coal or gas. The former is still widely used (and serves as the bulk of electrical generation in much of the world). Solar and wind are approaching parity with coal, but are not dispatchable. They're available when they're available, and you can shed excess, but there's no accelerator pedal: you can't turn on the sun (or the wind) when you need them.

Solar thermal gives the option of banking energy for a few hours (about 6 presently, proposals for several days' capacity exist). This would address load balancing to a significant extent, but solar thermal plants must be specifically constructed, they're not suitable for opportunistic deployment as solar PV is.

[icegreentea]

Because even if you rationed oil for transportation, it's still going to grow sparse - and there's no reason to believe that the demand for transportation is going to go down. At best, the rationing scheme will slow down the current problem, and then you're back to where they are right now, trying to find viable and cheaper replacements for oil.

[ars]

Lets solve the easy problems first.

Plus you can make oil from air plus energy. Coal plus water is even easier.

All we need to do is reduce the cost somewhat, it's not necessary to solve it fully.

[icegreentea]

They obsess over it precisely because it's the most difficult of all. High energy density is required for flight. Apparently people would like to keep relatively cheap flight a thing that stays around.