...but I really haven't seen much in the last while to change my basic understanding of what's necessary, what's coming, etc. And I got tired of repeating myself, and assumed the audience was getting tired of me repeating myself about energy. But in case you've forgotten, are new, whatever, this is basically where my head is these days:
Solar: the 800-lb gorilla of renewable energy. The Earth intercepts enough energy on a single day to power all of human activity for a quarter-century, if we could convert it all with 100% efficiency (clearly an impossibility, but it gives you a sense of scale.) Solar PV technologies have had a 30-year cost decline and production growth curve that makes Chinese exporters look like retarded slackers -- 20% growth last year. Still more expensive than you can get from the grid in most industrialized countries, but rapidly filling more and more niches across the world, including the developing world. And solar PV is a technology even the Amish can love.
Solar thermal plants are at least as promising, where the heat of the sun is concentrated on an operating fluid and turned in to grid-exportable energy. Some have proposed massive solar thermal plants in North Africa, exporting clean electricity to one of the world's industrial cores. I wonder if they've considered combining solar thermal with desalination: there's still a lot of waste heat to get rid of, and boiling seawater with it would be a good fit for parched North African countries. (Later answer: Yes, they do mention it in their materials. See #6 in this PDF.) On top of everything else, solar thermal is storable in a way that electricity is not yet.
So: clean energy, clean water, and giving poor countries an export that the industrialized world can't do without? Add to this the possibility of repeating the Israeli kibbutz' success -- making the desert bloom -- and I think you see the potential. By my quick math, if the countries of the EU were to fuel all of their electrical consumption from North African solar (again, an obvious impossibility, but go with me here) the 320 million inhabitants of North Africa would have, between them, 375 cubic meters of freshwater per person per year. (Assuming that only the electrons, and not water, are exported.) This would be roughly 15 times what the inhabitants of North Africa currently have available to them, and a bit less than the US's (absurdly profligate) irrigation use. Repeating the same math for the US gives us a figure of about 115% of the US's projected 2030 water demand could be met by desalination. Again, assuming the impossible 100% reliance on solar thermal. The cycle is virtuous, not vicious: the more energy we use, the more freshwater there is for the people of these countries.
And we're going to need more electricity, not less. Clearly, coal has to die a quick death as humanity's fuel of choice. So we've got to replace that with wind, solar, or efficiency. As hyrdocarbons of all kinds look worse and worse, the only real solution is to move transportation and heating from gas or oil to electricity generated by renewable sources (home heating can be substituted with efficiency and home geothermal.) Biofuels look more and more questionable, and in any case worse than the humble electron for most applications, including the lowest of low-hanging fruit, automobiles and light trucks. Add population and economic growth, and even with the most aggressive efficiencies plausible, I can't see energy demand (especially electricity) declining outside of the most wasteful industrialized countries (US & Canada.) California has cut pollution while keeping electricity demand level for decades by fuel-switching to natural gas in a big way, but I don't know of a western country that has reduced total energy consumption. (As always, corrections welcome.)
I keep stomping on this one because it's so obvious it's painful: if you truly value the economy, you should be pushing renewable energy as fast as you can. Not one of humanity's hydrocarbon crutches exists in sufficient abundance to power a growing global economy beyond 2050, optimistically. If you value an expanding economy capable of supporting your grandchildren in any kind of prosperity, renewable sources of energy are the only way to do that. We can fight over the last scraps of the fossil fuel age, or we can tap in to resources several orders of magnitude more abundant.