It would be great to switch to all electric cars. But wait, that electricity came from somewhere right? So instead, the key would be to create more efficient cars, like the Aptera (www.aptera.com). The key to their amazing vehicles is their aerodynamic efficiency. The hybrid model can get up to 300 mpg for up to 400 miles. I doubt the Chevy Volt or any Zap can match that.

This is starting to be a pattern -- if both I and the other guy break down and get reasonable, the inevitable conclusion is the "prioritized portfolio" approach, with conservation and efficiency as the highest priorities (easiest to do, and most effective due to multiplier effects), and then deployment of non-carbon-emitting power sources (of a variety of types) to take care of the rest.

Air travel definitely needs a sharp reduction, as well as trans-oceanic freight shipping. Long-haul trucking needs to be reduced where possible, and largely transferred to freight trains otherwise (pure-electric trains w/ power supply along the track will be the most efficient, as that's the only tech that doesn't need to carry the weight of energy-storage in the vehicle itself). And of course we need properly-designed housing (ideally with ground-source heat pumps), and greater-population-density arrangements with effective mass transit.

Note that a lot of these efficiency measures -- including transitioning to electric cars -- involve transferring the energy demands away from oil and natural gas, to grid-provided electricity. We will then need non-carbon electricity production. These transitions all need to happen roughly simultaneously. But it's quite doable.

Anyways, on batteries: Tesla has been pretty open and transparent on just about everything, so I'm willing to belive that their assesment is fairly accurate. They have some details here:

http://www.teslamotors.com/blog2/?p=39

Their estimate is that after 5 years and 50k miles driven, the batteries will have 70% capacity remaining. So that's closer to your numbers than what I thought I remembered.

Now also note this quote:

One of the most difficult challenges in battery design is increasing energy density while also maximizing battery life span. Li-ion chemistries have achieved better combinations of these parameters than anything that has come before.

It says "chemistries," plural. Even within Li-ion, there's plenty of variety. I don't remember the details, but it's entirely possible that the numbers you've heard were for a different (older) type of chemistry than what Tesla is using. Also, the page mentions that the batteries "lose the most [capacity] early in their life (year one) and then continue to lose capacity gradually thereafter." I suspect that what you stated may have been assuming that the 1st-year degradation would apply to all successive years.

On your other main point, regarding the energy costs of producing the alternative energy sources:

Those numbers look good if you assume that we were going to build a powerplant anyway. If, as has been suggested by many (but not you that I am aware of), we replace existing oil, coal, and nuclear plants with alternative sources before they reach end of service, ...

Well, I would argue that coal plants especially need to be retired as early as possible. They are so damaging, not just in CO2 but in heavy-metal and radiation release, and in the destructiveness of coal mining, that the costs (both energy and $$) of solar thermal plants or wind farms is pretty cheap by comparison with continued coal burning.

Even for natural-gas plants, we need to stop their carbon emissions ASAP as well. Some of these could switch to burning biogas instead.

I would not argue for early retirement of nuclear plants. The investment has already been made, the terrorist targets are already there, so adding a few more spent fuel rods to the pile won't make a lot of difference. Also, I favor moderate investment in the development of fast-neutron reactors with pyrometallurgical reprocessing, as that will be a way to "burn off" the "spent" fuel rods, and get some electricity out of the deal to boot. On the other hand, construction of new plants with current technology would be a huge waste of our energy and monetary investments, as it requires so much more of both to get a gigawatt of new nuclear capacity up and running, vs. the same capacity of wind and (soon, if not already) solar. Note that the marketplace has already rejected new nuclear as an option, as all new plants under development right now are almost entirely state-funded enterprises (mostly in China).

... you have to factor in the energy required to make the materials for the entire plant and transport them to the site, transport the workers, run the construction equipment, tear down the old plant and dispose of the waste... even the energy it takes to run the computers in the architect's offices.

Certainly, the real production costs must be factored in, to determine the true sustainability. But I think you're going too far -- e.g. the computers for the architects would probably still be produced and used for another purpose. The yields from these technologies will outweigh the costs to produce them by a pretty big margin.

The finite energy budget you're talking about does exist, but it really only applies to the first generation of new power production. The second will be able to leverage zero-carbon energy produced by the first, requiring much less fossil energy, then the third will get an even better ratio, and so on. Of course, this means we'd better get building as soon as possible. Fortunately, that seems to be what's happening.

We're not going to convince enough people to relocate to cities en masse , and change their culture so drastically, to do the trick alone. It might not be enough even if we did, as people will still want comfort, entertainment, etc. Improving the efficiencies of our infrastructure technologies, including the transitions to electric cars etc, and building out non-carbon energy infrastructure to feed it all, is also necessary.

Looks like they decided to go with gasoline for the backup in the production model. They were unable to get a small diesel to pass inspection in California.