There was a saying that recently featured on HN:

“A little bit of slope makes up for a lot of y-intercept”

So, sure, right now, the energy density of gasoline makes terribly inefficient combustion engines practical. But their energy density isn't going up (while lithium batteries are improving and coming down in price), certainly gasoline isn't going to get cheaper, and as for the combustion engine, well thats pretty played out after 100 years of trying to improve it.

It's a dumb saying. Let's say Bill Gates stopped making any more money tomorrow. How long would it take for you to catch up to his wealth?

Lithium-Ion battery energy density has about doubled in the last 25 years: http://futurist.typepad.com/my_weblog/images/2008/03/11/batt.... Even if gas technology stops improving tomorrow, it'll take 100-200 years to catch up on the energy density front.

Battery propulsion doesn't need to get anywhere near the energy density of fossil fuels in order to have equal utility, due to the huge difference in efficiency (both theoretical and practical). Ignoring utility and just thinking pure kWh for a moment, do you have a source for your 100-200 year claim, assuming maximum Carnot efficiency for fossil and 100% efficiency in electric motor conversion?

From my armchair perspective, the Tesla Model S would be equally useful to any gasoline car for all but a handful of edge use cases, with only the minor change of adding a metal-air battery as a range extender for excessively long trips. And that's today, not 100 years from now.

Arguably, Bill Gates has more than "a lot" of y intercept.

The saying also deserves an addendum: "... if you've got the time."

But there is probably a hard ceiling to the efficiency of safe and cost effective Li-ion batteries. We can't be entirely sure because we don't fully understand how Li-ion batteries work, but my best layman's educated guess is that those are close to tapped out as well.

The strength of the battery+motor electric drivetrain is that it's modular. Come up with another energy storage method, build it into a power pack, then plug it right into existing Tesla S cars, get the over the air software update, and you're back in business. There's also all of that frunk space.

Obviously batteries will not surpass 100% efficiency and are already reasonably close to that so yes, batteries are nearing a hard limit on efficiency. Energy density on the other hand is no where near its theoretical limits.

> Obviously batteries will not surpass 100% efficiency and are already reasonably close to that so yes, batteries are nearing a hard limit on efficiency. Energy density on the other hand

Energy density is what I meant. I found some graphs to look at. You are probably right about there being lots more room for improving energy density.

>my best layman's educated guess...

Can you elaborate on your reasoning?

Only that we've been trying for awhile now. I just looked at some graphs online, and maybe they'll get 50 to 100% times better in the next decade or so. That's pretty significant.

Gasoline and diesel engines have actually improved a lot in the last ten years.

I don't disagree (at least w.r.t electric cars), but to play devil's advocate: a factor of 50-100 is A LOT. We're talking about two orders of magnitude here, which would require a fundamental breakthrough in battery technology to achieve parity with gasoline. Even if we make batteries twice as efficient, we're still 25-50 worse than gasoline. And breakthroughs in battery technology are hard to come by. So if Toyota wants to hitch their wagon to fuel-cell technology instead, all the power to them! Batteries are not necessarily the future of portable energy.

If you now consider that the only way to use that energy is through combustion, and that an combustion engine is only 1/4th as efficient as an electric one, that factor suddenly shrinks to 12.5 - 25 already.

Frankly, energy density is a bit of an distraction. If we go by energy density alone, we would presumably all be cruising on Uranium, which energy density is... well off the charts.

But there a plenty of good reasons we don't fuel transport with Uranium, and there are just as many good reasons why we shouldn't continue to use gasoline.

But of course you're not just worrying about fuel/battery energy density difference. You should look at energy deliverable to the road per pound of fuel + engine + exhaust system versus electric motors + batteries, which I would guess is nowhere near a factor of 50-100.

And a hydrogen fuel cell can leverage more of the existing infrastructure and can be used in some existing ic engines.

whereas upgrading both domestic and the grid to support widespread electric charging has a lot of cost and infrastructure issues.

What existing infrastructure can hydrogen use? Sure, there are natural gas pipelines in place, just like there are electric transmission lines in place; what other infrastructure can hydrogen take advantage of? Why would that infrastructure need less upgrading than the electric infrastructure? (Serious non-rhetorical questions to which I don't know the answers)

The grid and power generation plus the fact that most us homes are 110V. and are limited in how much power they can charge.

Also My local small petrol station can fuel say 60 cars an hour have you any idea what sort of HVAC plant is needed to store and deliver that sort of power.

You can convert IC engines to burn hydrogen and they can just slot right into existing models.

You can also use intermittent wind and solar power to create Hydrogen for use later.

Most US homes have 220-240 volt service coming in that is split at the breaker panel.

Most A/C and heat, dryer, range are 240V.

An electric car can charge at night when load is low, so the power infrastructure that is engineered for high demand due to cooling in the middle of the day in summer will work just fine if everyone is charging at night. In other words, the grid is already mostly robust enough to handle this load.

Yes I know that its still low compared to the UK where a cooker circuit is 415.

Also what happens when a large number of people put their cars on charge when they come home from work.

If you're going to use electricity to make your hydrogen, you are certainly no better off than using it to charge a battery. Also, the energy density of hydrogen isn't exactly awesome either, and it's hard to store.

Burning hydrogen in an internal combustion engine is extremely impractical. Low efficiency, expensive to create, hard to store.