Leigh: "We are stuck with fossil fuels for the forseeable future, so there is not point in discussing the subject."

That is a problem, Leigh, because if you regard the forseeable future as something like 50 years, then it is almost certain we will run short of them. In fact I'd challenge you do find any OECD government organisation that says otherwise. That in itself makes it worth discussing, even if the only thing that comes of it is to raise awareness that we are going to make some very hard choices in the future. My guess is the "future" is something closer to 10 years, not 50.

Rusty Catheter: "Your car probably produces several hundred kilowatts. You possibly commute for half an hour a day. You just used a *hundred* kilowatt hours."

You back-of-the-envelope calculations are a little out. Yes, the engines can produce that amount of power. But when they do the wheels are spinning, chocking the neighbourhood with smoke and leaving a lot of rubber on the road. In reality a high Lexus travelling at 100Km/hr with the air-conditioning on chews 25kW, or so the power meter on a hybrid Lexus says. Thus 1/2 an hour of travelling uses 13kW Hr, not 100.

Foxy: "Nobody to date has discussed or analyzed on this Forum the potential of hydrogen-powered cars."

Hydrogen is an engineering nightmare Foxy. My rather embarrassing post directed to Judy Spence says why: http://forum.onlineopinion.com.au/thread.asp?discussion=1957&page=0#40508 Embarrassing because it wasn't Judy Spence. I regard Hydrogen as a noisy distraction. George Bush's championing of it told me a lot about the man's understanding of science and engineering, and how much attention he was paying to his technical advisers.

Foxy;
Even if the ERoEI on hydrogen could be overcome there are
horrendous problems with hydrogen.
For instance you would not be allowed to use the Westfield car parks
or any of the underground car parks.
Why, because it is almost impossible to stop it leaking.
It would accumulate up on the ceiling and when someone turned on the
fluorescent lights BOOM !

Special enclosed parking spaces are needed with forced air ventilation.
Remember the old Leyland P77 cars with their enormous boots ?
Well you would need a tank about that size for reasonable range.
The problems then are the enormous cost of the fit out of all service
stations, and that about three times as many delivery tankers would
be needed as now deliver petrol.
The problems go on and on. They are playing with it in California but
sooner or later they will give up.
Another problem is the lifetime of the fuel cells, they get about
six months use and then fit new ones.

Hydrogen cars have been done to death a number of times in various
places on the internet web pages and it aleays comes down to it not
being really viable on the large scale.

I think the most elegant description of the problem of extracting hydrogen from water was: "water is the ashes of hydrogen already burnt".
Combustion is essentially oxidisation. You can't break up hydrogen and oxygen, then recombine hydrogen and oxygen, and hope to get usable energy in the process.
personally, I think the most exciting innovation is the compressed air car. Imagine a long off ramp from the highway to a refueling station, with speed humps all the way. Each speed hump could cover a simple piston pump, so you effectively supply your own compressed air simply by driving in.
the question about cars powering houses brought back memories. When I built my solar powered home, I couldn't afford solar panels straight away, so I powered the house with batteries in the boot of the car.
Each day I would charge the batteries driving to work and back, and plug the car into the house at night.
Of course, we hadn't been married long then, so we didn't watch as much TV...

rstuart:
Your example is overly simple, even for a sedate commute. I drive approx 100k per day on city roads. I am routinely overtaken by tradies in laden utes, commodores with all the fruit and twits in twenty-five year old whatevers. Repeatedly they accelerate hard, leap about like Baryshnikov on speed, brake harshly and do it again. They wind up within view at the next lights. Sadly including seniors, they would appear to have gotten their licence out of a box of corn flakes. (glad I got that off my chest)
Point is, They are not driving optimally, at a constant speed, getting peak efficiency out of an immaculately-tuned Lexus with a recent engine, economically optimised compression, engine management, fuel injection, water injection and super/turbocharging. The *vast* majority are not hybrids, even when not driven by the maniacs we see every day.

So, my estimate my be high, but I think yours is low by a factor of at least two, easily up to four.

Otherwise we are in agreement.

Your own estimate still confirms my basic position. Even such a half-optimal modern car under ideal test conditions uses more power in a half hour drive than my whole house did (daily average) with one aircon on 24/7 last summer.

This is an awkward amount of energy to produce from a home energy installation.

Grim: The problem is still the original energy source, but I do like pneumatics as storage.
The problem with the humps is they only recover the energy corresponding to the amount they slow you down.
How about some sort of regenerative braking for compressed air cars?
Some elctrics can, while slowing, convert kinetic energy back into electricity for the next start. Maybe slowing could drive a compressor to (partially) recharge your tank? The only pneumatic prototypes I saw were a few years ago, and the controlling valves were all electrical. Adding regenerative breaking may be a simple matter of software to control the same valves, using the pistons as compressors when slowing or on long downhill slopes.

Examinator: if only we could harvest keystrokes!

Cheers

Rusty

Speed humps recover energy corresponding to half the weight of a (four or two wheel) vehicle. Clearly, the best energy recovery would come from a truck lane, with humps all the way. Truckies may conceivably object to having to wear bras...
Since the 'humps' are actually hydraulic, I wonder how bad the drive would be?
Sadly, the MDI car is designed to be ultralite, for obvious performance reasons, so this particular airy fairy idea is self limiting.
http://business.theage.com.au/business/air-car-to-call-melbourne-home-20071202-1ee6.html
What ever happened to it?
I agree, braking energy is currently an enormous waste, which needs to be recovered.

Rusty Catheter: "So, my estimate my be high, but I think yours is low by a factor of at least two, easily up to four."

Actually I was being very conservative. I wasn't quoting theoretical figures for some highly optimised car. I was quoting an actual figure for a real live high end hybrid sedan on a real road with every electronic component imaginable and airconditioning on, in summer. This particular car generates 360 kW when the pedal is to the metal. I mention this only because if you find my figure low you are going to find this next one difficult to believe.

Wikipedia says http://en.wikipedia.org/wiki/Electric_car#Energy_efficiency the Tesla uses 13 kW h per 100 km. This is an electric car with 185 kW motor, accelerates to 100 km/h in 4.2 seconds, has a top speed of 210 km/h, and a range of 350 km and an efficiency when cruising of 90%. But it gets worse. The EV1, which was more like your standard sedan, runs at 11 kW per 100 km.

Rusty Catheter: "Point is, They are not driving optimally, at a constant speed, getting peak efficiency"

The point is based on a misunderstanding. Unlike an internal combustion engine, an electric efficiency doesn't change much regardless of how it is driven. When cruising the Telsa gets 90% efficiency, but the absolute worst it gets is 80%. http://en.wikipedia.org/wiki/Tesla_Roadster

Just about every electric car has regenerative braking, meaning when they brake the motors are "put into reverse" and become generators, recovering of the energy that would normally be lost. The Tesla recovers 80% of it. http://www.teslamotors.com/blog4/?p=58

Rusty Catheter: "Even such a half-optimal modern car under ideal test conditions uses more power in a half hour drive than my whole house did (daily average) with one aircon on 24/7 last summer."

You said your house used 5kW hr .. 10 kW hr in a day. The EV1 would use 5.5 kW hr for a 1/2 hour drive.