An interesting steal from //www.dansdata.com this week. Something I've wondered about before too...
QuoteRods to the hogshead (http://en.wikipedia.org/wiki/Hogshead)
There is a question which I have been wondering about for a while, and thought that perhaps you might answer it.
An electric car (http://www.dansdata.com/danletters171.htm) that runs on batteries charged from grid power has a very efficient electric motor. But how efficient is the power plant, say a coal or gas or nuclear plant, when compared to a standard petrol engine? If a petrol engine is about as efficient as a power plant, I se no reason to use an electric car.
Or are there other things which make it worthwhile?
Fredrik
Answer:
The thermal (http://en.wikipedia.org/wiki/Heat_engine) efficiency of a petrol or diesel engine (diesel's better than petrol, but not a whole lot better) is frequently quoted as being in the thirty-something-per-cent range. That, however, is the ceiling efficiency, when running at optimum RPM. A lot of the time, the efficiency of a normal car engine is a great deal worse - when accelerating up a hill, for instance. When you're sitting at the traffic lights with your engine running, your efficiency is zero. When an electric car (or a hybrid) isn't moving, virtually no power is being used. Hybrid cars therefore have a big fuel economy advantage over ordinary small economical cars if, and only if, they both spend a lot of time in stop-start city traffic.
Now, fuel-burning power plants are quite horrifyingly inefficient too. Even a really modern coal-fired plant still manages less than 40% thermal efficiency. But it manages that efficiency pretty much all the time, no matter what.
But then again, the reason why major power plants run all the time is that they're generally used to supply "base load (http://en.wikipedia.org/wiki/Base_load_power_plant)" power - the amount of power that always has to be delivered, rain or shine, day or night. Most big plants are somewhat adjustable in their output, but not adjustable by a large enough amount, or quickly enough, to deal with peak loads (http://en.wikipedia.org/wiki/Peaking_power_plant) that happen when, for instance, everyone comes home from work in the summer and turns on their home air conditioners. Peak load plants are usually quite a lot less efficient than base load plants; most of them are monster gas turbines that can be turned up and down very easily, but pay for it with a horrible amount of energy wasted as heat.
And then there's yet another caveat - that waste heat can be re-used if the peak plant's somewhere near some humans who need heat for some purpose (keeping houses warm, industrial processes), whereupon you can pipe the heat to them, and greatly improve the aggregate efficiency of the plant. This is called "cogeneration (http://en.wikipedia.org/wiki/Cogeneration)", and it fuzzes up the calculations further.
Getting back to the electric cars - charging batteries is not anything like 100% efficient, and you lose a few more percentage points in the motor, and regenerative braking (http://en.wikipedia.org/wiki/Regenerative_brake) doesn't actually recover anything like as much energy as you might hope. The whole coal-to-driving efficiency chain for electric cars powered by modern but non-cogenerating coal-fired plants, though, still works out somewhat more thermally efficient than it does for petrol-powered vehicles, and it also works out considerably cheaper. Coal remains plentiful, oil does not.
The location of the pollution matters, too. Power plants are generally in relatively unpopulated areas and have tall smokestacks, so their output is well mixed with air before many people breathe it. Modern coal plants also have fly ash (http://en.wikipedia.org/wiki/Fly_ash) collectors that allow the nastiest of their pollution to be collected and buried.
Cars, in contrast, pollute at ground level everywhere they go.
Nuclear plants are a thorny issue. Their thermal efficiency is lousy, too - all that steam coming out of the cooling towers (http://en.wikipedia.org/wiki/Cooling_tower) represents wasted energy. But their pollution output is, arguably, close to zero per kilowatt-hour. Nuclear waste management seems to me to be a very simple issue that's only made complex by politics. But that still means it's complex, so you can't accurately estimate how much of a problem it actually is.
In a world run by rational people, you'd just leave the waste from 40 years of operation of a large nuke plant to cool inside the decommissioned plant for another 40 years - or longer, if you like - then finally truck it away in, oh, maybe ten standard shipping containers (each of which has had its volume halved by armour - that's really all the space it would take), drop it in a big geologically stable hole somewhere, and post ten guards to stop nuts from trying to steal it.
The waste from 40 years of equivalent coal plant operation would fill a fair-sized harbour. And it'd be radioactive, too - not radioactive enough that you should worry about it if you're not breathing it in (that's why fly ash collectors are such a big deal), but certainly radioactive enough that it'd be categorised as low-level waste and treated like Instant Death if it had come from a nuclear plant instead.
There's that politics thing, again.
I guess if the energy collected is solar/wind/wave/etc then electric is better. Oh and I read a thing about "new" solar cells that harness the chemical reactions performed by chlorophyl in plants :) that would be a good avenue I reckon.