Coal power plants are roughly as efficient as an internal combustion engine (around 40%) and considering the power transmission losses, charging losses, electric engine inefficiencies and so on, any electric vehicle has worse overall efficiency than the equivalent gas vehicle. Electric vehicles only make sense from a pollution reduction point of view if the power is generated from renewable sources.
Typical coal power plants have practical electric efficiency 40% but total energy efficiency is 60-70%, because they produce electricity and useful heat.
Also 40% is a theoretical (lab) value for a non turbocharged diesel engine - in practice most engines are operated out of their optimal range, they are turbocharged (a turbo increases power output at the cost of decreasing compression ratio and thermal efficiency), there are losses in the transmission, hence efficiency is much lower than 40%.
BTW, in lab, a coal plant with a steam turbine can achieve over 50% electric efficiency (some reports say even 60% is possible). They are too expensive to be used on large scale, though.
Hybrid cars let you operate IC engines at fairly high efficiency depending on setups but you now have to deal the overhead of charging batteries for both setups.
Also, if you want total efficiency in terms of C02 then you need to consider. Gasoline takes a lot of energy to extract, refine into a usable state, and transfer around the world. On the other hand hydrocarbons extract energy from hydrogen bonds not just carbon bonds so they produce less C02 per BTU.
Net result electric cars backed by coal power still win vs IC, but not by as much as you might think.
PS: You can also use turbines in hybrid car which would boost it's efficiency even more. But, you can also produce very cheap solar power which once again shifts things back to electricity.
What would you say is the typical efficiency of a modern gasoline car? Say, one that uses 7L/100km on average?
Also, why do the coal plants with higher efficiency so expensive? I've read somewhere that higher heat would be better, but the steel that can resist it, is too expensive. Is that correct?
I'm not am expert on turbines, but generally the turbine efficiency is directly related to the temperature and pressure difference between the inlet and outlet. Hence bigger plants have typically higher efficiencies. Bigger turbines have also more stages, so not only they have to withstand higher pressure, but simply there are more parts.
Are you sure about your statement on turbos reducing efficiency? Some of the most economical consumer engines are turbocharged--in fact auto makers commonly cite mpgs as a reason to use turbos; so I am confused.
Yes. Turbocharging increases mpg not by increasing thermal efficiency, but by allowing to use a smaller and lighter engine. A lighter engine means less mass to accelerate, therefore less energy to spend. A smaller engine means less internal friction so less energy lost. However this theory works well if you actually don't use the full power that turbo gives you, or you use it only occasionally. These engines have great advantage in lab mpg tests, but in real dynamic driving the advantage diminishes. The main problem is that by adding a turbo, you need to decrease the compression ratio of the engine, which decreases thermal efficiency. Another thing is that turbo needs some energy to be powered, and also has some of its own energy losses. This is not free.
The new Honda Civic comes in a 1.5 turbo and a 2.0 NA, the turbo being the heavier package--but which still delivers higher mpgs. And if the turbo has more efficiency due to less internal friction, that still creates more useful energy out of the same amount of fuel, no?
You are right, but now we are not discussing thermal efficiency, but total mpg which is related, but not the same thing. Efficiency being equal, you'll get more mileage from an electric car, because it can get back some energy from regenerative breaking, and it definitely has less internal friction.
How is the useful heat used? I know some places have central heating, so the hot water is just piped throughout the city, but if not that, what would they do with it?
The term that the original poster didn’t include is “Cogeneration” [0]. Another use case would be desalination in areas without an adequate supply of freshwater.
Ya, I get that, it just doesn’t seem to be always the case that you’d find something to do with the heat, especially given proximity of the coal plant to places that could use it. It wouldn’t seem to work well for Australia, at first glance (no serious heating needs, no desalination plants).
You would find it very hard, if not impossible, to run an ICE car at 40% efficient for normal driving. The same can not be said for a coal plant. So if the coal plant averages 35% and the ICE car averages 25%, that leaves some room for a coal-driven electric car to be more efficient. The conversion from grid power to mechanical power only needs to be over 70% efficient. If anything, that sounds easy to beat. Any counters?
What about refinement costs to turn oil into gasoline in the first place? That takes energy as well, and creates pollution. So we have a loss before we even get to the ICE.
I we say all three of: charging, motor controller and motor are about 90% efficient, that's already 72% efficiency from grid power to mechanical. So maybe not that easy.
While a 90% efficient motor is quite good, a 90% controller and a 90% charger is not. I would expect them to be closer to 95%. But I have to back down from easy, according to [1], some Tesla owners charge their vehicles at 80% efficiency and not the ideal 92-98%. I imagined that would be a problem at those energy levels, apparently not! Anyhow, there is nothing inherently worse about fueling a central ICE to pump out electricity to EVs than directly fueling an ICE car. Larger ICEs tend to be more efficient, especially so for diesels. If you add the savings by the regenerative charging enabled by electric motors, it becomes even more favorable to electrify cars. We need a lot of batteries though!
What's the power transmission loss from carrying crude to a refinery and then to Australia? The country is a net importer of oil, which means tankers burning foul stuff to carry it there.
Very true. Considering the whole supply chain for accurate comparison is complicated. Although I think my main point still stands : from an environmental perspective it's rather ineffective to have an electric car in a place where electricity comes from fossil fuels.
I think you're overstating the current situation and also leaving out the fourth dimension. If the grid gets cleaner over the useful life of the EV then it benefits from that. I believe basically all grids are projected to get vleaner over the next decade.
While electric cars might be worse for the environment, they're probably much better for people, because the pollution generation can be moved well away from dense urban areas. I imagine most people don't even remember what a city without gasoline pollution, like, smells like.
I imagine it will be similar to those before-after photos of cleaning smoker's apartments.
