Solandri said: ankitgu said: ubermichaelthomas said: Does your local electricity come from burning coal or is it nuclear energy? Most electricity in the US is generated from burning coal, which essentially means you're damaging the environment much more than if you simply burned gas in your car because extra coal has to be burned to compensate for the loss of energy going through the power lines and more energy loss when the batteries in the car are charged.
Essentially, you're doing more damage to the environment than if you simply used a gas vehicle. Unless you have nuclear power in your city, in which case nuclear energy is just wonderful for the environment.
I want to give you green for going a step further than 99% of people in this thinking. In a sense, the tail pipe of the car is simply moved from your car to a power plant. You're also correct about the efficiency loss. You could have even mentioned that unless we have good disposal of the battery chemicals, they are damaging to the environment.
Despite those items, I think we should remember that burning coal in a power plant is going to likely (I am no expert and haven't looked up numbers) to be more efficient than a person who uses an engine to convert fuel (which has to be delivered via semi vs coal via rail) into energy and heat. I believe the efficiency is roughly close to 30% for a standard gasoline engine.
Despite all the red ubermichaelthomas got, he's on the right track. Until we switch to mostly nuclear and renewables for electricity, EVs are mostly a pointless endeavor from an energy efficiency standpoint (they are better for emissions since the scrubbers on a modern coal plant do a much better job than a catalytic converter).
- The best coal plants are about 45% efficient (45% of the energy in the coal is converted to electricity). Oil and gas plants are 50%-60% efficient, but (except for Hawaii) they represent a small portion of our electricity generation.
- Transmission on power lines is about 95% efficient.
- EV battery charging is about 75% efficient. <-- This is the big one most EV proponents miss.
- Electric motors are about 90% efficient. It actually varies by load, but so does an internal combustion engine's efficiency, so I'll just go with near-peak values for both.
- Wheel axel friction and tire losses I'll assume are the same for the EV and the ICE vehicle.
So what do you get when you multiply all these efficiencies together?
45% * 95% * 75% * 90% = 28.9%
An EV charged with electricity from coal only delivers about 29% of the energy in the coal to the wheels. Contrast that with an ICE car which typically delivers about 25% of the energy in the gasoline to the wheels. (Around 30% efficiency at the engine, with the transmission and drivetrain being around 80%-90% efficient.) So if your electricity comes from coal, the EV barely beats out the ICE for energy efficiency. And that's assuming the highest efficiency coal plants currently in use. If you use the industry average 28% efficient coal plant, EVs are actually less energy-efficient than ICEs.
This is the same nail in the coffin for hydrogen fuel cell cars. While the fuel cells themselves can be 70%-80% efficient, the process of converting water into hydrogen is about 65% efficient. And the electricity you have to use to do it is (assuming the highest efficiency coal plants again) about 43% efficient. For an overall efficiency of 43% * 65% * 80% = 22%. The same as an ICE except hydrogen is much more difficult to store, transport, and dispense.
I don't want to discourage EV adoption, since I do believe they are the future. But I think it's important that people understand that everything will not be rainbows and unicorns just because we switched to EVs. Until we switch away from coal to nuclear and renewables for our electricity generation, there's really not much gain on the energy front. Until then, EVs are just advancing the state of the art, not really saving us energy. (Though they are saving us cost and reducing pollution.)
acrokpeterk said: Have you considered a VW Golf TDI? Similar mileage, much more efficient Diesel engine, and WAY more enjoyable to drive - with comfortable seats. Just throwing that in the discussion.
Diesels aren't that much more efficient. Most of their higher mileage is phantom. Diesel is heavier than gasoline. There's about 12% more "stuff" in a gallon of Diesel than there is in a gallon of gasoline. And per gallon there's about 10% more energy in Diesel than gasoline. In other words, a gallon of Diesel could theoretically be refined into 1.1 gallons of gasoline. So you really need to be multiplying the MPG of a Diesel by about 0.9 to compare it to a gasoline car's MPG on an equal-energy basis.
I generally agree with your post - but I want to touch on a couple things. The 75% efficiency on battery charging... the source is questionable, outdated and perhaps based on 110v. 220V is much more efficient in the roadster. I am sure the Model S is much better. I would estimate 90% is a better number for this efficiency.
25% efficiency across the board is a little high for an ICE. Most people here drive V8 SUVs that probably get 10% with idling and constant speed cruising and all the braking done. (these huge motors are more efficient at high loads such as acceleration, which of course just leads to more braking with the average driver)
Hydrogen only makes sense where you have EXCESS renewable energy and have nothing else to do with it. If we were to build another 1000 3GW nuclear plants in the country, hydrogen would be great bc it would eliminate batteries. But's it's just too inefficient to use with coal/nat gas/oil
edit: "here" means TEXAS