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Comment by throwaway613834 | Hacker News Reader

How much cleaner is electricity that comes from fossil fuels compared to direct burning of fossil fuels?

EDIT 1: Thanks for all the enthusiastic replies telling me that power generation is better optimized. Yes, I already understand power plants are much more likely to be better optimized than car engines. That's why I asked "how much" instead of "whether". I'm wondering if the difference ends up being something like 10% (by whatever the suitable metric is) or 30% or 60%. Numbers and/or references from actual data would be appreciated.

EDIT 2: Note that we also need to consider the energy loss in transferring the electric power and charging up the battery; it's not just about power generation efficiency. I don't know if this is significant or not.

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It is cleaner, as the power plants always run at peak efficiency while combustion engines in cars only achieve about 50% of that. So even in the worst case, the electric car is not bad. Of course, an electric car does not have any noxious exhausts inside the cities, nor does it make as much noise as a combustion engine.

But few grids are 100% fossil, and most importantly, most if not all grids are going to get significantly cleaner during the lifetime of the electric car. So electric cars are picking up any enhancements to the electricity production.

Not only are car engines run at sometimes-inefficient RPMs - they also have to optimize for weight, volume, and convenient torques/speeds for a car transmission, all of which come at the expense of efficiency.

It is my understanding that once efficiencies are factored in, electric cars powered by fossil fuel power plants are still cleaner than gasoline for the simple reason that internal combustion engines are rarely running at peak efficiency (efficiency is 0% when idling to use the extreme case), and even peak efficiency is lower than you can get from the power plant. That said, China is also investing heavily in alternative energy, so the situation would only improve over time.

Not to mention that EV's powered by fossils fuel power plants provide cleaner air where people are.

Further, a few large plants can better filter particulates and other exhaust more efficiently than millions of smaller engines in every car.

This article about Tesla and Musk has all the information you need to know and more:

https://waitbutwhy.com/2015/06/how-tesla-will-change-your-li...

Here's the money quote:

"2) Energy production is more efficient in a power plant than it is in a car engine. To use an example with an identical source fuel, burning natural gas in a power plant is about 60% efficient, meaning 40% of the energy of the fuel is lost in the energy production process. In a car, burning gas is less than 25% efficient, with the vast majority of the energy lost to heat. The larger more complex system at a power plant will always be far better at capturing waste heat than a tiny car engine. The increased efficiency means that even a car running purely on coal-generated electricity will emit carbon at the same rate as a gas car that gets 30 miles per gallon—which would be a significantly cleaner-than-average gas car."

Thanks! Yeah, this is the kind of number I was looking for. The remaining part is how much efficiency is lost in the transfer of energy from the power plant to your car (transmission, charging, etc.).

Re: Edit 2: Note that we also need to consider the energy loss in transferring the electric power and charging up the battery; it's not just about power generation efficiency

Do we then also need to consider then the energy cost of transporting gasoline from refineries to gas stations?

Good point! I didn't think of that. Yes, that should probably be included too.

IIRC, a car engine runs at about 25% efficiency and a power plant usually exceeds 40%.

Great! This is the kind of number I was hoping for; thanks!

The remaining part is how much efficiency is lost in between (charging, transformers, etc.)... hopefully it's not a significant fraction of the difference?

At least the pollution is more centralized and can be dealt with more efficiently.

Yes, the CO2 exhaust can be captured before it escapes!

If we're comparing with ICE vehicles, an easy way to think about this is how driving style alone can affect mileage. A power plant can be designed and run most efficiently to produce power all the time.

That aside, the fuels used in power plants aren't generally the same as those used in vehicles, are they?

Except with gas turbine plants, I guess. But those are more for peak demands than base supply.

Well, one of the benefits of centralization is economies of scale to do R&D. And thus the power generation can move to wind, solar, geothermal, nuclear and so forth.

And it can be supplemented by solar panels which is decentralized.

In addition can pollution (Co2, NOX, noise, etc) be effectively de-urbanized.

This seems relevant; China are investing heavily in renewable energy:

https://www.theguardian.com/business/2017/jan/05/china-inves...

China is also investing heavily in nuclear: http://www.world-nuclear.org/information-library/country-pro...

You don't get PM2.5, PM10 and NOX from the tailpipe so less carcinogens in the city.

The power for electric cars need not, of course, come from fossil fuels at all. Nuclear, solar, geothermic - the car doesn't care. As ever, naturally, workable fusion fixes much...

thats not what happens in reality. US and China still use tons of coal to generate electricity.

And they still build and sell millions of petrol vehicles too, but that's changing; my point stands.

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