Featured Why the auto industry is in trouble

It's not that simple, EV is not 100% efficient, grid distribution is not 100% and charging from the wall is not 100% efficient, NG production is not 100% efficient .... petrol refining is not 100% efficient....

EV is roughly twice as efficient with energy on board (56 MPG vs. 110 MPGe), but gasoline comes to a tank with <85% efficiency, electricity comes to a battery with <50% efficiency. Close call.

 

You are correct, it isn't that simple, yet it is as simple as
The above is from Life Cycle Electric Vehicle Emissions (2015) | Union of Concerned Scientists
Which also talks about cradle to grave energy use.

The above map is based on 2012 data, so EVs charged off the grid are even cleaner now, than they were then.

Of course, someone is actually concerned about the greenhouse gas emissions of an EV, they have choices to use renewable energy. With gas burners, unless you use bio diesel, you have no such choice.

 

I would even suggest its not a close call yet...EV are using more elec than tend to admit, and the cars themselves are more costly and disposable like electronics. However, there is some significant political support for electrification in the USA. So we are arguing a little bit about politics, attitudes, and advocacy, which is not the same in Slovania and Telmo-land (and Toyota/Japan) compared to USA.

 

Are these values direct comparisons to thermal efficiency of the engine. They are measuring the electric generated at the point the plant puts it on the grid. This factors in all the energy the plant uses, and not just the fuel into the engine.

My comment that started this sub-thread was on why some one might call a Prius 2% electric. Put the efficiency of sources aside for a moment.

Electricity for the grid can be made from a multiple of sources. This allows more options for switching to renewable 'fuels'; sunlight and wind being two possible ones. A car without a plug can't take advantage of that flexibility. It is stuck using whatever fuel its ICE was meant to run. If there isn't a renewable option, then it is stuck using the non-renewable.

Then costs, can be beyond money, of a renewable ICE car fuel can be greater than they are for a power plant; ethanol vs. wind or bio methane. So if a 100% renewable fuel was available, the cost of using it in non-plug cars might be too great for society to make the switch, or production levels may simply not be possible to meet demad. With plug ins displacing a car's fuel need away from the ICE fuel, a renewable ICE fuel might be able to replace the non-renewable fossil one completely.

 

There are several problems with that simplistic analysis. First, you are using about 50% for the thermal efficiency of power plants. The average is probably much lower than that. It also does not take into account transmission losses (about 5-6% typically) or battery charging losses.

On the other hand a big part of electrical generation is or could be hydro, wind and solar and the thermal efficiencies don't having an equivalent meaning (in terms of CO2 or smog production). Nuclear also has a 35-40% thermal efficiency yet produce no meaningful CO2 or smog.

If you just used solar PV to operate a car it would have a terrible "efficiency" number since PV starts at 15-20%, then you lose when you charge the battery.

Bottom line: you have to be very careful when comparing efficiency numbers. Combining them in a sequential series of steps to get an overall number is usually OK.

Mike