Anne--
I, too, am just a bit suspicious about EV vehicles. Overall reliability aside, I still have to ask myself about how good these vehicles are for the environment. I can address that question two ways--The (environmental) costs of manufacture & transport to site and the cost of fuel and operating.
The cost of manufacture are significant. The batteries involve a lot of metals like cadmium, cobalt. Cobalt is particularly troubling from a mining & extraction standpoint. Most Cobalt mining is done under conditions that are about one small step away from human slavery. They also really wreck the land around them. I am sure that cobalt mining could be done much more efficiently, humanely and safer for the environment, but at present most comes from some locations that have dubious reputations at best.
Then there is the environmental cost of running on electricity. On the surface, an EV sounds like THE perfect vehicle--what could be better than a vehicle that has no emissions. But that electricity has to come from somewhere and depending on where you are located, that electricity could come from a source like a dam which emits no CO2 at all or you could be like me and live in the middle of coal country and use the most CO2 intensive fuel possible. Most people live in a place where the electricity they consume comes from a mix of generating sources. But for these purposes, I will pretend that all the electricity is produced by coal (NOTE: Natural Gas is quickly displacing coal as the #1 source of energy for the United States so that change alone is a good, positive step. Now we need to continue moving further away from CO2, but a step in the right direction is nice indeed!
In a gas (and diesel) engine, the fuel is combusted to produce heat which then immediately causes an expansion of gasses that drives the piston and thus the engine and therefore the car. Heat to Motion happens in just a couple of steps. My understanding is that energy losses from the point of combustion to the running of the tire (called the tank-to-tire ratio) are about 90%, making the Tank-to-Tire ratio 10%.
In an EV, things get a little different. Assuming coal, the coal (which inherently burns dirtier in the CO2 sense than gasoline because the coal is pure carbon whereas gasoline is a mix of burning carbon and hydrogen--actually quite a lot of hydrogen. Anyhow, that coal burns to boil water to produce the steam that will run a steam turbine that will then turn the generating portion of the power plant. Those steam turbines optimistically run at about 35% efficiency. In a newer power plant, that 35% is achievable. In an older system, that efficiency drops to 25%. From there, the alternator that actually produces electricity has a variable efficiency, ranging from 50% to 98% or even slightly higher. The reason for the huge discrepancy is based on whether or not the alternator is running at their designated load--a sort of sweet spot where they perform optimally. For these purposes, I will 90% as the total efficiency of the alternator, though this can vary tremendously based on electrical load. And since coal plants can easily adjust to different load conditions, right here is a place where estimates will break down if examined thoroughly. From there, the electricity is then sent out over high voltage lines to substations where the voltage drops to 120/240 volts. This is another place where energy is lost, but I will say that the losses are only about 5% so the overall efficiency here is 95%. That load then get transmitted to your house where the AC is converted to DC (probably another 5% loss so 95% efficiency) to run the car charger. Things get really complicated here.
Lithium Ion battery charging is one of the most efficient chemistries to charge, in ideal condition exceeding 99% efficiency. But that is under really specific condition. Firstly, the temperatures are in a Goldilocks zone--neither too hot nor too cold. Deviate either way and the efficiency drops quickly. Next, the SOC--State of Charge matters. Is the car charging below 80% SOC (so say from 50% maybe), then the charging is rather efficient, but above 80%, the charging gets much more inefficient. Fast charging matters as well as fast charging heats the battery which then causes it to be less efficient.
From what I can gather, the overall efficiency of home charging looks something like this:
Level 2 240v charging--90-95% overall efficiency
Level 1 120v charging--75%-85% overall efficiency
DC fast charging--90%-95% or even a bit higher
So anyone who charges from their home no doubt wants a 240v fast charger. Its faster and more efficient. But if you are charging from 120v, the efficiency drops quite a bit. If you are doing direct DC, then you have the best option, but this likely requires a solar panel setup and full sun.
So to add all this up, I will use some back-of-the envelope calculations and guesses.
100% energy--straight from the coal
35% remaining after the steam engine 35
4% from the alternator 31
5% from transmission losses 29
10% from charging losses 26%
So at this point, with a combination of some calculation and some guesswork, I have the overall losses from the coal to the battery as being about 75% (I show 74% here, but I will round to 75% as these are very vague figures). And with 25% of the energy remaining as opposed to 10% of the energy remaining from the gasoline, it should look pretty clear that the coal-to-battery efficiency is not only very high, but over twice that of gasoline. Granted, these are some pretty optimistic figures and they assume 100% coal, but these are numbers we can work with. But we really want to know about CO2 production and after some poking around I found that coal produced about 40% more CO2 than gasoline, so that still makes coal-to-battery look good.
Gasoline 2.5 x 1 (unit of co2)=2.5
Coal 1 x 1.4(units of co2)=1.4
Coal still wins
But what if this is NOT the most optimistic charging condition? What if we change conditions to look like the following:
100% energy straight from the coal
25% after steam engine (maybe an old steam engine. Maybe not running at optimal conditions)
25%
80% from alternator 20%
5% transmission losses 19%
25% charging losses 14%
Gasoline 1 (x1) = 1 unit of co2
Gasoline 1.4 (x1.4)=1.96 (2) units of co2
Under these less ideal conditions, coal then looks about twice as bad as gasoline.
The verdict: There are far too many variables to say whether or not your battery or gasoline is the better option. This really is a case where you will simply have to make an educated guess on your own. If I were making the decision, it might look something like this:
Option #1 A small, light vehicle whose purpose is getting myself, maybe a passenger and some cargo (groceries?) to and from the house and local places. I might give serious thought to an EV. This would be especially good if I could work a solar system so that I can charge directly from sunlight.
Option#2 A working vehicle that must perform tasks such as towing or hauling (think a pickup). I would think a pickup truck. And I would give special consideration to a diesel truck as diesel is fundamentally a better fuel than gasoline--more power and lower fuel consumption! What more could one ask!
NOTE: I made a lot of educated guesses. If you spot something wrong or can think of a better way to calculate this, by all means correct me/improve on my list/etc. Maybe it fundamentally changes the outlook, maybe it makes no difference, but I would still like to see what you think and how you can improve.
I would live to hear your thoughts/improvements
Eric
