[Dutch]

In having a discussion with my friend about where EV and PHEV are, and were we need to get, I was trying to get him to understand that the overall efficiency of electric vs ICE means that we're closer to "fully practical" than most people think.

So here come the numbers [Note, I'm adjusting the kWH number for a gallon of gas to 34 make the math easier]

My Wife's Mazda is <very> roughly comparable to my Volt in size/shape/comfort... et-al.
The overall average for her car (city/hwy combined) is right around 27mpg
Given a 14.5 gallon tank that means her car holds right around 493 kWH of energy in the gas tank to go 390 miles
This gives us a relative efficiency of about 1.2 Miles/kWH.

Since a Volt (and similar EV/PHEV) generally run at an efficency of about 4 Miles/kWH, We don't need to store the energy equal of 14.5 gallons of gasoline, we "only" need to store 97.5 kWH or the equal of 2.8 Gallons of gasoline and if we somehow were able to store a full 493 kWH our range would be something like 1,900 miles (wouldn't that be cool).

Yes I know, "refueling" a 14.5 gallon tank is a much different proposition from charging a theoretical 493kWH battery in a reasonable time.... that is a different discussion.

Anyway, does my math check out?

 

[Slotracer577]

You are correct, we don't need to store the same amount of energy to got the same distance. Due to the effiency increase of electric motors 90%ish vs 30%ish for ic, a battery only needs to hold ~1/3 - 1/4 of the energy to have equal range. You can make it work right now with relatively effient shaped cars, i.e. The volt which gets 40 mpg on gas, the math gets a harder when you start looking at trucks and suv's that get in the low 20's.
Personally that is why I think tesla made the model X look like a big sedan, not a regular suv. The aero drag requires a lot more battery. I have an E350 that I haul with. It gets 18 mpg and holds 35 gallons of fuel. That will take a lot of battery to get equal range. even if you assume a 4x greater efficiency, to get equal range you would need a 300kwh pack. We will need big chargers if that will charge in any reasonable amount of time.

 

[obermd]

Another way to look at this is by looking at the cost to drive a mile. I track my fuel economy and my previous 42.5 MPG (lifetime pump/odometer calculated) car was costing me $120-$130 a month to commute depending on gas prices. My Volt will raise my electric bill by $35 a month for the same commute and have zero gas cost. In fact, the lack of gas consumption and the long intervals between routine maintenance stops means that tires are now the largest operating expense I have.

 

[bjrosen]

A simpler way to look at it is just comparing ranges. Because the Volt is both an EV and an ICE car you have two numbers to work with, the EV range and the MPG. Using the EPA numbers the Volt goes 53 miles on 14.1KWh of electricity and 42 miles on one gallon of gasoline. Normalizing the EV number to 1 gallon equivalent the Volt uses 11.2KWh to travel 42 miles so a nine gallon tank equivalent would be roughly 101KWh, you then have to add in the guard bands required to protect the batter, the Volt is 20% the Bolt seems to be more like 10%, and that gives you 120KWh battery to go 378 miles using the EPA numbers. As a sanity check the Bolt goes 238 miles on a 60KWh battery, if you could double the energy density of that battery to 120KW in the same 900 lbs you would be able to travel 476 miles which is as much or more as any ICE car. Looking forward if you did have a battery with twice the energy density as the Bolt you would probably drop the weight of the Bolt battery from 900lbs to 600lbs which would still give you 1/3rd more energy which translates into a range of 317 miles in a car that weighs the same as the current Bolt, and probably 350 miles or more in a car that would be 300lbs lighter.

The refueling issue isn't apples to apples. EVs are mostly fueled at home, they always start out with 100% charge in the morning. ICE cars are fueled as needed. The need for fast charging is highly dependent on the EV range. With current BEV ranges, Bolt or base Model 3, you would never need to charge for local driving. For road trips a big battery Model 3, 300 mile range, would be able to do many but not all without recharging. In my opinion the magic number for never needing to do on road charging is 450 miles. I take long day trips every weekend in good weather and since I bought the Volt last year I always monitor my trip length and MPG and EV range. In the last two summers the longest trip I've taken is 385 miles, with several that were 375 miles. These are all day trips arriving home late at night so I'm confident that 400 miles is the absolute most anyone can do in a day unless they are driving exclusively on Interstates which is why I claim that with a 450 mile battery you would never need to use a fast charger. My guess is that a 450 mile battery will be available in the middle of the next decade.

 

[Barry]

I question the use of the 34 kWh per gallon of gas conversion. I know it has some valid scientific basis in terms of energy content, but it seems out of whack to me for the purposes of driving efficiency. 34 kWh of energy in my Volt will carry it a lot farther than one gallon of gas will. More like 3 gallons of gas. And compared to how far the average car would go on gas, it is more like 4-5 gallons of gas.

Also, comparing the use of electricity to the use of gas based on energy content seems irrelevant. For instance, the environmental impact of drilling and burning a gallon of gas compared to the environmental impact of generating x amount (whatever the perfect conversion factor is) of electricity is very different. Especially if that electricity comes from hydro, wind or solar, in which case, 1 gallon of gas almost = infinity electricy.

Obermd’s analysis based on retail prices is a valid method. It is just one factor, though. It completely ignores what I mentioned above, or the geopolitical difference, the renewable resource issue, etc. So I just don’t see how these can be compared like you are looking for. It just seems obvious that using one fuel is better than the other, almost regardless of relative efficiency.

But for the average joe, they make decisions based on their wallet, not externalities. Plus range anxiety. So for any car that has sufficient range for a given person, comparing total cost of ownership (depreciation or amortization of net purchase price plus operating costs) is the relevant comparison. When an electric car has enough range and is cheap enough to compete with an equivalent ICE car, including operating costs, it’s “efficiency” is equal.

 

[Dutch]

In my opinion the magic number for never needing to do on road charging is 450 miles. I take long day trips every weekend in good weather and since I bought the Volt last year I always monitor my trip length and MPG and EV range. In the last two summers the longest trip I've taken is 385 miles, with several that were 375 miles. These are all day trips arriving home late at night so I'm confident that 400 miles is the absolute most anyone can do in a day unless they are driving exclusively on Interstates which is why I claim that with a 450 mile battery you would never need to use a fast charger. My guess is that a 450 mile battery will be available in the middle of the next decade.

I regularly drive 422 miles to my family in Upstate NY. Also the wife and I also do a straight 668 mile drive down to Montgomery AL every other year for Christmas and drive straight back after. Now personally I would happily split the Montgomery drive into two days each way but my wife is a maniac about it <blech>.

So on the whole I tend to agree that a -solid- 400 mile range (including winter time) with decent fast charging times (say an hour to 80% while we stop to eat) would spell the end of ICE vehicles for me.

 

[viking79]

Look at MPGe, that is a measure of how much energy is used relative to gasoline, and that number includes charging losses. So a car like the Bolt EV gets 120 MPGe, which means it uses 1/4 the energy as a car that gets 30 MPG.

A 100 kwh battery with 1 megawatt charging should be comparable to gas in all ways. Anything greater than 100 kw charhing might be doable if you consider where chargers are located (like somewhere to shop for 45 mins).

Once there gets to be more interesting EVs, more people will switch.

 

[Sean-a-Tron]

That's mostly correct. However efficiency isn't just how efficiently the power is converted to motion, it's also how efficient the power is produced, transferred and stored. With oil, it's pretty poor.

 

[Loboc]

..any car that has sufficient range for a given person, comparing total cost of ownership ... is the relevant comparison.

TCO is probably the best way to compare and contrast EV vs ICE. Since the Volt probably cost 2x what the Mazda did, those up-front dollars are more important to a consumer than fuel costs. Fuel is only one factor. Although a pretty big chunk over the lifetime of the car.

Once EV is TCO equivalent to ICE, it's all over for ICE.

 

[Dutch]

Since the Volt probably cost 2x what the Mazda did, those up-front dollars are more important to a consumer than fuel costs. <snip> Once EV is TCO equivalent to ICE, it's all over for ICE.

Well, the Volt (new) would have been about 60% more than the P5, but since I bought it used my TCO is way lower, but I understand your point overall.

Comparing year-for-year on a projection, it's surprising how fast the Mazda TCO exceeds the -NEW- cost of the Volt (roughly 4.1 years) and of course TCO doesn't remain linear over time, especially with the 100k items for the Mazda like timing belts and so forth.

Having bought used, my actual TCO turnover point is more like a year and a half LOL

 

[2VoltFamily]

OK i know you got the 34 kWh = 1 gallon off of an equivalency chart. However, it is not practical to use in your calculations since the equivalency is just based on energy content and not usable energy. About 2/3rds of that energy in a gallon is lost as heat. Also, it took about 6 kWh of electricity to produce that gallon of gas.

 

[Dutch]

OK i know you got the 34 kWh = 1 gallon off of an equivalency chart. However, it is not practical to use in your calculations since the equivalency is just based on energy content and not usable energy. About 2/3rds of that energy in a gallon is lost as heat. Also, it took about 6 kWh of electricity to produce that gallon of gas.

I understand your point, and it's a good one.
however
I'm trying to avoid -over- thinking it since I wanted to make the point in a "conversation between two guys" <grin>.

 

[viking79]

The 6 kwh used in production is a myth and has been disproved. For one, looking at refining costs and wholesale price of gasoline and they would lose money. The 6 kwh is the loss of energy content during the refining process, which is otherwise unusable to gasoline cars. When you refine oil, you lose some energy content, the input is not 6 kwh, but the gasoline product contains less energy than the oil it came from, but the gasoline is a higher quality fuel than the oil.

Comparing MPG to MPGe eliminates grid and distribution losses and focuses only on energy used by the vehicle. This includes the engine efficiency, which is why gas cars are rated 1/4 to 1/2 the MPG as an EV.

 

[flyingsherpa]

TCO is probably the best way to compare and contrast EV vs ICE. Since the Volt probably cost 2x what the Mazda did, those up-front dollars are more important to a consumer than fuel costs. Fuel is only one factor. Although a pretty big chunk over the lifetime of the car.

Once EV is TCO equivalent to ICE, it's all over for ICE.

When I bought my Volt in 2013, I used Edmunds TCO calculator and Volt came out better at 5 years than a Civic, Mazda 3, and a TDI. That's not necessarily why I bought it, but it helped me justify what I already wanted. I don't know how great their TCO is... I didn't compare other TCO calculators, but it did take all the normal things into account (depreciation, fuel, maintenance, insurance, etc).

 

[flyingsherpa]

Since a Volt (and similar EV/PHEV) generally run at an efficency of about 4 Miles/kWH, We don't need to store the energy equal of 14.5 gallons of gasoline, we "only" need to store 97.5 kWH or the equal of 2.8 Gallons of gasoline and if we somehow were able to store a full 493 kWH our range would be something like 1,900 miles (wouldn't that be cool).

The rough math is right, but I'm not sure it will convince anyone. To store that 97.5 kWh, Tesla has a 1400 lb monster battery pack, while the 14.5 gallons of gas are about 87 pounds, stored in a simple plastic tank.

Electric is more efficient, but it requires big/heavy/expensive "fuel" tank. However, once full, it can use the stored energy at 90-ish% efficiency.
ICE is less efficient, but uses a remarkably light, energy-dense fuel, though it can only pull the energy out at 30-ish% efficiency.

What we need is the revolution that happened with aviation propulsion when they went from reciprocating engines to turbines... they drastically cut weight with a huge increase in power and it transformed the industry. If we had a low-cost battery that could store 200kWh in a 100lb box the size of a normal fuel tank, that could take 3-4C charge rates when needed, it would change the industry (and the world). Maybe someone will have that kind of breakthrough, or maybe we'll just chug along with 3-5% improvements to our lithiums each year... though in either case, there's still the issue of at least half the country not living with a place to charge the darn things at home.

 

[bjrosen]

The rough math is right, but I'm not sure it will convince anyone. To store that 97.5 kWh, Tesla has a 1400 lb monster battery pack, while the 14.5 gallons of gas are about 87 pounds, stored in a simple plastic tank.

Electric is more efficient, but it requires big/heavy/expensive "fuel" tank. However, once full, it can use the stored energy at 90-ish% efficiency.
ICE is less efficient, but uses a remarkably light, energy-dense fuel, though it can only pull the energy out at 30-ish% efficiency.

What we need is the revolution that happened with aviation propulsion when they went from reciprocating engines to turbines... they drastically cut weight with a huge increase in power and it transformed the industry. If we had a low-cost battery that could store 200kWh in a 100lb box the size of a normal fuel tank, that could take 3-4C charge rates when needed, it would change the industry (and the world). Maybe someone will have that kind of breakthrough, or maybe we'll just chug along with 3-5% improvements to our lithiums each year... though in either case, there's still the issue of at least half the country not living with a place to charge the darn things at home.

It's theoretically possible. Lithium air batteries have 10X the energy density as Lithium ion, the problem is that they have very short lifespans which makes them unusable in their current form. Solid state lithium oxygen batteries are about 2X the density of lithium ions, I think that's the battery that Toyota is counting on for 2022. The historic rate of improvement has been about 2X per decade for the last couple of decades and it's probably reasonable that it will continue at that rate for another decade or two, the existence of lithium air batteries proves that it's possible. What that means is that the common estimate for the date that EVs become cost competitive with ICE of 2025 is realistic.

 

[jsmay311]

]The 6 kwh used in production is a myth and has been disproved.[/B] For one, looking at refining costs and wholesale price of gasoline and they would lose money. The 6 kwh is the loss of energy content during the refining process, which is otherwise unusable to gasoline cars. When you refine oil, you lose some energy content, the input is not 6 kwh, but the gasoline product contains less energy than the oil it came from, but the gasoline is a higher quality fuel than the oil.

Comparing MPG to MPGe eliminates grid and distribution losses and focuses only on energy used by the vehicle. This includes the engine efficiency, which is why gas cars are rated 1/4 to 1/2 the MPG as an EV.

+1

a Volt (and similar EV/PHEV) generally run at an efficency of about 4 Miles/kWH

The Gen 1 and Gen 2 Volt's EPA-rated electric efficiencies are 0.35 kWh/mile and 0.31 kWh/mile, respectively. That works out to 2.86 miles/kWh and 3.23 miles/kWh, respectively.

The Hyundai Ioniq and Prius Prime are the only vehicles currently sold that are rated for 4 kWh/mile (0.25 miles/kWh).

 

[saghost]

There is nothing wrong with your math. Whether the math is useful to your discussion is a different question...

Efficiency is a rather nebulous question when it's not being used by engineers, because there are many things you could be optimizing.

A car that uses far more of a cheap fuel may still be much less expensive to run than a car that uses very little of an expensive fuel. Solar panels are still typically less than 20% efficient when defined as light in to electricity out, but it doesn't matter much because there's a major surplus of light. Most folks don't install the most efficient panels because they cost more per kWh of electricity produce, so they only make financial sense when there isn't enough space to install more of the less efficient panels instead.

So yes, the electrical energy required to move the Volt is far less than the chemical energy contained in the gasoline used to move the Mazda, but it's Apples and Oranges.

You can see that in the Volt itself - a very efficient car with the most efficient engine GM makes and one of the most efficient around, but it goes 2.5x further on a unit of electricity than on an equivalent unit of gasoline, because ICEs are inherently rather inefficient in even the best cases (large ship diesels can sometimes exceed 50% in ideal cases.)

So what really matters in the discussion you're having?
Miles per dollar spent on fuel?
Miles per pound of fuel storage?
Miles per pound of CO2 released?

Outside of the realm of design engineers, the actual thermal efficiency is unlikely to be the important part.

 

[hellsop]

I question the use of the 34 kWh per gallon of gas conversion. I know it has some valid scientific basis in terms of energy content, but it seems out of whack to me for the purposes of driving efficiency. 34 kWh of energy in my Volt will carry it a lot farther than one gallon of gas will. More like 3 gallons of gas. And compared to how far the average car would go on gas, it is more like 4-5 gallons of gas..

And how efficient are internal combustion engines anyway?

 

[jcanoe]

Another consideration is that while the Volt's battery provides 14.1kwh of available battery capacity it can take ~ 17kwh to fully charge the Volt using a Level II 240V EVSE, approx. 20% charging overhead that never goes into the battery. Depending on the ambient temperature the Volt will heat or cool the battery during charging. This requires some power in addition to power losses within the onboard charger.

Electricity costs in my area are fairly high ~$0.16 per kwh (includes all fees and taxes). At current electricity rates a full gallon equivalent, 34kwh, would cost me $5.44 and that does not include any overhead losses while charging. However, the typical passenger car can travel ~27 miles on a gallon of gas while the Volt can potentially travel ~4X as far (106MPGe). So at recent gas prices of $2.25 per gallon, (current spot prices for gas are [Updated 9/1/17: $2.70] or more in some areas due to the after effects of hurricane Harvey), the Volt's equivalent cost is ~$1.36 versus $2.25 (~40% less than gas) or more for the average passenger car to travel the same distance (27 miles) on a gallon of gas. If the passenger car is a hybrid such as a Prius then the cost per mile delta between the Volt running on battery power and the hybrid running on gas is much closer.