Battery-Electric Fast-Charging Versus Time Explained

If BEV charging really an issue?

One often reads statements by ICE drivers that they will not buy a BEV until it can be charged as fast as ICE cars can be filled with gasoline; they often state a 5-minutes target fill time. I do not recall ever spending only 5 minutes at a gasoline station. I estimate 15 minutes as the minimum time I used to be at a gasoline station, and it was usually longer. I stop my Tesla Model 3 Long Range on long trips for personal reasons more often than needed to charge car. Tesla navigation on the screen tells me how long to charge at each Supercharger to minimize travel time; I often charge longer than that for personal reasons.

It is a fact that fast-charging (kW) a BEV battery is not at a constant speed as is the case for filling an ICE gasoline tank. In this document I examine the filling rate for fast charging of a BEV.

Consider three BEVS with maximum charge rate of 120 kW, 250 kW and 350 kW with batteries of the same battery chemistry and, therefore the same shape of the charging-power curve. If the 120-kW BEV is the Tesla Model 3 Long Range BEV (TM3LR) with about 75-kWh usable battery capacity, the power-proportional usable battery capacities for the other two cars would be about 155 kWh and 220 kWh. (I use 250 kW power because Tesla has indicated that will be the maximum power for near-future Superchargers. I use 350 kW because Electrify America is starting to install some stations with that maximum power.)

Using the mathematical formula for charging power in my previous study for charging the TM3LR using a Tesla Supercharger and TM3LR charging-power data I get the following approximate charging curves for the three BEVs:

The two higher kWh BEVs probably would not have as high efficiency as the 75-kWh BEV. The batteries would weigh more and the cars would be larger.Assume the following realistic efficiencies:



BEV kWh 75 155 220

Miles/kWh 4 3 2.5



The corresponding three curves for miles gained versus charging time using a Supercharger are:

The vertical line is about the half-way the time to full.

Note that a 75-kWh BEV with 4 miles/kWh efficiency would get about 150 miles added in twenty minutes. As the three curves show, when driving a BEV on a long trip it is not wise to fill the battery to near full; that should be done overnight at home or a hotel. Of course, the level-2 charging stations power at those locations will range from 6 kW to 19 kW, which have much longer level power curves, but the curves do tail off before reaching full. A constant 10 kW would take about 7.5 hours to fill the 75-kWh battery from empty to full, about 15.5 hours to fill the 155-kWh battery from empty to full and about 22 hours to fill the 220-kwh battery from empty to full.

It is not wise to charge from a high state of charge (SOC) to near full on a long trip because the average charging power is much lower than when starting at a low SOC. Here is such a Supercharging curve for the TM3LR starting charging at 68% SOC:

In the future, there may be new battery chemistry that possibly include super-capacitors for BEVs that charge much faster or without tailing off as quickly as shown below:

This article originally appeared on Inside EVs.

 

[TechOps]

The label for Energy Density should use the units W•h/kg.

 

[Odie]

At decent petrol pumps the average pumping speed is between 30 to 40 liters (europe mainland here, sorry!) per minute, truck-pumps are much faster. This means that for an average ICE with 60 to 70 liters tank the actual pumping time already is close to 2 minutes. Add 1 minute for opening and closing the tank and handling the plastic glove and add a few minutes for walking to the cashier, queueing/paying and walking back. I would guess that the average pitstop is more closer to 5 minutes, 10 at most. However, if you grab a coffee or a snack then the total pitstop time quickly increases to 15 or 20 minutes.

For Joe Average charging only becomes acceptable when they will see 1 to 1 comparable charging times, meaning having the equivalent of 70 liters diesel/petrol in about 10 to 15 minutes. According to the calculations in the article (and real world experience) we are not here yet. Is this a problem? For BEV early adopters who like BEV's and who like to spend some extra time for the greater good: no. For Joe Average who has no reason to move from ICE to BEV and only makes this move because "I have to, the Government is making me, ICEs are getting banned/expensive" this is still a problem.

We can reason that supercharging to the equivalent of a full tank is almost never required (just charge up to a SoC that is needed to get to your destination and slow charge there over night) but for a roadtripping Joe Average this is not really an argument: he or she just wants to fill it up as quickly as possible to the max range the tank/battery allows.

 

[King_M3D]

The average person is not accustomed to starting every day with a full tank of fuel. It doesn't take long to realize that with a 300 mile range every morning, fast charging is only rarely necessary. I have traveled 12000 miles since last August and only needed to fast charge twice.

 

[Odie]

The option to charge at home and start with a full battery is unprecedented and is one of the big advantages of EV's over ICE. Even with my current Volkswagen GTE (still awaiting my M3 delivery here in Mainland Europe) the current 50 kilometers (during wintertime) is enough for my daily commute to work, where I can charge again for the return trip. In summer the range is about 65 to 70 kilometers and this allows me to make a return trip on a single charge. I only see petrol stations during weekend trips and I can't wait to say goodbye to the ara of legacy ICEs.

 

[Saghost]

At decent petrol pumps the average pumping speed is between 30 to 40 liters (europe mainland here, sorry!) per minute, truck-pumps are much faster. This means that for an average ICE with 60 to 70 liters tank the actual pumping time already is close to 2 minutes. Add 1 minute for opening and closing the tank and handling the plastic glove and add a few minutes for walking to the cashier, queueing/paying and walking back. I would guess that the average pitstop is more closer to 5 minutes, 10 at most. However, if you grab a coffee or a snack then the total pitstop time quickly increases to 15 or 20 minutes.

For Joe Average charging only becomes acceptable when they will see 1 to 1 comparable charging times, meaning having the equivalent of 70 liters diesel/petrol in about 10 to 15 minutes. According to the calculations in the article (and real world experience) we are not here yet. Is this a problem? For BEV early adopters who like BEV's and who like to spend some extra time for the greater good: no. For Joe Average who has no reason to move from ICE to BEV and only makes this move because "I have to, the Government is making me, ICEs are getting banned/expensive" this is still a problem.

We can reason that supercharging to the equivalent of a full tank is almost never required (just charge up to a SoC that is needed to get to your destination and slow charge there over night) but for a roadtripping Joe Average this is not really an argument: he or she just wants to fill it up as quickly as possible to the max range the tank/battery allows.

That's a false equivalence. Admittedly, it's one that has been heavily promoted by folks who don't like or fear EVs.

There's no real reason the fast charge rate is a key performance parameter for an EV. Folks are thinking about that because they are trying to fit the EV into their existing "stop for fuel and wait once a week" paradigm.

A properly developed EV architecture won't require that, though. Charging at home or work means never waiting for a charge except for longer road trips.

With that in mind, I think once they experience electric driving you'll seer a lot of Joe Average people willing to trade rare longer charging stops on long road trips for instant torque, lower maintenance and running costs, a full tank every morning, and all the other EV features.

The EV doesn't have to beat an ICE on every single trait to be adopted - it just has to present a substantially better overall package based on what each consumer wants - and there are several inherent advantages to EVs to help offset the weaknesses.

 

[tonybelding]

Another factor that some seem to overlook is that you don't have to "babysit" your car and monitor it while charging. However, I've had those same kinds of conversations with EV skeptics before. They usually go something like this:

Electric cars will never get any traction until you can take road trips with them.

You know you can put 180 miles of range into the car in 20 minutes at a Supercharger station, right?

20 minutes? That's outrageous! I'd never be able to drive 1000 miles in a day if I had to stop for 20 minutes every 180 miles.

1000 miles, really? The most I ever drove in a day was 650, and I hated it and never wanted to do that again. I can drive 500 without much stress, though.

Oh yeah, well let me tell you about... [insert story about an epic Cannonball-like marathon trip they did one time many years ago] And we couldn't have done that in an electric car, so that proves they're not acceptable to anyone, anywhere!

But you know Tesla has sold hundreds of thousands of cars, right? People are shelling out hard-earned money for them.

Oh, a handful of irrational fanboys like you, sure... But normal people will never accept something like that.

I give up.

 

[SO16]

1000 miles, really? The most I ever drove in a day was 650, and I hated it and never wanted to do that again. I can drive 500 without much stress, though.

Oh yeah, well let me tell you about... [insert story about an epic Cannonball-like marathon trip they did one time many years ago] And we couldn't have done that in an electric car, so that proves they're not acceptable to anyone, anywhere!.

I would just respond with: “If you would rather have more convenience during the cannonball run you “might” do once in a lifetime (or even once per year) vs having more convenience the rest of the year with a full tank every morning, that’s fine. If I absolutely HAD to do the cannonball run, I’d just rent a gas car.”

 

[mswlogo]

You need to Amortize all your time at a gas station vs all your time charging (home + SC). I think, all in all, it comes out about even.
SC will get better though.

 

[SO16]

You need to Amortize all your time at a gas station vs all your time charging (home + SC). I think, all in all, it comes out about even.
SC will get better though.

Seeing as how I use SC stops as food stops, the time spent as superchargers is a good thing.

 

[Odie]

I can’t wait for my first 100% BEV is going to be delivered. Personally I consider the charging a challenge and a way to slow down long distance traveling a bit. For sure i’ll go for some road trips. Thinking of a trip to Norway (EV country #1 in Europe and stunning nature) or Spain/Portugal

 

[jboy210]

As I have gotten older I found I need to have a bathroom break every couple of hours. So Superchargers are perfect for me when I take trips.

In daily use I come home and plug in my phone and car, have dinner, watch TV, and go to bed. Magically the car and phone are charged when I get up. What could be simpler?

The whole concept of going somewhere near my home to get gas is now foreign to me, as are issues with gas stations. They might be closed, be out of the fuel grade/type I need, have a long line of cars, or .... Superchargers, and my garage plugs never close, and there is never a line.

 

[MHarrigan]

I believe that most people would be happy with EVs IF they had ready access to a network of DCFC stations that was ubiquitous, easy to find, and readily available as the Tesla SuperCharger network. It's not the time spent charging, it's the uncertainty of how long the trip will take and the amount of planning needed that puts people off.

Road trips in the U.S. for Tesla owners are not a problem due to the extensive supercharger network that is available to them. For some, charging at the supercharger is free. However, for other EV owners (Bolt, VW, etc.) finding a DCFC station is often difficult and even when you find it you may be waiting for others who are queued up waiting for the station, and even when it's your turn, you may be spending a lot of money. A Tesla is too expensive for many people, so if they were to buy an EV, they would be using the relatively rare, difficult to find, often in-use, expensive DCFC stations (Tesla competitors: take a hint!).

In short, I see their point.

 

[jboy210]

I wonder how much people in 1910 made the same type of arguments about convenience when Ford brought mass produced cars to the masses. After all gas stations where not ubiquitous especially in the country where many home were still lit by candles and lamps. They had to go to a tank out back, grab a bucket, put it under a tap, filled it and carried it to your car. Then they split a lot of it on the side of the car and your seats trying to fill the tank which you say on.

Sounds like too much work, and the car make noise and smell. Roads are dirt with ruts and impassable by car when it rained. Just give me a good old horse. He can get me wherever I want and gaze on the flowers on the side of the road. And he has pulling power to get through a muddy road. Sure most of us lived our entire lives within a 12 mile radius, but who would want to go any further than their horse can find his way home?

 

[mswlogo]

I wonder how much people in 1910 made the same type of arguments about convenience when Ford brought mass produced cars to the masses. After all gas stations where not ubiquitous especially in the country where many home were still lit by candles and lamps. They had to go to a tank out back, grab a bucket, put it under a tap, filled it and carried it to your car. Then they split a lot of it on the side of the car and your seats trying to fill the tank which you say on.

Sounds like too much work, and the car make noise and smell. Roads are dirt with ruts and impassable by car when it rained. Just give me a good old horse. He can get me wherever I want and gaze on the flowers on the side of the road. And he has pulling power to get through a muddy road. Sure most of us lived our entire lives within a 12 mile radius, but who would want to go any further than their horse can find his way home?

And the Horse had Advanced Summon mode and Self Parking too !!! You could probably Uber your horse out for the day and make few bucks too.

 

[Saghost]

I believe that most people would be happy with EVs IF they had ready access to a network of DCFC stations that was ubiquitous, easy to find, and readily available as the Tesla SuperCharger network. It's not the time spent charging, it's the uncertainty of how long the trip will take and the amount of planning needed that puts people off.

Road trips in the U.S. for Tesla owners are not a problem due to the extensive supercharger network that is available to them. For some, charging at the supercharger is free. However, for other EV owners (Bolt, VW, etc.) finding a DCFC station is often difficult and even when you find it you may be waiting for others who are queued up waiting for the station, and even when it's your turn, you may be spending a lot of money. A Tesla is too expensive for many people, so if they were to buy an EV, they would be using the relatively rare, difficult to find, often in-use, expensive DCFC stations (Tesla competitors: take a hint!).

In short, I see their point.

What I hear from this post is that the only thing you think is stopping folks from buying Teslas instead of ICE cars is price point.

That's great news, especially since EVs punch well above (or is it below?) their weight class when it comes to TCO - the lower fuel and maintenance costs make them more affordable than comparable cars of the same purchase price.

Depreciation is a question, but it's been pretty good for Teslas relative to their competition once you factor out the tax credit. And if there is an EV revolution soon like some folks expect, depreciation is going to hit the ICE cars much, much harder.

Oh, and that the other EV makers still need to step up their game. But since they are trying to make small sales without eating their own ICE sales in the process, that's not too surprising.

 

[SO16]

And the Horse had Advanced Summon mode and Self Parking too !!! You could probably Uber your horse out for the day and make few bucks too.

Not to mention self driving. The horse would often know it’s way back home.

 

[Nocturnal]

No, it's not an issue for 99% of people. The time I save by not gassing up each week dwarfs the extra time taken on long trips in the course of a year. Plus I've adjusted my plans to make the drive part of the trip. Stop for a beer and lunch instead of choking down fast food so you can "make good time".

 

[gjlian]

And the Horse had Advanced Summon mode and Self Parking too !!! You could probably Uber your horse out for the day and make few bucks too.

 

[gjlian]

Great comment !! I love the analogies . I was fortunate enough to meet someone last year who had worked for Ford for over 37 years. He was 87 yrs old and I asked him what he thought about electric cars and the industry in general. He said he absolutely thinks that EV's will be main mode of transportation in the next 5 to 10 yrs. When I asked him about the infrastructure and the challenges he made the exact point that you made regarding horses vs gas powered vehicles. Henry Ford had the same challenges that Elon Musk has today but it was even more difficult then. The infrastructure needed to make electric vehicles plausible is so much less than what was needed back in the day of Henry Ford. I also try and explain to my wife who is also a lover of gas cars that you dont need to wait at gas stations when you plug in at home or at work. It takes time to convince the masses but slowly but surely it will happen. In fact there will be a day when it will be very hard to find a gas station because they will be struggling to stay in business...