Op-Ed: Musing “3rd” Generation EVs And Range
The current situation
If you believe the press, by 2015 to 2017 we will see 150-200 mile range cars in the $25,000 to $35,000 price bracket. What would it mean to have cars with that range? The Tesla series cars are certainly a preview of it. A Tesla S model (85 kWh version) at 300 miles range (according to Tesla motors). This is similar to the average range of a gasoline car. I’m sure that it was not an accident that Tesla picked this range. Aside from the pesky charging issue, this makes the Model S a reasonable competitor for gas driven cars.
The Tesla model S is not immune from range issues. My co-workers (read: managers) with Teslas usually have to put up with a level 2 charger at work. That means about 20 miles per hour of charge, or 12 hours to reach a 80% charge. At 120 kW (the Tesla maximum supercharger rate), and 396 W per mile, that means 42 minutes to reach an 80% charge at the highest available Tesla supercharger.
The reason I mention this is because, with the expected 150 mile range Leaf and the 200 mile range Tesla model E, the charge times of the next generation leaf go up, and the charge times of the Tesla go down, both relative to the current generation cars. That is, if the same chargers are used. This is why you have to consider both the car and what is charging it.
Let’s start with an across the board way to measure charging, and the resultant mileage from the car. As often stated, charge times are linear up to 80%, then curve up after that. For example, it takes more time after 80% to get the same amount of mileage. So I will use “watt/hours per mile (KWH/mile). This is not the same thing as the power efficiency, or how many watt/hours the car expends to push itself one mile. Instead, it is the total cost, in watts, to push the car a mile, after the charging efficiency, the drive efficiency, everything, is considered.
So here are a few WPMs for the two cars studied here:
What’s notable here is how similar the WPM is across the two cars, even with very different chargers. It’s also a good number because it gives you a relative amount of power per mile you can understand. Run that 350 Watt halogen light for an hour, and that’s the power you would need to move a car one mile.
Of course, the number of miles you get from a given number of watts varies with driving conditions, the driver, and the car. Fortunately we don’t have to consider that. The Environmental Protection Agency calculates that for us. And all we do is use the measure for comparison. That is, whether the EPA mileage is a good estimate or a bad one, we assume it is equally good or equally bad for both types of cars, because the EPA is assumed to be an impartial judge.
For a long distance traveler, two figures on the car’s range are important. The 100% charge and the 80% charge range. The first because it defines the first leg of the journey. The second because all subsequent charges and legs are going to use the 80% figure. Otherwise, you would waste charging time and power trying to push the battery charge in its last, non-linear phase.
Now before we leave the realm of current cars, what does it mean that the charge time of the next generation, higher range leafs go up, but the next Tesla, the model E goes down in charge time? It’s a factor of the charger and the kWh capacity of the car. If Leafs get more capacity but use the same charger, their charge time doubles. If Teslas go down in capacity, but use the same charger, they actually get faster to charge.
The lesson of this is that it is not enough to increase the range of a car; you have to increase the charging infrastructure to match. Since Nissan will probably not want to have to explain why the new Leaf takes twice as long to charge, it’s a good bet that they will try to roll out a new charger with the new Leaf, most likely double the current Chademo 44 kW capacity. Whether this is an enhanced Chademo, or a completely new standard, is an open question.
For Tesla, there is no charger question at all. The model E will put no strain on their supercharger network. It will be a shorter range car, but it will make up for some of that by charging faster, on a percentage of total charge basis.
Calculating a long distance trip
Editor’s note: duty cycle should read 82% for the Tesla, and 65% for the Nissan in above chart
Note that the “duty cycle” is the percentage of time the car actually spends driving.
This is the worst case picture of how an EV drives, and does not reflect real driving. For common long distance trips, the rule is going to be “100/80…”, meaning that the first drive of the trip is going to be at 100% charge, then the second at 80% charge, and all subsequent charges are going to be at 80%. The reason is simple. Long distance trips are going to start after a 100%, all night charge.
Using 100/80 calculations, short trips are going to look better. Longer trips are going to increasingly flatten out to approach the 80% charge duty cycle of the car. Since that is true, let’s use a “standard trip” for comparison. I’ll use a 500 mile trip at 65 miles per hour. That’s 7 hours 41 minutes of driving, which I think we can all agree would require a break or two even without the need to charge. It’s also a full day of driving without going into heroics like 12 hour driving with short stops, typical of college kids trying to make it to spring break in Florida.
I have calculated the times using the 100/80 rule, and even accounted for a driver to only charges the amount needed to complete the last leg of the trip:
And of course you noticed that I have stuck a new competitor in the mix, a generic gasoline drive car with 300 miles range. Now we have a new subject, “what is a refill break for a gasoline car”? Let’s define it.
The “SBF”, of course, stands for “Spring Break Florida”, or the time it takes to refill for a college kid hyped up on caffeine, who starts the pump, enters the store on the run for more coffee, completes the fill, pays and bolts.
I think it’s safe to say that 15 minutes is more the average on-the-go break. Its time enough to get coffee, a doughnut, wander a few minutes to see what mix tapes the station has, and pay and leave.
A food break is McDonald’s, eaten in the store.
Finally, a dinner break is a sit down meal with service.
So getting back to our 500 mile standard trip, the Tesla driver has waited 32 minutes longer than the gas car driver (its 42 minutes for a 80% charge). The leaf driver has waited 3 hours and 17 minutes longer than the gas car driver.
The Leaf numbers aren’t great, as you would expect. They are reasonable for a ferry, instead of a trip. That is, they are reasonable if your goal is to move the car to a new place, instead of just have it move you. The alternative is a car dolly pulled by a gasoline car.
The 3rd generation (of EVs)
Now of course I will take it in the shorts for declaring the next generation to be the 3rd. I hope you will forgive me for a purely relative comparison. In this article, the 1st generation was the GM EV1, the second the current crop of (mostly) lithium based cars, and the 3rd is the coming generation of longer range/cheaper cars.
The contenders are (cobbled from a list of announcements, test cars, and blind speculation):
For the Telsa case, there just happens to be a car already in existence with the approximate specifications, the model S 60 kWh battery version. Thus, I have used the figures from the 60 kWh version of the model S for this future car.
For the Nissan Leaf NT, the test car Nissan fielded has 48 kWh. We assume here, perhaps wrongly, that the new doubled battery capacity vehicle has similar characteristics as the old one, and that the range is in fact doubled.
Note on above chart: duty cycle should read 82% for the Tesla, and 65% for the Nissan
The time to charge the Leaf to 80% has doubled. This is reasonable, since the charger power hasn’t changed, but the battery being charged has doubled. The resulting duty cycle is the same.
Here are the 500 mile trip specifications:
Here the Tesla driver has waited 44 minutes longer than the gas car driver (its 32 minutes for an 80% charge). The leaf driver has waited 2 hours and 40 minutes longer than the gas car driver. The Tesla model E driver waited an extra 12 minutes than the model S driver. The Leaf NT driver waited 37 less minutes than the Leaf 2013 model.
What about the charger?
So the Leaf NT numbers are better, but not great. That still does not mean that a real 150 mile range is not useful. It means a long distance commute is far more feasible, and that weekend wine country trips are going to be easier.
However, the numbers strongly imply that Nissan would need to come out with a faster charger to match the longer range Leaf. So now lets speculate what would happen with Nissan came out with a “double strength” charger of 88 kW, versus the existing Chademo charger at 44 kW:
Alright, now we are down to 1 hour and 13 minutes more than a gasoline powered car. The Tesla Model E and the Leaf NT would start to approach each other in performance. This makes perfect sense, because the basic specifications are converging.
In short, I suspect the numbers from a Leaf that is simply doubled in range, without an improvement in charger infrastructure, are poor enough that Nissan would be forced to go towards a higher power charger. If you believe the Chademo organization web site, they are against it. However, Nissan makes their own chargers, and could very well roll a double strength charger to their dealer organization.
This would not solve the problem overnight. It would still take a lot of time for the double strength chargers to become common. This is perhaps Tesla’s stronger hand. Their charger infrastructure is already north of 100 kW, and the new Model E would actually make less demands on it than the 85 kW model S.
The 4th generation (of EVs)
Let’s end this article with a twist on the usual “future projections”, of what the next, or the next after the next, EV might look like. Unfortunately (to my mind), the answer a lot of folks give is that the future EV should have similar performance figures to a gasoline powered car. This is unfortunate because in any competition between electric and gas powered cars, the gas powered car is going to win using the goals designed for gas cars. If you come out with a 500 mile range electric car, they will come out with a 1000 mile range gas car. Some gasoline cars are exceeding 400 miles of range simply because the fuel economy of the car was dramatically improved and the gas tank capacity has stayed the same. EVs need to compete on being different, not the same. Examples include: ability to charge at home, %100 clean, lower maintenance costs, etc.
Instead, let’s imagine that you are going to a rare (I suspect very, very rare), joint appearance of Carlos Ghosn and Elon Musk at the same EV press conference as part of a panel. You are in line to ask questions. You want to advocate for them to push for either higher KW chargers or longer range cars, but you don’t want to and don’t have the time to advocate for both.
So let’s imagine two future cars, one with 400 miles of range and a 100 kW charger, and one with 200 miles of range and a 200 kW charger. We’ll call them the Leafesla and the Tesleaf:
The 400 mile range, 100 kW charger Leafesla is the winner, but note that the time difference is down to the 13 minutes, about the time it would take to charge the car at 200 kW.
Note also that the 400 mile range car nearly converges in time with the gasoline car. This seems impossible with a 30 minutes charge time. However, it works because it is possible to short charge the car to reach the destination. Thus, only an 18 minute charge sufficies.
Telsa and Nissan appear to be headed for the same market, a $35k car around 200 miles range. This is a normal result of an open competition market, you go where the money is. In this contest, Tesla would seem to have the advantage because, although each maker built out a charger infrastructure to match their cars, Telsa starts at a high charger level and would be going downward, where the opposite is true of Nissan. Of course Nissan could aggressively roll out new chargers and even things up.
To write this article, I relied on constructing a BASS or “Big As you like it Spread Sheet”, of which you can have your own personal copy here. I’ll look forward to folks finding my errors on the sheet.
The Tesla numbers don’t strictly add up. The issue is that Tesla states 30 minutes on Supercharger to reach 170 miles of range, but gives us a time of “as little as 20 minutes” to reach half range. We use EPA figures for reasons discussed above. What we care about is the 80% range, since that is the linear section of the charge curve. With the Leaf, the maker specifies 30 minutes to 80% charge, meaning we have a fixed method to calculate. With Tesla, we can use either the 30 minute/170 mile figure or the 20 minute/133 mile range (half the EPA mileage). Naturally they don’t match. The 170 mile calculation is based on Tesla’s own 300 mile range. The way I “solved” this was to find for the 80% range given the 170 miles in 30 minutes figure by using the %80 range of their 300 mile figure as 240*30/170 or 42 minutes to reach 80% charge. Its reasonable because the charge times are stated to be linear until the 80% charge time is reached, and can thus be solved by a ratio. Thus, using the EPA figures together with the 80% charge time we calculate the rest, and these equations are applied the same way across both Leaf and Tesla.
You’ll also note that the EPA figures calculated against the WPM or Watts Per Mile didn’t quite match. That is, the Tesla Model S 60 kWh and 85 kWh did not quite match at the EPA stated ranges of 208 and 265 miles, respectively. I “solved” this by downgrading the range of our “model E” by subtracting 6 miles from the range. To me this made sense, because the two cars, running on the same charger, should have identical WPM figures in the linear range.