Unwinnable Race
EV fast charging will never be as fast as fueling a petrol car, but that’s okay…
Last week, the third heat of the women’s 100m dash at the World University Games in China went viral after Somalia competitor Nasro Abukar Ali clocked a comically slow time.
The race caused a mixture of laughter, embarrassment, and anger, and claims of nepotism have already led to the suspension of a Somalia sports official.
When watching a replay of the race, our energy brains 🧠🤓 couldn’t help but analogize the situation to EV fast charging. If an internal combustion engine (ICE) vehicle were to line up for a fueling race against an EV, the margin of victory would be similar to that of the 100m event.
However, would the race results hold up over time?? Sure, EV charging is slower than petrol fueling today, but will that always be the case? 🤔
Let’s do a quick analysis of the three major constraints of EV fast charging - car, charger, grid - to develop a realistic understanding of what’s possible.
Car
The first step in determining how fast an EV can charge requires defining a “fueling session.” With ICE vehicles, no such definition is necessary as the time it takes to fill a petrol tank 70% is virtually indistinguishable from fueling it 90% (even in different weather conditions). Unfortunately, life ain’t so easy with EV charging.
If it were, EV fueling session time would simply be battery capacity (kWh) divided by maximum charging speed (kW). For example, charging a standard 75 kWh battery pack with a 150 kW fast charger would take 30 mins.
Every EV is unique ❄️, but the relationship between state of charge (SoC) and charge speed (kW) can be roughly generalized as follows:
We’ll save you the technical explanation behind an EV charging curve 😴, but it explains why EV manufacturers and charging station operators often quote such different figures when advertising charging time. When they want to look the best 🤵♀️🤵🏻♂️, x mins to charge 100 miles will usually be the lingo used. Can you imagine talking to a used car salesman about EV charging speeds?! 😐
However, this used car salesman lingo refers to ideal conditions - charging from 20% SoC to 50% SoC. When you hear “20 mins to charge 100 miles,” that doesn’t mean it takes 60 mins to charge 300 miles.
For our purposes, we’ll define a fueling session as being from 20% to 80% SoC - 60% of the EV’s stated battery capacity. This definition strikes the balance of being a relatively full charge, without heavily penalizing ourselves for the trickle charging that occurs at either end of a 0 to 100% fill-up.
As the charging curve above demonstrates, EVs don’t maintain their peak charging speed on the march from 20% to 80%. To simplify things a bit, let’s assume that average charging speed is 75% of peak speed (a very generous assumption).
Charger
So what is the peak speed that a fast charger can deliver?
Power (aka charge speed) = Current * Voltage
As the flow of electrons (current) increases, so does the heat generated. This is why fast charging cables can be so heavy and cumbersome to use - they’re padded with enough insulation to dissipate said heat.
As liquid cooled fast charging cables become the norm, 500A cables will become more prevalent. Cables rated to handle higher amperage will require specialized engineering reserved for specialized use cases.
As far as voltage goes, most EVs utilize a 400V system architecture. Amongst other engineering reasons this design, bespoke pieces are expensive and the automotive industry standardized around 400V components in the early days of EV manufacturing. Let’s assume a 800V system as many OEMs and Tier 1 suppliers have expressed commitments to heading in this direction.
With our 500A and 800V assumptions in tow, we can calculate peak charging speed:
Power = 500A * 800V = 400 kW
This is why a nameplate capacity of “400 kW” is the fastest of the fast chargers available today.
If that’s peak speed, average charging speed from 20% to 80% SoC would be 300 kW (75% of 400 kW).
Grid
Are we done???
Let’s consider the Achilles heel of all things “energy transition” - grid constraints.
Putting aside CAPEX considerations that will limit the buildout of 400 kW chargers (as opposed to say, chargers rated for 150 kW), most fast charging stations will not have an adequately sized grid connection to operate multiple 400 kW chargers simultaneously.
A good rule of thumb is that anything over a 2 MW grid connection is massive. For context, 2 MW could power about 1,500 US homes. Charging stations with access to 2+ MW will exist, but it won’t be the norm.
With 2 MW available, a fast charging station could have 5 x 400 kW chargers. What’s more likely than 5 chargers, however, is 15-20 chargers.
If you showed up to the station during off-peak hours, you might be able to maintain the highest possible charge speed during your entire session. If you tried to charge during rush hour, the station congestion and limited grid connection will limit your speed below the charger’s nameplate capacity. Sharing is caring, after all.
Let’s assume that this results in a 20% reduction in average charge speed from 300 kW to 240 kW.
To summarize, we’ve made the following far-from-guaranteed assumptions:
EVs maintain 75% of their peak charging speed when charging from 20% to 80% SoC
EV OEMs transition from 400V system architecture to 800V
Fast charging operators improve the rating of their cables and equipment to 500A
Grid connection and station capacity limitations limit charging speeds by 20%
Finally, assuming an average battery capacity of 75 kWh, fueling session time would be 🥁🥁…
(75 kWh * 60%) / 240 kW = ~ 11 mins.
The driving efficiency of EVs is in the range of 3-4 miles per kWh, so that equates to about 158 miles in 11 mins. Our assumptions are (almost definitely) overly generous and a realistic fueling session is likely closer to 150 miles in 15 mins. For context, a Toyota Camry gets 600+ miles on a tank and takes 3-5 mins to fuel. 😅
In the EV vs ICE battle, fueling speed is an unwinnable race for EVs.
The practical implication of such is why the vast majority of EV owners have access to at-home charging. Owning an EV is a great experience when a) you can afford the upfront cost and b) you can do the vast majority of your charging when the vehicle is parked. If you need to rely heavily on public fast charging, the fueling experience will be substantially worse than filling up at the pump.
At the end of the 100m race, Somalia runner Nasro Abukar Ali did a jovial skip over the finish line. It was as if she knew that winning the race was never a remote possibly and that she was running a different race in her head.
In a fueling race against an ICE vehicle, our EV would also skip over the finish line. Why would we be okay with losing by such a big margin? Fueling speed is only one aspect, albeit an important one, to what drives vehicle purchasing decisions. Lose the battle but not the war sorta thing.
If you believe in EVs for everyone everywhere, the inherent limitations of EV fueling speed should give you a significant amount of heartburn. If you believe in EVs for some people some places (like we do), it should just help inform your perspective on how EV adoption might evolve moving forward.
Life comes at you fast, charge an EV to slow it down 😉
Thank you, An enlightening piece on the EV charging process.
Feel free to check out our piece on Green Hydrogen
https://open.substack.com/pub/eagleforge1/p/170-days-to-run-a-refrigerator?utm_campaign=post&utm_medium=web
No problem!
Even with “future battery tech” the problem remains... it just gets less bad. Again, it’s not to say that EVs aren’t great in some use cases, but a dose of realism is necessary!