This is another post on why plug-in hybrids are the right technology for the long transition to fully-electric transport.
To some degree, electric vehicles are perfect for around-town driving. They use next-to-no power when stopped (other than for heat or AC). They produce no engine or exhaust noise, and no tailpipe emissions. And they tend to be nimble at low speed, owing to full torque available at zero RPM.
EVs are less than convenient for long trips, owing to the need to charge. This was the point of an article on the NPR website today. It recounted a short road trip by the the U.S. Secretary of Energy, including a small fleet of EVs, and the various clown shows that ensued when they tried to charge them on the road. It seems like there weren’t enough working chargers to go around, in many of the locations they visited. Particularly when they showed up with three or four EVs, all at once, at a charging location.
Teslas have a dedicated charger network. Everybody else makes do. And one EV — the Leaf — is all but impossible to use for long distance driving during hot weather, owing to a lack of battery temperature management. (You can’t charge a hot battery quickly, and charging heats the batteries).
Everybody wants to wish this problem away. Oh, we need to build more charging stations. Oh, new generations of batteries will charge faster. Both of which are true.
But few people have a solid grasp of the basic physical limits of electrical charging. Stuff that no wishful thinking about future battery tech is going to get around.
So let’s review.
A typical U.S. gas pump can deliver gasoline at a rate of 10 gallons per minute (source). That is, in effect, a rate of flow of energy. In this case, it’s the chemical energy stored in the gasoline.
What would it take for an EV to accept electrical energy, at that same rate? Here, I’m going to calculate how thick the charging cables would have to be, assuming a 350V battery being charged (typical for EVs and PHEVs.)
To keep the temperature of the charging wire below 160F, the charging “wire” would be a three-and-a-half-inch diameter round copper rod. (Quick reality check: Most modern U.S. houses have 200 amp service. The wires needed for this fill-up would have 120 times the cross-sectional area, or about 11 times the diameter, of the wires feeding your house. That’s ballpark.)
Good news is, you don’t have to worry about being able to bend something that thick. That’s because you wouldn’t be able to lift it. A five-foot-long charging cable would weigh about 175 lbs.
Note that I’ve fully accounted for the difference in efficiency between a hybrid and a full EV, based on the Prius Prime:
In short, adding energy via electricity, at the same rate you add energy via gasoline, is not practical due merely to so-called “I-squared-R” heating of the wire carrying the current. If you don’t want to melt the wire, you need an impractically large wire. Not even getting into the issues of how you’d get that much electrical flow in one place, how the car would have to be wired to handle it, and so on. Just the hard, unchangeable physical limit of electrical current and copper wire and heat.
Note that this has nothing to do with the batteries. In this example, the batteries would have exploded long before you managed to melt the charging wire.
As a real-world check, Tesla claims you can typically add 200 miles of range in 15 minutes, at their fastest superchargers. (That claim would undoubtedly be for a vehicle with nearly-depleted battery, because an empty battery charges much faster than a nearly-full one). For the Prius Prime, you can add 200 miles of range at the gas pump in ((200/54)/10 = ) 0.38 minutes (or just over 20 seconds).
The upshot is that the fastest chargers today — respecting the limits of both the wiring and best current battery technology, under optimal conditions (empty battery) — take about 40 times longer than filling your tank with gas to deliver the same number of on-the-road miles.
And I would argue, based on the table above, that the sheer physical limit of how much current you can push through copper wire means it’s not going to get hugely faster than that. Putting aside all the rest of the practicalities of fast-charging.
This has to be moderated by acknowledging that the entire refueling transaction takes longer than just the pumping time. But not hugely so. For refueling my wife’s Prius, I’d say we’d could add a minute for getting out of the car, running the pump, and getting back into the car. So in real-world terms, under ideal conditions, with the best current technology, each refueling might take maybe 20 times longer with electricity than with gasoline.
As a matter of logic, this means that to provide the same level of peak or excess fueling capacity that we currently enjoy in our network of gas stations, we’re not just going to have to replace gas pumps with chargers. Under optimal conditions, with current technology, we’d have to replace each existing gas pump with 20 chargers.
Now, that doesn’t apply for around-town driving. Around town, I expect that most of the folks who buy an EV have a way to charge at home. So, around town, we might need fewer charging stations than we have existing gas pumps, to provide the same level of availability.
But for long road trips — for truck stops along the interstate? No matter how you slice it, a fully electric vehicle fleet, with no change in travel patterns, is going to require vastly more chargers at busy interstate refueling points, than the number of gas pumps those places have today.
So, in the end, it really is no surprise that showing up with a small fleet of EVs, at some particular charging station, would cause a backup. Even with apps that tell you when a charger is expected to be free, relatively long charge times, and a growing EV fleet, mean that charging hassle is likely to be normal, outside of the Tesla world.
To me, this is all the more reason why PHEV is the best choice right now. You electrify your local travel, where electification unambiguously makes sense. But you continue to rely on the existing gasoline infrastructure for long-distance trips.
Think of PHEV as a transition vehicle, in what is apt to be a long and bumpy transition to electrical transport. At the end of the day, the limiting factor for electrifying the US vehicle fleet is consumer acceptance. Charging hassles for long-distance travel are frequently cited as a reason not to buy an EV. So skip that, and buy a PHEV. That lacks the purity of EV. But sometimes the perfect can be the enemy of the good-enough.
Note: Illustrations are from Freekpik AI and Gencraft AI.
