Last Update: August 21, 2021
Every powered vehicle carries an energy storage unit. Energy is stored in gasoline, diesel, hydrogen, natural gas, or electricity. As we drive, that energy is consumed, and the vehicle can only travel as far as the energy storage unit lasts, and then it must be recharged. Any travel in any kind of vehicle must accommodate recharging the energy storage tank. The time to recharge is the main factor determining the effective trip speed.
Many people waiting for electric cars to be "good enough" are wondering how long it will take to drive an electric car to a far-off destination. They might have a favorite aunt to visit every year 1,000 miles away, or a daughter to visit every month 1200 kilometers away. Most of us are accustomed to just hopping in the car, stopping at gas stations every so often, and not having to think about the mechanics. To do this with electric cars requires some planning, but that's getting easier every year.
With modern electric cars and modern fast charging systems, the effective trip speed for a long road trip is close to that for gasoline or diesel vehicles. Success depends on there being suitable fast charging stations, 150 kiloWatts or more charging power, along the entire route.
The primary determiner for effective trip speed is the time required for charging. Reducing the charging time requires higher power charging stations.
What makes a road trip different from simple driving around town is the inability to return home to recharge the car. Most electric car owners charge at home, or at the office. Since daily driving usually fits into the range of the car, charging at home or at work means one rarely goes to a public charging station. But, since a road trip is about getting to a far away destination as quickly as possible, we need to know how to optimize the time required to recharge.
Effective trip speed, or the time required to drive a given distance
The time required to drive on any kind of trip is the vehicle speed, the range per charge, and the charging time for both the vehicle and the occupants. The effective trip speed is the distance traveled divided by the time required, accounting for all stops. In other words, literally, the effective miles driven per hour of driving.
You might be driving 65 miles/hr on the highway (or motorway or autostrada depending on your language), but you must stop every so often for refueling the vehicle, refueling your body, and taking care of other bodily needs. The total trip time is the driving time, plus time required for those stops. In other words, a 600 mile trip which takes 12 hours is 600 miles/12 hours, or effectively 50 miles/hr.
For those of you living in countries that sensibly use kilometers rather than miles, that's a 105 km/hr speed, and 1000 km distance.
Refueling, and refueling time, is very different between gasoline or diesel and electric cars. With gasoline (or diesel), recharging the storage unit simply means pumping liquid diesel (or gasoline) at an appropriate station. This is almost instantaneous, 300+ miles range in a few minutes. With electricity the storage unit is recharged with electricity that comes through specially designed electric cables attached to an electric vehicle service equipment (EVSE) unit. This can take several hours, but with modern (2021) fast charging equipment can be a half hour or less.
One way to express this is what's called range gained per hour of charging. This is the amount of driving range added by recharging the vehicle, and how long it takes to do this. This measurement is important as the main determiner of effective trip speed.
For electric vehicle trip speed to get close to that for gasoline vehicles, the recharging time needs to shrink considerably. That also means, for electric vehicles, increasing the charging power (kiloWatts). To understand why let's go over a few equations.
Calculating the range gained per hour of charging
Roughly speaking the charging time is calculated as so:
charging time (hours) = battery pack size (kiloWatt-hours) / charging rate (kiloWatts)
This isn't perfect since there are several variables, including the tapering-off of the charge rate as the pack reaches full capacity.
The range of any vehicle is based on the energy contained on-board:
range = energy stored / energy consumed per mile range on gasoline = gallons gasoline / gallons consumed per mile range on electric = kiloWatt-hours / kWh consumed per mile
Roughly speaking, the average electricity consumption for an electric sedan is 320 Watt-hours per mile. (see Energy storage, energy consumption, weather and electric car driving range)
The next measurement to learn how to calculate is the range gained per hour of charging in a given charging session. It's simply an application of the last equation, using the kiloWatt-hours added during the charging session.
kiloWatt-hrs gained = kiloWatt charge rate * hours of charging range gained = kiloWatt-hours gained / .32 kiloWatt-hours
The kiloWatt-hours gained per hour is simply the charging power (kiloWatts), for the time spent charging. Literally one kiloWatt-hour is one kiloWatt for one hour. Therefore the range gained is the kiloWatt-hours added during the charging session, divided by the energy consumption for the car. For this demonstration we've used the rough average of .32 kWh/mile.
|Gasoline car||Level 2 charging (6.6 kW)||50 kW Fast charge||100 kW Fast Charge||150 kW Fast Charge|
|350 miles range gained per 5 minutes||6.6 kWh gained per hour||50 kWh gained per hour||100 kWh gained per hour||150 kWh gained per hour|
|or 4200 miles range gained per hour of charging||or 21 miles range gained||or 156 miles range gained||or 320 miles range gained||or 468 miles range gained|
Don't take these figures as being accurate since these are rough estimates with many simplifications. For example, with fast charging the power level quickly drops off (a.k.a. tapers off) from the peak. Charging the last 10% of battery pack capacity can take a very long time. Take this as the general trend, however, that the higher the charging power the more quickly the car will recharge. Also, even with advances in electric vehicle fast charging, the highest electric charging rate does not match gasoline refueling.
Modern fast charging systems are good enough that people now routinely drive 1000+ miles a day with electric cars. That's surely enough for a serious road trip.
The activity pattern for a road trip is:
- Drive until the stored energy is "low" (but not empty)
- Find a recharging location. If the first location found is not suitable (broken, or fully occupied), the remaining energy is used to drive to another location. That's why in the previous step one does not drive until empty.
- Recharge the vehicle, recharge the human(s), take care of other human needs
The first phase has you driving on the highway (motorway) at the speed limit. You do obey the speed limits, yes? The second step is fairly quick, usually, since the refueling location should be next to a highway exit. Because 200-300 mile range electric cars are now widely available, those two steps are approximately the same whether the vehicle is gasoline/diesel or electric. The third step is where there is a vast difference between the two fuel types.
Therefore, optimizing the time for an electric vehicle road trip means maximizing the charging rate. One trick is to not charge to 100% full state of charge, which might seem counter-intuitive for a road trip. Because of the tapering effect, the last 10% or so of electric recharging can take a very long time. Therefore it's best to avoid the time required to charge that last 10% or so. If your next charging station is close enough, charging to 80-90% is more time effective by avoiding the long wait to reach 100% state of charge.
Gasoline car drivers also work to optimize the refueling time to drive the farthest per day. Instead of stopping for a full meal, and to properly stretch their legs, they'll instead buy snacks to eat while driving in the car, and get back on the road as quickly as possible. The longer time to recharge the electric car can therefore be seen as more healthy.
HINT: Gauge your electric car by its effective trip speed.
Virtual Experiment — what’s the effective trip speed?
As a virtual experiment, let’s take a 600 mile trip. To simplify the experience, lets assume the ground is flat, the weather is warm, there are charging stations and gasoline stations at frequent intervals. Those ideal conditions will let us to virtually drive freely, and come up with estimates of effective trip speed.
The gasoline powered car will complete the trip in about 10 hours of driving time, adding about an hour human for needs like toiletry, drinking and eating.
driving time: 600 miles / 60 miles/hr = 10 hours refueling time: 2 refuelings, 10 minutes each human time: 30 minutes per refueling? Depends on the driver effective speed: 600 miles / 11 hrs 20 minutes = 53 miles/hr
A few years ago affordable electric cars were limited to 80-100 miles range, and might be limited to AC Level 2 charging (6.6 kiloWatts). That means stopping after an hour of driving, for a 3.5 hour recharging session. It adds up to over 40 hours total between charging and driving.
driving time: 600 miles / 60 miles/hr = 10 hours recharging time: 9 charging sessions, 3-4 hours apiece, 27-36 hours total human time: at least one hotel stay, meals etc can be part of charging time effective speed: 600 miles / 50 hours = 12 miles/hr
Some of these 80 mile range EV's have fast charging that's limited to 50 kiloWatts.
driving time: 600 miles / 60 miles/hr = 10 hours recharging time: 9 charging sessions, 3/4 hour apiece, 6-7 hours total human time: 17 hours effective speed: 600 miles / 17 hours = 35 miles/hr
In some cases the affordable 200 mile range electric cars are sold without fast charging. It boggles the mind that the automakers do that, but they do. Such a car is limited to AC Level 2, but while it requires fewer charging stops each one takes much longer.
driving time: 600 miles / 60 miles/hr = 10 hours recharging time: 3 charging sessions, 10 hours apiece, 30 hours total human time: at least one hotel stay, meals etc can be part of charging time effective speed: 600 miles / 50 hours = 12 miles/hr
It comes out to about the same total trip time. Why? It's because of the 6 kiloWatt charge rate. If instead that 200 mile range EV were charged at a 50 kiloWatt fast charging stations, the effective trip time is much better.
driving time: 600 miles / 60 miles/hr = 10 hours recharging time: 3 charging sessions, 1.5 hours apiece human time: accomplished during charging sessions effective speed: 600 miles / 14.5 hours = 41 miles/hr
Let's give that 200 mile range the capability of 150 kiloWatt fast charging.
driving time: 600 miles / 60 miles/hr = 10 hours recharging time: 3 charging sessions, 3/4 hours apiece human time: accomplished during charging sessions effective speed: 600 miles / 12.5 hours = 48 miles/hr
Now we're starting to get close to the effective trip speed of gasoline cars.
Let's increase the driving range to 300 miles, and reduce charging rate to 100 kiloWatts. This is close to what was the normal capability of Tesla cars before the Supercharger upgrades.
driving time: 600 miles / 60 miles/hr = 10 hours recharging time: 2 charging sessions, 1 hours apiece human time: accomplished during charging sessions effective speed: 600 miles / 12 hours = 50 miles/hr
We're edging even closer to parity with gasoline trip speed.
Let's increase the charging rate to 150 kiloWatts. Note that both the Supercharger network, and the high end of Combo Charging System (CCS) fast charging is at 250-350 kiloWatts, currently.
driving time: 600 miles / 60 miles/hr = 10 hours recharging time: 2 charging sessions, 3/4 hours apiece human time: accomplished during charging sessions effective speed: 600 miles / 11.5 hours = 52 miles/hr
And, we've roughly reached parity with gasoline trip speed.
Remember that these numbers are under ideal conditions and contain many simplifications. Real world results will of course vary. For other disclaimers see the user guide for typical home electronics.
Electric cars should no longer be relegated to "around town driving"
Ten years ago the 80-100 mile range of most electric cars had them relegated to around town driving. The numbers here show why, because while it was always possible to take long range trips even with an 80 mile range EV, you'd have to be extremely dedicated to the cause. Taking 3 days to drive 600 miles when most people do it in about 11 hours will not be seen by your spouse or children as a good tradeoff.
We no longer have to pony up for a $100,000 car to enjoy road trips on electricity. The new affordable electric cars have fast charging capabilities that are good enough for road trips, even with cranky family members asking "Are we there yet?"
Rule of Thumb
These numbers are courtesy Tesla Motors, but are more-or-less true for any other electric car:
- 120 volt 12 amps: 3 miles range gained per hour of charging (typical line cord charger)
- 120 volt 15 amps: 4 miles range gained per hour of charging
- 240 volt 16 amps: 12 miles range gained per hour of charging (older model 3.3 kiloWatt on-board chargers)
- 240 volt 30 amps: 25 miles range gained per hour of charging (newer model 6.6 kiloWatt on-board chargers)
- 240 volt 40 amps: 29 miles range gained per hour of charging (Tesla Model S mobile connector)
- 20 kiloWatt: 58 miles range gained per hour of charging (Tesla Model S high powered wall connector)
- Tesla Supercharger: 170 miles range gained per half-hour of charging
Take this rule of thumb with a grain of salt.