The world of EV charging often features a battle for the fastest possible charging. 150kW or 250kW are not enough, people want 350kW with an 800v battery, or the mostly mythical 5 or 10 minute charges demonstrated in China. Counter to this intuition the right charging power and time is actually the slowest one that makes sense for the way people visit the location of the charging. The demand for more is an artifact of “gasoline thinking,” the old method we’re all used to where you drive around until the tank says “E,” and then hunt for a filling station to do a 5-minute fill-up.
While everybody might like charging to be as fast as they can get it, all other things being equalall other things are not equal. The faster the charger, the more it costs, both for the hardware and the grid connection. It’s not just higher cost, it also means fewer stalls at the station, and more need for “idle fees” that force you to move your car when it’s done. This extra cost is quite serious, and the majority of “fast charge” stations today bill more as more or more than the cost of gasoline in a decent gasoline car. People didn’t buy EVs to end up spending more for energy than they do with gasoline, and if this goes on, it will stall the EV revolution, even if EVs underprice gasoline cars at the dealer.
That price gas parity price ranges from 24 cents/kWh if you compare a Prius on the East coast to more like 65 cents/kWh to beat California’s expensive gasoline in an average gasoline car. Beating a 35mpg hybrid in California needs getting below 50 cents/kWh.
The best mantra for charging is “charge where you park, don’t park where you charge.” You want to charge at places you already intended to park and stay for a bit. That way charging takes zero time out of your day. Ideally you are sleeping or eating or shopping or anything else, never sitting around waiting.
To figure out how big and fast a charging station should be, you want to look at how long people typically spend at the location, and how often they go to it.
Home and Office
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At the end of a large parking lot are these Level 2 charging stations, which probably cost around $6K each but can only handle 8 cars. When there are more cars, people must regularly come out and swap spaces.
Brad Templeton
The best locations by far are homes and offices. Cars spend 10-24 hours at home, and usually 8-9 at the office. And they go there every day (or every weekday for the office.) That combination means you need very little power. In fact, for most cars, Level 1 (1.5kW) will do the job, and it’s super cheap. That’s because the average car needs less than 10kWh per day. Level 1 will deliver that. It’s so cheap you can have 5 times as many stations for the same power budget as you can have faster stations.
Another option I call “Level 1.5.” It’s 240v Level 2, but with just 3kW. It’s often also quite cheap, and can deliver well over 100 miles of added range in a home/office session, far above the average daily drive.
At an office, some cars will need more, and so you would mix your large number of lower power stations with a few faster ones, like 7kW Level 2 and maybe a single DC Fast 25kW or 50kW station.
Of course, if you can put in 7kW for all the cars, that’s great. Many offices focus on that, but consider at an office with 20 cars, bringing in 72kW, compare the experience with:
- 20 stalls, 4 with 6kW and 16 with 3kW. Every car plugs in on arrival and unplugs to leave. 4 cars can recharge a full 10 to 80% recharge, the rest also fill up as they just have to hit their average. Everybody is happy.
- 10 stalls with 7.2kW. Only 10 cars get to plug in when they arrive. They must go out when done and move their car to another spot. The other drivers must find out a spot is free, then go out and move their car to get their charge.
The first approach, with more stalls with slower charging, is the clear win.
Hotel
Two Teslas charging at a hotel at Bryce Canyon National Park. The left one is keeping itself warm and meling the snow.
Brad Templeton
Hotels are the other place people spend 10 hours. People often just spend one night there, so in that case they need 7kW to get a full refill in one night. Since some guests spend 2-3 nights, you can have some 3kW for them, mixed with the 7kW. There’s no need for DC Fast.
Food and Shopping
- Sit-down restaurants: (1 hour, occasional visits) 50-70kW
- Counter serve fast restaurants: (40 minutes) 100kW
- Grocery stores: (30-60 minutes) 120kW. People visit these 2-3 times a week though they only need to fill about once/week on average. There are few other retailers people go to so reliably. In theory any retailer people visit for more than 30 minutes can be a good place to charge, but the grocery is the one they visit most regularly.
- Shopping malls: (30-120 minutes): Mix of 10kW, 40kW and 150kW
- Cinema (2 hours): 40kW (plus some 7kW.) Those needing a full charge would like lower cost 40kW unit to deliver that. Most cinemagoers probably don’t need a full charge at the movie, so a slower Level 2 unit could deliver the price (and quantity) of stalls they need.
Rural freeway rest stops
Buc-ee’s is the grandest of highway filling stations. Many also have EV charging. Beyond bathrooms, these offer counter served food, so can merit a 30 minute stay.
Brad Templeton
These are the one place where people might stop to just sit and wait (or web surf) while charging. Thus they want it fast as they can get it, such as the 350kW or faster chargers. Indeed, while it will cost a lot, some even would like a 5-10 minute charge during a bathroom break.
The problem is, charging that fast comes with even more costs than electricity that is pricier than gasoline. Only cars with new special batteries can take a charge in 5-10 minutes, and it tends to be much harder on battery life to charge at that speed rather than more slowly. Because it will only be used by those on hard-slog road trips who are not taking longer breaks to eat or visit attractions, it will be a specialty use, which could make it harder to justify paying for the ability. But if only a minority of cars use it, it makes the 500kW-1mW charging station have fewer economies of scale. Charging stations need to be in use most of the time to be properly economical.
Stops for newbies
This concept looks a lot like a gas station. Some are even built at gas stations.
Electrify America
There are drivers who can’t charge at home or work, and towns where there is not charging at places people frequently stop like shops and restaurants. There are also drivers who are new to EVs and don’t realize they should be shopping and eating at such places if they can. For those drivers, they may seek out a “gas fill up” style charging session. If they are just going to sit and wait, they will want charging as fast as they can get, like 350kW. The problem is, these stations are going to be expensive, so those drivers will be highly motivated to find more affordable charging at places they already park, as soon as it becomes available or they become aware of it. This makes the urban fast-charge station a doomed proposition, only serving users who have no other way to charge, all eager to stop charging there. You don’t want to be in a business where all your customers will go somewhere else as soon as they get the chance.
