Slower chargers (2KW and 50KW) might be better for EVs than 7KW and 250KW


In EV charging, there's a big contest to see who can be the fastest, with 250KW and 350KW chargers competing with Tesla's superchargers. But charge-really-fast is "gasoline" thinking and it's much more expensive. For the same money, for example, a corporate parking lot would be better served with 40 Level 1 (2KW) chargers and 4 Level 2 (7KW) than 15 Level 2. And a new generation of cheaper 50KW chargers in places we stop for an hour could make more sense than 250kw ones.

Read the analysis in my article on at The future of EV charging may be at 50kw


Hi Brad,

Agree on the 50KW chargers to pair with conventional batteries who has a shorter constant charging tolerance.

When the constant charging can be extended, then bigger chargers make sense, especially in the sense manufacturers can install fewer batteries to lower the upfront car costs, or shorten the charging idle times, for the ROA considerations of commercial applications.

If you won’t mind, may I provide you updates about the eXtreme Fast Charging (XFC) development by my team?


People dont want to drive the speed limit on highways that are still at 55mph. They drive at 75mph+ and get mad for you doing 60mph.

I really don't see how you'll convince people to take time out of their day to even charge for 10 minutes when they want to "save" that 2 or 3 minutes driving faster. Especially those who rack on a ton of mileage as is. You dont even have charging stations 99.99% of where you park. Who's going to pay to put them there?

EVs plain and simple are only for the niche market. It's still too far from being able to be reality let alone practical right now. We should be exploring alternative/synthetic fuels for existing combustion engine vehicles which is a more practical and more cost effective method where little needs to be done to make it happen.

And most of them change their minds after they buy one. But the point is you want to do charging that takes zero time, not 10 minutes. It takes zero time because you arrange to do it when you are doing something else. All cars make stops for other than fuel, except on the most extreme road trips. On the most extreme road trips, then you can think gasoline style, and hate it. If that's all you do, an EV is not for you.

4th year with an EV. Charging is a nothing burger. A non problem.

EVs may be a niche market for now Midnightsection, but the technology is well established and accelerating. ICE with whatever fuel is complicated and changes are slow. The growth opportunity is EV, so good luck getting serious capital for synthetic fuels to eke out just a few more years of a matured technology.

The biggest cohort of EV users I know don't even own a car: they live in cities with no place for a car (on street parking), so use car shares when they need a vehicle. EVs are the preferred type so I'm having an outlet installed at my home for visitors — and when I make the move to EV.

I'm in a rural location and tend to use my ICE vehicle intermittently for trips that vary from 2 kms to a neighbour, 60 kms into a nearby city for shopping, to 500+ kms for occasional road trips — and some are to remote cottage on gravel roads far from any grid connection. I've been coaxing my 10yo 290K km ICE vehicle to last until I can go fully EV — and all obstacles to doing do have been falling rapidly.

Solar panels & battery storage at the cottage and panels with grid interconnect at home can provide all I'll need for most trips. For the occasional long trips, I can't see a problem stopping & topping up as I enjoy a leisurely meal. The current pandemic is forcing us all to slow down a bit, and I'm certainly finding it a welcome change.

It'll be interesting to see if it also ends up accelerating the change from ICE to EV. Niche market? Perhaps not for much longer.

75% of vehicles do less than 40 miles a day. That can be recharged at the same power as your electric water heater (3.6 kW) in three hours a day off a standard single phase circuit. A car with 300 mile range starting on a highway journey at 65 mph average that stops for ten minutes after two hours and charges at 50 kW will add 33 miles. After another two hours driving it might stop for 25 minutes for a meal/bathroom break and add then after another 2 hours driving it has covered just under 400 miles and still has 30 miles of range, one 15 minute stop at a 150 kW charger anywhere along the way would extend the daily range by 120 miles.
While everyone dreams of the big road trip very few people actually do 400 miles in a day, it would be less than 0.1% of journeys and even if that journey takes 10 minutes longer than an ICE vehicle, the time saving is more than offset by the time savings in home and work charging every day rather than visiting gas stations and quarterly service visits.
So in contrast to your contention in fact for sedans and small SUVs, there is almost no case for a new ICE vehicle vs an EV

Fast charging does make sense for the long haul road trip. There are two sorts of driving on road trips for many folks. One is "getting there" and the other is "enjoying the drive." For enjoying the drive, with lots of stops, going more than 300 miles is unusual.

For "getting there" trips 500 to 600 miles in a day is not unknown. For this, the ideal approach is to refill each night while sleeping, and recharge mid-day during lunch, or twice during lunch and dinner. For that fast charging is needed, but all charging is done while doing something else.

Frequent short stops aren't quite as good.

Right now, there is also a challenge in getting road trip charging off the major routes. Thus what I propose for RV parks. 50kw at RV parks, particularly if they can serve you a nice meal or are in a nice location for a short hike etc. could go a long way to making everywhere EV-friendly.

You need to go look at some charging rates. Most EVs charging rates fall off the cliff at 50% to 60%. so it could be 33 miles if the battery is below 50% or it might be 15 miles if the battery is at 80%.

Charge speed drop off only applies to the DC Fast Charging, not to the level 1 and level 2 AC charging (aka destination charging) During DCFC the charge speed tapers down to level 2 speeds because it needs to fill all the battery cells to their maximum without risking overfilling any of them.

I do not agree. Most people regularly drive short trips from their home base where they can charge their car when ever they are at home. This is convenient: you never need to go to the gas station. On longer road trips everyone needs to stop and take a break, eat, go to the bathroom and stretch their legs. This is the opportunity to plug in and charge up while doing so. No need for this to involve any loss of time given the current battery size of a Tesla. I also think people want to drive faster not to get there sooner (as you point out this often only makes the difference of a few minutes) but due to juvenile pent up aggression: it is not rational or related to the functionality of travel, just an animal drive to dominate and impress.

The author seems misinformed about level 2 chargers. First off they typically max out at 9,600kw, not 8kw. There are also a few 13,440kw chargers out there with 19,200kw right around the corner. The author calls them expensive and seemingly tries to make them sound like they're not as cost effective as the extremely expensive DC charging but they cost practically nothing compared to what the author is pushing for.

Hell, fast/"faster" charging isn't really all that necessary in the first place. At 9,600kw and using the author's 4mi/1kw you get 38.4mi per hour of charging. Considering that Americans drive an average of 29.2 miles a day you'd only need 46 minutes of charging a day at that rate but since the charging would occur at the halfway point (you still have to return home) you will only be able to recover half the total round trip expended charge when starting out with a full battery. This means 14.6mi and about 23 minutes for the halfway point. Charging at that rate would recover the whole expended charge within the time it takes to eat or go shopping.

Charging is meant to be done primarily at home or wherever else you're staying and almost exclusively on level 2 chargers. Level 2 chargers away from home are meant to slow down the loss of charge while going about your business, while fast/"faster" chargers are only meant for extreme cases for long trips where there's no way to get from point A to point B in a set amount of time without them. Manufacturers (including Tesla) recommend against using anything other than leven 1 or 2 because anything else can seriously degrade the battery over time.

I fear you may not understand level 2 "chargers." There is no such thing as a level 2 charger, or rather the level 2 charger is built into the car. The thing by the parking spot is not a charger, but often mistakenly called one. It is properly called an EVSE. While it has a power limit, most EV chargers (the real ones inside the car) have limitations. The Tesla model 3 comes with either a 7.2 or 8KW charger. Doesn't matter how much juice is in the EVSE you use, it won't draw more than that. (Technically newer oens can do a bit more if you have 277 volts.)

The chargers inside other cars like the Bolt etc. are even lower powered than the Tesla.

Real DC chargers (the 50kw ones) are hugely expensive at present. But they can be much cheaper.

For the your last paragraph you are quoting from the article. Tesla recommends against excessive use of their DC fast superchargers, but does not recommend against moderate use, but it's always a little better to go slow if you have the time.

There are a lot of moving parts in the EV arena. While charging speed is a major consideration there are many others that are the bigger fish to fry. I have a 230m range Leaf, and it’s the third Leaf I have owned. Each has been a great car. My home charger is Level 2, 6.6KW.

For EVs to become mainstream, a number of things need to change or be addressed.

A. Many charging stations just don’t work at all. It’s a list of things that go wrong, and so far I see this maybe 40-50% of the time. I got my current Leaf less than a month ago from a distant dealer and had to charge along the route to get home. Two of the four places I stopped didn’t work.

B. Most people know almost nothing about the mechanics of EV charging. Many sales people are not in much better shape.

C. Any kind of real trip is hard, as you can’t risk running out anywhere. It can easily be 75+ miles to the next station. We will need a lot more stations and much closer together.

D. EVs with range in the 200 or so miles are only good for local travel. For any kind of real trip you need something closer to 400 and options for charging in less than 45 min.

E. Every ICE gas pump has pretty much the same nozzle. With EVs, there are at least 4-5 different kinds and most aren't interchangeable.

My Leaf can charge at 100KW, but I have yet to find any stations with anything more than 50KW so far. While faster changing would be good, it’s way more about whether they exist at all and are actually working on a given day.

Road trips are not practical in the Leaf. They are barely practical in the Bolt, and only recently as the CCS network just got some big upgrades in the USA. However, they are actually pretty reasonable in Teslas, with surprisingly few limitations, if you stick to the major routes. I mean in the 250 mile Teslas. The longer range Teslas are quite good at road trips. You will read thousands of reports online of them.

Teslas can charge from anything except CCS, and Tesla could make them do CCS with a bit of work. However, almost all fast stations are combined CCS/Chademo so it's extremely difficult to find a charging station a Tesla with the Chademo adapter can't use -- unless it's broken of course.

As to why they are broken? A lot of stations were put in using grant money, not for any rational reason. With no real justification, if they break, nobody feels inclined to fix them. Why would they? They are in the wrong place.

In Europe, a much more mature EV market, we see lots of 11kW and 22kW stations (AC). All destination chargers on the street, in hotels, at IKEA, etc. At home people usually also install an 11 kW charger.

50-250 kW DC chargers are available but require much(!!) more space and are much more expensive, even the cheap ones. The scenario you paint is only relevant for people that drive extreme distances continuously, so much that they even need that one hour of charging during visiting the grocery store, because they can't charge at home or at work. Or drive crazy distances.

Furthermore the electricity grid may not be able to accommodate quick charging everywhere. In Amsterdam they're already seeing the effects of the higher load on the net and they now have smart charging stations that vary charging speed depending on time of day and available solar power. Sunny day means higher kW (up to 22 kW). Evening peak when people get home from work means lower speeds (3.6 kW)

I'm guessing your scenario is a relatively small number of users. By far the most people will fit the European scenarios. Home charging, destination charging (including at work), and supercharging. Anything else is just an edge case. You can see that this is true in Europe.

I do not believe very many current EVs can take 11KW or 22KW of AC. Larger Teslas can but my Model 3 can only use 7KW of AC. The larger model 3 can only do 8KW. Yes, the Model X and some other very high end cars can use more. Is it different in Europe?

As for the grid, you may have missed the section where I went into that in detail. Chargers can be built which are connected to a simple circuit which detects how much current the facility is drawing from the grid, and adjust their current available down if the load goes up, assuring no overload of the service, or the grid.

Yes, that means stations that don't have full power on those very rare days of a facility using all its available power or grid brown out. But that's fine, because it's vastly cheaper with no service upgrade.

Even though they barely use it, almost all charging stations are computerized and easily able to respond to local and remote loads to control what power they provide. Most of the non-peak time, there's tons of reserve power to be had, which is to say every day until about 4pm and after 9pm.

Efficiency of the EV is key because it effectively buys you faster charging forever. This needs clever electrical design but above all, excellent aerodynamics. The Tesla Model 3 and Hyundai Ioniq electric are the best examples; all Hyundai-Kia electric cars are proving to be more efficient than the competition. Then even a 50kW charger can deliver a couple of hours driving in ~30 minutes. Or, a single 7kW post at work can charge two cars per day, not just one.

It is true that slower charging can be less efficient and I should have noted that.

But the difference in the office parking lot is that the average car needs about 10kwh per day. So you could put in a 7kw post and have 5 cars charge on it in a day, but you then need to do a dance, as every hour somebody has to come out and move their car and another person has to move theirs. You can try to create clusters where at somebody can move a plug from one car to another, but it's a pain. People have meetings, and they don't always park so close to where they will be at the appointed hour.

If you put in 6 slow chargers, everybody plugs in to one in the morning, and comes back to the full car in the evening. So much easier. Those who happen to need more than day can use one of the smaller number of 7kw stations and do the dance.

The conclusions of this article lend themselves to support the very reason that I bought a 2018 Mitsubishi Electric Outlander - SUV. For the short term the PHEV is an excellent match for existing infrastructure. My typical urban driving hardly ever exceeds 22km, covered nicely by Home Level-1 overnight, or cheaply installed 2 hour Level-2 charging. If I need the odd occasion to go further, I can use the existing Gas Station network, supplemented by overnight Electric charging at hotels & restaurants. And furture supplemented by 20 minute Chademo Fast charging by the Flo Network, while driving for vacation distances.

We got our Model S 6 years ago and immediately took a 2,000 mile trip to a wedding in Mobile, Alabama then back up north through Mississippi. Very few Superchargers back then. Made several stops at RV parks and did a lot of educating. Not many people knew what an electric car was back then, let alone what to $ to charge us to use a spot for a couple of hours. Generally the RV parks are wooded and in a nice setting so we didn't mind stretching our legs. Now we can go pretty much anywhere in the US we want to go and find a Supercharger for free. We will always choose driving over flying if it is practical and have gone coast to coast. As a result, we have degraded the battery capacity quite a bit. Started with a range of about 268 and can now only charge to around 230 and only count on about 180-190. Last time at a service center, they said we supercharged about 40% over the life of the battery which surprised us since we have a home charger but we only drive 2 miles to work (when we drive) so I guess that makes sense. We will definitely get an EV next car and most likely a Tesla - we love how smooth, quiet and fast the car is.

I think hotels and restaurants need to get onboard ASAP. They could charge a couple of cent premium on the electricity and have a nice flow of ancillary income. In addition, people may seek out those businesses specifically because of the charging capability. It reminds me of some of the convenience store chains who sell their gas considerably cheaper than the competing gas stations because they aren’t in the gas business. They are just using the gas as a way to funnel people into their stores where they actually make all their revenue.

KWH aka kilowatt-hour. Or 8kwh equal to 133 watts divided by 110 volts at 1.2 amps. If you charged your car at 250KW it would turn into a pile of ashes. 250,000 divided by say 220volts at 1136 amps. Articles of lost explanation.

The commenter may wish to look up the Dunning-Kruger effect. At any rate, no, DC fast chargers do operate at 150KW (most Tesla), 250KW (newest Tesla) and 350KW (fastest CCS.) This is done with DC at 440 and 800 volts in the latter case. KWH is a measure of energy (ie. battery size or consumption per mile) while KW is a measure of power (ie. charging rate.)

The author makes many interesting points about how people are using chargers. I have a Model 3 (300 mile range), I charge exclusively at home. I use 120v. I plug it in when I get home, and unplug it when I leave. That covers 99% of what I do. For long range trips, I never spend more than 15 minutes at a super charger, I stop, put it on the charger, walk around, use the facilities, and never fill it up 100%. I just make sure there's enough juice to drive another 200 miles, stop at the next super charger, do the same thing.

As a Tesla model 3 long range owner, this article seems rooted in the technology of perhaps 5-10 years ago, when electric cars had fairly short ranges. If you've got 90-120 miles of range, then maybe you'd be interested in all the places there are public chargers. Our experience is that we charge the car 2 maybe 3 times a week, at home, at night while we sleep. Against this backdrop, we have almost no interest in the various public level 2 chargers in our area. When we go on a road trip, then we will use the supercharger network. You stop for 20-30 minutes which will get you back up to about 260 miles of range, and you're good to go. This article assumes that charging stations = gas stations, but if you already had a gas station at home, would you ever stop at one unless on a road trip?

The article says just what you say -- that for people with charging at home, that is all that is needed and it is the way to go. I have taken many trips on the Tesla supercharger network.

The article is all about the exact opposite, that we should not think of charging stations like gas stations.

I agree with the thoughtful approach but not the conclusion. 50 kW is too expensive to install for normal businesses, and not fast enough for travel. L2 is perfect for homes and workplaces and can be as low as ~ $400 more per tap compared to L1.

At current prices. The point is that new, cheaper DC fast is coming. But for a business like a store or restaurant, where people stay 20=60 minutes, Level 2 is generally not even worth plugging in unless it's free maybe, and even then I often don't bother.

The posit here is slow level 3 at a reasonable mass production price of a few thousand. Which is already happening, though not at 50kw. It is necessary for v2g so people are building it down at 10kw.

Hi, wow you are the first person that has talked about changing charging current based on load. I live in Southern California and we all have smart meters. I actually have an app that allows me to read my meter. What I have been looking for is a charger that would monitor how much power my solar panels are generating. I want a charger that to send the excess power that my solar panels generate to my car. It is a simple calculation if you know the usage. Are you aware of any chargers that have this feature?

People talk about this, but not enough, and not many people make it. There are products that will monitor other devices in your house and cut power to your EVSE if they are turned on. You can even get a dryer plug that cuts off the car if the dryer starts drying. This very simple approach assures total house current remains within code.

But it's not the real smart thing, which is to change the pilot wave to tell the car to reduce current, not cut it off. (Cutting it off triggers an alert in some cars too.)

A new EVSE on kickstarter is doing something I have thought for a long time would be good -- reduce current when the voltage drops. So if somebody turns on a fat appliance in hour house, the voltage drops over the whole house, which the EVSE (or car) can see and reduce current.

What you want, people have hacked together for some of the smart arduino controlled EVSEs. You want the device monitoring solar output to tell the car when to take current. In time, I expect you will see more of this. As well as responding to demands from the grid -- we'll reduce your price if you'll charge when we tell you. Several companies do this. The simplest way to do that is actually with software in the car. Tesla could do it with a software upgrade.

I'm not sure 2 kilowatts is going to be worth it for many people. Do you really think having 2 kilowatts 5 days a week at your office is better than having 7 kilowatts one day a week? 7 kilowatts is a lot more versatile.

I think I'll take 15 level 2 over 40 Level 1 and 4 Level 2. That's better today (charging once a week beats charging 3 or 4 times a week), and looking at the future the level 1 chargers will be obsolete much sooner than the level 2 ones. They almost already are.

Naturally anybody would prefer 7kw over 2kw if they were the same price. They aren't. Level 2 EVSEs with install in a corporate parking lot are very expensive. In theory, you can install Level 1 by just installing a series of standard 15a receptacles (though 20A are naturally better and not much more costly.) That's because every car comes with its own EVSE to handle that. The EVSEs I seen in corporate parking lots cost thousands of dollars, and often come with accounting systems and network connectivity which you might need since at 7KW, strangers might come to charge. No company cares much about a stranger charging at level 1, and if they do, it takes so long it's easy to see.

So when it comes to the in-lot install, the Level 2s probably cost at least 10x, even 20x the cost of the Level 1s. And would you rather have a single Level 2 that everybody has to fight over and constantly move cars to share, or 15 level 1s so everybody gets charging when they park, and never has to move?

If I were an EV driver I would want my company to have mostly Level 1 and a small number of Level 2. Most days, I would just come and take a Level 1 and one would always be free. On the days I am low, I would check out the Level 2s. Probably already in use, so I would leave a note on the car that was charging and then come move my car later. Ideally the company would build a system to handle the queue. A pain, but I need the power that day. At least I am not competing with the people who only need 50 miles that day.

Most people don't want to charge once per week. People tend to want to be "ready" for surprise trips and want to keep the car topped up. If they were happy to charge only once/week, and you scheduled it, the level 2s would be useful.

Anyway, the answer is, you can figure out the balance. How many people are very happy with the level 1s -- never having to hunt for a spot, never having to move your car in the middle of the day, and able to use the level 2s some days -- and how many people need the levels 2s. And install the right mix. But I mostly see a small bank of really expensive Level 2. Which was too many when they put it in, but now is not enough and they're full most of the time.

BTW, the levels 1s would be nicer if they made a cheap and simple EVSE for corporate lots. I would perhaps try to make one to do 240v or 208v at 15 to 20 amps. That's technically level 2, but can be done with much lower cost components because the max current is lower. 240v and 20 amps is actually 3.8KVA which is actually plenty for almost everybody. (Most corporates have 208v though.) If made in quantity, a hardwired EVSE that just sits spooled up could easily be built for $150 or less. (They retail today for $200 at 16A and Telsa sells their 32 amp/240v one for $300.) Compare that to the typical chargepoint commercial which lists for $7,000!

I didn't say 7kw was just better. I said 2kw was nearly useless. Then I used your example of the trade-off and said I'd prefer the level 2s.

I don't think you can install 15 level 1 chargers in a parking lot for $2000. Not unless you're going to use extension cords and duct tape to get the power to the equipment. Cheap and simple is not what I want at my place of business.

What's your evidence that "people want to keep the car topped up"? You yourself have repeatedly said that this isn't the case for people who actually own the vehicles. You've also said right above that you often don't bother plugging in to get 30 extra miles of charge even if it's free. Do you keep your car "topped up"?

Having accounting systems and network connectivity is a good thing. It's part of why the level 2 system will be useful for many many more years than the duct tape and extension cord solution. Charging shouldn't be free and first-come, first-served. The people who benefit from it should pay for it (preferably by the hour). This way more level 2 chargers can be added as demand grows. A reservation system might make sense, and that could be done without even having connected charging stations. Just reserve your 4-hour slot on a web based system and give your license plate number. If someone is in your spot you can report them and have them towed away (if it's just someone overstaying their slot the web based system could text them a 15 minute warning first). If there's always contention, despite a fee, then the better solution is to add more capacity. But maybe there will be higher demand on Mondays, or Fridays, or whatever, so you could have reservations to spread people better throughout the week. There shouldn't be a need to swap cars more than maybe once a day at lunch time. If you can't use at least 56 miles of charge (4 hours7 kilowats2 miles/kilowatt), you don't charge. You shouldn't always have your battery at 100% anyway. If you've got 150 miles range and less than a 20 mile (each way) commute, you can charge for 4 hours whenever you're under 70 or so. That's still going to leave you with enough range for almost all spontaneous trips.

If you have a surprise trip once or twice a year, and you don't have charging at home, head over to a supercharger. Preferably a 250 kilowatt one, rather than a 50 kilowatt one. (You really don't know even one business day before you have a 100+ mile trip? How often does that happen for people who have a regular office job?)

How many office complexes even have a use for 15 level 1 chargers? The spaces, which will probably be premium spaces (to save on duct tape), will sit unused most of the time. If they're free, and presumably they'll be free (because who's going to pay for 2 kilowatts?) when they are used they'll be used by people who don't really need them, but just want to take advantage of the premium parking spot and free top-off. Who is it that's going to use these chargers for something more than a high cost, low-value perk? People who can't afford to have chargers at home? You'd be better off giving them $500 and let them have their duct tape and extension cord solution installed at their house. Or better yet, they can pool their $500 with $500 from a few of their neighbors and put a level 2 charger somewhere where they can share it.

I do agree that more widespread, slower charging, is usually better. But only to a point. 2 kilowatt is probably below that point, and it definitely will be far below that point in 5-10 years.

No, people still like to keep it topped up. It is pretty standard to plug in every night when you get home, level 1 or level 2. With a short range car that was a must. With a long range car it's not a must any more but you still want it. Cars drive an average of 40 miles/day, but of course it's in bunches, and some days you drive 100 or more even around town, and some days you do that 2 days in a row. The large battery can buffer that (but it can't handle 3 days like that.) It does handle even 4 days like that if you top up the night before, and every night -- but you do have to have topped up the night before that stretch.

15 for $2K is not so far out of reach. It's 4 outdoor boxes each with 4 receptacles spaced 20 feet apart in a parking lot with a barrier between the back to back spots. Plus conduit with your conductors along that barrier, 2 phases at 120 amps (#3) plus neutral and ground or 6 #6 wires plus ground. If you have a special level 1 EVSE at the endpoint you don't need sub-breakers, as the cars regulate the current. At level 1 and 2, the charger is in the car, not in the "charger."

This could be even cheaper if it became a standard mass produced thing. In that case though, I would propose the creation of a low cost Level 1.5 EVSE 4-plex. By Level 1.5 I mean 208v/240v at 15-20 amps. Due to the low current this gear can be a lot cheaper.

Of course, the service and wires to the charging array are more, but you need those for the Level 2 6kw station too.

Accounting/control has virtue, but not at high cost. Employers generally wish to give this free to employees and visitors. With Level 1, there is no first-come first-served, you put in enough for everybody.

I do agree that a camera based accounting system can be a good choice, particularly because you could put one camera on a light pull facing a row of 8 cars to do it.

But reservations etc.? That can work but is not nearly as pleasant. Pleasant is, "pull in, there is always a spot available, take it, plug in, return in 8 hours." Not book time, come out and move your car at the appointed start, move it again at appointed end.

Not knowing about a 100 mile trip the day before? Very common for me and everybody else in Silicon Valley, because that's a trip to San Francisco or Oakland (or vice versa) at about 45 miles each way.

Who would use these chargers? Employees who want an electric car but can't plug in at home. They don't have to be premium location the way most Level 2 spots are, though since it's easier to wire close to the building they might well be. Employees who can charge at home will probably also use them unless told not to. (Employer can offer a sticker to employees who certify they can't charge at home, or even to those who also only have L1 at home.)

I am not sure why this changes in 5-10 years. I still think the average need per day will be 10kwh in 10 years.

BTW, I think you could still make a 4-plex 240v/30A EVSE for a pretty low price too. The reason you would still consider doing it at the smaller current is you need much heavier duty gear at all levels to do 30a over 15a. More electrical service, thicker wire, much more expensive other components.

What you could do (and I posted about a few years ago) is make a 4 plex or 8 plex EVSE which shares the power among the 4/8 cars. (And 8 plex has 4 slightly longer cables and is put at the center of an 8-block of parking spots.) All cars plug in but they share the power, nobody has to make appointments or move their car. The only people who need to do anything special are those who need a lot more power or won't be there for the normal workday -- they can be given the power they need because most of the cars only need 10kwh.

That does require something fancier in terms of UI. You want to be able to somehow talk to the car to know how much it needs, and to the driver to know their schedule. Though cars reduce their current demand as they get near full so you can learn something from that. Teslas transmit data over their power cable, it would be nice if all cars did that.

I think the number of employees willing to offer this as a perk is pretty low. And just because it's free doesn't mean there isn't any accounting necessary. Right now maybe businesses can get away with not putting the value of the fringe benefit on employees W2s, but as the number of people with EVs increases that's probably not going to last.

For this to go beyond a perk and a tax dodge, to something ubiquitous, I think we're going to need level 2.

But I am not so sure they will clamp down. Government actions which stop EV perks get a lot of criticism. Only now are EVs having to pay road tax to replace the gas tax and people are trying to stop that.

The perk is pretty small -- less than $1/day at national averages. I mean they give free parking, free coffee etc. at prices more than that.

It's not hard to account for it in the future. Especially if they put in a communication protocol into the cables the way Tesla did. The biggest cost of the accounting is the UI -- needing to actually tap your phone on something or go to a console or tap a card, and any specialized hardware.

Or another good way would be to sell it to the employee for $200/year or something and not bother to enforce other than the parking patrol checks every so often that the cars have the EV paid sticker or a registered plate.

However, today there is no cheap way to do all this. If there were big demand for accounting (which there isn't yet) it can be made cheaper.

At 2 kilowatts you could probably have a permanently assigned parking spot. That'd simplify the accounting a lot.

It's probably worth significantly more than $1/day to someone who doesn't have charging at home. For someone who does have charging at home, it's a fairly tiny perk (and will cost the employer much more than it saves the employee).

That all could possibly change if the off-peak times move to mid-day.

Most perks do not always make economic sense. The company may be able to buy power at a better price, and many companies are putting in solar generation as well.

If the station can be installed for a low price as I lay out, it may not cost more. However, employees with charging at home might not need a dedicated spot. And there are actually still a lot of 100 mile cars out there, and they are certainly economic to make and will continue to be cheap. Short range electric commuter cars can be quite cheap -- under $10K -- and such a car works well with level 1 at both home and office.

There are some other interesting options in commercial. For example, new Teslas will charge at 277v. That is the power of a single phase of 480 volt 3 phase which many commercial buildings use. Using this you can wire 4 12AWG connectors and change 3 cars at a quite decent 3.3kw. Almost 100 miles of range in a workday. In the past, nobody thought to make the chargers in the cars work at 277v, but many do anyway and I suspect people will spec them to do this to use commercial parking lots that have 480v 3 phase.

To reiterate one important point. If the employee has to go out twice during the day to move their car at a Level 2 charger, and that takes 5 or more minutes, that 10 minutes of employee time dwarfs the other costs, and that's reason enough to just equip a lot of spaces with chargers big enough to handle most needs in a day. Either packs of Level 1 or Level 1.5 or an octopod of chargers sharing a single 240v 50a circuit or similar could do the job.

I'm not sure where you're getting the idea that they'd go out twice during their working hours. Once, once a week, during their lunch break, when they're probably going out anyway, when they could use the break, and when it's not charged to company time.

Sure, alternatively they could just stay at the spot all day. This would be more expensive, though, and I still think the employees that use it should be the ones that pay for it. Otherwise you're essentially making all employees pay for it. And for a perk that you seem to admit probably makes no economic sense (it'd be very rare for an employer to pay less for lots of power during the day than for a residential customer to pay for it overnight).

"Free" is never free.

(I guess you could also offer the slower chargers, but I'd expect they wouldn't be as popular, especially if you charged enough for using them to cover your costs, including power, installation, maintenance, etc. And if you have premium spots sitting empty most of the time, you've done something wrong. That's why I say if you're going that route, might as well lease the spots out rather than making them first-come first-served or underutilized.)

People want to charge every day. They don't have to but they prefer to. Because today may be the day you go somewhere. Superchargers can also solve that but they have many downsides. The easiest thing is to have a charger in your home spot and plug in each night. No decisions to make. Always works.

So that means that if you get to work and there are 5 Level 2s and 20 drivers who want to share them that day, the first person in moves only once, and the last person only once, but the middle people have to go out after #1 is done to move their car in, and then go out again and move the car again after they are done. If it coincides with lunch it's easier (if you are leaving the building for lunch, which not everybody does.)

I would rather just have a slower charger that is mine all day.

Last night I needed to 'top off' my Tesla to make it to a Supercharger this morning to start a 550 mile trip home. I did it with the 'convenience charger' that comes with every Tesla and most EVs. The hotel only had a 110v GFCI outlet I could reach, so I charged at about 4 mph. I got about 40 miles overnight. Anywhere I go all I need is a 240v dryer plug to use my Tesla charger. Forget the SAE J-1772 Level 2 connector. 240v at 30 amps is 7.2 kW which is good for 30 mph. It will give a complete charge overnight, but a useful increase while dining or shopping.

I have not found the increase while dining from level 2 to be useful. I mean if I'm desperate, or it's free, sure, but I need to be desperate. Once in a year I'm like that.

You don't want to live like that very often. You want it to be a couple of times a year thing.

Overnight is another story. Level 2 is just about perfect overnight. Enough to refill, but not too fast.

Level 2 is just about perfect overnight?

Do you top it off every night just in case you go on an unexpected cross-country road trip?

I mean level 2 means all the needs of a driver if they have it at home. They can refill their car from empty to full during the night, and you don't need more than that. Supercharging heats the battery too much, that is better. Level 1 is sufficient for many drivers, but can't pull off the full recharge.

If they're perfect at home, why aren't they perfect at work, for people who can't install them at home?

If it's acceptable at home to have more power than you usually need, why not at work?

Maybe the issue is that level 2 costs a lot more to install at work? Maybe the level 2 at work can be fairly barebones. If you put a master switch inside the building to cut the power off, the first one in the office in the morning can turn it on and the last one out can turn it off (or whoever is using it can turn it off). Then there's no worry about people stealing power, and you can have a simple rotation for who gets to use it each day, if there's more demand than supply.

I do think it's important to account for the usage, but it doesn't need to be a fancy, expensive system. You could even do it with pen and paper if you had to.

Yes, you need a unit that can handle the elements outside, and you've gotta run the power out to the unit, but you need that with the level 1 as well.

I think handling things this way is what's going to be needed as electric cars move from something that is bought because of incentives or selfless concern for the environment to something that is more ubiquitous.

By perfect I mean they can do everything you need to do at home, but no more.

At the office, you would have a mix of Level 2 for the few people who need it, and Level 1 for most of the people who don't. Most people at home only need Level 1 most nights, but a few nights they need Level 2, so they put in Level 2.

Level 2 at work could be much cheaper and simpler.

For the best convenience you don't want to have to get the driver to pull out their own EVSE. It's cheapest if you do it that way, but it's not a lot more to have a low current J1772 plug -- even at level 1. I don't know if anybody makes a J1772 only for level 1 other than the ones that come with cars, but they don't have to be that expensive. As I have noted, I think that "level 1.5" which I will call 240v 15a might be a great middle-ground, needing lower current, smaller wires, less fire risk etc. and thus lower cost.

Not all EV charging is the same. The same with lithium ion batteries. Solid state batteries from BOAO are unlike anything you've seen so far, and fast charging can take as little as 10 minutes, adding 80% towards a full charge.

When better batteries and charging systems are deployed at massive scale that will be great. Many have promised this, but it is not available at present to consumers. Even when it does happen, it usually is better for the battery to not charge that quickly when there is no need. But the existence of these systems does not alter the high cost of the charging systems to charge at these speeds, because that is the cost of just bringing in that much electricity to a parking spot, as well as the DC conversion electronics to handle a megawatt.

So you misunderstand the point of the article. Faster charging batteries change little. They allow you to think like a gas station, but you don't want to. Charging while you sleep/work/eat/shop takes ZERO time. Ten minutes is a lot longer than zero.

Thanks for taking the time to document this, there's a lot of misinformation, hype and misguided expectations around charging. It's taken us 20 years to figure a lot of this out - so far - and communicating it in a headline or sound-bite is leaving a lot of important nuance on the table. I'd love to know what you would put down for the top, maybe five key points?


  • Charging is ideally done mostly when doing something else -- sleeping, eating, working, shopping. Especially sleeping. For this, it only matters if it can do the job during your task.
  • Charging is best when simple -- plug and go
  • Fast charging is usually great (though not ideal for batteries) but it's very expensive right now. When speed is not so crucial (like in office parking lots) having lots of slower chargers can be better than having a few faster ones.
  • Forget gasoline style thinking, driving until empty then filling up while you watch it fill. Charging while you sleep takes zero of your time, you can't get faster than that!
  • Putting in new electrical service is expensive, chargers which are smart and manage charging to fit the local capacity can avoid that.

Your concern about expense would be better directed toward hydrogen refueling stations, which are mind-bogglingly expensive unless subsidized. And yet, people seem to think that gasoline thinking may be worth it. Winning converts from gas to electric power is hard enough at 150 kW, but of course we also need batteries that can take it and thrive.

It is hard to fathom the love for hydrogen. It is a combination of gasoline thinking -- insisting on something that can refuel fast -- and the dream of someday fixing hydrogen's many problems, including the weight of the tanks and systems, the fossil fuel sourcing, the inefficiency and cost of the fuel cells and the lack of infrastructure. If you fixed all those, H2 is a low weight store of energy. I could see it for long haul trucks or buses which only refuel in a few special places. It's lost in cars.

Brilliant article and matches a lot of what I started thinking now that I have a full BEV and tried out DCFC. You make a good deal of sense and your facts match a lot of what I was seeing and thinking. I have some evidence that the original J1772 standard proposal actually wanted to include a very low level (20kW) DC capability to the Yazaki connector (much like Tesla did do), but probably time ran out before cars like the i-MiEV and Leaf started coming out. It's too late for that now, but an affordable, easy to implement, lower power (<=50kW) charging station might turn out to be the real key to increased EV adoption. Thank you for your article.

Well, you have to hand it to Tesla. Their connector is clearly a better design. Small, capable of 250kw or more in one connector, data protocol for doing billing. Story is that Tesla offered the design to the world but either it refused or Tesla put some condition on it that made that happen -- would love the details.

Tesla does the lock in the vehicle. There are arguments over putting the lock in the connector or the vehicle, there is not a clear winner on that.

In the USA, Tesla is most of the cars, so things have gone well for them. In Europe, Type 2 got so much push that Tesla yielded and uses it, and thus CCS Combo 2 as well. It's inferior to the Tesla connector -- much bigger and clunkier, but that's defeated by having uniformity.

I predict one more connector has to evolve, and that is the connector for robotic vehicles. You want to design that connector so that the vehicle can plug itself in, without needing much or any robotics in the plug. The Tesla connector would work if it were in the front or back of a vehicle and level, so that a Tesla plug suspended in space could be driven into (or backed into) by a car.

However, better is probably just a system with pins that can swing down or up and go onto plates or sockets underneath the car. (It could be the car which extends down to the box on the ground or the box which extends up.) This requires some actuators -- one to raise/lower the pins, another to open the cover that protects them -- but they are simple and cheap. A car would drive itself precisely over a box, pins would connect and charging would begin. Doing it in a box allows drive-through and easy placement even at homes.

Of course there are also those who like inductive. But it costs money and efficiency, compared to the car just doing most of the motion.

We need to standardize plugs and make charging universal. My ICE car does not care which brand of gas goes in and my EV should not care if the charging stations says Tesla, EV Go, etc. Love my EV and will not go back to ICE but the lack of J1772 high speed charges can be frustrating.

You car definitely cares if you give gas or diesel or avgas and some care about the octane.

Your Tesla can charge at all the stations using adapters. The Chademo adapter is expensive, but found at a growing number of stations.

The different connectors came about for a reason. Sure you might say it would be nice if everybody had figured it out in advance but people are not that smart. The alternative is to let the different forms fight it out and have adapters, otherwise you are stuck with the first one which probably was not right.

Now there was a nearly universal standard for a while in the Tesla adapter. It was also the best -- small, capable of doing both fast and regular. It was overwhelmingly the dominant form of fast charging, and more cars than the other types combined. But the world wanted to go a different way with a huge bulky system that wasn't as good. And you think Tesla should have made theirs worse to go along with them when they had the most stations and cars?

It’s all very well assuming that everyone can simply charge at home, but the reality, especially in countries such as the UK, is that many people have to park on the road and don’t have off-street parking at their home. Governments are banning Petrol vehicles from such and such year, but no one has outlined who will pay for lining every street with chargers and adding them to every parking lot. The middle to lower classes are always forgotten when talking about moving to modern technologies wholesale and those people will be unable to charge at home, so will need 1-2 minute full charges at filling stations.

As I have said, if you can't charge at home or work, an EV may not be yet right for you. The talks of banning gas cars are a very long time away, and even after they stop selling new petrol cars (2035 in California) you will be able to buy them used, and from other countries, for years after that if you truly need them.

But there are a lot of solutions in the works for solving this problem, and I think not just one but several of them will be workable, and if somehow none are, then I don't think the cutoff will happen.

I think this is overall looking in the your direction. I can attest to the work scenario describe and agree with the conclusions presented.

I own a 40kwh LEAF with a range of around 150 miles and mostly charge at home on 240v Level 2 infrastructure but most nights would be fine at 120v. On the rare occasion I come home late with a depleted battery and need to leave early in the morning I want to have the the faster capacity.

At work there is a single Level 2 EVSE that is free not only for employees but the community at large. It is often available because EV adoption is relatively low at this time but there is another employee who drives a Volt as well as a handful of other vehicle's ranging from Teslas to older Prius plug-ins. As I said the station is often not in use but there are other times when it will have multiple cars parked next to it trying to coordinate charging. This is not easy to do because non of us actually work together or know each other (I have had one conversation with the other employee when we happened to show up at the same time but she work in a building across the street from where I work).

At level 2 if I show up to work with I completely depleted battery I t would take about 6 hours to get to full. however rarely will I show up completely empty and even if I do I mostly would only need to charge enough to get home. this means on a level 2 charger I am usually looking to be plugged in for 1-4 hours. For an 8 hour workday that either means I am sitting at the EVSE longer than needed or coming out at some point in the middle of the day. Occasionally this can coincide with a meal break but not always and it can be a crap shoot trying to guess when a complete stranger will be done charging. So yes this is an award dance with no music and a partner you have never met or can even see most of the time.

From this experience I can attest that it would be far more convenient for multiple people potentially all wanting to charge at the same time who are working for an 8 hour day to have multiple level 1 spaces available. If it is no more expensive to put in level 2 then level 1 fine but in this use case more stations is better than faster charging. Even if I had a longer range EV I still think this would hold because its not about percentage gained but miles gained in an eight hour period from a level 1 vs level 2 EVSE. If 40 Miles can top of or get me home in a 150 Mile LEAF it can can do the same for 400 Mile Tesla. The issue comes from either having a longer commute in which case yes a level 2 (or 1.5) would be appropriate or for people who can't charge at home who are reliant on work charging for more than just their commute. I would define both of these as separate use cases that should be able to be anticipated by an employer based on the geography of their location.

Basically there are workplaces that need level 2 but a lot that would be better of with a greater number of level 1.

For 300-600 mile EVs the real need for high power level 2 (9kw-11kw) is at hotels where it would be common to expect drivers to show up empty and want to leave 1st thing in the morning with a full charge. other locations would be theaters and dine in restaurants where people expect to stay longer than an hour but less than four and are also mostly looking for just a top up or enough to get home. The 24kw-50kw and in some cases up to 150kw is appropriate for restaurants and retail where people routinely park for less than an hour. this should be more along the lines of 50kw-150kw along major freeway corridors where people are pulling off for a quick half hour lunch. Finally at rest stops/truck stops you have gas station style 150kw-400kw with bathrooms and a convenience store. All of these need to be ubiquitous enough so that the one you need at any given time is readily available with out much planning needed. (Signage will be important.)

Basically to fight some theoretical man made global warming, Americans will have to give up the most valuable commodity of all. Their time. No thank you. Either make better electric cars or I'm pushing for gas vehicles. I would be happy with gasoline or natural gas.

Apparently you would be happy to let the rest of humanity perish in exchange for a bit of comfort.

Apparently you would be happy to let the rest of humanity perish in exchange for a bit of comfort.

So, you feel there's no global warming. Probably not going to convince you otherwise, but it doesn't matter. People buy these cars because they are faster, much more fun to drive, cheaper to operate and cheaper to maintain. And forget greenhouse gasses, the other pollution from burning gasoline kills hundreds of thousands each year and all moral people would work to avoid burning the stuff.

The best use case for a level 3 150Kw charger I'd imagine would be as a mobole service, somwhat like AAA, that would have vans that would metup with EVs along a route, and topoff their charge on the spot.

Such a service if reliable enough would allow end of journey or bottleneck top ups, a totally different use model over gas stations.

As an exotic energy source that might wind up cheaper in fleet use than batteries they might use a large capacitor instead of a battery, or a microturbine generator running ammonia.

It turns out that EV drivers almost never run out of energy the way gas drivers run out of gasoline at the side of the road. It's due to two things, I think. One, running out is much harder to fix so people are more motivated to avoid it. Two, there are much more accurate meters and planning tools to make sure you don't run out.

So the business of roadside charging isn't really a business.

Add new comment