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EV Charging at Home - should it be banned?

Doug Houseman's picture
Visionary and innovator in the utility industry and grid modernization Burns & McDonnell

I have a broad background in utilities and energy. I worked for Capgemini in the Energy Practice for more than 15 years. During that time I rose to the position of CTO of the 12,000 person...

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  • Mar 31, 2022

When one looks at the number of vehicles in the EU and the US there are too many for the distribution grid to support in many areas.

In many cases the distribution circuits will be 200-400 percent loaded based on current charging behavior.

Should we:
1) Socialize the cost of charging at home, even though that is social unjust right now?

2) Require an off-grid DC solar PV system, and battery and only allow charging from that system?

3) Allow the distribution grid to overload and burn out?

4) Raise rates for EV charging to cover the cost of the upgrades directly without subsidy from any other use?

5) Regulate charging times and amounts via direct load control?

6) Ban all EV charging at home?

Unfortunately we need to pick a couple of these options. If we do nothing that we have picked option 3.

How do we deal with this load growth, understanding that much of the distribution infrastructure is at or beyond the design capacity already based on 24,000 real distribution circuits worth of data.

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Julian Silk's picture
Julian Silk on Mar 31, 2022

2) will occur, as well as PV systems attached to the grid that do the charging, and there will be be additional microgrids built to support the EVs.  6) would be like Prohibition in the U.S.

Matt Chester's picture
Matt Chester on Mar 31, 2022

6 got me wondering-- is there any theoretical limit already in place that simply isn't tapped into? For example, if somehow I wired my home to implement some ridiculous level of industrial equipment with the type of load that far exceeds what any residential customer would ever be expected to use, is that hypothetically allowed? Is there anything the utility could/would do beyond charge higher demand rates? 

Roger Arnold's picture
Roger Arnold on Apr 1, 2022

To do that, you'd have to bypass the master circuit breaker on your service panel. Its job is to limit the current that can be delivered to your residence; bypassing it is both very unsafe and very illegal.

Our house was built in 1960, and until recently had only 100 amp service. That was sufficient to support a 220 volt level 2 charging system. But when we installed solar panels and a battery system, there was a mandatory upgrade to 200 amp service included in the project. The project was completed a couple of months ago and signed off by city building inspector. But we're still waiting for PG&E to send their inspector around to check out the system and grant formal "permission to operate". Until then, the system sits idle. It's infuriating, because in the time since we could have been using it, we've endured two neighborhood power outages. And, of course, we're continuing incur full monthly utility bills from PG&E.

robert maxwell's picture
robert maxwell on Apr 4, 2022

You left out these two options:

7.) Meter the energy consumed by a home each month and then send a bill that is calculated from the total usage (we do this already). Charge a marginal cost per kwh that is greater than the marginal cost of generating that kwh (we also do this already), use the difference to recover the cost of distribution system upgrades (we are supposed to be doing this already). The average IOU serves about 35 customers per mile. 70 EVs (2 per home) travelling 1200 miles each per month would add about 28,000 kwh of usage per mile of line per month. An average retail margin of $0.04 per kwh would bring in additional income of $13,440 per line mile per year. If 10% of the distribution line miles must be upgraded at a cost of $500,000 per mile, the additional kwh sales provide a payback of less than 4 years without a rate increase.


7-1/2.) Do exactly the same thing as in option 7, but provide incentives to customers to defer EV charging during times of peak demand, rebuild a smaller percentage of distribution line miles, and enjoy larger profit increase per mile of line. This won't work with a traditional time-of-day model that pre-defines peak and off-peak hours - most people don't cross the road to save a few cents on gasoline and they won't accept the inconvenience of daily charging deferral to save a few cents per kwh. This would work with a program that provides a monthly credit to customers for allowing connected chargers to defer charging for a few hours at a time when their specific transformer or feeder is approaching a capacity constraint. For example, defer charging only when a line section or component reaches 75% of its rated capacity and, initiate a capacity upgrade to any line section or component that triggers charging curtailment for 20 hours or more per year.         



My household has 3 EVs which increase our electric bill by about $100 per month, but decrease our gasoline bill by about $400 per month. We charge them at times that are convenient to us, and I'm confident that we are paying for our share of required distribution system upgrades. I would be happy to allow a utility to curtail our charging for a reasonable number of hours per average month, if they provided an appropriate incentive to do so.

The 'incentive' offer from the utility that provides my home's electric service is for me to pay an extra $15 each month to rent a connected charger that only works for a pre-defined 6 hour period each day. Without even considering the inconvenience of curtailment, I suspect that few people would choose to pay $15 every month to avoid a one-time purchase of $600. The minimum incentive that a rational consumer would accept is probably closer to one that either provides supplies complimentary charger or provides a monthly 'bring your own charger' credit of somewhere in the range of $5-10, and promises to curtail it no more than a total of 20-40 hours per year.  

Doug Houseman's picture
Doug Houseman on Apr 5, 2022

In most states inclining block rates are not allowed by regulation. California has mostly moved away from it. 

In most states you need approval to spend capital and add it to the rate base. In most states the requests to increase capital spending on distribution have been denied or cut back significantly. 

So at the present time, with the present regulation, 7 is not possible for utilities to do. 

robert maxwell's picture
robert maxwell on Apr 7, 2022

I didn't mean to imply inclining block rates in my original comment. The average US retail rate is a little over $0.10 per kwh, and wholesale rate is a little less than $0.05 per kwh. Subtract some for variable transmission costs, and the result is a difference of around $0.04 per kwh. Assuming that the fixed costs of the existing distribution system are covered by existing sales, then the additional kwh sales brought on by EV charging should cover the additional distribution capital spending to support those sales. Keeping the price per kwh constant produces a rapid payback for the distribution upgrades, declining block rates could still pay for them with a slightly longer payback.

Julian Silk's picture
Julian Silk on Apr 5, 2022

This is very good.  But the interesting question it raises is whether the charging costs, however you do them, should exclusively be used for distribution upgrades.  What do you really want as a source for the charging?  Once this is answered, if there were some guarantee of privacy, the utility of whoever was involved with the electricity supply might do some sort of real-time pricing or locational pricing for the charging, and that might be designed, too.

Bill Meehan's picture
Bill Meehan on Apr 6, 2022

Great post Doug. I've been thinking about this same thing for quite some time. In fact, I wrote a post in energy central last month, called Party Lines for Electric Vehicles. My argument was the existing infrastructure can't sustain more than a couple of EVs per distribution transformer charging at the same time. Just look at the math. Most residential homes in the US are fed from 25 to 50 kVA transformers. A kVA is more or less equal to a kW.  A typical EV might have a 60kWh battery that takes 6 hours to charge. 60 divided by 6 equals 10kW. So for 6 grueling hours, the EV uses 10KW every hour. Now if there are 5 houses connected to the poor 25kVA transformers all charging at the same time, that's 50kW demand, blowing the 25kVA transformer to bits. Sure, solar panels will help. The reality is that home EV charging is good only for topping off. The answer is a network of commercial fast DC chargers that are just as convenient and numerous as corner gas stations. 

robert maxwell's picture
robert maxwell on Apr 7, 2022

DC fast chargers are critical for long trips, but Level 2 chargers at home will be the workhorse of EV charging. In about 40,000 miles of EV driving so far, my family has used roughly 13,000 kwh for transportation. Less than 10% of those kwh were provided by DC chargers (which we've only used during trips of about 250 miles or more).

A vehicle driven 1200 miles per month consumes an average of about 12 kwh per day, so recharging takes about 2 hours with a 6.6 kW L2 charger. If every vehicle is charged at the same time, transformer overloads will occur. Overloaded transformers and line sections could easily be avoided, however, if utilities and regulators are willing to provide incentives for managed charging. 

When every vehicle in the US is electrified, our distribution systems will need to deliver about 30% more energy per year than they currently do. If full transportation electrification happens over 10 years, that's a very manageable increase of about 2.5% per year.  

Bill Meehan's picture
Bill Meehan on Apr 13, 2022

Hi Robert. Great that you have direct experience with your EV.  You make some good points. Certainly, home charging will supplement commercial charging stations, but we are so used to filling up our gas cars in just a few minutes that for full deployment of EVs, I believe fast DC chargers (as opposed to slow AC charging) will become the norm provided there are as many fast chargers as gas pumps. Today, there are only a fraction of fast chargers. That will change. The IIJA is setting a target (and funding) for 1/2 million fast-charging stations. Getting a fill-up in 15 minutes comes close to the convenience we get at gas stations. Many people, particularly renters, low income, apartment dwellers will rather go to the gas (electric juice) station than invest in upgrading their wiring. The nice part of home charging is that you can top off. We can't do that with gas cars from home.

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