The Future of EV Home Charging and the Grid

[Feathermerchan]

So do you have TOU on your cell phone? I'll guarantee you that their cell system is built for peak load too.
Truth is we HAD TOU for cell service. You could buy a plan with 2, 3, or more pricing tiers depending on time. The public decided it wasn't worth the money and hassle of never knowing what your bill was going to be. So sometimes even when possible TOU rates are rejected by customers. Even if it is technologically possible.

The regulators incentivise the utility to minimize costs. At the generating level, for instance, this is done by building units meant to be run infrequently to handle the peak load. They are less efficient (typically jet engines repurposed) but offset the lack of efficiency by having low capital cost. IE they require very little physical footprint, no cooling lake/pond/tower, no steam system, etc.
Lots of other examples but there are many ways to reduce overall costs.

 

[gnuarm]

Regulators are supposed to provide balance in a natural monopoly. 'Build and Grow' is the business model of the utility but that's not always in the public interest.

TOU is a failure... unless it involves no routine intervention on the part of the consumer. If someone can save ~$10/mo by enabling the delayed charging that comes with most EVs they'll do that. Basically for TOU to be effective it needs to be largely automated. But without TOU there's no market for automated systems....

I think most consumers know little about TOU. Also, in general TOU doesn't provide the full cost benefit to the consumer that is gained by the utility. The marginal rate to the utility can be quite high at peak times. My TOU service is five times higher during peaks and half the rest of the day. If I don't change my usage it costs me a bit more. But I was already cutting my AC during the peaks. The utility had sent out emails asking people to cut back at peak times and I tried programming my thermostat to cut off AC then. It wasn't so bad, but it did let my temperature run up a couple of degrees over the four hours. Now that I am on TOU I cut off everything I can. I even cut off the water heater unless I am going to take a shower, lol. But then I'm only there three days a week so better I forget to turn it back on when I return than forget to turn it off and have it cycling for the rest of the week.

It's not really about the money. I'm doing this because I have hourly electrical records from the utility and I want to see what is practical to do and what is not and how much benefit can be gained.

 

[Feathermerchan]

In my area backup or supplemental heat for heat pumps is usually electric heat.

Yes things change but here EVERY house here is built with A/C and heat. In your case, the distribution system may have been built due to the winter load which if resistance heat, is generally larger than the summer A/C load. Hence transformers would not have to be replaced when A/C was added.

You cannot design a distribution system without knowing what the load is. The load sheet method was invented before smart meters but not without a lot of statistical surveys. It was updated as things changed but it has to be conservative because you know a few will install hot tubs, pools, additions and other things. We set a 100 kVA pad mount transformer max in new construction because we know we can replace it with a 167 kVA pad mount if necessary. We use 25 kV underground cable even in 12kV areas because we know that it will probably be converted to 25kV at a later date. That gives us lots of expansion potential.

Charging at 72kW is a huge load. With a 100 kWh pack I'll bet it never stays there for more than an hour. And then not when the weather is super cold or super hot. The batteries and charger will make it taper down.

Even Texas is not fully deregulated. The CooPs have a super strong lobby and were able to add an option for each CooP to opt out of deregulation if they wanted. Guess what? They all but one did. So if you are unfortunate enough to live in a CooP territory you have no choice but to move.

 

[nwdiver]

My car charges at 72 amps, 17.28 kW at 240 volts.

How often is there an advantage to charging at 72A vs even 20A? In 6 years I can recall maybe ~5 or 6 times that a charge rate >20A was useful.

I think most consumers know little about TOU.

Until they get tired of their $300 electric bill and want to find a cost effect way to reduce it.

A lot of the solutions to the grid problems of EV charging don't exist because by and large the problems don't yet exist. To presume that means the solutions can't work is absurd. I'm currently defenseless against a Tiger. That doesn't mean it's impossible to defend against a Tiger... if I had to worry about Tiger attacks it would be fairly easy for me to find a defense...

Demand Response and TOU aren't common yet because the grid problems they solve aren't common yet. There are dozens of solutions 'standing by' once the need arises.

 

[gnuarm]

In my area backup or supplemental heat for heat pumps is usually electric heat.

Yes things change but here EVERY house here is built with A/C and heat. In your case, the distribution system may have been built due to the winter load which if resistance heat, is generally larger than the summer A/C load. Hence transformers would not have to be replaced when A/C was added.

You cannot design a distribution system without knowing what the load is.

Ah, but where I am, the electrical distribution is and has been in place for a long time. Houses are added. A bit rural. My other house is in an older part of town built in the 60s before heat pumps were common, so planned service was low. In the meantime houses have been built and heat pumps added to older houses.

The load sheet method was invented before smart meters but not without a lot of statistical surveys. It was updated as things changed but it has to be conservative because you know a few will install hot tubs, pools, additions and other things. We set a 10 kVA pad mount transformer max in new construction because we know we can replace it with a 167 kVA pad mount if necessary. We use 25 kV underground cable even in 12kV areas because we know that it will probably be converted to 25kV at a later date. That gives us lots of expansion potential.

I can't say I know enough to understand the implication of each of those figures. 10kVA verses 167 kVA seems like quite a jump. I think you are saying that they are generous with installing above requirement wiring and allow for the expansion of transformers.

Charging at 72kW is a huge load. With a 100 kWh pack I'll bet it never stays there for more than an hour. And then not when the weather is super cold or super hot. The batteries and charger will make it taper down.

Not sure what this is in regard to. You mean an urban charger? I mentioned charging at 72 amps/17 kW. Is that what you mean? It was pointed out that model 3s will likely be charging at 32 amps/8 kW more than anything else, so not as dramatic a rate, but still significant given that it will be charging for some hours which provides a lot more opportunity to draw power concurrently with everything else we use.

Even Texas is not fully deregulated. The CooPs have a super strong lobby and were able to add an option for each CooP to opt out of deregulation if they wanted. Guess what? They all but one did. So if you are unfortunate enough to live in a CooP territory you have no choice but to move.

I knew a friend who worked for one of the private Telcos in Texas. Seems the small, independent utility is a thing there.

My rural house is on a coop. They are smaller than the big utilities, but they are still "evil" in my mind. I read the terms of service and I have to indemnify them. Really? How does a private citizen protect the utility against losses?

 

[nwdiver]

Ah, but where I am, the electrical distribution is and has been in place for a long time. Houses are added. A bit rural. My other house is in an older part of town built in the 60s before heat pumps were common, so planned service was low. In the meantime houses have been built and heat pumps added to older houses.

Let's look at his mathematically; I'm in an older part of town too. I've got a 25kVA transformer feeding 4 homes. That's potentially ~18MWh/mo of energy that's deliverable. Meanwhile the average monthly energy use of a home is <2MWh/mo. So that's a utilization factor of <50%.

 

[gnuarm]

How often is there an advantage to charging at 72A vs even 20A? In 6 years I can recall maybe ~5 or 6 times that a charge rate >20A was useful.

I've had my car about six months and I already would have done well with a 72 amp charger on two occasions. It is not infrequent that I arrive with virtually nothing in the tank and need to go back out the next day. Once I had to reroute through a city with a Supercharger so I would have enough charge to reach a Supercharger the next day. The other time I was lucky enough that they had just opened a new Supercharger along my route I could charge about 70 miles from the house which again got me enough to get to a Supercharger the next day. In both cases it meant I was delayed enough that it cost me some sleep time.

They say charging at home is best and I agree. Sometimes I need to turn it around quickly and get back on the road early the next day and even 8 hours at 7 kW is not enough.

Until they get tired of their $300 electric bill and want to find a cost effect way to reduce it.

I'm not sure how getting a large bill teaches you about TOU. I only found out about this because I am the sort of geek that explores the utility web site. It's not like they advertise this stuff.

A lot of the solutions to the grid problems of EV charging don't exist because by and large the problems don't yet exist. To presume that means the solutions can't work is absurd. I'm currently defenseless against a Tiger. That doesn't mean it's impossible to defend against a Tiger... if I had to worry about Tiger attacks it would be fairly easy for me to find a defense...

Who ever said solutions can't be found??? I think you are reading what isn't being written. My only issue is that I think we need to be involved in the process of finding the problems and solutions so they aren't solved for us in ways that won't be best for us. I see on a regular basis that people are very unhappy with the way things work, but when I ask them what they did when it was being planned and inputs were invited, I find they had done nothing. Even at the time of public meetings and solicitation of comments, it is largely too late to change much. Unless major F'ups are found, the planning has already been done and approval is largely a matter of rubber stamp. So the time to be involved is before the utilities have made their plans.

Demand Response and TOU aren't common yet because the grid problems they solve aren't common yet. There are dozens of solutions 'standing by' once the need arises.

TOU doesn't solve grid problems. It solves generation problems. What are these "dozens" of solutions?

 

[Feathermerchan]

I corrected my original post. We install pad mount (sit on the ground) transformers as large as 100 kVA. The pad and other infrastructure is sized to accommodate a 167 kVA transformer.

CooPs do not follow the same rules as corporations. I believe each customer is a member of the coop and somehow shares in the ownership.

The 72 kW was another mistake. Sorry should do more proofreading. Corporations are not intrinsically evil. But they can be corrupted.

I think we are going to be OK if the utility utilizes some kind of TLM (Transformer Load Management). The rest of the distribution grid is built for expansion. Look around you and see if you think the load has increased in the past 30 years? How has the CooP managed that growth? Have they added more transformers to existing substations? Have they replaced them with larger ones? Have they built more substations? Have the overhead lines been changed from single phase to three phase? Have the overhead lines been replaced with larger ones?

Typically distribution grids are built with expansion in mind because areas are prone to growth.

 

[gnuarm]

Let's look at his mathematically; I'm in an older part of town too. I've got a 25kVA transformer feeding 4 homes. That's potentially ~18MWh/mo of energy that's deliverable. Meanwhile the average monthly energy use of a home is <2MWh/mo. So that's a utilization factor of <50%.

I don't get why you converted to kWh??? Why is the average utilization in a month important? Isn't the local distribution sized by peak loads?

If you have 25 kVA for four houses and let's say the houses currently use half that worse case. Add just two Teslas charging at 7.68 kW each (the minimum you would plan for and they can charge at up to 11.5 kW) and you are up to 27.86 kW. I'm sure that it is not a big deal to run these transformers over capacity for short times, but EV chargers don't typically run for short times. Even an oven can run for an hour or more in the evening when someone is baking a cake. Heating typically doesn't run with a high duty cycle until it is very cold out. I think my heat pump has a 15 kW heating coil for backup. I've seen the usage above 12 kWh within an hour, so the duty cycle is pretty high in cold temps.

I think the 25 kVA transformer would be rather marginal even if there aren't any extras thrown in like a hot tub.

If people can show me that I am wrong with the numbers I'm happy with that. But I need to see good numbers. I appreciate that you know your transformer is 25 kVA and is supplying four houses. That's good info to work with.

 

[nwdiver]

I don't get why you converted to kWh??? Why is the average utilization in a month important? Isn't the local distribution sized by peak loads?

Because it demonstrates the amount of surplus capacity available for stuff like charging cars....

If people can show me that I am wrong with the numbers I'm happy with that. But I need to see good numbers.

If you want everyone to be able to have an EV and everyone can charge all at the same time their hot tub is going and everyone can charge at 72A; No that's not going to happen but it doesn't need to. If you want to know if the infrastructure can handle the necessary energy demands of charging EVs with a small degree of planning there's about as much surplus capacity available as there is demand which is far more than is needed. A typical EV needs <400kWh/mo. So if each of the 4 homes sharing the transformer each had 2 cars that's ~8MWh/mo for a total of 16MWh/mo. That's pretty much worst case and you're still able to deliver sufficient energy for fulfill their needs. That's without considering other mitigating factors such as solar and storage.

You're attempting to manufacture an unrealistic argument. Why a 72A charge rate? Over the last 6 years I can think if maybe ~5 or 6 times there was any benefit to a 72A charge rate. I usually charge at 20A because that's plenty and it's more efficient. If there are 8 cars that want to charge at 72A they won't take down the local transformer... the car will force them into a slower charge rate when voltage dips.

 

[gnuarm]

I corrected my original post. We install pad mount (sit on the ground) transformers as large as 100 kVA. The pad and other infrastructure is sized to accommodate a 167 kVA transformer.

Which transformer would that be exactly, distribution or substation? What I don't know much about are the details of the hierarchy of electrical distribution. How much expansion is possible before major changes are needed. But even swapping out transformers is not cheap and if that ends up being required en masse, I expect the utility will want to recoup that cost. I know plenty of other stuff ends up on my electric bills.

CooPs do not follow the same rules as corporations. I believe each customer is a member of the coop and somehow shares in the ownership.

The extent of "ownership" is they return profits to us in the form of a credit on the bill, we receive a monthly magazine (which I believe is an official communication as I've tried to get them to not send it and they can't/won't unsubscribe me) and an annual election of I assume a board.

The 72 kW was another mistake. Sorry should do more proofreading. Corporations are not intrinsically evil. But they can be corrupted.

I'm not so sure. I even bought a cell phone from a company that had printed on the package "no evil" indicating they didn't pass on any of the usual fees and such. Then some time later they started charging an E911 fee. lol

As I mentioned, my coop has many issues where they just stiff arm you when you try to deal with them. I only got a satisfactory response when I contacted the state regulatory office. Yes, even a coop can be "evil".

I think we are going to be OK if the utility utilizes some kind of TLM (Transformer Load Management).

qu'est-ce que c'est TLM?

The rest of the distribution grid is built for expansion. Look around you and see if you think the load has increased in the past 30 years? How has the CooP managed that growth? Have they added more transformers to existing substations? Have they replaced them with larger ones? Have they built more substations? Have the overhead lines been changed from single phase to three phase? Have the overhead lines been replaced with larger ones?

My one house is on the edge of a commercial area. Very significant growth on that side of the street and major changes to the power distribution. My side street has seen nothing change, but then there is no real growth in 50 years other than one business built. It is not clear what changed to accommodate the business. My power comes from pole mounted transformer. I can't say if that was upgraded or not.

The other house was built 30 years ago on a building lot with several building lots next to it which I'm sure were all planned for and now built up. So what happens if half of these houses get EVs and start charging every other night at 11 kW? What happens when every one of the half with EVs charge at the same evening (like a Friday night) or the holiday weekend when they have a party and two or three other EVs show up and they get charged continuously for a day all the while hot tubs are being used? That reminds me that I need to get my hot tub going.

Typically distribution grids are built with expansion in mind because areas are prone to growth.

I get that, but I'm not sure they are sized adequately for the sort of growth expected at the time they were built now that EV charging will be on top of that.

Would you say that the utilities are not going to need to give any real consideration to EV charging going forward? The distribution grid will be expanded seamlessly through the normal processes? That's the part I can't picture given the magnitude of the added loads and the rapidity of the expansion. It will be 10 years before we see significant growth in the ownership of EVs, but somewhere in this path the expansion will be much more rapid than it is now as EV ownership approaches 50% of all personal vehicles. Also keep in mind that many homes will have two or three EVs.

 

[nwdiver]

I get that, but I'm not sure they are sized adequately for the sort of growth expected at the time they were built now that EV charging will be on top of that.

What would convince you that EV charging is not going to be 'on top of' existing peak demand?

If someone tries to charge their car at 72A at 5pm on a 4CP day and the grid is stressed it's likely the voltage simply won't be there to support 72A. You'll have to wait a couple hours. Won't be the end of the world.

 

[gnuarm]

Because it demonstrates the amount of surplus capacity available for stuff like charging cars....

There is no disagreement that there is plenty of generation capacity for EV charging. In fact, EV charging will allow higher utilization of generating resources which potentially can lower the per kWh cost of electricity. It's a good thing.

If you want everyone to be able to have an EV and everyone can charge all at the same time their hot tub is going and everyone can charge at 72A; No that's not going to happen but it doesn't need to. If you want to know if the infrastructure can handle the necessary energy demands of charging EVs with a small degree of planning there's about as much surplus capacity available as there is demand which is far more than is needed. A typical EV needs <400kWh/mo. So if each of the 4 homes sharing the transformer each had 2 cars that's ~8MWh/mo for a total of 16MWh/mo. That's pretty much worst case and you're still able to deliver sufficient energy for fulfill their needs. That's without considering other mitigating factors such as solar and storage.

Ok, you keep talking about generation and I'm talking about distribution. I won't bother to respond to this.

You're attempting to manufacture an unrealistic argument. Why a 72A charge rate? Over the last 6 years I can think if maybe ~5 or 6 times there was any benefit to a 72A charge rate. I usually charge at 20A because that's plenty and it's more efficient. If there are 8 cars that want to charge at 72A they won't take down the local transformer... the car will force them into a slower charge rate when voltage dips.

I picked 72 amps because that is the rate I can charge at. But use a lower rate, who cares? It doesn't appreciably change the result. Read my reply to Feathermerchan. There will be no small number of house with more than one EV.

So you are saying rather than EV charging being a problem for the local grid, the local grid will be a problem for EV charging. Still have a problem...

I'm curious. How much do you save with the increased efficiency of charging at 20 amps?

 

[nwdiver]

Ok, you keep talking about generation and I'm talking about distribution. I won't bother to respond to this.

I'm curious. How much do you save with the increased efficiency of charging at 20 amps?

No.... the monthly capacity of the local transformer IS distribution. You're attempting to artificially constrict it by demanding a 72A charge rate. Sure, you can overload it by doing something that has no benefit OR it could easily support 8 EVs at a lower charge rate.

The savings are probably negligible but it's also the decreased thermal cycling of the components. What's the savings of charging at 72A?

Can the grid support every EV charging at 72A all at the same time? No. Why is this a problem?

Next time you're somewhere with a sketchy grid connection try to charge at 72A... it won't go. No sparks, the lights won't go out.. the car will just slow the charge rate.

 

[Feathermerchan]

The transformer example (100 kVA and 1678 kVA) is a distribution transformer like the 25 kVA for your house (and my house coincidentally). Substation transformers are rated in MVA.

FYI corporations recover ALL of their costs or they must write them off which investors are not fond of.

A Transformer load management program does what the name implies. It looks at transformer load parameters and flags problems so that action may be taken before failures cause outages. Customers hate outages more than than high bills or electric utilities. Plus most utilities have to report outage times to their regulators and can be subject to penalties for exceeding designated outage rates.
So how does a TLM work? Well as mentioned above monthly utilization ie kWH thru the transformer in a month vs capacity.
Example: AA 25 kVA transformer can pass 25 kVA X 30 days X 24 hours per day or 18,000 kVAh.
If the metered load for all customers connected to the transformer for that month is 9,000 kVAh then the transformer is at a 50% load.
Transformer manufacturers have lots of operational data on transformers and share that data with utilities. So a utility knows when a transformer is being overloaded or underloaded and can take action. By that I mean economically over or under loaded. Remember that the utility's mission is to reduce the cost of service to customers. Peak loads are not so important to transformers as they are very heavy and so tend to change temperature slowly. But now many utilities have 15 minute data from the smart meters so there is even more data to use.

BTW my 25 kVA padmount transformer was replaced after about 30 years with another 25 kVA transformer. It failed during a 40 degF rain filled week. I do not know why it failed. It is connected to 4 houses one is all electric.

 

[nwdiver]

BTW my 25 kVA padmount transformer was replaced after about 30 years with another 25 kVA transformer. It failed during a 40 degF rain filled week. I do not know why it failed. It is connected to 4 houses one is all electric.

Do you know what the 'rated' load of a 25kVA transformer is? Logic would say 25kVA but a friend built a new house with 400A service (~76.8kVA) and they installed a 25kVA transformer.... so 25kVA seems like maybe a 'continuous' rating? But I've seen A LOT of weird stuff like connecting 200A service with #6 AL wire....

 

[Feathermerchan]

We used to use a factor of 160% for winter and 130% for summer meaning you could load it to 1.6 X 25 = 40 kVA winter and 1.3 X 25 = 32.5 kVA in the summer. That is for residential. Commercial I don't remember. No those are not continuous ratings. They are ratings with consideration given to the typical load shapes for residential customers in our service area. Those load shapes and load factors are always subject to change over time. There used to be far fewer pools and hot tubs behind houses like mine but we keep making things cheaper to build and install. So sure those will change as they need to. The utility I used to work for is starting a new research project to further identify the effect charging EVs will have on the distribution grid. It has done these in the past for other emerging loads like water heaters and air conditioners. If you do a google search or two you'll find many papers written on the subject already.

 

[Feathermerchan]

A more succinct reply is that the 25 kVA rating is for a certain ambient temperature, solar radiation, and wind velocity probably at sea level. So no it's not a 25 kVA transformer in Denver.

 

[nwdiver]

A more succinct reply is that the 25 kVA rating is for a certain ambient temperature, solar radiation, and wind velocity probably at sea level. So no it's not a 25 kVA transformer in Denver.

Which kinda goes back to my point that an EV ain't gonna overload the local equipment if it was installed correctly. When you're pulling 30kVA on a 25kVA transformer the equipment can handle the current but voltage has probably dropped >30v and the car has slowed and possibly stopped charging.

I stopped to charge at a little RV park last year. There were 3 RVs on 50A circuits and I took the last spot. It was cold so all the RVs probably had their heaters going. My car wasn't happy... I think the best I could get was ~24A... but the grid survived because my car was 'smart' enough to only pull 24A.

I happened to have my FLIR with me, the transformer was 110F and the air temp was ~40F.

 

[Feathermerchan]

I don't remember max allowable transformer temps but 110 is not very hot. It gets that hot here in the summer. Probably more like 150F. There are published max and min voltages allowable. I think it was 114 min and 130 max (maybe 129). That would translate to 228 to 260V. In an RV park I would think it may swing lower.

So what will something really large like the Rivian truck do? It has a 180 kWh battery. Basically like charging two Tesla's at once.