# Future-proofing a house: 300-amp (or larger) electric service?



## garsh (Apr 4, 2016)

If I were outfitting a new house today, I'd ask for 300- or 400-amp service.
I can't find such a beast (for residential use) for sale easily, but I've got to think that this will be the norm as vehicles switch to being electric.


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## GDN (Oct 30, 2017)

garsh said:


> If I were outfitting a new house today, I'd ask for 300- or 400-amp service.
> I can't find such a beast (for residential use) for sale easily, but I've got to think that this will be the norm as vehicles switch to being electric.


Do you think we'll need bigger than 200 amps as our products get more efficient? There are a lot of people here that have bigger houses than mine, but 2300 sq ft w/ Central AC running solid most of the summer days, with pool, electric oven and 2 cars charging and no issues with 200 amps.

Here is why I'm thinking we may not need bigger panels - most all of this equipment has become more efficient over time taking less electricity. My highest bill will be about $250, maybe $275 with all of that. (OK - it may increase in TX this year, currently .08/kWh) 7 years ago I had bills hitting close to $400 and prices were about the same, also I had no pool and no electric cars. What else changed? The biggest was replacing the AC unit. The new one from 6 years ago is dual speed, huge gain on energy efficient, a 17 SEER unit. The pool was added 6 years ago and it has a very efficient variable speed pump (now required by law in many places), then 3 years ago we added both cars. We've never had any issues with the 200 amps. The oven and the clothes dryer are also both electric. We do have natural gas water heater and central heat.

To say the least, even though many houses may add more cars to the load, with all appliances getting more efficient over time (even our PC's and TV's) I don't see the average house needing it. Perhaps some big ones will, but I'm hoping that we continue to drive enough efficiency to offset the need for more electricity and bigger panels

However, if you find yourself needing more ,then don't forget - https://teslaownersonline.com/threads/my-little-electrical-project.7842/post-128061


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## garsh (Apr 4, 2016)

GDN said:


> Do you think we'll need bigger than 200 amps as our products get more efficient?


Yes. I'll still want to charge my efficient car _quickly_, and that requires more amps.
And if I have two or three cars each capable of charging at up to 80 amps, I'm going to need more than 200 amp service.

Besides, charging at higher rates is more efficient than charging at lower rates.


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## Klaus-rf (Mar 6, 2019)

garsh said:


> If I were outfitting a new house today, I'd ask for 300- or 400-amp service.
> I can't find such a beast (for residential use) for sale easily, but I've got to think that this will be the norm as vehicles switch to being electric.


Now you're talking 480VAC 3-phqase. 400 AMP service is most unlikely - the cable sizes and transformer taps in residential areas aren't common at all. Depends on your power provider and specific residential area. 480 3-phase is pretty costly also.


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## GDN (Oct 30, 2017)

garsh said:


> Yes. I'll still want to charge my efficient car _quickly_, and that requires more amps.
> And if I have two or three cars each capable of charging at up to 80 amps, I'm going to need more than 200 amp service.
> 
> Besides, charging at higher rates is more efficient than charging at lower rates.


I just watched a live walk through of a new Plaid and the max home charging is 48 amps, like the 3 and Y. So from what we see from Tesla you'll never have use for that 80 amps at home again.


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## msjulie (Feb 6, 2018)

We did pretty much a full electrical renovation (1943 house) so we have a 200 amp panel and another smaller 60 amp (2 30amp breakers) that the solar panels feed into, slaved off the 200amp box so power is available in the dark. 

This 60 amp panel supplies all of the home office plus a good assortment of lights throughout the house. This means during the sunny days, the office runs for free. Any excessive juice from the panels is then pushed back to the grid after the batteries are topped off.

The garage has a completely standalone 150amp panel which runs a couple small lights, has some 20amp outlets for 'tools' and has 2 50amp Nema 14-50 outlets for the 2 chargeable cars.

PG&E calls our home service 340/400 <- not sure why they name it that way as the cables coming in are basically 400amp service but the available power at the street I guess is capped at 340 or some nonsense. The new box on the house is therefore a 400amp box, which then splits the power to the boxes inside the house and garage.

Maybe more than you asked but I guess the point is as much service as you can get/afford with thoughts on solar + battery so you can have lights, etc when the power invariably goes offline.


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## garsh (Apr 4, 2016)

Klaus-rf said:


> Now you're talking 480VAC 3-phqase.


I'm just talking about two houses-worth of 240v two-phase.


Klaus-rf said:


> 400 AMP service is most unlikely - the cable sizes and transformer taps in residential areas aren't common at all.


I'm sure the same was true back when 50-amp and then 100-amp service was the norm. But then air conditioning became popular and 200-amp service became the norm.


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## garsh (Apr 4, 2016)

GDN said:


> I just watched a live walk through of a new Plaid and the max home charging is 48 amps, like the 3 and Y. So from what we see from Tesla you'll never have use for that 80 amps at home again.


Still, having two or three vehicles that could charge simultaneously at ~50 amps would seem to make 300-amp service a reasonable choice for new homes.


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## JasonF (Oct 26, 2018)

garsh said:


> Still, having two or three vehicles that could charge simultaneously at ~50 amps would seem to make 300-amp service a reasonable choice for new homes.


Simultaneous charging when households begin to commonly have 2 or 3 EV's is going to be a difficult problem to solve. It's where, oddly enough, people's tendency (at least from what I've seen in this neighborhood) to plug in and charge only when the battery is low will actually_ help_ for a change - because it generally means they will only charge one car at a time. But I can also see situations where people will try to plug all 3 EV's into a power strip plugged into a 110 volt garage outlet that was badly wired and/or hadn't really been used in decades, and that might cause a rash of garage fires at some point. We might even see insurance discounts for people who install a well planned out charging infrastructure because it poses less risk.


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## PNWmisty (Aug 19, 2017)

garsh said:


> Yes. I'll still want to charge my efficient car _quickly_, and that requires more amps.
> And if I have two or three cars each capable of charging at up to 80 amps, I'm going to need more than 200 amp service.
> 
> Besides, charging at higher rates is more efficient than charging at lower rates.


I have an electric on-demand water heater running on 150 amps worth of breakers (3 50 amp). As soon as I turn on a hot water faucet it draws 28,800 kW instantly. Plus an all-electric range, clothes dryer, 60 amp circuit for a Tesla Wall Connector, mini-split heat pump, all-electric 7 person hot tub, electric radiant bathroom floor, electric towel warmer, microwave, espresso machine, coffee maker, blender, space heater, electric boot dryer, ventilation and ceiling fans, electric deck blower, multiple high amp battery chargers and a bunch of electric baseboards. In short, it's an all-electric three-bedroom ski cabin with no oil, gas or propane. All on a standard 200 amp service.

The reason this is to code and works is because all of this stuff is never drawing maximum amperage at the same time. But I can't figure out what kind of residence would need to charge three EV's at 80 amps each all at the same time? I mean, people don't have gas pumps in their driveway either (and if they did, they wouldn't have two in case one was in use). People can share the resource. In the same way that 6 people can live in the same house that only has 2 showers and a 60 gallon water heater. Because they are not all taking showers at the same time (and if they find themselves running out of hot water they adjust the times they shower). Charging an EV is even less time sensitive than when you take a shower. The Tesla Wall Connector can load share 100 amps with up to 4 or 5 EV's.

Large high-end homes that are all electric already have 300-400 amp service. You order the electrical service you need from your electric company, it's not a big deal. If you have three EV's that can all charge at 80 amps it's probably not going to be a hardship to order 300-400 amp service. But why bother? It's totally unnecessary because they don't all need to charge at the same time at 80 amps.


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## JasonF (Oct 26, 2018)

PNWmisty said:


> The reason this is to code and works is because all of this stuff is never drawing maximum amperage at the same time.


It's also because "200 amp service" is kind of a misnomer. You get TWO legs of 200 amps, which means you can only use 200 amps at 220 volts (because it uses both legs), but you can use 400 amps at 110 volts.

It's kind of odd though that someone installed an instant electric water heater on the main phases. Usually installers do that by bringing in separate service just for the instant hot water.


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## garsh (Apr 4, 2016)

PNWmisty said:


> But I can't figure out what kind of residence would need to charge three EV's at 80 amps each all at the same time?


I think of it this way.

If I have 200 amp service and three electric cars, I can make it work. I can schedule each car to charge during different hours of the day. I can limit each car to charge at a lower power setting. I can pay extra to install load-sharing EVSEs that will intelligently provision the available power in a reasonable way. These are all perfectly good options.

But if I have 300- or 400-amp service, I can install three 60-amp circuits, each with a simple dedicated EVSE, and not worry about cars charging simultaneously. I don't have to throttle down charging to avoid tripping a breaker. I can avoid paying extra for load-sharing EVSEs. I don't have to worry about the fact that Tesla load-sharing wall connectors only work with Teslas, and can't load share with other third-party chargers (since my Rivian truck can't use a Tesla wall connector ) .

Electricity doesn't cost any extra when you charge at a faster rate. In fact, if you have time-of-use pricing, you'll be better off being able to completely charge all three of your EVs at night when the price is low. The only downside is the up-front, one-time cost of installing a 300-amp service panel in the house. For new construction, I think it's a no-brainer - install 300-amp service. For existing 200-amp houses, it's not worth the expense as there are ways to make it work. But for a 100-amp house where you're looking to upgrade your service anyhow, I would seriously look into it and see how much more it would be.


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## JasonF (Oct 26, 2018)

garsh said:


> Electricity doesn't cost any extra when you charge at a faster rate.


I think that might change when EV's reach a certain saturation point, because it's going to create a new demand peak right where the old off peak point began. Power companies might start to charge more based on peak usage rather than a time, encouraging EV owners to spread out charging as much as possible, or lower the amps and charge slower.

I also believe power companies might eventually either require or strongly encourage households with more than one EV to install either a 3 phase power source to help balance the residential grid, or maybe install a battery like a Powerwall dedicated just for filling up slowly all day and then delivering at least part of the EV's charging without creating a lengthy peak.

Another option from power companies might be to help homeowners with multiple EV's to install a kind of DC fast charging, with the theory that the faster the cars charge, the shorter the peak.


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## GDN (Oct 30, 2017)

We have celectric ompanies here that already offer cheaper rates at night, in fact, some offer free nights. Of course that is offset by whatever they charge you during the day, but they are encouraging off peak usage. I figure we will have many smart inventions and laws and pricing that will push people to charge off peak.

Also to the point of speed of charging - what difference will something like the new 4680 cell do? Electricity isn't something I've ever cared to get into the bits and watts and amps of. So for the new cell designs that can charge much faster likely, will it take more amps? more volts? more watts? What and how will Tesla still limit on this setup? Much faster DC/Supercharging? Faster Home charging - but they severely limit it because homes don't have the electrical capacity today without upgrades like @garsh wants?

Or is it about the SuperCapictor @Jason F you note - trickle charge it 24 * 7 - plug your car in and Supercharge at home in 20 minutes? Something like that could definitely be the answer, but figure cost will be high and again, 99% don't need that. I'd argue that the majority of us could still survive on that dedicated 20 amp 120 volt plug at 5 MPH, as long as we remembered to plug in each time we got home.


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## PNWmisty (Aug 19, 2017)

JasonF said:


> It's also because "200 amp service" is kind of a misnomer. You get TWO legs of 200 amps, which means you can only use 200 amps at 220 volts (because it uses both legs), but you can use 400 amps at 110 volts.
> 
> It's kind of odd though that someone installed an instant electric water heater on the main phases. Usually installers do that by bringing in separate service just for the instant hot water.


That must be a regional thing, I've not heard of using a separate electrical service for hot water. To me, separate service means service from the utility. I can't imagine why that would be necessary if the main panel already has enough capacity. The extra monthly meter charge would cancel any savings of having on-demand hot water. If you just mean a sub-panel, that might be done to simplify wiring runs. In my case the main panel was very close to the water heater so it made sense to direct wire it. But even if I had a sub-panel the water heater would still be wired to 3 50 amp breakers in the sub-panel so I'm not sure what you are getting at.


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## DocScott (Mar 6, 2019)

JasonF said:


> Simultaneous charging when households begin to commonly have 2 or 3 EV's is going to be a difficult problem to solve. It's where, oddly enough, people's tendency (at least from what I've seen in this neighborhood) to plug in and charge only when the battery is low will actually_ help_ for a change - because it generally means they will only charge one car at a time. But I can also see situations where people will try to plug all 3 EV's into a power strip plugged into a 110 volt garage outlet that was badly wired and/or hadn't really been used in decades, and that might cause a rash of garage fires at some point. We might even see insurance discounts for people who install a well planned out charging infrastructure because it poses less risk.


For Teslas, at least, I think their charging is too smart for much risk of fires of that kind. I plug my M3 in to a 120 V outlet on the outside of the house. At 15 A, it wasn't that the circuit breaker tripped, it's that the M3 decided the outlet wasn't reliable and would tend to refuse to charge. I told the M3 to limit the draw to 12 A, and now there are no problems. So my guess is that if you overload a circuit enough that you're risking problems, a Tesla is likely to refuse to charge. If that doesn't happen, of course, the circuit breaker will trip or the fuse will blow.

I'm not sure if other EVs do that same kind of circuit testing, though.

(Oh, and for those who are curious, I just contacted an electrician to upgrade the outlet...to 20 A. I looked at getting a 240 V outlet before, and it's not worth the cost based on our use pattern. But a 20 A outlet means we can probably run with a 17 A limit as opposed to a 12 A limit. That's nearly 50% better. But at least as important is the fact that it will be much more efficient on cold winter nights. On the coldest nights in the NYC suburbs right now the car can't charge at all because it needs 12 A just to heat the battery sufficiently to receive charge.)


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## PNWmisty (Aug 19, 2017)

GDN said:


> I'd argue that the majority of us could still survive on that dedicated 20 amp 120 volt plug at 5 MPH, as long as we remembered to plug in each time we got home.


Yeah, statistics bear that statement out. But some people use more than average so I'm a fan of having robust charging solutions. But I still don't see the sense in taking it to the level @garsh is contemplating (100 amp breaker for every EV). While I suppose it's possible a family might have 3 EV's capable of being charged at 80A and all with 100+ kWh batteries that are all drained most of the way on the same days and all arriving home at the same time and all needing the fastest possible charge, it just doesn't seem like a mainstream kind of scenario, particularly with the trend towards consuming less energy and making things more efficient and having more numerous distributed level 2 charging at places of work and recreation so people can charge during peak solar hours.

We have a detached carport that had no electrical service when we bought our first two EV's in 2018 so we had the power company drop a 200 amp service to the carport. Other than some LED lighting we added at the same time, the 200 Amps is just for charging the two EV's. We have a Tesla Wall connector on a 100 Amp service (AWG #3) and a NEMA 14-50 on a 50 amp circuit that has a Gen 1 Mobile Connector capable of charging at 40 amps max. The Wall Connector can charge at 48 amps max.

But here's the thing: Since we generally only drive about 50 miles a day or less between the two of us, our cars only take about 30 minutes to charge each day. Even if we both drove huge miles every day, came home late at night at the same time as each other with depleted batteries and both had to leave early in the morning, I can't imagine wanting more power than 48 amps per vehicle. That's probably why they are equipped with chargers capable of 48 amps max. Even when we take delivery of our Cybertrucks which will be considerably less efficient, I don't think we will want for more. At all. If we had Time of Use billing, the cheap rates tend to be in the middle of the night so we would still be OK. The fact is, even people who average 100 or more miles a day are generally not coming home with completely depleted batteries.


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## PNWmisty (Aug 19, 2017)

DocScott said:


> For Teslas, at least, I think their charging is too smart for much risk of fires of that kind. I plug my M3 in to a 120 V outlet on the outside of the house. At 15 A, it wasn't that the circuit breaker tripped, it's that the M3 decided the outlet wasn't reliable and would tend to refuse to charge. I told the M3 to limit the draw to 12 A, and now there are no problems. So my guess is that if you overload a circuit enough that you're risking problems, a Tesla is likely to refuse to charge. If that doesn't happen, of course, the circuit breaker will trip or the fuse will blow.


That's true. When a circuit is overloaded it has more voltage drop as more current is drawn. Tesla measures the voltage drop and stops charging if it senses a problem. There are also thermocouples in the Mobile Connector that can sense excessive heat in the outlet (being conducted through to the Mobile Connector) so it will shut down if that gets too warm. Of course I would never charge with substandard wiring simply because I thought I could depend on the EVSE to detect every problem. They can't do that in every instance.



DocScott said:


> (Oh, and for those who are curious, I just contacted an electrician to upgrade the outlet...to 20 A. I looked at getting a 240 V outlet before, and it's not worth the cost based on our use pattern. But a 20 A outlet means we can probably run with a 17 A limit as opposed to a 12 A limit. That's nearly 50% better. But at least as important is the fact that it will be much more efficient on cold winter nights. On the coldest nights in the NYC suburbs right now the car can't charge at all because it needs 12 A just to heat the battery sufficiently to receive charge.)


That will be a big improvement. But still very far from ideal for efficiency. I would strongly recommend you continue to explore getting a 240V outlet installed. Depending upon what you have to work with, a creative electrician can often find a less expensive solution that is safe, efficient and meets code. Even a 15a or 20a 240V outlet will offer a big jump in charge times and efficiencies over that 20a 120V outlet.


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## JasonF (Oct 26, 2018)

PNWmisty said:


> That must be a regional thing, I've not heard of using a separate electrical service for hot water.


I researched installing a tankless water heater a few years ago, while living in a neighborhood with underground power. The mains cables coming to the house only supported 200 amps each, so everyone I talked to recommended trenching in a new mains, and setting up a 2nd service just for the water heater. Obviously I decided against it at that point.



DocScott said:


> For Teslas, at least, I think their charging is too smart for much risk of fires of that kind.


True, but notice I said plugging 3 cars into a _power strip_. Even if the cars are well behaved with splitting up the 15 amps among themselves, 1500 watts continuous through one cheap power strip is probably going to cause a fire. And you know someone out there _will_ pick up a cheap made-in-China power strip with undersized wiring and extra melty plastic and plug 3 cars into it eventually.



DocScott said:


> Oh, and for those who are curious, I just contacted an electrician to upgrade the outlet...to 20 A.


Aside from the cost of copper, it shouldn't really cost much more to upgrade an outlet to 20 A as it does to switch it to 220 volts. Unless the wiring to it was already 12 guage, then it's already a 20 amp outlet, and just needs the end hardware swapped out.



GDN said:


> Or is it about the SuperCapictor @Jason F you note - trickle charge it 24 * 7 - plug your car in and Supercharge at home in 20 minutes? Something like that could definitely be the answer, but figure cost will be high and again, 99% don't need that. I'd argue that the majority of us could still survive on that dedicated 20 amp 120 volt plug at 5 MPH, as long as we remembered to plug in each time we got home.


Something like a battery/supercapacitor would be ideal for people who insist on charging all of their EV's at once at home without negatively impacting the grid with sudden increase in demand, sort of a time delay for the huge power drain.

I've mentioned this before - I surveyed the handful of people in my neighborhood who have Teslas, casually asking them how they're charging. Besides me, only one other person charges at home at all, and I'm the only one who has a 220 volt outlet. I'm also the only one who plugs in daily. Most of them treat their cars like cell phones and plug in only when the battery is low, and the majority of those are using J-1772 stations or Superchargers in the area. And these are people with homes and garages, not high-rise apartments downtown. One house actually has twin Model S and a Model X (same model year and color) and they park both in the driveway, quite obviously too far from the house to plug in a cord.

So if that pattern translates to the average EV owner charging behavior, most of the home charging issues might just solve themselves, because you're not going to have a household with 3 EV's drain the batteries at the same time, and the odds will be at least one of those will charge away from home instead.


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## garsh (Apr 4, 2016)

PNWmisty said:


> Yeah, statistics bear that statement out. But some people use more than average so I'm a fan of having robust charging solutions. But I still don't see the sense in taking it to the level @garsh is contemplating (100 amp breaker for every EV). While I suppose it's possible a family might have 3 EV's capable of being charged at 80A and all with 100+ kWh batteries that are all drained most of the way on the same days and all arriving home at the same time and all needing the fastest possible charge, it just doesn't seem like a mainstream kind of scenario


How about a family with three EVs. Both parents work, and the (driving-age) kid had errands that day too. So all three EVs need to be charged overnight. They're on a TOU plan, so they'd like to constrain their charging between the hours of 12am and 6am to keep costs low. That feels like a pretty near-future mainstream scenario. They may not need to charge all three vehicles simultaneously every day, but it will happen from time to time.


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## oshw (May 9, 2018)

The HPWC will get a firmware update (eventually or soon™) which should enable advanced power sharing features.

Basic sharing ensures all chargers don't exceed some allowable max current for all EV charging (say 24 to 80 amps).

I could see them doing some kind of priority based sharing features, where cars are charged based on priority and whether or not you want to charge at max rate or not. Including in the region specific time of use as well as any solar/generating sources...


Running the chargers at least than 100% of their rating should prolong the life of the charger (example, 48A model 3 LR - running at 32~36A extends the life of the electronics at a slightly lower efficiency)


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## GDN (Oct 30, 2017)

oshw said:


> The HPWC will get a firmware update (eventually or soon™) which should enable advanced power sharing features.
> 
> Basic sharing ensures all chargers don't exceed some allowable max current for all EV charging (say 24 to 80 amps).
> 
> ...


Yep- and the Gen 2 WC already has power sharing via a dedicated wire. As we get more EV's our chargers and options will get smarter. It will be a small percentage of new homes that need much more just to support EV's (I do understand there are millions of older homes that may need to be retrofitted). There will definitely be some, but a small percentage for the cost of the upgraded panels. To truly make it happen anyway it will have to become law or code as there is likely no builder that will incur the upgraded costs of the bigger panels at build time unless you pay specifically extra for the upgrade.

I've got a friend building new now - signed a contract back in November. Their panel is going to be in the garage. They asked me what they might have wired to support a future EV - best I could tell them now was a simple 14-50. They inquired and the builder wanted $750 to add it now. His costs were likely less than $100 for the copper, labor and outlet.


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## PNWmisty (Aug 19, 2017)

garsh said:


> How about a family with three EVs. Both parents work, and the (driving-age) kid had errands that day too. So all three EVs need to be charged overnight. They're on a TOU plan, so they'd like to constrain their charging between the hours of 12am and 6am to keep costs low. That feels like a pretty near-future mainstream scenario. They may not need to charge all three vehicles simultaneously every day, but it will happen from time to time.


Times are changing and EV charging at places of work and schools is becoming more commonplace. Shopping centers too. I think parking spots will be associated with having 240V level 2 charging. My point is simply that I think arriving home with a fully depleted battery is not all that common now (either due to not using all the available range and/or adding in charging at work/school, etc). It's not common now and will only become less common over time.

With the increase in solar production we have already seen, and that will certainly continue, it makes a lot of sense to charge vehicles in the middle of the day when solar production is highest since demand doesn't peak until the end of the day. These vehicles don't have to be charging from solar facilities for this to make sense - there is a surplus of solar grid energy during daytime hours in most areas. If we want to decarbonize, solar is the way to do it so it makes sense to use it when it's available. Those low rates in the middle of the night are a function of not wanting to turn off all the fossil fuel powered generation when demand is low.

In general, I'm a fan of more distributed charging (including at home, work and school) at moderate power levels combined with fast DC charging for interstate travel. It would be a very special use case to need 3 100 amp chargers at a residence and that will only be more true in the future.


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## JasonF (Oct 26, 2018)

oshw said:


> The HPWC will get a firmware update (eventually or soon™) which should enable advanced power sharing features.


The trouble with that is you need a minimum of TWO of those, so the entry cost of power sharing is $1500 (adding in $500 for an electrician install). Since we're talking about EV's becoming mainstream, a majority of people aren't going to spend $1500+ to get two cars to charge at once unless they're either desperate or it's required by law. And then there's the issue of what if they don't have two Teslas? It's a good concept, but not a comprehensive solution.



PNWmisty said:


> With the increase in solar production we have already seen, and that will certainly continue, it makes a lot of sense to charge vehicles in the middle of the day when solar production is highest since demand doesn't peak until the end of the day.


That does sound like it makes sense, but unfortunately it's not entirely the way power generation works. Generation capacity (including solar) is most efficient just below the point where more generation capacity has to be added. If a bunch of EV's charging across the area bump it above that point, it pushes demand over that point, and then more generation capacity has to spin up. So the power companies would either have to add a _lot_ more solar panels to keep up with EV demand, or charge more money per kWh to make up for the higher peak.


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## PNWmisty (Aug 19, 2017)

oshw said:


> The HPWC will get a firmware update (eventually or soon™) which should enable advanced power sharing features.
> 
> Basic sharing ensures all chargers don't exceed some allowable max current for all EV charging (say 24 to 80 amps).
> 
> ...


I agree. Also, I haven't seen any direct evidence that the 48 amp charger in the Model 3 LR runs at peak efficiency at 48 amps. I _have_ seen direct evidence that efficiency is very low at very low power levels (like 20 amp, 120V) but it's common for electrical equipment to run at peak efficiency around 90% of it's rated design. You will see this in inverters and chargers. Also, the wiring that supplies the current has higher losses as it's rated capacity is approached.

For safety and longevity (mostly) and perhaps a tiny efficiency gain, we tend to charge at 44 amps on the Tesla Wall Connector and 36 amps on the Gen I Mobile Connector (capable of 40 amps). I don't know that this is peak efficiency but it's certainly close to it. Even when we charge at reduced current the cars are charged very quickly. They are plugged in 100% of the time they are parked at home but only charging 5- 10% of that time.


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## PNWmisty (Aug 19, 2017)

JasonF said:


> The trouble with that is you need a minimum of TWO of those, so the entry cost of power sharing is $1500 (adding in $500 for an electrician install). Since we're talking about EV's becoming mainstream, a majority of people aren't going to spend $1500+ to get two cars to charge at once unless they're either desperate or it's required by law. And then there's the issue of what if they don't have two Teslas? It's a good concept, but not a comprehensive solution.


That's a common argument amongst the anti-EV adoption crowd, but I don't buy it. When people buy a car they regularly spend more than that just to upgrade the wheels for aesthetic reasons. $1500 for the addition of residential electrical infrastructure to charge two cars is not a show stopper! People spend more than that on a lot of unnecessary stuff that won't reduce their monthly expenses and will are essentially worthless once they've blown the money. Adding EV chargers to your garage will save thousands in gas and/or Supercharging in just a few years. It also makes the home easier to sell and worth more. Electric cars are becoming more mainstream very rapidly and the trend is accelerating, not slowing down.



JasonF said:


> That does sound like it makes sense, but unfortunately it's not entirely the way power generation works. Generation capacity (including solar) is most efficient just below the point where more generation capacity has to be added. If a bunch of EV's charging across the area bump it above that point, it pushes demand over that point, and then more generation capacity has to spin up. So the power companies would either have to add a _lot_ more solar panels to keep up with EV demand, or charge more money per kWh to make up for the higher peak.


Studies have shown that the most cost-effective way to decarbonize our power grid is to add about 5-6 times more total solar generation than we can use (overall). All that surplus power is going to be very low cost in the middle of the day in just a few years because up to 80% of it would otherwise go unused. Those who make the most money are aware of these trends and harness them to their advantage. In other words, yes, more solar panels are going on-line every year and the steady drop in the price of solar panels every year is driving this change. They are already so cheap that in many use cases it already makes economic sense to over-install solar generation AND add battery storage to replace more expensive electricity generated with coal. Solar is already so cheap it already makes economic sense to over-install solar, even without battery storage. Even though much of the generation capacity will go to waste, it can be worth it, for example, when solar generation is reduced on cloudy days it reduce the need for backup fossil generation.


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## oshw (May 9, 2018)

Always two sides to everything... If you didn't want to invest in the HPWC units... Tesla in theory could also use the cars themselves to load share if you had regular outlets installed instead of investing in the future of the home.

That would appear to be the cheapest option and doesn't seem too difficult considering the cars and the HPWC would both use WiFi to load share or schedule. No cross manufacturer support in that regard though...


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## GDN (Oct 30, 2017)

We can take this all the way when it talks about leveling out the grid too. If it became a requirement for all EV's to have Vehicle to Grid - we could charge them all over night and then those sitting at home not being used could feed power to the house to offset some of the usage during the day. I don't think we'll see standards change for a while, but if we add anything, this type of setup should be included. I personally wouldn't want to charge and discharge my EV battery every day considering the cost, but it would be a huge plus for emergencies when the power is out.


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## JasonF (Oct 26, 2018)

PNWmisty said:


> It also makes the home easier to sell and worth more. Electric cars are becoming more mainstream very rapidly and the trend is accelerating, not slowing down.


I already have 220 volt charging, so it's not me you have to convince. I'm saying that the _average _future EV buyer isn't going to bother installing anything extra unless they absolutely have to. With non-Tesla EV's, even more so - you can walk into a dealer and buy an ID4 or Mach-E and take it home right away, and plug it into whatever is handy (110 volt garage outlet). And that's what the majority of future EV buyers will do. I wouldn't be surprised if households with two EV's would just plug a power strip into the 110 volt garage outlet and charge both at once at 2 mph each.

The only things that would prevent that from happening is if the manufacturers would start having proprietary home charging standards to force 220 volt adoption (which is undesirable and counter to pushing EV adoption; If dealers would install the charging station for you (expensive and unlikely); or if it becomes illegal to charge EV's off of 110 volts.


PNWmisty said:


> Studies have shown that the most cost-effective way to decarbonize our power grid is to add about 5-6 times more total solar generation than we can use (overall).


I think power companies should offer to lease solar panels to every home in their territory, and switch them from metered billing to flat rate in exchange. That way they only pay for the panels and labor, without the overhead of having to buy land and pay tax on it, and they can pass along the savings.

The likely reason they don't is because they have a lot of legacy infrastructure and generation capacity and they're determined to use it until it's retired.


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## Ed Woodrick (May 26, 2018)

garsh said:


> I never did. My example was just that all three cars were used, and they'd like them all charged again for the next day's errands.
> 
> Cmon Ed, stop beating your strawman.


Really? I'm talking reality, I'm not talking the "it will never happen" of needing to charge 3 cars from 0 to 100% in a single night.

I've got 400A service in my new house, but I doubt if I will worry installing 2 60A plugs. I just don't need it.


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## JasonF (Oct 26, 2018)

If you have 3 EV's, there is the possibility of mixing types of charging according to need. Like if you have a 14-50 220v outlet and a 110v outlet in your garage, you can plug the car that needs the most charging into the 220, the one that needs the 2nd most into the 110, and charge them at the same time gradually, and the 3rd one can wait in line. If all 3 of the cars tend to not charge daily, there's a chance they might all have completely dead batteries at the same time, but that can be prevented simply by alternating charging days.


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## AG1812 (Jun 25, 2019)

garsh said:


> If I were outfitting a new house today, I'd ask for 300- or 400-amp service.
> I can't find such a beast (for residential use) for sale easily, but I've got to think that this will be the norm as vehicles switch to being electric.


I'd be certain to include SOLAR and perhaps geothermal heating. With these, you could be energy POSITIVE most of the year, as my daughter is in...Connecticut!


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## garsh (Apr 4, 2016)

ag1812 said:


> I'd be certain to include SOLAR and perhaps geothermal heating.


Oh, good point about geothermal. A geothermal heat pump wouldn't be so bad to install if you already have equipment on-site to dig a foundation.


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## brur (Nov 15, 2018)

PNWmisty said:


> That's a common argument amongst the anti-EV adoption crowd, but I don't buy it. When people buy a car they regularly spend more than that just to upgrade the wheels for aesthetic reasons. $1500 for the addition of residential electrical infrastructure to charge two cars is not a show stopper! People spend more than that on a lot of unnecessary stuff that won't reduce their monthly expenses and will are essentially worthless once they've blown the money. Adding EV chargers to your garage will save thousands in gas and/or Supercharging in just a few years. It also makes the home easier to sell and worth more. Electric cars are becoming more mainstream very rapidly and the trend is accelerating, not slowing down.
> 
> 
> 
> Studies have shown that the most cost-effective way to decarbonize our power grid is to add about 5-6 times more total solar generation than we can use (overall). All that surplus power is going to be very low cost in the middle of the day in just a few years because up to 80% of it would otherwise go unused. Those who make the most money are aware of these trends and harness them to their advantage. In other words, yes, more solar panels are going on-line every year and the steady drop in the price of solar panels every year is driving this change. They are already so cheap that in many use cases it already makes economic sense to over-install solar generation AND add battery storage to replace more expensive electricity generated with coal. Solar is already so cheap it already makes economic sense to over-install solar, even without battery storage. Even though much of the generation capacity will go to waste, it can be worth it, for example, when solar generation is reduced on cloudy days it reduce the need for backup fossil generation.


nope.


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## RonAz (Oct 16, 2018)

Teslas already have load sharing for multiple Tesla owners. Just set them to charge at different times.
My utility has EV TOU rates from 11:00 pm to 5:00 am. If I had two Teslas I would start one at 11:00 pm and one at 2:00 am. This would most likely keep peak demand at less than 60 amps while charging two cars overnight. 
I don't know about other brands because I have not owned them.


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