Using Car to power house

Mr. Sparkles

Member
Location
Northern California
Occupation
Electromagician
Hello,
I am helping a customer design the electrical for a new house. They want to be able to use a generator to power house in times of power outages, as well as use an electric vehicle. They don't currently own an EV but said they have a friend who does this. Has anybody done such a thing out there? I have a 2 pole 40 amp circuit going out for the charger, I'd assume you would need to include a separate circuit that backfields the manual transfer switch. I can't upload a photo of a drawing showing what I'm doing, but basically, a 200 amp main feeds line side of DPDT transfer switch, power comes out on load to Main lugs on 200 amp load center. bottom of DPDT transfer has wire coming from 30 amp generator inlet for when power does go out. Could I land wire from the EV charger on those bottom lugs as well? Doing this would backed 200 amp loadcenter.
 

Mr. Sparkles

Member
Location
Northern California
Occupation
Electromagician
I suppose that is the critical part. You would need a charger that converts the power to 240 AC obviously. Maybe they make bidirectional EV chargers but I haven't seen one. I believe Tesla is 350-400 volts. Really, the charger would need to be a rectifier and an inverter in that case.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
The technology is generally called "V2H", vehicle to home, or "V2G" vehicle to grid. It generally uses a bidirectional Level 3 (DC) connection to the vehicle to both charge and discharge the vehicle's propulsion battery. There are Chademo based solutions available in Japan, I believe. I don't know that anything has come out here in the US yet. Also not sure if CCS supports it yet.

And operating during a power outage would require an isolation switch.

Cheers, Wayne
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
There are less expensive and less labor-intensive ways to interlock a second source than using a 200a DPDT switch.
 

Mr. Sparkles

Member
Location
Northern California
Occupation
Electromagician
Thanks for the advice. I see a couple manufacturers of the V2G but I don't believe it is available just yet, like you said Whitney. The one with the Most info (nuuve) only supports Leaf or Mitsubishi according to the website. I will try to call the makers tomorrow.
An interlock would be ideal Larry. However, if the customer wants to be able to charge the car, you can't lock out that circuit and only turn it on if you shut off the main. The generator circuit can be locked out all the time, but the EV needs power from the grid. There needs to be a manual transfer switch and that would isolate a subpanel from the meter main. I was imagining standby side of the DPDT transfer switch for the generator. One 40 amp circuit in the subpanel would power the EV charger but also be able to backfeed the subpanel if I can get a bidirectional charger. That way, the customer could use whatever one they wanted to backfeed house, but also be able to use generator if car power is low. Transfer switch isn't cheap (~$400) but I can't think of any other options. If you know of a setup where I could use an interlock and have possibility to lock out a 200 amp main and keep 4 spaces on I'm curious to hear. Thanks.
 

Mr. Sparkles

Member
Location
Northern California
Occupation
Electromagician
After pondering more on it, you are correct Larry. All I need is the interlock for 2 pole 30 for the generator. I am assuming the car charger acts like an inverter and won't backfeed if it doesn't see 240 VAC. Otherwise it would be dangerous and have potential to feed grid. So the generator has to be on regardless if the power is out. I think the homeowners thought (and talked me into believing) they could just use only the charger, so the generator wouldn't have to be running all the time if the power was out. It seems the best use of these bidirectional EV chargers is to get the best time of use if utility charges different rates during the day.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
2020 now has language to support an EV powering a dwelling unit
:rolleyes: I suppose it could work. The typical EV battery is what, about 80-100kW-hr for capacity? I don't know how deep a discharge they can handle or where the voltage roll-off gets critical, but if your home uses 30kW-hr like mine does, you might get up to 3 days, if you do a little energy belt tightening.
 

Barbqranch

Senior Member
Location
Arcata, CA
Occupation
Plant maintenance electrician
It would also work well if you have an auxiliary generator to use during the day, but don't want to run it at night when the load is very low.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
In California (PG&E, SCE and SDG&E), in order to have that, the charger/inverter would need to have UL1741 approval as "line interactive equipment", because in theory, if connected improperly, it could kill a utility lineman. UL1741 requires qualified monitoring of the line source so that if the utility power fails, the inverter cannot feed energy back to the grid, on purpose or accidentally. So far as I am aware (as of a talk I attended about 1 year ago), no V2G or V2H EV inverters have received that or were pursuing it.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
:rolleyes: I suppose it could work. The typical EV battery is what, about 80-100kW-hr for capacity? I don't know how deep a discharge they can handle or where the voltage roll-off gets critical, but if your home uses 30kW-hr like mine does, you might get up to 3 days, if you do a little energy belt tightening.
And then you are stuck there because your car isn't going anywhere. I've said this before- why would anybody do such a thing?

Install a generator. At least if that runs out of fuel you can get out in an emergency.

-Hal
 

wyreman

Senior Member
Location
SF CA USA
some of those tesla guys get free charging for life.
If they can backfeed 240v to the house
they can run the car pretty low and then go out and supercharge the car back up pretty quick
 

kwired

Electron manager
Location
NE Nebraska
Buy a $40,000 dollar car plus$1000 of misc to keep from buying a $600 generator. Makes sense to me, but then I pull my LR, BR, KITCH and Bath on vacations to save on motel rooms.
Actually in OP they are wanting both the car and the generator to be able to power the house. Guess I can't speak for others, especially in other places but I haven't had a power outage that lasted long enough to justify connecting the generator since 2006. And that one was long enough an EV battery wasn't lasting for that duration either. All other outages were only a few hours tops. Grab flashlights and candles if it is dark for those. Most the time just went to bed if it was dark.
 

Barbqranch

Senior Member
Location
Arcata, CA
Occupation
Plant maintenance electrician
Some people on life support equipment can't tolerate a outage of more than a few seconds. The car battery could pick up the load right away and cover it till the generator was started, or even over night when the total load is very small and you don't want to run a 10 or 20 KW generator.
 
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