Powering home with Tesla

Powering home with Tesla

Within the last few days, Elon has hinted twice on twitter the idea of using your car as a power source. (once for using 240V power tools with the P/U and today with the ability to charge anothers car who could be stranded.

Being in FL, the idea of possibly being able to run your house off the car for a few days is already enough to convince me to go LR over SR..

What to you think the complications of doing so would be? I know you'd have to turn off the main breaker, and maintain only using a certain draw of amps, but I think it would be a relatively simple alternative to having a home generator.

I also dont think it would impact Tesla energy negatively as it wouldn't be very practical to run your house off your car everyday..

jamespompi | 2018年7月5日

Guess I probably should've put this in the general thread.. Oh well

Magic 8 Ball | 2018年7月5日

Good question and I am surprised it doesn't come up more often.

Many BEV and PHEV manufacturers have said it can be done but then abandon the implementation for some reason or another. I think it would be a car warranty nightmare.

spuzzz123 | 2018年7月5日

And maybe cannibalize powerwall sales...

jamespompi | 2018年7月5日

@Douwe, Good point. If not set up correctly could fry the car or your house, both bad news for Tesla.

@Spuzzz I thought the same at first, but being as most people wouldnt utilize it like a powerwall on a regular basis and maybe just for outages maybe it wouldnt affect PW sales.

Also, thought doing something like this could prompt additional state rebate programs for the car, FL just offered generators tax free a few weeks ago..

CharleyBC | 2018年7月5日

If there was even a way to get power from the car (charge port?), I assume it would be DC. Your house uses AC. So you need an inverter. If you have solar, you already have an inverter. Some--but definitely not all--inverters are designed to take battery input as well as PV input. Otherwise you'd need a special inverter just for the car connection. And a new breaker, etc. Oh, and probably permission from your electric utility since you're attaching a power source to the grid.

Anyway, it's a very interesting question, but I suspect the answer will not be trivial.

EVRider | 2018年7月5日

This question does come up a lot in the forums. Tesla has shown no interest in allowing people to power their home from the car’s battery, even if they could technically support it. First, using the battery in this way could reduce the battery life and impact the warranty; second, Tesla sells the Powerwall, which already solves this problem.

As another FL resident, it would be nice if we could do this, but don’t expect to see it happen anytime soon.

Rocky_H | 2018年7月5日

@douwe, Quote: "Good question and I am surprised it doesn't come up more often."

Believe me--it does. I just did a quick search and found five previous threads asking this just with the first wording I tried in the search.

Magic 8 Ball | 2018年7月5日


I have only been here a few weeks and haven't seen it yet. As an owner of a CMax Energi the question came every few days or was floated to the top on the Energi forum.

SUN 2 DRV | 2018年7月5日

Look up V2G or V2H, Vehicle To Grid or Vehicle To Home... There are LOTS of technical, economic and safety complexities of tying your car to another complex system like your home or the grid.

And a battery on wheels doesn't make a very good backup power source unless you can leave it at home all the time.

A Powerwall is much less expensive than your car and is a much better back up system.

gballant4570 | 2018年7月5日

This is not a new idea, and Tesla is no stranger to the concept. Some of it is already happening in Europe. They use car batteries to store renewable power produced during the day for use at night. Cars are charged at their work locations, and plugged in for the evening, supplying some of the lower levels of power required during the night.

david.fox22 | 2019年9月18日

How are Europeans doing that though? Can the tech be leveraged in the US?

bjrosen | 2019年9月18日

Using your car for backup power seems like a bad idea for a few reasons. 1) the battery isn't that big, it will only power your house for a day. 2) You don't want to run your battery down to 0, it's bad for the battery. 3) It's complicated, you will need an inverter. And finally and most importantly 4) You can't drive a car with an empty battery.

If you lose power on a regular basis then you should get a proper backup generator. I have a 20KW Kohler and two propane tanks which is enough to give me power for a week but if I need more then all I have to do is call the propane company any they will come fill my tanks. I got the generator after I had a total of two weeks of outage during the winter of 2017. Last winter I had a few days of outage, used less than half a tank of propane. The backup generator, plus automatic transfer switches, installation and permits cost about $12K, about what a Powerwall would cost you but it will power a house for much longer. Powerwalls make sense in the context of a solar power installation because they get charged during the day and get used at night which reduces or eliminates the need for grid power. They don't make sense for emergencies because they can't store enough energy to last for multiple days. If you're outages are only for a day then the best thing to do is to just ride them out, even in the winter (which you don't have) the house won't get intolerably cold in 24 hours but it will if the outage lasts for multiple days.

TabascoGuy | 2019年9月18日

@bjrosen, I didn't go to quite that extreme when we bought our home in '94. We lost power 3 times that first winter for up to 4 days each time so I bought a 12KW generator, manual switch box, installation, etc. We've only lost power once for about 20 hours since then. Go figure. | 2019年9月18日

@david - The key is they are using standalone lead-acid car batteries, not a Tesla car. One enterprising guy here in the USA took the battery pack from a totaled car and used it as a home battery backup system. This was before the PowerWall became available.

@byrosen - good reasons for not using your car as a backup, but for me, the #1 reason is warranty. Let's say you use the car to power the house often, such as the life of the battery is cut in half and fails after 7 years. Should Tesla replace it under warranty because you used the battery far more than the use over the 100,000-mile warranty?

The batteries Tesla uses in the PowerWall are a different formulation than those used in the car. They are optimized for the backup application, where the batteries in the car are optimized for vehicle use. These are different uses cases that affect battery longevity.

Now, I do expect there are ways to deal with many of the issues. Perhaps the battery warranty is rated in hours of use rather than vehicle miles. Perhaps it has some major limitations, like only available for home backup for 20 hours a year and it will not power a home below 20% SOC.

So far Tesla does not seem interested in using the car battery to power homes as they do have a good solution with the PowerWall, one that is engineered for the backup purpose.

CharleyBC | 2019年9月18日

"the battery isn't that big, it will only power your house for a day"

Well, actually, it's pretty huge. The Model 3 LR battery is 75-80 kWh, depending on whom you believe. Let's go with 75 kWh. A Tesla Powerwall 2 is 13.5 kWh. So a Model 3 is bigger than five Powerwalls!

If such a thing were possible, I'd imagine the car would stop offering power when the battery got to some threshold, similar to how Sentry stops working at 20%. You wouldn't want to brick the car.

But it is indeed not a multi-day solution, unless you scale back to subsistence usage until the grid is restored.

Now, of course, there's the technical problem of whether the car and the UMC could invert the DC back to AC and jam it into your panel... | 2019年9月18日

@CharleyBC - Agreed the vehicle battery is huge! All this assumes you'd have a new HPWC version that includes the inverter, power switching, and monitoring electronics. None of this is in the car that could be used.

I saw such an external device during the Leaf 60 kW pre-release show, and it was huge. Then again, Nissan started saying they would offer something like this since 2011 with the first Leaf, and nothing is available yet.

rxlawdude | 2019年9月18日

Hey @amusee, your spam is being flagged in every thread (!!) you posted this. WTF, man?

kaffine | 2019年9月18日

The main issue is grid disconnect means. It can't just back-feed into the WC as there is no way to guarantee the main breaker is off and grid disconnected. It would require a transfer switch of some kind and a separate connector on the house the car plugs into when it is supplying power vs charging.

The connector on the car only has 2 power wires (US version anyways). To power a house it would need 4 wires, 2 hots a neutral and a ground.

The car does have inverters not sure if they are pure sine wave or not. Pure sine wave would be better for powering a house. However if using them then it would require a different connector. They are not setup to power things outside the car. Would need to add a set of contactors to switch between the motors and the external output. They would have to fail to the external output as you wouldn't want a failure to cause your car to suddenly apply power to the motors.

The way I could see them doing it would be to require a power wall installed and the Tesla plugs into the power wall the power wall would control power into and out of the car. The power wall would handle the disconnect means, has the inverter built in. The connection to a Tesla would just increase the battery capacity. This could be done with the hardware already installed in the car it would just connect the DC to the charge connector like it was at a SC however instead of getting charge it would supply DC output to the power wall.

Zeus140 | 2019年9月20日

An inverter would handle the wire issue - hots, ground and neutral.
The use of a Powerwall to handle the entire thing is a GREAT idea. Tesla take note!

Model3.Tesla | 2019年9月20日

I remember seeing an EV manufacturer suggesting that their cars could be tied to the grid.

The goal was to make the battery available "On Demand" so that the grid could use the cars to help when a spike in demand exceeded generation.

I don't remember the details, but the requirements could be specific if the battery is 80% or more, allow the battery to be used to supplement the grid, but only provide energy until the battery reaches 60% (I just made up the values, but these limits should be "Kind to the Batteries."

If the spike persists, the grid could fire up more generators relieving the need to use the batteries.

This isn't quite using your car to power your house, but I could see something like that being part of the grid one day.

kaffine | 2019年9月20日

I will say there is a large difference between powering the house in case the grid goes down vs sending power the grid. It is actually easier to power the grid.

If I am only powering the grid I only need to sense if the grid goes down and stop putting power out. This is something that is done frequently with inverters on solar installs.

If I want to power the house with the grid down now you need a way to disconnect from the grid before starting to generate power. Then you would also likely need load shedding. If it is an automatic backup it needs to be able to supply the entire load so it is likely only critical circuits will be backed up. If it is a manual switch over to backup then you can get away with manual load shedding and the generator doesn't have to supply the entire load.

Maxxer | 2019年9月21日

The battery is huge

It would be a powerwall sale killer

calvin940 | 2019年9月23日

I would like Tesla to build in the option to augment my current system.