Powering house from car - Kia Niro Forum
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post #1 of 8 (permalink) Old 11-06-2019, 03:28 AM Thread Starter
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Powering house from car

I live in the SF Bay Area, where the utility company, PG&E, has decided to start shutting off the power for days at a time when they feel like it.

I've got 7kW of solar panels on the roof, and a 64 kWh battery in the car in the garage, which is all the pieces I'd need to be able to ride out an outage indefinitely (as long as the car was home), they just can't work together to do that. I'm wondering if I can come up with some kind of home brew partial solution to this problem. Even if I can't use the solar panels, I'm thinking I could use a third-party inverter to run my refrigerator off of the car battery. Has anyone tried something like this?

My main concern is that unless there's some way to connect directly to the high-voltage battery, I'd probably need to connect via the 12v battery. What's the capacity of the system that recharges the 12v battery from the main battery?

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post #2 of 8 (permalink) Old 11-06-2019, 08:48 AM
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Quote:
Originally Posted by mbbush View Post
I live in the SF Bay Area, where the utility company, PG&E, has decided to start shutting off the power for days at a time when they feel like it.

I've got 7kW of solar panels on the roof, and a 64 kWh battery in the car in the garage, which is all the pieces I'd need to be able to ride out an outage indefinitely (as long as the car was home), they just can't work together to do that. I'm wondering if I can come up with some kind of home brew partial solution to this problem. Even if I can't use the solar panels, I'm thinking I could use a third-party inverter to run my refrigerator off of the car battery. Has anyone tried something like this?

My main concern is that unless there's some way to connect directly to the high-voltage battery, I'd probably need to connect via the 12v battery. What's the capacity of the system that recharges the 12v battery from the main battery?
I know people have talked about ways to use EVs as grid storage but I don't think anyone has actually demonstrated the concept. Trying to connect to the traction battery is wildly dangerous and would likely result in some combination of damage to your car, your house and you personally. Plus I doubt any commercially available inverter is capable of handling the 356V out of the traction battery.

Like you I'm not sure of the capacity of the DC/DC converter that runs the 12V accessories. For comparison most conventional cars have alternators in the 100A - 200A range. I would assume that an EV would have a similarly sized 12V supply, maybe a little more.

For example, a stock Kia Forte has a 110A alternator. If we assume you can safely draw half of that continuously that's 55A which works out to 660W. Inverters have an efficiency around 90% so that equates to just under 5A @ 120VAC. That's not a lot. Even if it's 200A you still looking at less than 10A @ 120VAC. Domestic refrigerators use about 200W but that doesn't count start up current which can be a lot higher.

TLDR, I doubt it's possible to power home appliances from your car easily or safely.

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post #3 of 8 (permalink) Old 11-06-2019, 09:08 AM
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I believe the Leaf is the only EV that is capable of such a connection. The car's programming has to allow the electricity to flow out instead of in. It's referred to as V2G, or Vehicle to Grid, although you obviously wouldn't want the power actually flowing to the grid under these circumstances.

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post #4 of 8 (permalink) Old 11-06-2019, 10:06 AM
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I believe the Leaf is the only EV that is capable of such a connection. The car's programming has to allow the electricity to flow out instead of in. It's referred to as V2G, or Vehicle to Grid, although you obviously wouldn't want the power actually flowing to the grid under these circumstances.
That's pretty cool. To take the discussion further off topic I do wonder about the real world utility of this concept though. From this article:

Quote:
Our own Kyle Field says V2G could be perfect for electric school buses, which spend most of the day parked and waiting for school children to transport. Think of the energy that could be stored in all those yellow vehicles and how it might be cheaper to tap into it rather than building dedicated fixed battery storage facilities.
If you use the power stored in an electric school bus to supplement the grid during the day how do you use that same bus to drive the kids home in the afternoon? Do they really sit there fully charged for hours on end?

Here's what seems to be a typical electric transit bus. It takes 2.5 hours to recharge its 500kWh traction battery. If a similar school bus finishes its morning route at 9:00 it will be fully charged by 11:30 assuming it was completely discharged. Let's say it has to start picking up kids at 3:00. That means if it discharges by 50% supporting the grid it needs to start recharging before 2:00. That gives us 2 1/2 hours of grid support time. Is that worth the extra cost of infrastructure and maintenance? Obviously these are worst case numbers and it may be that the bus has significant range left over after its morning route. In any event the amount of time that a school bus could be used for grid support is limited by its fixed schedule. Sure, the math works much better overnight, but generally we're concerned about peak usage hours.

I love the idea of being able to use MY personal EV to power MY personal home when needed. I can trade off vehicle range for home power if I want / need to. I'm not sure about having my neighbor power his man cave with my range leaving me stranded when I want to go pick up pizza in the evening.

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post #5 of 8 (permalink) Old 11-06-2019, 10:27 AM
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Don't even think of using the car's 12 volt system to power the house. So many issues. Yes, an outside inverter from the traction battery would be the way to go, but you would need to watch the charge level on the battery closely. You don't want to damage it by dropping too low.
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post #6 of 8 (permalink) Old 11-06-2019, 01:28 PM
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Assuming:

1: You don't damage your car hacking the traction battery to connect your inverter
B: You don't kill yourself in the process
III: You have a bunch of money

Something like this would probably work:

https://www.schaeferpower.com/conten...cac-inverters/

If you are a true wizard you could address yticolev's concern about discharging your battery using the CAN bus interface on this model:

https://belfuse.com/product-detail/p...rtersundefined

If you try it, take lots of pictures and make sure they upload to the forum automatically in case you're not around to do it.
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post #7 of 8 (permalink) Old 11-06-2019, 03:32 PM
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Yes don't use the 12v. outlets at all for powering anything in the house. It can charge you cell phone and things like that. Try looking at www.priuschat.com and see if the discussion there can b apply to the Niro. I know when I had my Prius and use to hang out there, there were lots of discussions about this. I believe there was a kit available where you could just plug your house into the car and just use the car like and emergency generator to power your house. I don't know if the "kit" could be used in the Niro but there seems to lots of people there that are very educated about this electrical stuff. Most of it was "over my head".

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post #8 of 8 (permalink) Old 11-07-2019, 12:12 AM
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Quote:
Originally Posted by mbbush View Post
I live in the SF Bay Area, where the utility company, PG&E, has decided to start shutting off the power for days at a time when they feel like it.

I've got 7kW of solar panels on the roof, and a 64 kWh battery in the car in the garage, which is all the pieces I'd need to be able to ride out an outage indefinitely (as long as the car was home), they just can't work together to do that. I'm wondering if I can come up with some kind of home brew partial solution to this problem. Even if I can't use the solar panels, I'm thinking I could use a third-party inverter to run my refrigerator off of the car battery. Has anyone tried something like this?

My main concern is that unless there's some way to connect directly to the high-voltage battery, I'd probably need to connect via the 12v battery. What's the capacity of the system that recharges the 12v battery from the main battery?
I share your interest in this, but ...

What many people don't realize about backup power systems is that they need to guarantee that they don't backfeed into the grid during a power outage. This is a legal requirement, and its primary purpose is to prevent your backup power from electrocuting some poor power-company lineman who is trying to repair the grid and thinking that it's de-energized because they've switched off the feed from the power company end.

For this reason, most PV installations (including mine) use an inverter that automatically shuts down when it doesn't sense electrical power from the distribution grid.

There's a simple model to do what you want to do (but it doesn't involve your car battery). You purchase a portable, gas powered generator. When the power goes out you wheel it outside, put some gas in it (or hook it up to a natural gas supply line if it's designed to run on natural gas), and run a long extension cord into your house to run the refrigerator, maybe your wifi and a phone charger, but not much else. You can do this for maybe $300 - $500.

There's a more complicated model (and it still doesn't use your car battery): You hire an electrician to install a generator outlet and generator switch. You purchase a (possibly larger) gas powered generator. When the power goes out, you wheel it outside, provide it with fuel, and connect a special cord to the generator outlet that the electrician installed. You flip the generator switch, which physically disconnects your house wiring from the grid, and simultaneously connects your house wiring to the generator outlet. Now your whole house is running on generator power, legally. You can probably do this for about $1200, if you find a reasonable electrician.

The fuel part is kind of a challenge: when the electricity goes out, the gas stations can't usually pump gas. So you need to store a few gallons of gas, and you need to replace it every few months or put fuel stabilizer in it to keep it from going bad while it's sitting around in a gas can. And storing it has its own set of concerns.

There's a "Mickey Mouse model": you can purchase a 120 volt inverter that will plug into the 12V power outlet on the car. That would be capable of running something like a wifi router, but plugging even something as small as a crock pot into it might be too much power draw. The higher end Niro trim packages have a 120 V inverter built in, but I think the same power draw limits apply: maybe you can pump up an air mattress or run a router, but I think mine still won't run my crock pot.

If you want to substitute your car battery for the gas generator in either the simple model or the more complicated model, you need to find an inverter that can deliver higher current loads and you also need a safe way to connect it to the battery without electrocuting yourself. And then you're either stuck with the simple model's limitations (anything you run has to be plugged into an extension cord) or the more complicated model's requirements (need a generator switch and a generator outlet and a generator cord).

It drives me crazy to think that I have a PV system on the roof that generates more electricity than I use in a day (most of the time), but if the grid goes down, I can't use any of it. But when I look at what it would take to be able to use that in a power outage, it's up around $10,000 to install something like a Tesla Powerwall and all of the additional switching technology. Compared to a gas generator and a small amount of electrician work, it's about 10 times more expensive to install the Powerwall.

If you find a solution that strikes a happy medium, I'd love to hear it.


If you go the generator route, be aware that the less expensive high power ones can be really loud.

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