# V2H - V2G - Using EV car as backup



## Ampster (Oct 6, 2012)

First off you will need a safety disconnect switch to protect the grid from backfeeding. These are generally made for use with generators. Then you will need some safe way to connect and disconnect to the high voltage pack. Then you will need an inverter, sized for the kW that you want to consume in your home.
The inverter also needs to work with the voltage of your pack. 

With those inputs you will have what you need to get estimates of cost and do a cost benefit analysis. 

I have solar and have often wondered if I could spoof the 60hz and make my solar inverter backfeed my home in the event the grid went down. In the end I haven't seen a blackout in years so it is not cost effective for me.


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## dougingraham (Jul 26, 2011)

I charger slowly at night. When I am at work my car is not plugged in. When I am at home my car is charging. I would not want to use the stored energy in my car to drive my house in the event of a power outage. If I did I might not be able to make it to work. This seems like it would be a common issue. Where I am we have a few blips per year and perhaps an hour outage once per year. It would not be worth the cost to me to provide for such infrequent events.

I know people talk about using EV's as storage for peaking loads but I dont see this as practical. The same problem occurs because peak load is mid to late afternoon when I am at work and my car is not plugged in. If your car is plugged in while you are at work and the power company uses your stored energy to offset their peak demand when do they charge it back up so you can get home? The times are just wrong for this to work.


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## anlashok (Sep 15, 2013)

The utility already gives a safety disconnect as a required part of hooking up to the grid.
I just expect that rates will rise, and also I will have at least 2 EVO at all times, maybe 3. Already wired garages to have 3 240v connections.
If Toyota and Nissan are both working on this, then its definitely worth looking into because they see this as the future. Ford is also working on something similar for home energy management.
With mortgage rates still low, government rebates, and chance to have solar panels pay for themselves its worth looking into. Not to mention a way to disconnect from the grid by dual using the batteries already in your car if you want. Investing in a separate battery backup that's one use only is pretty expensive still.


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## Woodsmith (Jun 5, 2008)

From what I understand, from past research into 'Vehicle-2-Grid' systems, the premise was that you could 'programme' the system to ensure that your vehicle would be charged sufficiently for your next expected journey while allowing the grid to use the pack as required in the mean time. 

It would be most useful where your car was significantly over capacity for your day to day needs and you were plugged in when not driving, both at home and at work.

Not sure what effect it would have on the number of charge cycles, or battery life, of the costly and valuable battery pack in the car though.

A part of me would rather have a small and light weight pack in the car and a lower cost, heavy, high capacity, static pack in the garage or basement of the house for grid connection.


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## Ampster (Oct 6, 2012)

anlashok said:


> The utility already gives a safety disconnect as a required part of hooking up to the grid.
> ........


In my case, in California, the safety disconnect for solar is a manual switch in addition to the automatic ones in gridtie inverters. 
The type of safety disconnect/crossover switch for generators is usually automatic. I suppose as long as it disconnects to protect the utility feed, that is all that matters.

Do some utilities give them to customers, or am I misreading your post?


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## anlashok (Sep 15, 2013)

the automatic and manual are both required, but they are included as part of the fee to hookup unless below 10kw. I may be wrong, but I know both have to be installed to prevent injury to firefighters etc on the roof and to prevent feedback.


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## anlashok (Sep 15, 2013)

Woodsmith said:


> From what I understand, from past research into 'Vehicle-2-Grid' systems, the premise was that you could 'programme' the system to ensure that your vehicle would be charged sufficiently for your next expected journey while allowing the grid to use the pack as required in the mean time.
> 
> It would be most useful where your car was significantly over capacity for your day to day needs and you were plugged in when not driving, both at home and at work.
> 
> ...


Yes, but how do you program to switch back and forth? Haven't found any specific devices with that ability already setup.
Electric Motor Werks told me that one of their converters could be theoretically programmed, but haven't found anyone documenting how to or selling a device to install.


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## Ampster (Oct 6, 2012)

anlashok said:


> Yes, but how do you program to switch back and forth? Haven't found any specific devices with that ability already setup.
> Electric Motor Werks told me that one of their converters could be theoretically programmed, but haven't found anyone documenting how to or selling a device to install.


Good question. The OEM's haven't been able to implement a simple timer to make sure a car charges during some of the off peak windows when rates are the lowest.

I don't hold out any hope we will see gridtie implementation any time soon. EMW has some great ideas and theories.


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## Underh2oguy (Nov 13, 2016)

I would love a system where my EV could automatically provide backup power to my home when the grid is down. For longer outages I could limit my home a/c and maybe get 4 days worth of power.
Alternately I thought of using a couple of the Tesla Powerwall 2.0 units for automatic backup and then finding some way to get power from the EV battery to the Powerwall battery in the case of outages lasting more than 12 hours.
Is any of this feasible? How do I go about getting this done?


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## Ampster (Oct 6, 2012)

Underh2oguy said:


> I would love a system where my EV could automatically provide backup power to my home when the grid is down. ..........
> Is any of this feasible? How do I go about getting this done?


I had a system like that and have learned a lot in the process. The biggest issue is finding a match between the pack voltage and a large inverter that can power your home or your critical loads panel . Most of those kind of inverters run at 48 Volts but a new group of inverters like SolarEdge run at 360 Volts DC. Also, Outback Power and others have announced new inverters that will run at higher voltages. Those are the same voltages that solar strings generate and the conversion from 360 VDC to invert 240 VAC is more efficient that going from 48 VDC. The market is in transition. 

I rewired the pack on my Amped VW to be able to switch it from 96 Volts to 48 Volts and back again when I wanted to drive the car. That involved a lot of Anderson connectors that took a lot of time to change around when I wanted to drive the car. I have since sold the VW to make room for a Tesla. I bought some used Thundersky's to run my inverter. 

I still have my Outback inverter and I use it to shift loads and provide backup. Because my Thundersky's were used and have lost some capacity I recently acquired a Nissan Leaf pack and plan on setting that up at 48 Volts to run my inverter. I also have solar on Enphase inverters so my two systems are not coupled and there are efficiency gains to be had with the new stuff. If I had it to do all over again I would go with a good hybrid inverter that could run off 360 Volts on the DC side. But that equipment was not even on the horizon two and a half years ago when I installed my solar system.

Yes it is feasible and will become more feasible as the new inverters come into the marketplace. The new 2.0 Powerwall reportedly contains and inverter and a DC to DC converter. If that can be programmed to take energy source like a vehicle then it can be done. To get it done you will have to wait until the new generation of inverters hits the market and there are sufficient trained installers. To do it your self will require a lot of trial and error as I discovered. Do you have solar and what Voltage does your vehicle run at?


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## Caps18 (Jun 8, 2008)

I have a 2000W true sine wave inverter for a boat/RV I could hook up to my DC-DC converter. It would only be good up to 800W since that is the max the DC-DC converter can output, but that would still be enough to run the refrigerator, HDTV, lights, furnace fan, and laptop.

I live close to a hospital and can't remember the last time the power went out here though. If the grid went down for good, I'm not sure if I would have the parts to create my own or not. I have solar panels, batteries, inverter that makes a sine wave, etc... I'm not sure if it would need to be a 240V (two hots) sine wave though or how to connect the pieces together.

It also wouldn't be worth the wear and tear on the batteries I'm afraid. Maybe with the next generation of 200,000 cycle batteries.


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## Dave98002 (Nov 12, 2016)

I will follow this type of thread to see where its going. But up here in the Great North*W*et, solar just does not work well for us, too overcast and too many TREES. 

But Tesla just announced that they have a new roofing system that is solar panels and will have a wall bank of batteries. 

We moved out here in the sticks in 2003 and we have had 4 long power outages. Two were for 24 to 36 hours, one was 6 days and 2012 was 12 days and I spent $360 on "Road Tax'ed" gas to run my generator. The cost of a battery pack, BMS and the solar array is many times the cost of my 5600 watt gen set, the "Gentrans" isolation switch and the gas

We have one rate for day and night, so charging at night to save will not work. When I was stationed in Germany and lived off base, my apartment would switch to night grid and my room heater and water heater would kick on. The room heat was a massive slate and oil "BANK" that heated all night and only a small fan worked during the day.


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