Is my idea crazy or should I pursue it further?

[tsedge]

Hi,

I've been learning more about solar/battery setups and it seems to me that a great DIY way to maximise savings would be to directly use a cheap old EV as battery storage and home power backup.

The car wouldn't even need an MOT, so long as it had V2L and a decent battery capacity left. This would seem to be far cheaper than buying a brand new home battery and also much less work than removing the battery from the EV and installing it on the outside of the house in a custom side building or shed.

The main drawback would seem to be the space that a whole car would permanently take up, but assuming that was available, it seems like a good solution.

What have I missed or not taken into account here?
Has anyone done exactly this (as opposed to taking a battery out of an old EV)?

Thanks in advance for your comments, I am still at the beginning of learning about all of this.

 

[MG Clive]

I'll be honest, I know nothing about solar battery storage, but surely a proper solar storage battery set-up wouldn't cost as much as an old used (scrap) EV, would it?

 

[NikLiverpool]

Depends on what type of battery you are after.
For home batteries what I found quite important during my research on the matter was not only the capacity but also the discharge rate.
This was the main reason I went for the Tesla ones. One powerwall 2 can discharge up to 5 kWh. 2 10 and the setup of 3 15 kWh.
Now you may ask why would you need such a high rate?
Well on occasion during spring and summer the car draws, home usage and the batteries support the solars.
My neighbour has a massive solar system and batteries but they give up to 2.5 KWh which is ridiculously low.
But 3 powerwalls are a significant investment, more than an old EV. On the other hand though the EV cannot provide the same power levels.

 

[tsedge]

I'll be honest, I know nothing about solar battery storage, but surely a proper solar storage battery set-up wouldn't cost as much as an old used (scrap) EV, would it?

Well I was thinking/comparing with a high capacity setup, perhaps up to 20kWh, which is still pretty expensive to buy from new, but could run a big house virtually off-grid (or at least top-up only in off-peak hours.

Old EVs destined for the scrapheap are practically worthless, so the cost differential would be large.

Depends on what type of battery you are after.
For home batteries what I found quite important during my research on the matter was not only the capacity but also the discharge rate.
This was the main reason I went for the Tesla ones. One powerwall 2 can discharge up to 5 kWh. 2 10 and the setup of 3 15 kWh.
Now you may ask why would you need such a high rate?
Well on occasion during spring and summer the car draws, home usage and the batteries support the solars.
My neighbour has a massive solar system and batteries but they give up to 2.5 KWh which is ridiculously low.
But 3 powerwalls are a significant investment, more than an old EV. On the other hand though the EV cannot provide the same power levels.

Yes, discharge rate would need to be enough to run the house with normal (no EV charging) load, so perhaps 5kW, I am thinking.

I can't think of any reason why I would need anything like 10-15kW, of course this assumes intelligent uses of appliances and making sure high power devices are disabled or in a low-power mode when on backup battery power.

For example, I'd be happy for the kettle to draw only 1.5kW when on battery power, which requires some work to do, so power hungry devices are restricted (or just replaced with less power hungry ones).

I really like the idea of doing it all on a shoestring and seeing what is possible.

 

[Rolfe]

I believe Euan McTurk is doing this with an elderly Leaf, as the ChaDeMo has VtH capability.

 

[decrep]

Yes, discharge rate would need to be enough to run the house with normal (no EV charging) load, so perhaps 5kW, I am thinking.
.

my A/C draws 3.5 kW, the water heater and oven about the same the same. dishwasher and washing machine slightly less. Ok if there's only one on at a time, but 2at a time is going to need at least 8kWs to cover all needs.

 

[NikLiverpool]

Yes, discharge rate would need to be enough to run the house with normal (no EV charging) load, so perhaps 5kW, I am thinking.

I can't think of any reason why I would need anything like 10-15kW, of course this assumes intelligent uses of appliances and making sure high power devices are disabled or in a low-power mode when on backup battery power.

For example, I'd be happy for the kettle to draw only 1.5kW when on battery power, which requires some work to do, so power hungry devices are restricted (or just replaced with less power hungry ones).

I really like the idea of doing it all on a shoestring and seeing what is possible.

It's certainly doable if your energy demands are not that high on discharge rates.
I am a bit of a heavy user all year.
Heat pump during the winter, electric oven etc, 2 EVs .
During summer heat pump is only for water but then on top of everything else I have a pond where due to heavy feeding the filter pumps run heavily, up to 2 kWh. Thank God I got variable ones and they are lowered during winter...

How would it work with cooling the battery etc? I know for example that Tesla doesn't touch the cooling liquids in their cars while other manufacturers replace every 4 to 6 years.
Also from a house insurance point of view, what would be the complications since the car-battery I presume will be Sorned and not insured.

 

[T1 Terry]

Look at insurance write off auctions, even a poverty pack MG4 51 has a 51kwh battery, that gives around 38kwh recoverable storage and can be drawn at 7kw.
If you have subsidised solar/battery deals available, cash in on one of the deals, then power a Victron Multiplus or Quattro 48/5000 from the 48v nom. battery.
Feed the V2L into the Victron via the mains supply connection and set the max input current to 30 amps, so you don't overload the MG4 system and the Victron will use the MG4 battery to charge the house battery when the load is small, gradually reducing the charge current as the load increases to remain below the 6,600w input limit, if you need any more on the load, the Victron will become an inverter and add to the 6.6kw up to the max inverter capacity of 5,000va = total continuous 11.6kva ..... the Victron can also handle a short term load of up to 100%, so for big start up load or short load duration items, you can have 16.6kva available ......

If you need more, you can parallel another 48/5000 Victron inverter and have a short term peak load supply of 26.6kva ...... you could add another EV with V2L to that inverter and increase the storage capacity and the load capacity .......

Space to park the vehicles is really the only limitation, if you can get good money for selling back to the grid at peak times, yet buy power cheap to charge an EV or what ever ..... you could actually profit by being an energy storage/provider, as well as live electricity bill free ....

T1 Terry

 

[tsedge]

my A/C draws 3.5 kW, the water heater and oven about the same the same. dishwasher and washing machine slightly less. Ok if there's only one on at a time, but 2at a time is going to need at least 8kWs to cover all needs.

No AC here, we're British!

Fair point, but I am assuming not using electricity for heating. Now I realise that's a big assumption, but there are alternatives.

Space to park the vehicles is really the only limitation, if you can get good money for selling back to the grid at peak times, yet buy power cheap to charge an EV or what ever ..... you could actually profit by being an energy storage/provider, as well as live electricity bill free ....

That's very useful information, thanks.

I think selling back to the grid would be out of the question entirely due to regulations here (I might be wrong), but I'd settle for no significant electricity bills.

Export power is heavily restricted in the UK, so I think creating a "junkyard" power plant - while an exciting idea - would land me in jail pretty quickly!

 

[GaryMG4]

I did see a YT video recently of a guy that was able to use an eNV200 van (chademo) with a specific charger that allowed V2H to power his house. It sounded a good solution for me as I was considering replacing out tip/fishing/horse feed car with an electric van.

 

[tsedge]

How would it work with cooling the battery etc? I know for example that Tesla doesn't touch the cooling liquids in their cars while other manufacturers replace every 4 to 6 years.
Also from a house insurance point of view, what would be the complications since the car-battery I presume will be Sorned and not insured.

I suppose I could still change the coolant every few years.

Insurance is probably a bigger issue, I haven't thought about that.

 

[T1 Terry]

No AC here, we're British!

Fair point, but I am assuming not using electricity for heating. Now I realise that's a big assumption, but there are alternatives.


That's very useful information, thanks.

I think selling back to the grid would be out of the question entirely due to regulations here (I might be wrong), but I'd settle for no significant electricity bills.

Export power is heavily restricted in the UK, so I think creating a "junkyard" power plant - while an exciting idea - would land me in jail pretty quickly!

If you get the solar/inverter/battery package, I believe that connects you to the power seller market .....

If you already have solar and the inverter, there are plenty of companies that would love to sell you a battery .......

Once you have all that setup, you can piggy back the Victron onto the house battery, plugging the EV's in as addition storage/supply, doesn't interfere with their system at all, it just keeps the house battery charged, so you would be selling power out of your house battery .....

If you don't have the grid connect inverter, or any solar, but you would like to set up your own offgrid system, it's not that hard, but there is quite a bit of physical work involved running cables and setting up batteries for the base house unit .... but I'd recommend getting someone to do the solar part ..... that falling off the roof can be real nasty .....

T1 Terry

 

[tsedge]

Thanks Terry, that is all very helpful.

 

[Bam Bam]

Interesting point.

An LFP pack should be suitable for full charge/discharge once a day for 10 years, but we are only charging our car every three or four weeks.

A few things that occurred to me:

1. What about the 12v battery that would also need to be working in order to keep the car functioning.
2. What output would you get? I think that the MG4 V2L is about 2kW if I remember. It boiled a kettle of water for us, but slower than usual.
   Or would you not be using the V2L capability?
3. Is it that difficult for someone who knows what they are doing to drop out a battery? There are lots of You Tube videos where people do that. Would be more manageable to put a pack somewhere than a whole car. Dala in Finland does this with old Leaf packs.
   
4. You'd have a car rotting on your property. At some point it would need to be removed and disposed of and it won't be as easy to get it out as it was to get it in.

Good thought as a potential use for written off EVs, though, rather than scrapping them. Apparently LFP batteries may not be worth recycling so getting maximum use out of them would be great.