Electronics > Power/Renewable Energy/EV's

EV battery as mains power source?

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OK, so I know next to nothing about EV battery and power systems but I'm trying to work out if an EV battery, from a scrapped vehicle, could be used as a battery powered mains system for a domestic property?
This is in response to the epic increase in UK energy prices with more to come in April when our price cap is revised to account for market conditions.
My thoughts are that an EV battery pack could be used to charge from night time, low cost, off peak mains electricity, then during the day provide mains power for the house instead of the grid.  I think that the charge side is easy, because the batteries normal charger could be used, but it's the conversion side that I am concerned with. The battery output would need to go through an inverter of course, but there is the question of voltage compatibility and conflicts with the batteries control systems etc.
Has anyone done this, or knows the system parameters etc?

This is a complex issue.  The nub is the inverter.  Depending on the load, it may need to have sinusoidal output.  That is difficult to generate.  For lighting it doesn't matter, especially if the lamps are incandescent.  For motor loads such as refrigerators and fans and HVAC the motors may not operate well unless driven by sine waves.

In addition, one must plan for starting surges such as refrigerator compressors.

Take a clue from the solar panel people and see what they are doing.

In addition, there are difficulties in connecting the system without conflict with the mains system.

Yeah, would have to be sine wave, which all Solar PV inverters are.  I have an Excellent Solar PV inverter which would defo do the sine wave part, but it has a 300 volt minimum input voltage, obviously intended for PV panel strings.  So, it depends on the battery voltage output and how much hacking of the control systems is neccessary, or not!  Thing is, EV batteries have a really high KWH rating and are relatively cheap on the EV breakers market, compared to purpose designed home battery storage systems.
On the mains changeover side, thats no problem as there are off the shelf solutions for that.

Look up "DIY Powerwall". Easiest way would be to use a bidirectional inverter. It would operate as a charger off peak and switch to operating as a zero export inverter on peak.

A Prius inverter could be modified for that purpose although the controls side is going to be complex. That's basically what I'm doing (but with added solar and a thermal storage system for HVAC), the biggest thing to note is the large inductors needed for pure sine output. If you're OK with square wave or modified sine for backup operation and don't mind a poor power factor, in principle you could have the inverter only supplying current on the peaks, with the boost converter inside the inverter following the AC waveform and the outputs switched on during the correct times of the cycle. In that case, the inductors would be much smaller and only need to limit EMI to acceptable levels.


--- Quote ---My thoughts are that an EV battery pack could be used to charge from night time, low cost, off peak mains electricity, then during the day provide mains power for the house instead of the grid
--- End quote ---

One of the big players did this....using old EV batteries...it was so bad that they stopped....they go unbalanced big time and you loose loads of battery capacity (they get so unbalanced you cant rebalance them)....using EV batts is not vaiable, so they concluded, after multiple customer complaints....if you do it, you might be lucky and get that golden EV battery that lasts ages.

What you propose in the top post sounds like a great idea...but the practicalities win out...and in the end , its a pretty miserable thing.......your payback time is very long....and when you start breaking even, your batteries need replacing because they have lost so much capacity....also, your inverter....goodness hope that doesnt fail, it will eventually (say its el caps go bad), because then that eats even further into your payback........then theres the size and weight of the inverter and batteries and charger.......its a big piece of hardware..........then theres the noise of the fans.........unless you buy a tesla power-wall which doesnt have fans...but they cost something like ???...is it £13k ??? for 8kwh (???)

..you can look this up on the web.

I think powervault do the lowest cost system...and they can also do it in conjunction with eOn **(???)....and if you want to save money , you can agree to be a "mini power station", and give the el co occasional control of your system so they can use it to re-balance the grid.....

........and if you are cunning, you can opt for this, and get the discount, but then disconnect your system from the internet, so that they cant get control of your system...and you just pretend its not your fault..and that there is some problem with their management of your internet connection in your unit.....lots of customers do that

..**OK my  question marks came out as faces, sorry about that

..But having said all the above, if the differential between night time rate and day time rate gets massive, (and stays like that ) then the battery storage starts to look good.

Also, i think in the UK , there is a limit  to the power of the Grid Tied Inverter that you are allowed to use on the mains....i think its 5kW..........they dont want people using more than this because otherwise the mains voltage  level could get too high, and sOme people could transmit  too much  power to the grid, and not let others get a chance...say if it was a very sunny day...remember a GTI wont turn on if the mains is above a certain level....and loads of people transmitting loads of power to the grid raises the grid voltage.

But if you want to "island" your system, then obviously you can have inverter and batteries as big as you like.........just hope you dont get the wrong batteries that go unbalanced and loose capacity...because this is a gamble....if you kop it, it will be a very expensive situation for you to replace them.

I think if you go with say powervault, then for 10 years or something, they will replace any bad batteries....i think the warranty on batts is 10 years, i coudl be wrong.

Remeber also that if you have a 5kW inverter.....its efficiency is pretty bad at low power levels, say a couple hundred watts.....so theres even more misery into it.

Also, how are you going to make sure your solar doesnt put into your storage  battery when you car battery needs charging?...because its inefficient to put solar into the storage battery, and then from there to the car battery........there is conversion efficiency losses.

I could be wrong, but i think its only the tesal power wall that can be instealled outdoors?.....the others need to be indoors, or in  the garage, but the fans whirring away annoys some people.....and the fans go on at night because thats when you are shovellign in the cheap rate electricity.


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