Using my Electric Car as Extra storage?

WaihibushWaihibush Registered Users Posts: 2
We live close to the mountains and often have 7 - 10 days of heavy cloud during the winter. My electric car has 18KwH of storage, which should be enough to get us through a couple of cloudy days and then I could take it into town for a fast charge while I have a coffee. Has anyone used their EV like this in practice?


  • BB.BB. Super Moderators, Administrators Posts: 29,994 admin
    Sort of... There is the Prius Hybrid system. Some folks have connected a small 12 VDC to AC inverter to the 12 volt accessory battery (the 12 volt accessory battery is recharged by the larger traction battery--Of course, this is done with the older Prius cars that have a relatively small capacity traction battery--I have not seen any projects with the new Prius models--But I have not looked either).

    Another is to connect to the high voltage traction battery directly with a high DC input voltage AC inverter.

    If I recall correctly, you leave the "car on", the the engine will auto start as needed to keep the batteries charged.

    The downside has always been the fact you are using a very expensive portable battery system (your hybrid or e-car) and cycling it to power an off grid power system--Which typically can use big/heavy lead acid or other batteries just fine--And use a "cheap" backup genset (many times with already on-site propane stored fuel).

    It was interesting reading about the Prius systems... It appears that the battery management was very sophisticated (or possibly very simple with good system coverage) and handled "unusual loads" (on 12 volt or traction battery packs) very nicely.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • WaihibushWaihibush Registered Users Posts: 2
    Thanks for your thoughts Bill. The other way of looking at it is that you have a very cheap car, if you take off the cost of buying equivalent storage. Mine is a BMW I3 REx with the 650 cc back up motor.
    We are just starting to design the power system for an off grid house.
    My thoughts was along the same lines at 'techntrek' in the 'using a Prius as a generator' thread', in that I don't want to have more gasolene motors than I have to.
    I love the idea of, and driving my BMW, so why not use it as extra storage on bad solar days, and because it still has a wee gas motor, I can if necessary do the 10min trip into the closest "fast charger" and top up the batteries again.
    I am still planning to have a 2 day storage 48volt lead/acid/carbon battery bank in the house, but hoping to do without the need for a separate backup generator.
    I am not highly tecnical, but it doesnt make sense to me to load the on board DC-DC converter that drives the 12 volt battery, but I cant figure out how to tap into the 240volt normal charge port or the Fast Charge into the 36 volt system.
    Any ideas?

  • mcgivormcgivor Solar Expert Posts: 3,249 ✭✭✭✭✭
    edited April 2018 #4
    A little off topic perhaps but if the BMW has any warranty, the on board computer will most likely record events that involve power loss without motion, or something along those lines which could, or more likely would, void any warranty. Their M3 for example records the number of launch control events peformed, amongst other things to verify abuse, so why not the I3 REx.?
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • BB.BB. Super Moderators, Administrators Posts: 29,994 admin
    I don't have the answers on how to convert your car, or even if it is a good idea.

    If you read through this website, you can see that he did not just plug in a 240 VDC input inverter and away he went... Instead, he did lots of testing first with load banks (aka filament light bulbs) and saw how the system behaved and what the traction battery bank operational voltage range was--Then got a used computer center AC inverter that accepted high voltage DC for input power.

    Lots of interesting reading on his website if you are interested in the details. And a good way to start testing on your vehicle to see if it is workable for your needs.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jonrjonr Solar Expert Posts: 1,360 ✭✭✭✭
    edited April 2018 #6
    I'm waiting for someone to throw a Tesla Powerwall into their trunk and charge it while at work (presumably a place with utility power).   Might actually work OK for a home that is off-grid.

    I am available for custom hardware/firmware development

  • bill von novakbill von novak Solar Expert Posts: 887 ✭✭✭✭
    jonr said:
    I'm waiting for someone to throw a Tesla Powerwall into their trunk and charge it while at work (presumably a place with utility power).   Might actually work OK for a home that is off-grid.
    An EV is sort of a mobile powerwall.  With very minor mods you can pull about 1KW off the 12V system of an EV (most DC/DC converters will go to at least 80 amps.)  With more expensive mods (i.e. a modified ChaDeMo charger) you could get rated power of the traction battery - tens of kilowatts.
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