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Off Grid solar for charging 2 EVs

  • 22-01-2022 11:42am
    Registered Users Posts: 1,228 ✭✭✭ celtic_oz

    Have solar at my house (6.5Kwp) tied to the grid with a solis 6KW inverter.. all good

    Have a big shed with lots of roof space and potentially a second EV coming.

    Thinking 8KWp of solar panels, 6Kwp off grid inverter, 10KWh of batteries.

    Understand that battery would fill up quickly in the summer but one of the EV's would be plugged in usually.

    Q: When the battery is full and energy is available and not collected will it damage the system, do I need a dump load ?

    Q: What kind of inverter do I need for off grid ? What's the largest single phase I can get, any recommendations ?

    Q: Any recommendations of where to source the kit for a self install.



  • Moderators, Sports Moderators Posts: 17,392 Mod ✭✭✭✭ slave1

    Before those questions, I'd question the economics of that ~€7k investment just for charging EVs

  • Registered Users Posts: 7,770 ✭✭✭ the_amazing_raisin

    Victron inverters are built for off grid applications and they've a lot of expertise in the area. Not many installers in Ireland but they've a good knowledge base online

    They do have guides around battery sizing. Most of it seems focused on ensuring the battery has sufficient discharge current available for any sudden power draw

    A lot of the documentation around overloading the battery seems to be focused on AC coupled solar. From what I can tell if you have everything in the DC range and use Victron MPPTs then it'll just throttle the MPPT when the battery is full

  • Registered Users Posts: 1,228 ✭✭✭ celtic_oz

    Dont worry about that, just the questions, thanks

  • Registered Users Posts: 7,770 ✭✭✭ the_amazing_raisin

    All problems can be solved with more solar panels 😁

  • Registered Users Posts: 1,700 ✭✭✭ SD_DRACULA

    Why would you go with 8kwp of panels and 6kwh inverter when you can easily go 8kwh inverter or higher if off grid?

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  • Registered Users Posts: 1,228 ✭✭✭ celtic_oz

    I said that's what I was thinking of .. its literally one of the questions

    Q. What kind of inverter do I need for off grid ? What's the largest single phase I can get, any recommendations ?

  • Registered Users Posts: 5,625 ✭✭✭ Ubbquittious

    No dump load

    You might not need any inverter, convert to AC to rectify & fill battery would be a bit of a waste

    I don't know if an existing charger exists that will fill EV batteries.

    Essentially all you need is your solar panels and a fairly hefty charge controller that can speak the can bus protocol your EV uses. I don't know if they exist.

  • Registered Users Posts: 3,523 ✭✭✭ graememk

    Well the openevse could be a runner,

    Cars and charge points don't communicate over CAN they have their own protocol J something and it's to do with resistance and PWM signals.

    The openevse has a "solar" function that you give it a mppt feed of your "excess"

    If you have batteries and able to measure/get that information (eg monitor the flow to and from batteries ie your "grid" ), it should work!

    As for inverters look at the off grid garage on YouTube he's currently rebuilding his battery and charge controllers.

    I understand the off grid, as you don't need a RECI as it's not connected to the grid.

  • Registered Users Posts: 1,228 ✭✭✭ celtic_oz

    sorry I should have said 220 for the shed ( lights, tools etc ) would be good.

    Anyone with specific recommendations for the inverter ?

  • Registered Users Posts: 7,770 ✭✭✭ the_amazing_raisin

    Victron Quattro comes in 8, 10 and 15 kVA ratings

    Would you be feeding the AC output into the house, you mentioned you have solar on the house already?

    If so, then you've got an extra consideration, you need to ensure the inverter can also handle the power coming from the house solar, otherwise you could overload the shed inverter and batteries

    More info

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