Using V2L as alternative to generator in Sonnen ECO system

I live in Maine, USA. I have a Sonnen ECO battery system (max 16kwh, currently at 12kwh) with PV. For the most part, it works great. The one part of the design I am not crazy about is . . . If the PV panels are covered with snow and the grid is out, I only have available the power left in the battery system. I have compensated for this by have an external plug that I can hook a generator to to charge the batteries if, in this situation, the batteries get too low.

I am exploring purchasing an EV and one of the things I am wondering is whether I can use V2L technology (provided the EV supports) to plug in my EV to recharge my Sonnen battery array in the situation I mentioned above. Would this work?

The reason this seems preferable to me as opposed to V2G or V2H is that I would not have to change my system or my relation with the power company (I would also avoid needing to buy a bi-directional EV charger.


Hi Fran, if you are already using a plug-in generator to charge the batteries, then there is no reason why you couldn’t use a vehicle with V2L in place of the generator. The only issue may be with the power rating of the generator compared to the EV. I’m assuming your generator is rated at 5 to 8kVA, while most EV’s with V2L are limited to 3.5kW (4kVA).

A better option, as explained in the V2L article, is to use an AC changeover switch to directly power the backup loads via the EV. This would be much less complicated and reduces the risk of potential issues using the EV with the Sonnen ECO system.

The biggest concern with using any alternative power source (Generator or EV) to charge a battery in a Hybrid solar system such as the Sonnen ECO, is the potential for the Hybrid system to back feed (or export) excess solar into the source causing irreversible damage.

Thank you for your response.

While not fool-proof, it seems it could be relatively safe to charge the Sonnen battery system and power my house if:

  • I am definitively running in off-grid mode. The Sonnen system “throws the switch” when grid power is unavailable and only throws it back when grid power is detected. If the battery has declined (e.g. say 30% remaining) and PV generation not producing (e.g. due to snow cover), I then throw the main switch to grid to make sure no backfeed to grid occurs.
  • I flick off the breaker associated with the SolarEdge inverter connected to my PV array. This should disallow PV as a source of backfeed.
  • I keep usage in house to under whatever the V2L EV rating is. The excess would then be used to charge the battery.
  • I disconnect the EV once Sonnen battery is charged and flick all the switches to their starting positions,.

Is this sound thinking? Am I missing something?

Hi Fran,

Yes, if you are careful and follow the steps you listed, then I think you should have no problem using an EV with a V2L rating of at least 15A (3.3kW). You may have difficulties with an alternative power source rated less than this as the Sonnen ECO system requires at least 3.3kW, depending on which model you have.

Do you have the latest Gen 3 Sonnon ECO or an older one? The older models were only rated at 3.3kW, so you should be fine. The newer models are more powerful and could potentially draw overload the EV when it tries to charge the battery. Can you set the charge rating using the Sonnen App?

Thanks again for responding.

I have a Gen 2. The Sonnen app does not show me the settings (that is reserved for the authorized installer) so I sent a query to support and will report back when I hear.

I do not have a sub-board with essential loads. The Sonnen is set up as a whole house backup. With that in mind, I don’t think the transfer switch mentioned in the V2L article is applicable. Am I reading that correctly? Or are there advantages to setting that up?

There is really only one non-discretionary load and that is the electric hot water heater. If I am home in a storm or I am away for more than a day or two, I shut that off at the circuit board. I then just use the stove judiciously and avoid the dryer, etc.