# Off Grid 3P 15k Quattro's with AC Coupled Solar

**URL:** <https://community.victronenergy.com/t/off-grid-3p-15k-quattros-with-ac-coupled-solar/63368>\
**Category:** Q&A and troubleshooting\
**Tags:** pv-inverter, 3-phase, expert, cerbo-gx, quattro\
**Created:** [30 September 2026 09:32 UTC](https://community.victronenergy.com/t/off-grid-3p-15k-quattros-with-ac-coupled-solar/63368 "2026-09-30T09:32:35Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![Kieran](https://avatars.discourse-cdn.com/v4/letter/k/3d9bf3/32.png) [@Kieran](https://community.victronenergy.com/u/Kieran)\
**Post date:** [30 September 2026 09:32 UTC](https://community.victronenergy.com/t/off-grid-3p-15k-quattros-with-ac-coupled-solar/63368/1 "2026-09-30T09:32:36Z")

</div>

Existing off grid system is as follows -

- 3 x 48V/15k Quattros in 3 Phase - Switched as a group.
- Cerbo GX
- 110kwh of BYD Lithium.
- 4 x 450/200 MPPT RS.
- 3 x 5kw SMA Sunnyboy MPPT’s on the Quattro’s AC Output’s controlled w/ frequency shifting through the PV Inverter Assistant (1 x Sunnyboy on each phase).
- Single phase 16kva Generator powering a 15k MultiPlus-II as a charger only onto the DC bus (networked to Cerbo w/ MK3 interface).

I had planned to add another 5kw Sunnyboy to L1 (2 in total on this phase, 1 on each of the other phase’s) - The PV inverter assistant mentions to that “each phase must have the same solar power installed” - What are the implications of not following this? Being that the AC coupled solar is a variable charge source between phases, I can’t understand how this is an issue?

I also plan to upgrade the single phase generator to a 3 phase unit into each of the Quattro’s - How does frequency shifting on the AC Output work when the Generator is running? Do I just program the generator to stop at around 95% SOC to allow the Quattro’s to be able to frequency shift, to throttle back the Sunnyboys when required?

Thanks in advance.

---

<div class="post-metadata">

**Author:** ![Jeroen2](https://dub1.discourse-cdn.com/victron/user_avatar/community.victronenergy.com/jeroen2/32/7234_2.png) [@Jeroen2](https://community.victronenergy.com/u/Jeroen2)\
**Post date:** [30 September 2026 10:04 UTC](https://community.victronenergy.com/t/off-grid-3p-15k-quattros-with-ac-coupled-solar/63368/2 "2026-09-30T10:04:31Z")

</div>

Good Morning,

You can use different pv inverter power in each phase but never more than the 1 to 1 rule, I use just 2 phases already for 11 years, the 3rd is still spare.

The generator running and solar is indeed a bit tricky, I would switch the gen off already at below 90% soc with solar, to give the PV inverters enough space for frequency control reduction.

Regards, Jeroen.