2 strings per MPPT - what are the drawbacks?

The DNO is trying to scupper my net zero ambitions by saying I can't have another inverter... very irritating.
So I'm back to working out how to get more solar on my existing inverter... it's a 20kw 3ph and has 2 MPPTs with 2 strings per MPPT. If this was 3 or 4 MPPTs I wouldn't hesitate, but I've no idea if adding another string to one of the MPPTs (I have 1 in each of the MPPTs already) would work acceptably ... in other words, does anyone know the drawbacks of having 2 strings in 1 MPPT ... in particular one that is designed for that, as I have?

(I'm aware we need to watch voltage and current limits)

Thanks

Surely the DNO can't stop you having another inverter... they can just block more export?

alas, they can ... an inverter changes the direction of the flow by increasing the voltage so tehy can limit your inverters too - very frustrating.

My experience with 2 strings on one MPPT is that they really need to be a matched pair as the performance of one string impacts the other. In my case we ended up making the 2 strings into 1 big one. Is that an option?

Yeah that was my expectation. However, the GE setup says 2+2 (2 MPPTs with 2 strings per MPPT) and so far they seem to be saying that there won't be a problem - but I'm loathed to go ahead with all of the work if there will be!
Surely if we make one big string then it would definitely impact performance?

1 MPPT is fully loaded with one string (close to voltage limit)
The other is fine. The new string would come from the shed facing roughly NE/SW on a 15deg slope so the plan is to have each side in series and join in parallel as a single string - that would be close to the 30A limit so it really needs to go into the MPPT as string 2.
(I know it's not ideal to join NE/SW but actually we've seen research which says it's fine for a shallow angle)

Thanks for any further thoughts.

in my case the 3 strings were all facing the same SW direction and feeding a solis inverter. The 2 strings on the same MPPT were different sizes (7+4) and the performance of the those was worse than the other MPPT with a string of 8. It effectively ignored the extra 4 panels in terms of power output. Making an 11 panel string resolved it. I have subsequently added a second solis to cover the NE, all feeding into an AIO which handles the DNO side of things.
I dont believe combining strings from my 2 faces would have been very effective because with a standard roof angle they come on and off stream at different times but also my kit is different to yours so may not be indicative of what you might see.

In your case I guess a second inverter would also need to be directly grid connected, unlike mine, but both could be export limited to meet the DNO requirement so have you confirmed the rejection reason and possible options?

Rather than an additional inverter, could you change to a new inverter of the same rating with 4mppt?

Hopeful Thanks for that. Sorry for the late reply I didn't get a notification! Yeah I think we need confirmation from GE that the setup we envisage would work well else a colossal waste of money.

Second inverter won't be directly connected ... it would push back through one of the phases and the main inverter would regulate the export. But unless I take the second inverter off grid totally DNO will say no. Very irritating. It's the second inverter they are objecting to.

kram thanks. Yes we could but again colossal waste of money paid for inverter etc. Very tempted by Sigenergy with the DC bidirectional charger ...