H3 Pro 15 max running / oversizing

[merango]

Hi all,

I currently have a Fox ESS H3 Pro 15kW 3-phase hybrid inverter with 3-phase supply/export.

The existing solar setup is:

* 24 × 440W panels on the rear roof
* 10 × 440W panels on the front roof
* Total currently: 34 panels / approx. 14.96kWp

I'm considering adding another 14 × 440W panels to the front roof, which would give:

* 24 panels rear
* 24 panels front
* Total: 48 × 440W = approx. 21.12kWp

My installer has mentioned that Fox ESS inverters may allow PV oversizing up to around 150% of inverter rating, which would put a 15kW inverter somewhere around 22.5kWp PV input in theory.

Before I proceed, I wanted to ask those with more technical knowledge:

1. Is this level of oversizing officially supported on the H3 Pro 15kW?
2. Would running around 21.12kWp of panels on this inverter risk clipping, overheating, warranty issues, or long-term reliability problems?
3. What is the actual recommended maximum PV array size for the H3 Pro 15?
4. Does the inverter simply cap output at 15kW, or can it safely handle the larger DC input provided the string voltages/currents are within spec?
5. Would this be a sensible setup given that the front and rear roofs face different directions, so peak output may be spread across the day rather than all panels peaking together?

As an alternative, I'm considering putting the additional 14 panels on a separate inverter/string, possibly feeding into a solar diverter for a new hot water system.

We are also planning to replace an oil boiler with an air source heat pump, so the extra generation may help with future daytime electrical demand.

Any advice from installers, Fox ESS users, or anyone familiar with the H3 Pro range would be much appreciated.

Thanks.

[merango]

One additional point I forgot to mention:

The array is split across two roof orientations:

* Rear roof: South-West
* Front roof: North-East

So although the total panel capacity would be around 21.12kWp, the panels would rarely all peak simultaneously due to the split orientation and UK irradiance levels.

Does this make higher DC oversizing more acceptable on the H3 Pro 15 in real-world use, assuming all MPPT voltage/current limits are still respected?

Thanks again.

[MaterialBarracuda48]

There is a datasheet here that might help you with numbers/calculations.
https://midsummerwholesale.co.uk/pdfs/e ... 251021.pdf

[merango]

Thanks, it's just what I needed.

After consideration, I'm going to oversize the setup to 48 x 440w panels and max the inverter across 2 of the MPPT's - 12 panels x 2 strings on one MPPT, and the other 12 panels x 2 strings on the other MPPT keeping the 3rd MPPT free:

MPPT 1: 2 x 12 sets of panels
MPPT 2: 2 x 12 sets of panels
MPPT 3 : EMPTY

Only on the very best generation days will I clip the extra generation but with the new ASHP on order, this will be likely pence to £1 as day loss which is more than acceptable. And on cloudy rubbish days (UK most of the year ) and winter, this is where the extra panels will help shoulder the losses.

[MaterialBarracuda48]

Most people, me included will get around the clipping by keeping room in the battery. After Winter I use HA automation to check solar forecast, and do a discharge cycle in the morning to make capactity available.

So if you are going to get clipping, the battery can mop this up during the day / use HA to run a heatpump legionella cycle as an alternative / or if you have an EV plugged in, you can divert excess PV into it.

[merango]

Many thanks, I'm building an HA setup at the moment so will likely come back to this at some point, but apricate the suggestions. Very useful thanks.