This is a bad idea. Unless you have 3ph equipment, which you don’t, do not make a 3ph solar installation.
I’ll briefly go into some obvious why not to do its.
- There are 3 times as many things to go wrong. Why is this bad? It is bad because the entire 3 ph system stops when 1 inverter fails. If you had 3 inverters in parallel on a 1ph system and 1 failed, you could be back up and running in a hack on 2 inverters whilst the other is being repaired/replaced.
- Speaking of the replacement of a single inverter, these inverters can only be parallel or replaced with an identical model. And by identical, I mean identical chipset in the guts of the inverter. The same model inverter can have a range of chipsets. That chipset changes relatively frequently on certain models. In six years’ time, finding a replacement in a hurry is going to be a mission. All the while, those other two healthy inverters cannot provide a 3 ph supply. In a 1ph setup, there would be minimal downtime.
- 5kW /phase is quite limiting, exceed that on 1ph and the system is in overload. There is far more load combination flexibility if that was 15kW on a 1ph supply before you overload it.
- And now the converse of point 3. It is an inefficient waste of capital. These are very expensive bits of kit.
Ideally, you want to buy an inverter that is capable of your requirements and not a watt more. Well, practically, that is difficult to gauge, but a 3 x 5kW set-up makes that nigh-on impossible. Something is going to be underutilized. Going back to my statement that the units have to be identical, that means you still have to put a 5kW inverter on a phase that may only use 2kW peak max.
That 3kW worth of idle inverter cost is best deployed elsewhere. - Cabling and switchgear requirements are more and, therefore, more expensive.
- It is understandable that, at this stage, you cannot visualize what a 15kW system looks like in terms of batteries and panels. Be it either 1ph or 3ph. There should be a number of panels and a number of batteries balanced with that 15kW of inverter capability. I think once you cut the coat to suit the cloth, your aspirations will tame.
There are probably, more good reasons, but I hope that is enough to convince you.