Three phase vs single phase inverters

I’m in the process of getting quotes on the installation of solar panels. I have decided to go with SunPower E20 327 panels and a Fronius inverter. I am still to decide if I will go for a 4 Kw system on the north facing roof or a larger 6Kw system by adding an extra 2Kw on the west facing roof.
I have 3 phase power to the house.
My first question is do I need to go with a 3 phase inverter or can I go with a single phase inverter? What are the pros and cons of each?

I assume if I go with the 4Kw system I use a 3Kw inverter and a 5Kw inverter with the 6Kw option.

If I was to decided to go with the 4Kw option with the idea of adding the extra 2Kw later can I use a 5Kw inverter with the initial 4Kw installation

Hi Roger, you can go with a single phase inverter. It really depends on what you have connected on each phase as to what will work better I believe. If unsure, it would be best to discuss with an electrician, preferably you should get an electrician to quote your solar and they should be able to assess if best to use 3 phase or single phase inverter.

You can oversize the inverter by 30%, and there’s often good reason to do so. Fronius does a 3.5kW inverter which is probably better suited, or a 4kW inverter Is fine on a perfect nth facing roof with no shade. There’s some details here in the Guide To Going Solar eBook on oversizing the inverter:

I would strongly recommend making a decision now about whether you want 6kW or 4. If in doubt, go for 6 I think, but no, I wouldn’t recommend getting a 5kW inverter to upgrade later, it just gets messy. Plus labour cost is the big killer, getting it all done in one hit will be far cheaper.

Hope that helps.

Hi Marty

Thanks for the advice. I very much appreciate the time you put into help people like me out



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I am not familiar with you guys down under but do you actually have three phase power as far as oversizing the inverter we always put in a larger inverter and a larger wire size to accommodate future expansion use the 6 KW fronius which we use exclusively fronius the Primo has the data manager built in and not a bolt on later the data manager let you see your system via the Internet on the fronius website you need to correctly size the inverter for any future needs solaredge claims their inverters will go 30% higher then the name plate value I have had 3 inverters burnout as a result of that

When we first started out years ago we put in smallest systems almost everyone came back and wanted to increase the size of their system now we always oversized The Wire and the inverter it is not that much more at this point