Solar quote options for high electricity usage

Hi all,

Context: I have just moved in to a house in Metro Melbourne 2 months ago. The house has underfloor slab heating which eats up a lot of electricity - we experimented with it a little bit and think during winter 80kw/day usage is on the higher end (and that’s only turning on the main zone!). I would like some guidance / opinions on the system size, inverter options and ballpark costs. Note that I have a 3 phase system.


  • Option 1: 10.73kW system, with 29x panels North and West facing, 1x 10kW inverter
  • Option 2: 13.32kW system, using 36x panels North, West, East facing, 2x 5kW inverters (due to 3 panel direction)
  • Option 3: 16.65kW system, using 45x(!) panels North, West, East facing, 1x 5kW and 1x 10kW inverter
    Question on options:
    a) What would be the ballpark price difference between each options?
    b) Does it make any financial sense to do option 3 as I assume the costs would be quite high?

To make a more informed decision, I’m trying to get comparable quotes across retailers by asking them to use similar products. It is hard though to ask them to give me prices for the 3 options above and with different products for the different options!

Solar panels - I’ve asked them to use the CER recommended ones, the ones put forward were Trina / Jinko / Canadian Solar / REC.

Solar inverters (remembering I have a 3 phase) - I’ve been given 3 options:

  1. Fronius Symo
  2. Sungrow SG5KTL-D
  3. Solaredge SE10K with the optimisers
    My questions on the inverters are:
    a) Is the Fronius much better than the Sungrow for the 3 phase models? How much more expensive are they as a ballpark? It seems hard to justify going with the Fronius with 5 year warranty (with additional 5 years for parts) compared to Sungrow’s 10 years.
    b) I assume that the SolarEdge is a more expensive option. I don’t have shading so am thinking either the Fronius or Sungrow should do the job well?
    c) Are there any other inverters I should consider for 3 phase?
    d) Is it worth considering adding a battery in the future when prices are cheaper seeing that I don’t generate enough solar for winter with the underfloor heating? Will batteries be compatible with all 3 of these inverters / is there anything I need to consider?

Thank you in advance!

First and foremost I would make sure the perimeter of the slab is insulated, unless you intend to heat the ground around the house. I have run across this here inVA

This is a simple heat transfer equation

we use Fronius exclusively and if you are considering adding batteries none of these will work. Grid tied /battery backup is a different type of inverter

Hi @sh33pz

You can check our ball park price using our Solar Calculator.

As long as you can comfortably afford the upfront cost, then whether it makes financial sense I would have thought depends on the payback period of your investment, and overall return on your investment. You can get a rough idea of those figure using the calculator as well.

Relative to the overall cost of the system, the cost of a Fronius vs Sungrow is not that great. We rate the Sungrow quite highly, but Fronius has the advantage of longevity in the market. It’s well regarded, and has runs on the board if you like.

Personally, I don’t think you need to consider other inverters than what you’ve mentioned.

Not sure what you mean here. If you don’t generate enough solar, then you won’t have any excess to store.

Either way, I would worry about that when it’s time. You can add batteries to these systems.

Hope that helps.