In Solar Maintenance

It’s one of the first questions you should ask when looking for solar: What size solar system should I get? This post will first dispel the “Goldilocks solar” myth of accurately sizing a solar system to match your daytime power consumption. I’ll then explain why for several years, a 5kW inverter with 6.6kW of panels had been our biggest seller. It sounds like one size fits all – right?
Next, I’ll explain how times are changing, and why in 2018, it is not uncommon that the best size solar system is just to cover the usable roof with solar panels



People often approach purchasing solar with Goldilocks wisdom. They know they don’t want a system that’s too small, and they don’t want to waste money on a system that’s too big.


This seems reasonable. Why would you waste money on an oversized system that you won’t ever use?

The problem with attempting to size a system with the aim of covering daytime usage only – is that there are so many seasonal solar production and household consumption variables. If your system is too small in one situation, it will be too big in another situation. But let’s say you monitor your usage and you somehow find that a 3kW size solar system will closely match your usage patterns from sunrise to sunset, and from mid-winter to Chrismas day. Not too big and not too small. So you get onto Google and type “3kW Goldilocks Solar System”. The first thing that comes up is this blog “what size solar system do I need?” (because I just coined the term.)

Our pricing page shows an indicative price:
(Prices current January 2019)



Don’t get me wrong, we could sell you an entry-level Solar system for $4200. Or you could pick up some nasty roof bling, AKA “solar land-fill” with a drive-away warranty for under $3000.
I’m comparing a good quality 3kW system to a good quality 6.6kW system. But why isn’t the 3kW size solar system around half the price of a 6.6kW system?

  • A 3kW Fronius inverter only costs about $200 less than a 5kW, because it’s essentially the same as a 5kW inverter with different programming and a different compliance stamp. It’s about economies of scale. Most inverter manufacturers do the same.
  • Every panel we install attracts a “rebate” (technically called an STC) so the more panels you put on, the bigger the “rebate” you get. At today’s rate, a 3kW size solar system will attract a $1910 “rebate” where a 6kW system will attract a $4250 “rebate”. (This is a point of sale discount so it is already factored into the system prices above.)
  • Installing a 3kW size solar system may take 6 hours for a team, installing a 6.6kW system may only take 8 hours. (All of the switchboard work and the cable run between the inverter and the panels has to be done either way).

So the only real cost of installing the larger system is 11 extra panels (that are largely paid for by the STC “rebate”), extra rail to mount panels on, a few hundred bucks for a 5kW inverter, and a couple of extra hours labour for the blokes on the roof.

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