6.6kW Solar System Costs, Output, Returns

6.6kW Solar System Overview

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If there’s a ‘standard’ solar system that is commonly sold in Australia, it’s a 6.6kW size, or commonly referred to in the industry as ‘a 6.6’. There’s a couple of reasons why the 6.6kW solar system has become so ubiquitous with solar system sizing in Australia.

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Firstly, a 6.6kW solar system is usually paired with a 5kW solar inverter. In most areas of Australia this is usually to the maximum solar inverter size allowed on a single phase installation without export limiting. Export limiting is where the DNSP (or distributor, ie. the company that owns/operates the poles and wires) limits how much you can feed back to the grid at any one time.

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Secondly, a 6.6kW system used to be a great option for most single phase homes (ie. most residential properties) when it came to drastically slashing their energy bills. I say used to be because in 2024 feed-in tariffs are lower than they’ve been historically, and we’re also using more electricity than ever before - especially as many households transition away from gas. So whilst a 6.6kW system might still be appropriate, it’s far from a ‘one size fits all’ solution - more on this later.

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What Is a 6.6kW Solar System, Really?

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Somewhat confusingly, the number quoted when it comes to solar system size is the total PV (solar panels) connected to the inverter.

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Thankfully, it’s a simple thing to calculate - simply multiply the number of panels by their rated power.

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For example, if you were using…

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…410W panels - 15x panels would equate to a 6.56kW system size

…420W panels - 15x panels would equate to a 6.3kW system size

…475W panels - 14x panels would equate to a 6.65kW system size

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The formula - if you’re a math nerd - is simply [Panel power (kW) each] x [Number of panels].

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So My System Is Close to but Not Exactly 6.6kW Total?

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You might be wondering how 15x 410 or 420 watt panels can be referred to as a 6.6kW system when they’re close to (but not exactly) 6.6kW total PV generation.

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Most of the time solar inverters are not rated to have more than 1.33 times the inverter output connected, and consequently the federal government will not allow any more than 1.33 times the inverter output for the purposes of claiming STC incentives.

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If the inverter’s rated output is 5kW this means that the maximum amount of PV that can be connected (and therefore STCs claimed) is 6.65kW.

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Going back to the 420W panel example used above to illustrate, if we connected 16x panels for a total of 6.72kW it would a) exceed the inverter manufacturer’s specifications for the amount of solar connected and b) prevent us from claiming STCs.

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Some people obsess over getting a panel size that allows you to get to 6.6kW or 6.65kW. We’d suggest that this is a bit of an overreach. Choosing a quality brand of panel and inverter is far more important than getting to exactly those numbers.

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Is a 6.6kW System Right for Me?

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The short answer is it depends.

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If your roof space is adequate, energy bills are within a certain range, and solar self-consumption potential is high enough, we can (and do) recommend 6.6kW solar systems to certain clients.

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However, if your bills are over (or under) a certain threshold, you’re limited in roof space, or you consume the vast majority of your energy at night time, a 6.6kW solar system may not be the right thing for you.