6.6kW vs 10kW Solar: Which System Is Right for an Illawarra Home?

For most Illawarra homes in 2026, a 10kW solar system is the better choice over 6.6kW — even if your current bills suggest you "only need" a smaller system. The extra capacity costs about 35–40% more upfront but produces 50% more energy, pays back in a similar timeframe, and positions you for battery storage, EV charging, and rising grid prices. The 6.6kW system still has a place — just a narrower one than it used to.

Why 6.6kW Was the Default for So Long

The 6.6kW system became the "standard" Australian install for two reasons. First, it's the maximum size most single-phase homes can export to the grid under default Endeavour Energy and Essential Energy connection rules (5kW inverter with 6.6kW panels, a 30% oversizing ratio that's permitted by the Clean Energy Council). Second, it comfortably offsets the bills of a typical pre-2020 household with modest daytime usage.

Both of those assumptions have shifted. Endeavour Energy now routinely approves 10kW single-phase systems with export limiting, and household energy use has climbed as we've added EVs, heat pumps, ducted aircon and home offices. The result: a system that was "just right" in 2018 is often undersized in 2026.

Side-by-Side: What Each System Actually Produces

Assuming a north-facing tile roof in Wollongong with minimal shading:

6.6kW system:

• Panel count: 18–20 x 330–440W panels
• Inverter: 5kW (typically Fronius Primo or Sungrow)
• Annual generation: ~9,500–10,500 kWh
• Average daily generation: ~26–29 kWh
• Winter daily average: ~18–22 kWh
• Summer daily average: ~33–40 kWh
• Installed cost after STC: $6,800–$8,500

10kW system:

• Panel count: 24–28 x 400–440W panels
• Inverter: 8–10kW (Sungrow SH10, Fronius Symo, or similar)
• Annual generation: ~14,500–16,000 kWh
• Average daily generation: ~40–44 kWh
• Winter daily average: ~28–33 kWh
• Summer daily average: ~50–60 kWh
• Installed cost after STC: $10,800–$13,500

The 10kW produces 50% more energy at 35–40% higher cost. That's a better dollar-per-kWh return — but the story is more nuanced when you factor in feed-in tariffs vs self-consumption.

The Self-Consumption Question

Every kWh your solar produces goes one of two places: you use it yourself (worth 30–34¢), or you export it to the grid (worth 5–10¢). The more of your production you use directly, the faster you pay back.

Smaller systems tend to have higher self-consumption rates because there's less "excess" to export. A typical 6.6kW system in the Illawarra self-consumes 40–55% of its generation. A typical 10kW system self-consumes 30–45%. Without a battery, the 10kW produces more cheap exports.

Here's where it gets interesting. For a household using 22kWh/day:

• 6.6kW: ~12kWh self-consumed (worth ~$3.80/day), ~14kWh exported (worth ~$1.05/day). Daily benefit: ~$4.85
• 10kW: ~15kWh self-consumed (worth ~$4.80/day), ~27kWh exported (worth ~$1.95/day). Daily benefit: ~$6.75

The 10kW delivers ~39% more dollar benefit per day at ~40% higher cost — a wash on payback period, but substantially more lifetime savings. And if you ever add a battery, all that exported energy becomes self-consumed at full retail value, which is why battery-owners nearly always wish they'd installed the larger system.

When 6.6kW Is Still the Right Call

Despite the general case for going bigger, 6.6kW remains the correct choice in several real-world situations we see across the Illawarra.

Limited roof space. A 10kW system needs roughly 55–65 m² of unshaded, suitably-oriented roof. Smaller single-storey homes, apartments with dedicated roof access, and heritage homes with broken rooflines may not have it. If your installer would need to use east- or west-facing panels to reach 10kW, the extra generation may not justify the added complexity.

Very low bills. If your quarterly electricity bill is under $300 and will stay that way (no plans for EVs, heat pumps, or pool heating), your self-consumption ceiling is low. A 6.6kW system may be the right pragmatic choice.

Strict export limits. Some pockets of the Illawarra — particularly older parts of Woonona, Thirroul and some coastal suburbs with weaker grid infrastructure — are subject to export limits that cap your export at 5kW. This doesn't prevent a 10kW install, but it does reduce the marginal benefit of going bigger without a battery.

3-phase homes that want a 15kW+ system instead. If you have 3-phase power, the conversation isn't really 6.6kW vs 10kW — it's 10kW vs 15kW vs 20kW. In that case 6.6kW is rarely the best option unless roof space forces it.

Future-Proofing: Why 10kW Wins the Long Game

Even if your current bills don't justify 10kW, three trends make the bigger system look smarter with each passing year.

First, electricity prices keep rising. NSW retail rates have increased 3–5% annually for the last decade. Your 10kW system exports more energy at current tariffs, but every year those exports are worth more.

Second, home electrification is accelerating. EV adoption, induction cooking, heat pump hot water and ducted reverse-cycle aircon have all pushed up residential electricity usage. A home that consumed 15kWh/day in 2020 may easily consume 25–30kWh/day by 2028 with an EV added.

Third, batteries are getting cheaper and the Cheaper Home Batteries Program is active. The natural upgrade path for most Illawarra homes is solar now, battery within 2–3 years. A 10kW solar system pairs far better with a 10–13kWh battery than a 6.6kW system does.

The upshot: the incremental $3,500–$4,500 you pay to go from 6.6kW to 10kW today is almost always recovered over the life of the system — often well before the solar loan (if you've financed it) is paid off.

Use our free Solar Savings Calculator to see your personalised payback period.

Frequently Asked Questions

Can I install 10kW on a single-phase home in the Illawarra?

Yes, in most cases. Endeavour Energy and Essential Energy both permit 10kW systems on single-phase homes, typically with an 8–10kW inverter and export limiting if required. Some older parts of the grid (particularly in areas with heavy existing solar penetration) may restrict the inverter to 5kW export. Your installer will check your NMI and connection approval before quoting.

What if my bills don't justify a 10kW right now?

This is the most common concern — and often a misleading one. Current bills rarely predict future usage accurately, especially with EVs and home electrification on the horizon. If your roof supports 10kW, the marginal cost to install the larger system now is far lower than retrofitting extra panels later. Our standard advice: size for where you'll be in 5 years, not where you are today.

Do I need to upgrade my switchboard for 10kW?

Sometimes. A modern switchboard with RCBO protection typically accommodates 10kW without modification. Older switchboards (pre-2000) may need an upgrade — budget $800–$1,800 if so. We assess this during the site survey and include any upgrade in the quote.

How long does a 10kW installation take vs a 6.6kW?

Usually only a few extra hours. A 6.6kW install takes a two-person team one full day; a 10kW takes a three-person team one full day or two people 1.5 days. Both fit comfortably within a single installation appointment in the vast majority of cases.

Is a 13kW system a better choice than 10kW?

For 3-phase homes with big roofs, yes — 13kW is often the sweet spot. For single-phase homes, 10kW is the practical ceiling because of export and inverter constraints. If you're 3-phase and your roof can support 13kW without splitting across multiple awkward orientations, it's usually worth the extra $2,500–$3,500.

Ready to get your personalised quote? Contact our CEC-accredited team — we'll call you back within 5 minutes.