6.6kW vs 10kW Solar — Which Size Is Right for You?

6.6kW has long been the default solar system size in Australia, but 10kW is increasingly popular as homes electrify — adding heat pumps, induction cooking, batteries and EVs. Which is right for you? It comes down to how much power you use, when you use it, your roof, your phase supply, and your plans. This guide works through all of it, with the numbers.

The quick answer

• 6.6kW suits a typical household that uses a moderate amount of power and isn't planning a battery or EV soon.
• 10kW suits larger homes, all-electric households, or anyone adding a battery or electric vehicle — and it better covers Victoria's winter generation dip.

Generation and cost compared

	6.6kW	10kW
Annual generation (VIC)	~8,000–9,500 kWh	~12,000–14,500 kWh
Typical panels	~16–18	~24–28
Roof space needed	~30 m²	~45 m²
Installed price (after STCs)	~$4,000–$6,500	~$7,000–$9,500
Inverter	usually 5kW	usually 8–10kW

Because the federal STC discount scales with system size, the larger system earns a bigger dollar rebate — so the cost per kilowatt is often lower on the 10kW. You're not paying double for ~50% more power; you're typically paying around 50–70% more for 50% more capacity.

Five questions to size your system

1. How much power do you use? Check your bill's average daily usage (kWh/day). Under ~15 kWh/day leans 6.6kW; over ~20 kWh/day, or trending up as you electrify, leans 10kW. Heavy users — ducted air conditioning, a pool, electric hot water, an EV — want the bigger system.
2. When do you use it? Daytime usage favours self-consumption, which rewards a larger system. If the house is empty 9–5 and you won't shift loads, the extra generation mostly exports cheaply (unless you add a battery).
3. How much roof do you have? 6.6kW needs 16–18 panels (30 m²); 10kW needs 24–28 (45 m²). North-facing space is ideal, but east–west works well for spreading generation across the day.
4. Battery or EV on the horizon? If yes, go larger now and ask for a hybrid/battery-ready inverter — retrofitting later costs more.
5. What's your budget and payback goal? 10kW costs more upfront but usually delivers a better long-run return if you can use the extra generation. If you can't, the marginal panels just export at a few cents.

The inverter, clipping and the panel-to-inverter ratio

A "6.6kW system" usually pairs ~6.6kW of panels with a 5kW inverter — a common, rebate-friendly ratio (the rules allow panel capacity to exceed inverter capacity by up to a third, i.e. a 1.33 oversize ratio). This is deliberate: panels rarely hit their rated output, so a slightly smaller inverter is cheaper and still captures almost all the generation. On a handful of perfect midday hours the inverter may "clip" a little excess — a small, intentional trade-off that improves overall value.

A 10kW system needs a larger inverter (8–10kW). Keeping a sensible oversize ratio still applies, so a 10kW-panel system often pairs with an 8–10kW inverter. Your installer should explain the ratio and any clipping.

Export limits and network rules

This is where many 10kW decisions actually get made. Your local distribution network (in Victoria: AusNet, CitiPower, Powercor, Jemena or United Energy) sets export limits — how much you're allowed to push back to the grid. On single-phase supply this is commonly capped around 5kW per phase, and some areas are tighter.

The key insight: an export limit doesn't stop you using all your own generation — it only caps the surplus you export. So a 10kW system on a 5kW export limit still powers your whole home and charges a battery; you just can't sell more than 5kW back at any instant. Because export earns only a few cents anyway, this rarely changes the economics much — which is another reason self-consumption, not export, should drive a 10kW decision.

Single-phase vs three-phase

If you have three-phase power, larger systems are easier — you can often export more (e.g. 5kW per phase) and fit a bigger inverter without network friction. On single-phase, a 10kW system is still very doable, but you're more likely to meet an export limit. If you're renovating or have the option, three-phase is worth considering for an all-electric, battery-and-EV future. Don't install three-phase just for solar, but factor it in if it's already on the table.

Don't forget the winter dip

Victoria gets less winter sun than the northern states, and generation can roughly halve from summer to mid-winter. Sizing a little larger (closer to 10kW) helps cover the darker months, so even a moderate user can benefit from going beyond 6.6kW — the extra summer generation is a bonus, and the winter floor is higher. For an all-electric home that leans on the grid most in winter, this is a real argument for the bigger system.

A worked ROI comparison

Say you use 18 kWh/day and are home enough to self-consume 45%:

• 6.6kW (25 kWh/day summer, ~12 winter): covers your daytime use most of the year; modest export. Lower upfront cost ($5,500 after STCs), ~4-year payback.
• 10kW (38 kWh/day summer, ~18 winter): comfortably covers daytime use even in winter, leaves headroom for a future battery/EV. Higher upfront cost ($8,500 after STCs), similar or slightly longer payback — but far more future-proof and more total lifetime savings.

The 10kW's payback is similar precisely because the per-kW cost is lower and it generates more usable power in winter. If you're electrifying, the headroom usually wins; if your usage is modest and flat, 6.6kW is the value pick.

Self-consumption is the lever

Whichever size you choose, the return is dominated by how much of your own solar you use rather than export. With a 10kW system you generate more surplus, so the case for using it — via a heat pump on a daytime timer, daytime appliance scheduling, pre-cooling, and ultimately a battery — is even stronger. A 10kW system whose surplus all exports at 4c is poor value; the same system feeding a heat pump and a battery is excellent.

How to read a solar quote

• Panel brand and model (tier-1: Aiko, REC, LONGi, Q Cells) and the product + performance warranties.
• Inverter brand (Fronius, Sungrow, GoodWe, Enphase) and whether it's hybrid/battery-ready.
• A generation estimate specific to your roof (orientation, tilt, shading) — not a generic figure.
• Whether a switchboard upgrade is included if yours is older.
• The export limit that applies and how the system is configured around it.
• The after-rebate price and the rebate breakdown (STCs + any Solar Homes rebate).

What about 13.2kW and beyond?

For big roofs, all-electric homes with an EV, or where you want maximum battery-charging headroom, 13.2kW follows the same logic as 10kW — more so. The per-kW cost keeps improving, but export limits and inverter sizing become more important, and three-phase is often preferable. If you genuinely use or store the generation, bigger keeps paying; if you don't, you're funding cheap exports.

FAQ

Can I start at 6.6kW and add panels later? You can, but it's rarely economical — a second install means a second set of fixed costs (scaffolding, electrician, paperwork) and may require an inverter change. Size for the next few years now.

Does a bigger system void anything or need approval? No, but a 10kW+ system is more likely to need network approval for export and possibly a switchboard upgrade. Your installer handles the paperwork.

Will an export limit waste my generation? No — you still use all of it yourself and can charge a battery; the limit only caps the surplus you export, which earns little anyway.

Is 10kW overkill without a battery? Not if you self-consume well (daytime loads, heat pump on a timer) or cover a winter-heavy all-electric load. If you export most of it, 6.6kW may be the better-value choice.

Single-phase — can I still get 10kW? Usually yes, often with a ~5kW export limit. You keep the self-consumption benefit; you just can't export more than the cap at once.

Which matters more, panels or inverter? Both — but the inverter is the part most likely to need replacing within the system's life, so don't skimp on it.

Roof orientation, tilt and shading

System size is only half the story — where the panels go determines how much of that capacity you actually harvest.

• North-facing panels produce the most total energy across the day and peak around midday. Best for maximising generation and for households that can shift load to the middle of the day.
• East–west split sacrifices a little total output but spreads generation across the morning and afternoon — often a better match for a household that uses power before work and after it, and it can help dodge an export-limit ceiling by flattening the midday peak.
• West-only is worth considering if your highest use is late afternoon (it pushes generation later), though total output is lower than north.
• Tilt in Victoria is typically 20–30°; most roofs are close enough that tilt frames are rarely needed except on flat roofs.

If your roof faces awkwardly, that's an argument for a larger system: more panels compensate for a less-than-ideal orientation, and the per-kW cost advantage of 10kW helps offset the lower per-panel yield.

Shading is the silent killer of solar returns. Even partial shade on one panel can drag down a whole string with a standard string inverter. If you have trees, a chimney, a neighbour's roofline or vents casting shade, ask about microinverters (Enphase) or DC optimisers, which isolate each panel so one shaded module doesn't penalise the rest. They cost more but can pay for themselves on a shaded roof — and they make a larger system viable where shade would otherwise waste it.

Panel degradation: the 25-year view

Panels don't last forever at full output, but quality ones come close. Tier-1 panels typically guarantee around 0.4–0.5% degradation per year, so a panel rated 100% today is still warranted to produce roughly 85–90% at year 25. Budget panels degrade faster and may use weaker warranties, which is where a cheap 6.6kW system can quietly underperform a quality one over its life.

This is why the size decision and the quality decision interact: a 10kW system of mediocre panels can end up generating little more than a 6.6kW system of excellent ones after 15 years. Choose the brand and warranty first, then the size — and compare lifetime generation, not just day-one watts.

What the switch looks like on your bill

It helps to picture the before and after. A typical household on ~$2,200/year of grid electricity might see:

• 6.6kW, 45% self-consumption: grid bill falls to roughly $800–$1,100/year (plus small export credits) — a saving around $1,100–$1,400.
• 10kW, 45% self-consumption + winter cover: grid bill falls to roughly $500–$900/year, with more surplus available to feed a heat pump or future battery.

Add a battery and a heat pump on a timer, and the bill can shrink toward the daily supply charge alone for much of the year. The exact figures depend on your tariff and habits, but the shape is consistent: bigger systems plus self-consumption plus electrification compound into a much smaller bill.

Sizing solar and a battery together

If a battery is on your roadmap, size them as a pair rather than in isolation. A rough rule: you want enough daytime surplus to fill the battery and still cover daytime load. A 6.6kW system often can't fill a 13.5kWh battery and run the house on a short winter day; a 10kW system can. So households planning a battery frequently land on 10kW (or more) precisely to keep the battery fed year-round.

The order also matters financially: solar first (it has the fastest payback), then a battery once you have surplus to store and the federal Cheaper Home Batteries Program discount in hand. Specifying a hybrid or battery-ready inverter now — even if the battery comes later — avoids paying to replace the inverter down the track.

A note on larger and commercial systems

Beyond residential, 15kW+ systems enter commercial territory with three-phase requirements, different metering, and commercial STC/LGC considerations. For a home, 13.2kW is usually the practical ceiling before you're constrained by roof space, export limits and switchboard capacity. If you're running a home business with heavy daytime load (workshop, server room, multiple EVs), it's worth a tailored design rather than a standard residential package.

Red flags in a solar quote

A few things should make you pause before signing:

• Mystery-brand panels or inverter. If the quote won't name the exact panel and inverter model, walk away — you can't assess quality or warranty.
• "Today only" pricing. High-pressure, time-limited discounts are a classic solar sales tactic; a good system is still a good deal next week.
• Full payment upfront. A deposit is normal; the full amount before installation is not.
• No generation estimate for your roof. A generic figure (rather than one based on your orientation, tilt and shading) suggests a cookie-cutter sell.
• No mention of export limits or switchboard. On a 10kW system these matter; silence on them is a sign of a rushed quote.

Common sizing mistakes to avoid

• Sizing to your roof instead of your usage. A roof that fits 10kW doesn't mean you should fill it — if you can't use or store the generation, the extra panels just export cheaply. Start from your kWh/day and your daytime habits.
• Ignoring the winter dip. Sizing tightly to summer leaves you short in June–August. A little headroom keeps winter covered.
• Forgetting the battery/EV plan. Installing 6.6kW now and adding a battery or EV in two years often means wishing you'd gone 10kW. Size for the next few years.
• Skimping on the inverter. The inverter does the hard work and is the most likely component to need replacing — a quality unit is worth it on either system size.
• Choosing on price-per-system, not value-per-kWh-over-25-years. Cheap panels on a big system can underperform quality panels on a smaller one over the long run.

Avoid these and the 6.6kW-vs-10kW decision usually answers itself based on your real usage and plans.

Key takeaways

• 6.6kW = great value for a modest, stable household that won't shift much load to daytime.
• 10kW = the smarter pick if you're electrifying (heat pump, battery, EV) or want to cover the winter dip — and the per-kW cost is lower.
• Self-consumption beats export every time; size and habits should maximise using your own power.
• Export limits don't waste generation — you still use it all yourself and can store it in a battery.
• Quality first, then size: tier-1 panels and a good inverter outlast and out-generate a bigger system of budget gear.

The bottom line

If you're electrifying — adding a heat pump, battery or EV — 10kW is usually the smarter long-term choice, and the per-kilowatt cost is friendlier than people expect. If your usage is modest and stable and you won't shift loads to daytime, 6.6kW remains excellent value. Get quotes for both sizes with a generation estimate for your specific roof, confirm the export limit and any switchboard work with your installer, and compare the payback — and the lifetime savings, not just the upfront price — on each.