The most common question we get: “Should I go 6.6kW or 10kW?”
It’s a real decision because it changes your upfront cost by $1,500–$2,500, your daily generation by 30–40%, and how much of your bill you actually eliminate.
Here’s how to figure out which actually makes sense for your home.
The Basic Math: What’s the Difference?
6.6kW System
- Panels: 18–22 panels × ~330W each = ~6,600W total capacity
- Peak output: On a perfect sunny day, generates ~6.6 kW at peak (roughly 11am–1pm)
- Daily generation (Melbourne average): ~22–26 kWh on a clear day, ~12–15 kWh on an average day
- Cost: $5,500–$7,000 installed (after solar rebates)
- System size: Medium—suits most 3–4 bedroom homes
10kW System
- Panels: 30–31 panels × ~330W each = ~10kW total capacity
- Peak output: On a perfect sunny day, generates ~10 kW at peak
- Daily generation (Melbourne average): ~35–40 kWh on a clear day, ~18–24 kWh on an average day
- Cost: $7,500–$9,500 installed (after solar rebates)
- System size: Large—suits bigger homes or high-consumption households
The difference: 10kW generates roughly 50% more energy than 6.6kW, but costs only 30–35% more. Economies of scale.
Why 6.6kW Was the Standard (And Still Is)
For years, 6.6kW was the magic number in Australia because of export limits. Many homes can only export 5–6.6 kW back to the grid at any time. A 6.6kW system hits that ceiling, so all your peak generation can flow either to your home or the grid—nothing’s wasted.
A 10kW system exceeds that limit, so on perfect sunny days, you might cap out. However:
- It still generates 30% more energy overall (especially on cloudy days or mornings/afternoons)
- It’s increasingly standard as grid operators upgrade export limits
- Most newer homes in Melbourne can support 10kW export without issues
Real talk: Export limits matter less for customers with batteries or high daytime consumption. If you use power during the day (remote work, hot water heating, pool pump), a 10kW system uses more of its own generation instead of exporting it.
How to Actually Decide
The Key Question: What’s Your Quarterly Bill?
This is the real filter.
6.6kW is right if:
- Pre-solar bill is $200–$350/quarter
- You’re a light-to-moderate power user
- You work outside the home most days (less daytime consumption)
- You want lower upfront cost and simpler system
- You’re not considering a battery anytime soon
10kW makes sense if:
- Pre-solar bill is $350–$550/quarter
- You have high consumption (big family, multiple AC units, pool, hot water heating)
- You work from home or use power during daylight hours
- You plan to add a battery (bigger system = more to store)
- You want maximum bill reduction and future flexibility
Real Melbourne Examples
Example 1: David, Caulfield (4-bed, works away)
- Pre-solar bill: $280/quarter
- Household: Family of 4, but usually only home after 6pm
- Daytime loads: Minimal (heating/cooling off, kids at school, one person working away)
- Recommendation: 6.6kW
- Why: Your daytime consumption is low, so extra generation (from 10kW) would mostly export at lower rates
- Result: 6.6kW covers your evening load; you save money on reduced upfront cost
- Bill after solar: ~$60–$80/quarter (most consumption shifted to evening grid, or minimized)
Example 2: Priya, Northcote (4-bed, remote worker)
- Pre-solar bill: $420/quarter
- Household: Family of 4, two adults home during the day
- Daytime loads: High (heating/cooling running, remote work, cooking, hot water)
- Recommendation: 10kW
- Why: Your daytime consumption is real—a 10kW system will offset more of that high-consumption period
- Result: 10kW generates during the day when you’re using power; evening bill drops further
- Bill after solar: ~$100–$150/quarter (high daytime self-consumption)
- Note: If she adds a battery later, it’ll have more generation to store
Example 3: Marcus, Werribee (3-bed + pool)
- Pre-solar bill: $480/quarter
- Household: Couple, pool equipment runs daily
- Daytime loads: Very high (pool pump ~4 hours, heating/cooling, hot water heater)
- Recommendation: 10kW
- Why: Your pool alone creates high daytime consumption; 10kW maximizes self-use
- Result: Pool pump runs on solar generation; evening grid bill is low
- Bill after solar: ~$120–$180/quarter (pool fully solar-powered, evening use covered by stored solar)
- Plus: Future battery addition would pair well with 10kW generation
The Generation Reality: Melbourne’s Seasonal Variation
This is crucial and often overlooked. Melbourne’s weather is moody.
Summer (Dec–Feb):
- 6.6kW system: ~25–28 kWh/day average
- 10kW system: ~38–42 kWh/day average
- Clear days: Both systems hit their rated capacity; export limit might cap 10kW
Winter (Jun–Aug):
- 6.6kW system: ~10–13 kWh/day average
- 10kW system: ~15–20 kWh/day average
- Cloudy days: 10kW’s advantage shrinks but still wins
The difference is that 10kW pulls further ahead in winter (when 6.6kW falls short), but both are hampered by cloud.
For a 6.6kW system: You’re relying on grid power more in winter (a 10kW system would help). Budget for higher winter bills.
For a 10kW system: You still need some grid power in winter, but less. More consistent year-round.
Cost Per Kilowatt-Hour
Here’s a useful way to think about it:
6.6kW system:
- Cost: $6,500 / 6.6 = ~$985/kW
10kW system:
- Cost: $8,500 / 10 = ~$850/kW
The 10kW system is actually cheaper per kilowatt because you’re spreading infrastructure costs (wiring, inverter, installation) across more panels.
Over 25 years, that efficiency advantage is significant.
With a Battery: 10kW Wins
If you’re adding a battery (now or later), a 10kW system is better because:
- More generation during the day means more to store for evening
- A 10kW + 10kWh battery system is genuinely complementary (generates enough to fully charge the battery most days)
- A 6.6kW + 10kWh battery is slightly mismatched (some days the battery doesn’t fully charge)
If battery is even a possibility in your future, go 10kW.
Without a Battery: 6.6kW Can Be Fine
If you’re purely focused on solar (no battery), and:
- Your bill is moderate ($250–$350/quarter)
- You work away most days
- You want simplicity and lower cost
Then 6.6kW is genuinely fine. You’ll save money, keep your investment lean, and avoid overthinking it.
Grid Connection & Export Limits
Worth checking: Does your home have an export limit, and what is it?
Most Melbourne homes can export 5–10 kW. A 6.6kW system fits snugly. A 10kW system might hit limits on peak sunny days (meaning some generation gets curtailed, not utilized).
This is increasingly rare as the grid upgrades, but it’s worth a 30-second check with your network operator (Powercor, AusNet Services, Jemena, depending on your area).
We check this during site assessment, so it’s not something you need to worry about alone.
The Financial Truth
Choose 6.6kW if:
- You want lower upfront cost ($1,500–$2,000 savings)
- Your consumption is moderate
- You’re not considering a battery
Choose 10kW if:
- Your bill is high ($350+/quarter)
- You use power during the day
- You might add a battery later
- You want maximum long-term savings
The 10kW system costs more upfront but saves more over 25 years, especially as electricity prices rise.
One More Consideration: Roof Space
Both systems need roof space. 6.6kW typically needs 18–22 sqm. 10kW needs 30–35 sqm.
If your roof is shaded, small, or unusual, 6.6kW might be all that fits. That’s a real constraint, not a preference.
We assess roof space during site visits, so this isn’t a surprise later.
Bottom Line
For most Melbourne homes: 10kW makes more financial sense if your bill is over $300/quarter and you plan to stay 10+ years.
For modest-use homes or those on a tighter budget: 6.6kW is still perfectly valid and will absolutely save you money.
The difference isn’t “right vs. wrong.” It’s sizing to your actual consumption and long-term goals.
Next Steps
Book a free solar assessment. We’ll look at your bill, your roof, your consumption patterns, and your plans (battery? Stay 10 years?). Then we’ll recommend 6.6kW or 10kW with real reasoning—not just “go bigger.”
No pressure, no guesswork. Just the system that makes sense for your Melbourne home.
