“How many panels do I need?” is the question that sounds simple but has a complicated answer.
Because the real question isn’t “how many panels?” It’s “how much solar capacity?” And that depends on your bill, your roof, and what you’re trying to achieve.
Let’s untangle this.
Panel Wattage: The Starting Point
Modern residential solar panels are typically 330–450 watts each. Most installers use 330W or 380W panels as standard.
So when we talk about system sizes, we’re translating kW into panel count:
- 6.6kW system: 18–20 panels (if using 330–370W panels)
- 10kW system: 26–31 panels (if using 330–380W panels)
- 5kW system: 15–16 panels
- 8kW system: 21–24 panels
The actual count depends on the panel wattage your installer uses. Higher-wattage panels (450W) mean fewer panels for the same capacity. Lower-wattage panels (300W) mean more.
But the number of panels isn’t the real measure. The total capacity (kW) is.
Why? Because two 6.6kW systems might use 18 panels from one brand and 22 from another, depending on panel efficiency. The output is the same; the panel count is different.
Let’s focus on capacity instead.
How Much Solar Do You Actually Need?
The core calculation:
Your quarterly bill ÷ 3 months = average monthly usage (kWh)
Average monthly usage × 25% = suggested solar capacity (kW)
Here’s the logic: A 1 kW solar system generates roughly 4 kWh per day in Melbourne (accounting for seasonal variation). That’s about 120 kWh per month.
If your bill shows 900 kWh per month, you need enough solar to offset 25–30% of that (roughly 225–270 kWh per month). That’s a 2 kW system at minimum, but most people want to offset 50%+ of their bill, which means 6.6–10 kW.
Real Melbourne Examples
Example 1: Imogen, South Yarra
- Quarterly bill: $340 (approx 2,550 kWh/quarter)
- Monthly average: 850 kWh
- Target: Offset 60% of bill
- 850 × 60% = 510 kWh to offset per month
- 510 ÷ 120 (kWh/kW/month) = 4.3 kW needed
- Recommendation: 6.6 kW system (18–20 panels at 330–370W)
- Result: Covers 60–70% of annual bill; saves ~$2,000/year
Example 2: Jasper, Toorak
- Quarterly bill: $520 (approx 3,900 kWh/quarter)
- Monthly average: 1,300 kWh
- Target: Offset 75% of bill
- 1,300 × 75% = 975 kWh to offset per month
- 975 ÷ 120 = 8.1 kW needed
- Recommendation: 10 kW system (26–30 panels at 330–380W)
- Result: Covers 70–80% of annual bill; saves ~$3,200/year
Example 3: Leah, Outer East
- Quarterly bill: $250 (approx 1,875 kWh/quarter)
- Monthly average: 625 kWh
- Target: Offset 50% of bill
- 625 × 50% = 312 kWh to offset per month
- 312 ÷ 120 = 2.6 kW needed
- Recommendation: 3–4 kW system (10–12 panels) OR 6.6 kW (if future-proofing for battery)
- Reality: A 3 kW system is smaller, cheaper, simpler. But 6.6 kW gives more flexibility
Why We Don’t Recommend “100% Offset”
Here’s the honest bit: Sizing to 100% offset your annual bill is usually a waste of money.
Here’s why:
Melbourne’s weather is seasonal. Summer’s sunny; winter’s cloudy.
A system sized to generate 100% of your winter consumption would massively overgenerate in summer. That excess? Exported to the grid at ~10 cents/kWh instead of saving you money.
The smart sizing: Cover 50–75% of your annual consumption with solar. Your system works hard year-round, you save on your biggest consumption periods, and you avoid oversizing.
In winter, you buy grid power (expected). In summer, you sell excess (bonus revenue). Over the year, the savings are optimal.
Roof Space: The Real Constraint
This is where panel count matters practically.
Each panel is roughly 1.6m × 1m (about 1.6 square meters).
- 6.6kW (18 panels): ~29 sqm of roof space needed
- 10kW (26 panels): ~42 sqm of roof space needed
Not all roofs can fit these. Factors that reduce available space:
- Roof pitch and angle (panels only work on sun-facing roofs)
- Shading (trees, buildings, vent pipes, skylights)
- Colorbond/tiled surface area
A north-facing roof without shading? You’ll fit the panels. A partially shaded east-facing roof? Space becomes tight.
This is why we do site visits. A 10kW system sounds good until we show you it only fits on a shaded east slope. Then 6.6kW on a clear north roof becomes the smarter choice.
Daily Generation Expectations (Melbourne)
Once you’ve got your system size, here’s what to expect for daily generation:
Summer (Dec–Feb) – Clear Days
- 6.6kW system: 25–28 kWh
- 10kW system: 38–42 kWh
Summer – Cloudy Days
- 6.6kW system: 10–15 kWh
- 10kW system: 15–23 kWh
Winter (Jun–Aug) – Clear Days
- 6.6kW system: 15–18 kWh
- 10kW system: 23–27 kWh
Winter – Cloudy Days (Common in Melbourne)
- 6.6kW system: 5–10 kWh
- 10kW system: 8–15 kWh
The pattern: Bigger systems win year-round, but the advantage shrinks in winter. Don’t expect consistent summer-level generation in June.
With a Battery: Sizing Changes
If you’re adding a battery, the calculation shifts.
Without battery: You offset bills through daily self-consumption + grid export at night.
With battery: You want enough solar to fill the battery and cover daytime use.
A rough rule:
- Battery kWh × 1.2 = suggested solar kW
So a 10kWh battery pairs well with a 12 kW solar system (or you make do with 10 kW and accept incomplete daily charges on cloudy days).
This is another reason 10 kW systems are increasingly popular—they pair naturally with 10 kWh batteries.
Common Mistakes in Panel Counting
Mistake 1: “I’ll just get 20 panels”
Reality: Panel count doesn’t matter; capacity does. 20 high-wattage panels might be a 9 kW system. 20 lower-wattage panels might be a 6 kW system. Always talk capacity, not count.
Mistake 2: “My neighbor has 25 panels, so I need 25 too”
Reality: Your neighbor’s roof, bill, and usage are different. Their system might be wrong for their home, too. Size to your consumption, not your neighbor’s system.
Mistake 3: “The installer said I need 30 panels, so that must be right”
Reality: Get a second opinion. Different installers use different panel wattages and design philosophies. Multiple quotes should all converge on similar capacity, even if panel counts differ.
Mistake 4: “I’ll oversize because energy costs will rise”
Reality: Oversizing costs upfront money now. That’s a bigger financial hit than relying on rising electricity costs. Size sensibly; let efficiency gains justify future upgrades.
The Panel Quality Question
Not all 330W panels are equal. Some are:
- Tier-1 panels (LG, Panasonic, SunPower, Jinko, Longi): Proven track records, better long-term degradation, better warranties
- Budget panels: Cheaper upfront, but degradation curves are steeper, warranties less robust
We use Tier-1 panels because over 25 years, the difference in degradation saves you real money. A $100 cheaper panel that loses 2% per year instead of 0.5% costs you thousands over the system’s life.
Your panel choice matters as much as your panel count.
Real-World Sizing Process
Here’s what we actually do:
- Get your bills (last 12 months)
- Calculate average monthly consumption
- Determine target offset percentage (usually 60–75%)
- Assess your roof (space, shading, aspect)
- Run simulations using Melbourne’s specific solar data and your home’s orientation
- Recommend capacity in kW (e.g., 8.8 kW)
- Translate to panel count based on your roof constraints (e.g., 23 × 380W panels)
- Show you the projected generation and bill savings for each season
It’s not a guessing game. It’s data-driven.
Bottom Line
You don’t need to think in panel counts. Think in system capacity (kW). Think in how much of your bill you want to offset (50–75% is smart). Think in your roof’s available space.
From there, panel count follows naturally—and it’ll vary depending on which panels we use.
Next Steps
Get a professional assessment. We’ll look at your bills, your roof, your shading, your weather patterns, and your long-term plans. We’ll recommend a capacity that makes sense.
Then we’ll tell you how many panels that translates to—and we’ll use quality, proven panels that’ll actually save you money over 25 years.
Book a free solar assessment. No commission-driven upsizing, no generic advice. Just real sizing for your Melbourne home.
