Solar System Sizing Guide: How Much Solar Do You Really Need?

One of the most common questions: "What size solar system should I get?" The answer depends on your electricity usage, roof space, and budget. This guide helps you calculate the perfect system size.

Quick System Size Calculator

Based on Your Electricity Bill

Quarterly Bill → Recommended System Size:

Average Australian Household

The 6.6kW System: Most popular choice for Australian homes:

• Generates: 24-27 kWh per day (Sydney average)
• Covers: Typical 3-4 bedroom home
• Cost: $4,000-$6,000 installed (after rebates)
• Payback: 4-6 years

Step-by-Step Sizing Process

Step 1: Find Your Daily Usage

Check Your Electricity Bill:
Look for "Total Usage" in kWh over the billing period.

Example Calculation:

• Quarterly bill shows: 1,800 kWh used
• Days in quarter: 90
• Daily average: 1,800 ÷ 90 = 20 kWh/day

No Bill Handy? Australian household averages:

• 1-2 people: 12-18 kWh/day
• 3-4 people: 20-25 kWh/day
• 5+ people: 30-40 kWh/day

Step 2: Calculate Generation Needed

Simple Rule: Size your system to generate 80-100% of your daily usage.

Why not 100%+?

• Self-consumption is key (export rates are low)
• Seasonal variation means summer overproduction
• Battery storage changes this calculation

Example:

• Daily usage: 25 kWh
• Target generation: 20-25 kWh
• System needed: 6.6-8 kW

Step 3: Check Your Roof Space

Space Required per kW:

• Modern panels (2025): 5-7 m² per kW
• 6.6kW system: 35-45 m²
• 10kW system: 50-70 m²

Optimal Orientation:

• Best: North-facing
• Good: East or West-facing (90-95% of north)
• Okay: North-East or North-West
• Avoid: South-facing (60-70% of north)

Tilt Angle:

• Optimal = Your latitude (Sydney: 34°, Melbourne: 38°)
• Roof pitch 15-35° works well for most locations
• Flat roofs need tilt frames

Step 4: Consider Your Usage Pattern

When Do You Use Power?

Scenario 1: Home During Day

• Usage: 60-70% during daylight hours
• Recommendation: Standard system (6.6kW)
• Self-consumption: 60-70%
• Battery: Optional

Scenario 2: Work During Day

• Usage: 70-80% evening/night
• Recommendation: Smaller system (5kW) + battery
• Self-consumption: 30-40% without battery
• Battery: Highly recommended

Scenario 3: Pool/Aircon

• Usage: High daytime demand
• Recommendation: Larger system (8-10kW)
• Self-consumption: 70-80%
• Battery: Less critical

System Size Limitations

Physical Limits

Single-Phase Homes:

• Maximum export: Usually 5kW (varies by network)
• System size limit: Typically 10kW inverter
• Reality: Can install larger panel array on 10kW inverter

Three-Phase Homes:

• Maximum export: Usually 15kW (5kW per phase)
• System size limit: Up to 30kW in some areas
• Advantage: More flexibility for large systems

Network Connection Rules

Before Installing 10kW+:

• Contact your Distribution Network Service Provider (DNSP)
• May need export limitation
• Some areas have waiting lists
• Application fees may apply

System Size vs. Cost Analysis

Price per kW (2025 Prices After Rebates)

Sweet Spot: 6.6kW offers best value per watt for most homes.

Common Sizing Mistakes

Mistake #1: Oversizing

Problem: Installing 10kW when you only use 15 kWh/day

• Wasting money on excess capacity
• Low export rates (5-10c/kWh)
• Longer payback period

Solution: Size for self-consumption, not maximum roof capacity

Mistake #2: Undersizing

Problem: Installing 3kW when you use 25 kWh/day

• Minimal bill reduction
• Opportunity cost of roof space
• Will wish you went bigger

Solution: Go as large as budget allows (within reason)

Mistake #3: Ignoring Future Needs

Problem: Not considering upcoming changes

• Adding electric vehicle
• Installing pool
• Working from home
• Growing family

Solution: Size for 3-5 year future needs, not just today

Special Scenarios

Planning to Add EV

EV Charging Adds:

• Tesla Model 3: 10-15 kWh per day (12,000 km/year)
• Average EV: 12-20 kWh per day

Recommendation:

• Without solar: Add 6.6kW+ system
• Existing solar: Upgrade or add 3-5kW
• Best: Charge during day with solar

Have a Pool

Pool Pump Usage:

• Standard pump: 2-4 kWh per day
• Energy-efficient: 1-2 kWh per day
• Run during solar generation times!

Recommendation: Run pool pump 10am-3pm to use solar

Working From Home

Additional Usage:

• Heating/cooling all day: +5-10 kWh/day
• Office equipment: +1-2 kWh/day
• More cooking: +1-2 kWh/day

Recommendation: Add 2-3kW to standard sizing

Should You Oversize?

Yes, if:

• Planning to add EV
• Have three-phase power
• Battery planned for later
• Want to maximize roof value
• Feed-in tariff is decent (8c+)

No, if:

• Limited budget
• Single-phase export restriction
• Very low feed-in tariff (< 5c)
• Roof orientation is poor
• May move house soon

Adding Battery Changes Everything

With Battery Storage

You Can:

• Use all solar generated
• Size system larger (store excess)
• Achieve 80-90% energy independence

Sizing With Battery:

• System size: 1.5-2x daily usage
• Battery size: 70-100% of daily usage
• Example: 25 kWh/day usage = 10kW solar + 13.5kWh battery

Without Battery

Best Approach:

• Size for daytime self-consumption
• Export excess at low rates
• Aim for 60-70% self-consumption

Real Examples

Example 1: Young Couple, No Kids

• Usage: 15 kWh/day
• Pattern: Home evenings/weekends
• Recommendation: 5kW system
• Reasoning: Covers weekend usage well, modest export

Example 2: Family of 4, Both Work

• Usage: 28 kWh/day
• Pattern: Evening peak
• Recommendation: 6.6kW + 10kWh battery
• Reasoning: Battery stores day generation for evening use

Example 3: Retiree Couple, Home All Day

• Usage: 22 kWh/day
• Pattern: Consistent all day
• Recommendation: 8kW system
• Reasoning: High self-consumption, can use all generation

Example 4: Large Family + Pool

• Usage: 45 kWh/day
• Pattern: High all-day usage
• Recommendation: 13kW system + battery
• Reasoning: Maximize generation, battery for evening

Your Action Plan

Step 1: Calculate Your Usage

Find average daily kWh from recent bills

Step 2: Assess Your Roof

Measure available space and orientation

Step 3: Consider Future Plans

EV? Pool? Home office? Kids?

Step 4: Set Your Budget

Realistic budget for system and possible battery

Step 5: Get Quotes

3-4 quotes with different size options

Step 6: Compare Options

Don't just pick cheapest - compare per-watt pricing

Use Our Calculator

Want personalized sizing recommendations? Use our Solar Calculator - it factors in:

• Your location and sun hours
• Roof orientation and tilt
• Electricity usage patterns
• Shading analysis
• Budget considerations

Bottom Line

For Most Australian Homes:

• 3-4 people, typical usage: 6.6kW system
• Budget tight: 5kW minimum
• Want to future-proof: 8-10kW system
• Adding battery: 8kW+ recommended

Remember: Installation quality and panel choice matter more than getting the exact size perfect. A slightly smaller quality system beats an oversized cheap one every time.

Start planning your solar system with our Solar Calculator today!