How Much Solar Do You Actually Need? A Step-by-Step Sizing Guide

If you're considering solar for your home, one of the biggest questions is also the most straightforward: how much solar do you actually need? With electricity prices rising across Australia and new energy incentives emerging - including initiatives like the newly launched federal Cheaper Home Batteries Program - more households are looking to make informed decisions about their solar system size. Getting this right ensures you produce enough clean energy to reduce bills while avoiding unnecessary system size (and cost).

This step-by-step guide breaks down exactly how to calculate the right solar setup for your home, taking into account energy usage, roof space, budget, and future energy needs.

Start With Your Electricity Usage

Your electricity bills are the best starting point for sizing your solar system. Look at the "average daily usage" section, usually measured in kWh.

For most households:

• Small households (1-2 people): 8-12 kWh/day
• Medium households (3-4 people): 13-20 kWh/day
• Large households (4+ people or high appliance use): 20-30+ kWh/day

Record your:

• Average daily usage
• Seasonal changes (summer vs winter)
• Peak daytime consumption

This forms the foundation of your solar calculation.

Convert Your Usage into Solar System Size

A simple rule of thumb is:

1 kW of solar generates about 4 kWh of electricity per day (on average across Australia).

Using this rule:

• 5 kW system → ~20 kWh/day
• 6.6 kW system → ~26 kWh/day
• 10 kW system → ~40 kWh/day

To size your system:

Required system size (kW) = Your daily usage (kWh) ÷ 4

Add a buffer if you plan to electrify more of your home-such as hot water, heating, EV charging, or a pool.

Consider Your Daytime vs Night-time Usage

Solar panels only generate energy during sunlight hours, so consider how much of your usage happens during the day.

• High daytime usage: washing machine, dishwasher, pool pump, home office → you'll self-consume more solar, boosting bill savings.
• High night-time usage: cooking, heating, TV, EV charging → a battery may greatly improve your solar ROI.

If you're planning ahead for storage, you may choose a slightly larger system so you can generate enough energy to fill a battery consistently.

Assess Your Roof Size and Panel Layout

Roof space limits how large your system can be. Typical modern solar panels are around 1.8 m x 1.1 m and produce 400-440W each.

Approximate roof space required:

• 6.6 kW (15-18 panels): ~30-35 m²
• 10 kW (22-26 panels): ~45-55 m²

Also consider:

• Roof orientation (north-facing ideal, east/west still excellent)
• Shading from trees, chimneys, or neighbouring properties
• Structural integrity and tilt

Installers can use mapping software to check how much usable roof space you have.

Factor In Local Solar Conditions

Australia is one of the sunniest countries in the world - but generation varies by region.

Average daily solar production:

• Brisbane / Perth / Darwin: 4.5-5.5 kWh per kW
• Sydney / Adelaide: 4-5 kWh per kW
• Melbourne / Hobart: 3-4 kWh per kW

If you live in a lower-sunlight region, you may need a slightly larger system to achieve the same output.

Decide Whether You Want to Add a Battery

While a battery isn't essential, it can significantly increase your energy independence.

A battery may be right for you if:

• You use a lot of electricity at night
• You want backup power during outages
• You plan to maximise your return from solar
• You intend to participate in a Virtual Power Plant (VPP)
• You want long-term bill stability

With government support like the newly launched federal Cheaper Home Batteries Program, storage is becoming far more accessible - making it a smart long-term investment for many households. For battery-ready systems, consider sizing slightly larger (e.g., 8-10 kW) to ensure ample solar generation for charging the battery year-round.

Balance System Size with Budget

Solar is incredibly cost-effective today, but it's still important to match your investment to your needs.

Typical system costs (approximate):

• 6.6 kW: $4,500-$8,000
• 10 kW: $8,000-$12,000
• Battery add-on: $7,000-$15,000 depending on size and brand

The best value is usually achieved by:

• Maximising self-consumption
• Installing the largest system that fits your roof + budget
• Planning for future electrification (EVs, reverse-cycle heating)

Think About Future Energy Needs

Solar systems last 20-30 years. It's wise to consider future changes, such as:

• Buying an electric vehicle
• Switching from gas to electric appliances
• Adding a pool or spa
• Working from home more regularly

Sizing up slightly now can save you from needing costly upgrades later.

Recommended System Sizes Based on Lifestyle

Here's a rough guide based on common household scenarios:

Household Type	Typical Daily Use	Suggested Solar Size
Apartment / very small home	6-10 kWh	3-5 kW
Small family	10-15 kWh	5-6.6 kW
Medium family	15-20 kWh	6.6-8 kW
Large home / high usage	20-30+ kWh	8-10 kW
EV owners / electrified homes	25-40+ kWh	10-13 kW

Sizing your solar system doesn't need to be complicated

With a clear look at your household usage, roof capacity, and future needs, you can design a setup that's efficient, cost-effective, and built for long-term energy independence.