Solar System Size Calculator Guide: How Many kW of Solar Do You Really Need?

1. Your annual electricity consumption

This is the most important starting point. Look at your electricity bills and find your annual usage in kWh. If your bill says you use 5,000kWh per year, that gives a much better basis for system sizing than simply saying: "My electricity bill is $250 a month." Electricity prices vary between retailers and plans, so two households with similar bills can have different energy consumption.

Our recommendation: If you know your annual kWh usage, use that figure when using a solar calculator. If you don't know it, your electricity bill can still be used to estimate consumption.

2. When you use electricity

This is where solar sizing becomes more interesting. Imagine two households that both use 6,000kWh per year. House A uses most of its electricity during the day. House B uses most of its electricity between 5pm and 10pm. They may have the same annual consumption, but their solar requirements and battery opportunities can be quite different. Daytime-heavy household: Solar can directly supply appliances while the panels are generating electricity. Evening-heavy household: A greater proportion of solar generation may need to be stored in a battery or exported to the grid for later use. So when sizing solar, don't look only at "How much electricity do I use?" Also ask: "When do I use it?"

3. Your roof

Your electricity consumption might suggest a 13.2kW system, but your roof may not have enough suitable space. Roof considerations include usable roof area, roof orientation, pitch, shading, skylights, vents, chimneys, multiple roof sections, structural considerations, access, and existing solar panels. A site assessment is therefore still important even when an online calculator gives you a useful starting point.

4. Your location

Solar generation differs across Australia. A system installed in Melbourne won't necessarily generate the same amount of electricity as the same-sized system installed elsewhere. That's why a useful solar calculator needs to account for location rather than applying one national generation number to every home.

6.6kW Solar System

A 6.6kW system is a common option for Australian homes. It can make sense for smaller households, moderate electricity consumption, homes with suitable roof space, customers looking to reduce daytime grid electricity use, and households that may add a battery later.

Choose 6.6kW if: your electricity usage is relatively moderate, you don't have major future loads, your roof space is limited, or your energy requirements don't justify a larger system. However, don't automatically choose 6.6kW simply because it is common.

10.56kW Solar System

A 10.56kW system can provide a larger generation base for households with greater electricity requirements. It can be worth considering for family homes, higher electricity consumption, work-from-home households, homes with significant daytime usage, households planning battery storage, and homes expecting future energy loads.

For many families, this can provide a useful middle ground between a smaller residential system and a high-capacity installation.

If you're a small household

You may not need a very large system. Start with: Your annual kWh usage + roof suitability. A 6.6kW system may be worth investigating if your consumption is moderate and the roof is suitable.

If you're a typical family home

Your electricity usage may be higher because of multiple refrigerators, heating and cooling, washing/drying, cooking, hot water, children's appliances, and longer operating hours. A system around 10.56kW may be worth considering depending on actual annual consumption and roof space.

If you work from home

Working from home can increase daytime electricity consumption. That's actually useful for solar because your household may be consuming electricity while the panels are producing it. For example: Solar generation → home office → air conditioning → appliances can increase direct solar consumption and reduce the amount of electricity purchased from the grid.

If you have an EV

An EV changes the calculation. Instead of treating your vehicle as separate from your home energy system, consider its electricity requirements alongside your household consumption. For example: Home electricity + EV charging = total future electricity demand. If you regularly charge at home during daylight hours, solar can potentially supply part of that charging directly. If you charge mainly at night, a battery or suitable energy-management strategy may become more relevant.

Household:
- Location: Melbourne, Victoria
- Occupants: 4
- Annual electricity use: 8,000kWh
- Existing solar: None
- EV: Yes
- Future battery: Yes
- Main goal: Reduce electricity purchases

This household shouldn't simply say: "I need 8,000kWh of solar." Solar panels don't produce their rated capacity continuously. Instead, we need to estimate how much electricity a particular system can generate at the property.

Suppose the planning calculation indicates that a 10.56kW system is a suitable starting point. The next question becomes: How much of that generation will the household use directly? If the family uses a substantial amount of electricity during the day, direct solar consumption could be relatively strong. If most of the household's electricity use happens after sunset, a battery could become more valuable.

Important: The figures above are an illustrative planning scenario, not a guaranteed Samsun Energy quote or guaranteed savings figure.

Example: Smaller Melbourne Household

- Annual electricity use: 4,000kWh
- No EV, no pool, moderate air-conditioning use
- Daytime occupancy: Moderate
- No major future loads

A 13.2kW system may be unnecessary. A smaller system could potentially provide a better match between generation + consumption + roof space + investment. The correct answer comes from the household's actual energy profile.

Choose 6.6kW if...

• ✔ Your household electricity consumption is moderate
• ✔ You have limited suitable roof space
• ✔ You don't have significant future electricity loads
• ✔ You want a straightforward residential solar system

Consider 10.56kW if...

• ✔ You have a family household
• ✔ Your electricity consumption is moderate-to-high
• ✔ You work from home
• ✔ You have higher daytime energy demand
• ✔ You are considering battery storage
• ✔ You expect electricity consumption to increase

Is 6.6kW enough for a house?

It can be, particularly for a smaller or moderate-energy household. However, the right size depends on annual electricity consumption, roof conditions and future energy requirements.

Is 10.56kW solar better than 6.6kW?

Not automatically. A 10.56kW system generates more electricity, but whether that makes financial sense depends on how much electricity your household uses and when you use it.

How do I calculate what size solar system I need?

Start with your annual electricity consumption in kWh, then consider your location, roof, energy-use patterns and future loads such as an EV or heat pump.

Should I get 13.2kW solar?

A 13.2kW system may make sense for a high-energy household or a home with significant future electricity demand. It shouldn't be selected solely because it is a larger system.

Does an EV change the solar system size I need?

Yes. Regular home EV charging adds electricity demand and should be included when planning your solar system.

Should I install a battery at the same time?

It depends on your energy usage, solar generation, electricity tariff, battery economics and backup requirements. If a battery is part of your future plan, it is sensible to consider it during solar system design.