What Size Solar System Do I Need? An Australian Home Guide
As more Australian homeowners adopt solar energy, many ask, “What size solar system do I need for my home?” Without clear guidance, they risk choosing a system that generates too little electricity for their household needs or is unnecessarily large and expensive. Future additions such as an electric vehicle, a heat-pump hot-water system or extra air conditioning can also increase household electricity demand. This guide walks you step by step to match your real power needs with the right solar system size.
What Determines the Right Solar System Size?
The right solar system size depends on how much electricity your home uses, when you use it, and how suitable your property is for solar.
Daily Electricity Use
Your average daily electricity use provides the starting point for system sizing. Review a full year of bills so seasonal heating and cooling demand are included.
Also consider:
high-use appliances such as air conditioners and pool pumps
changes in household size
expected future electricity demand
Daytime Versus Evening Use
Solar panels generate electricity during the day. Homes that use more power during daylight hours can usually consume more solar electricity directly.
Common daytime loads include:
washing machines and dishwashers
pool pumps
air conditioners
home office equipment
heat-pump hot-water systems
Homes with high evening use may still need grid electricity after sunset unless they shift appliance use or add battery storage.
Location and Solar Exposure
Solar output varies across Australia. The same system may produce different amounts of electricity depending on:
local solar exposure
seasonal weather
panel temperature
roof orientation
shading
Use a property-specific production estimate rather than relying on one national average.
Roof Space, Orientation and Shading
The usable roof area affects how many panels can be installed. Installers should assess:
roof size and condition
panel dimensions
roof pitch and orientation
shade from trees or nearby buildings
chimneys, skylights and other obstructions
North-facing panels generally provide strong annual output in Australia. East-facing panels favour morning generation, while west-facing panels produce more later in the day.
Budget and Export Limits
A larger system costs more and may export more electricity than your household can use.
Compare:
installation cost
expected self-consumption
feed-in tariff
estimated annual savings
available Small-scale Technology Certificates
Your local electricity network may also limit inverter capacity or solar exports, so these restrictions should be checked before installation.
Future Electricity Loads
Allow for planned increases in demand, such as:
an electric vehicle
heat-pump hot water
induction cooking
extra air conditioning
a swimming pool
Discuss these loads before choosing the inverter and panel layout, as future expansion may be limited by roof space, equipment compatibility and network rules.
How to Calculate What Size Solar System You Need
To estimate what size solar system you need, compare your household’s daily electricity use with the expected output of a system in your location. The following steps provide a practical starting point, but the final size should be based on a site-specific assessment.
Step 1: Calculate Your Average Daily Electricity Use
Check your electricity bills to find the total electricity consumption for each billing period, measured in kilowatt-hours (kWh). Divide this figure by the number of days covered by the bill.
For example:
Quarterly electricity use: 1,350kWh
Billing period: 90 days
Average daily use: 1,350 ÷ 90 = 15kWh per day
Use bills from the past 12 months where possible, as heating and cooling can cause significant seasonal changes. Smart-meter data can also show how much electricity you use during solar-generating hours.
Step 2: Set Your Target Solar Generation
Your solar system does not necessarily need to generate the same amount of electricity as your home uses every day. Before choosing a system to generate electricity at home, consider how much of your household consumption you want solar to offset.
For example, a home using 20kWh per day might target:
12–15kWh if the goal is mainly to reduce daytime grid use
around 20kWh if the goal is to offset most annual consumption
more than 20kWh if future loads, such as an electric vehicle, are expected
Generating more than your current use may be worthwhile, but only if the roof, budget, inverter and network export limits support the larger system.
Step 3: Estimate the Required System Capacity
Solar panel capacity is measured in kilowatts (kW), while household consumption and solar generation are measured in kilowatt-hours (kWh).
Use this formula for an initial estimate:
Estimated system size = Target daily solar generation ÷ Expected daily output per installed kW
As a broad planning range, each installed kilowatt of rooftop solar may generate approximately 3.5–4.5kWh per day on average, depending on location, season and site conditions.
For a target of 20kWh per day:
At 3.5kWh per installed kW: 20 ÷ 3.5 = approximately 5.7kW
At 4.5kWh per installed kW: 20 ÷ 4.5 = approximately 4.4kW
This suggests initially comparing systems of around 5–6kW. A 6.6kW option may also be considered where the roof, budget, expected future use and network limits allow.
Step 4: Compare Common Solar System Sizes
The table below provides an indicative comparison using an output range of 3.5–4.5kWh per installed kW per day.
Solar System Size | Indicative Daily Generation | Indicative Annual Generation | Possible Use Case |
3kW | 10.5–13.5kWh | 3,830–4,930kWh | Smaller household with modest electricity use |
5kW | 17.5–22.5kWh | 6,390–8,210kWh | Small to medium household |
6.6kW | 23.1–29.7kWh | 8,430–10,840kWh | Medium household or higher daytime demand |
8kW | 28–36kWh | 10,220–13,140kWh | Larger household or planned electrification |
10kW | 35–45kWh | 12,780–16,430kWh | High-use home, EV charging or multiple major loads |
These figures are preliminary estimates, not guaranteed output. Actual generation depends on location, roof orientation, tilt, shading, weather, panel temperature, equipment efficiency and network curtailment.
Not every household needs or can install a permanent rooftop solar system. Renters, homes with limited suitable roof space, and households that mainly need power for selected appliances or outage backup may consider a portable solar generator instead.
If you are looking for a practical household solar power solution, the EcoFlow DELTA 3 Max Plus Portable Power Station + 400W Portable Solar Panel offers flexible energy storage and solar charging. The DELTA 3 Max Plus supports fast solar charging and stores power for selected household appliances and essential devices. Paired with a 400W monocrystalline solar panel, the system can make better use of available sunlight and improve overall charging efficiency. Together, they provide a convenient way to use more solar energy and reduce dependence on grid power.
For homeowners looking for a powerful backup power solution that can support their energy needs, the EcoFlow DELTA Pro 3 Portable Power Station + 400W Portable Solar Panel is an excellent choice. It delivers higher output power, allowing it to easily handle high-wattage household appliances. It also supports higher solar input for faster solar charging, helping store more energy for periods of peak demand. It is also paired with an IP68-rated 400W Solar Panel, capable of withstanding Australia’s diverse weather conditions.
Step 5: Confirm the Size Using Installer Estimates
Before choosing a system, obtain several itemised quotes based on the same electricity-use data. Ask each installer to provide:
estimated monthly and annual generation
assumptions about roof orientation and shading
panel and inverter capacity
expected self-consumption and grid exports
applicable network export limits
equipment models and warranties
STC deductions and metering costs
The connection agreement may limit inverter capacity or the amount of electricity exported to the grid. The designer should account for these limits before recommending a larger system.
Also confirm that the designer and installer hold suitable Solar Accreditation Australia accreditation and that the proposed panels and inverter appear on the relevant Clean Energy Council approved product lists.
How to Set Up a Solar System Safely
Correct setup is essential for safe operation, reliable solar generation and long-term system performance. The process differs between a fixed rooftop solar system and a portable solar power station, so always follow the requirements for the type of system you are using.
Assess the Installation Area: A qualified installer should confirm that the roof and proposed panel location are suitable. Portable panels should be placed on a stable, open and unshaded surface.
Use Suitable Components: Solar panels, inverters, batteries and connectors must be compatible with one another. Whether the system uses solar panels in series or parallel depends on the voltage and current limits of the inverter, charge controller or portable power station. For fixed rooftop systems, this configuration should be determined by an appropriately qualified designer or installer. Portable-system users should only use panel combinations permitted by the manufacturer.
Secure the Panels Properly: Fixed panels require mounting equipment designed for the roof type and local wind conditions. Portable panels should be fully unfolded, supported securely and positioned where they are unlikely to move, fall or obstruct access.
Leave Electrical Work to Qualified Professionals: Rooftop panels, inverters and installed batteries should be designed and installed by appropriately accredited and licensed professionals. Do not connect a portable solar power station to the home’s fixed wiring unless the connection has been installed by a licensed electrician.
Check System Performance: After installation or setup, confirm that the system is charging and operating as expected. Rooftop system owners should keep installation documents, warranties and shutdown instructions, while portable-system users should monitor solar input, battery level and connected appliance loads through the unit or its app.
Conclusion
When asking, “What size solar system do I need?”, start with your average daily electricity use, daytime consumption and local solar conditions. Roof space, network export limits and future energy demand should also be considered before making a final decision. A properly sized rooftop system or portable solar power station can help you use more solar energy, but the most suitable option will depend on your property, appliances and backup requirements.
FAQs
Will a 10kW solar system run my house?
A 10kW rooftop solar system can generate a substantial amount of electricity for a larger Australian home, but it does not guarantee continuous whole-home power. Actual generation depends on location, roof orientation, shading and weather, while nighttime use will still require grid electricity or battery storage. The inverter capacity and the household’s simultaneous appliance load must also be considered.
Can you run AC all day with solar panels?
Solar panels can help run an air conditioner during the day, especially when cooling demand overlaps with strong solar generation. However, whether solar can cover the full load depends on the system size, air conditioner power consumption, weather, household electricity use and inverter capacity. Grid electricity or battery storage may still be needed during cloudy periods, late afternoon or after sunset.
Can a solar system work on cloudy days?
Solar systems can continue generating electricity even on cloudy or overcast days, though output will be lower compared to direct sunlight. Modern solar panels can capture diffused sunlight and produce usable energy. When a compatible battery is installed, surplus solar energy generated in sunnier periods can be stored for later use. This can improve access to stored power when solar generation is low, although available energy will still depend on battery capacity and household demand.