Choosing the right solar system size is one of the most important decisions you will make when going solar. Too small and you keep paying high power bills. Too large, and you may export energy for very little return. At Steadfast Solar, we design solar and battery systems around the way South Australians actually use power. This guide explains how to find your ideal size.
Key Takeaways
- Start with your daily electricity use, not a standard size.
- In Adelaide, 1 kW of panels produces around 4 kWh a day.
- A 13–14 kWh battery may suit higher evening energy demand.
- Batteries, EVs and electric appliances may need a bigger system.
- Roof space and export limits also shape the final design.
Why System Size Matters
Solar has become part of everyday life in Australia. According to the Australian Government's YourHome guide, around one in four Australian households now has solar panels on the roof, the highest rate of household uptake in the world.
Yet not every system delivers the same value. The right size depends on how much energy you use, when you use it and what you plan to add in the future.
A well sized system helps you:
- Cover more of your daytime electricity use
- Reduce reliance on expensive evening grid power
- Charge a battery fully on most days
- Prepare for future appliances or an electric vehicle
- Achieve a faster payback on your investment
Step 1: Understand Your Daily Energy Use
Your electricity bill is the best starting point. Look for your average daily usage in kilowatt hours (kWh). Many bills show this as a daily average for the billing period.
YourHome notes that a typical home uses around 15 to 20 kWh per day, though this varies widely between households.
Usage also changes with the seasons. Heating in winter and cooling in summer can push your daily figure well above average, so it helps to check bills from different times of the year rather than relying on a single quarter.
Things that increase your usage include:
- Ducted or reverse cycle air conditioning
- Electric hot water systems
- Pool pumps and spa heaters
- Working from home
- Large families or multiple fridges
Step 2: Work Out How Much Solar Produces
As a general guide, YourHome explains that 1 kW of solar panels produces around 4 kWh of electricity per day on average. Adelaide's strong sunshine makes this a reasonable starting estimate.
Here is a simple way to estimate system size:
- Find your daily usage from your power bill.
- Divide by 4 to estimate the kW of solar needed.
- Add extra capacity if you plan to add a battery or EV.
- Check your roof space to confirm the panels will fit.
For example, a home using 20 kWh a day would need roughly a 5 kW system to match that usage on paper. However, because much of that energy is used at night, many homes choose a larger system and pair it with a battery.
Solar Batteries and Energy Needs
A 13–14 kWh battery may suit households looking to store surplus daytime solar energy for evening use. The right capacity depends on your daily electricity consumption, evening usage, solar generation and backup requirements.
Consider your household’s energy patterns before choosing a battery. A tailored solar and battery design helps balance storage capacity, solar production and overall energy needs.
Systems are getting bigger across the country. The Clean Energy Council's latest Rooftop Solar and Storage Report, covering January to June 2026, found the average rooftop system size reached 10.45 kW on a six month rolling basis, up 4.5 percent on a year earlier.
Step 3: Plan for a Battery
If you are considering a battery, your solar system needs enough capacity to power your home during the day and charge the battery as well.
Research supports sizing solar and storage together. A Flinders University research paper modelled the optimal mix of rooftop solar and battery capacity for grid connected South Australian homes, using local tariffs, household load and solar data, and found the best combination depends heavily on each household's energy use.
Solar and battery rebates can also influence the decision.
Step 4: Think About Future Energy Needs
Your energy use will likely grow over time. Many households are switching from gas to electric appliances or buying an electric vehicle.
An EV adds load, but often less than people expect. SA Power Networks notes that the average South Australian drives about 35 km a day, so most EV owners do not need to plug in every night. It also points out that midday is generally the cheapest time to charge, when the state's grid is often powered entirely by solar. Charging from your own panels during the day makes the most of a well sized system.
Hot water is another major factor. As reported by The New Daily, UNSW researchers found electric hot water systems can use up to 30 per cent of a household's energy. They also recommend the SunSPOT calculator to help estimate the right system size for your home.
Step 5: Check Roof Space and Export Limits
Your roof sets a practical limit on system size. Consider:
- Roof area available for panels
- Orientation, with north facing roofs producing the most energy
- Shading from trees, chimneys or nearby buildings
- Roof condition and structural suitability
Panel direction can also change the ideal layout. A University of South Australia study found that north facing panels work best for smaller systems, while larger systems can benefit from adding north west or west facing panels to better match afternoon and evening demand.
Network rules also matter in South Australia. InDaily reported that SA Power Networks introduced Flexible Exports, allowing eligible new solar customers to export up to 10 kW per phase when the network has capacity, compared with the standard 5 kW per phase limit.
Why Bigger Is Not Always Better
A larger system produces more energy, but exported solar earns very little. Using more of your own solar is where the real savings come from.
The smartest approach is to match your system to your usage, then add a battery to store the excess for the evening.
Get a Tailored Design
Every home is different, so a professional assessment gives the most accurate result. A good solar design considers your bills, roof, lifestyle and plans.
With ANYTIME Solar and Battery Plan at Steadfast Solar, you can install solar and a battery with no upfront fee and start saving before you finish paying.
Conclusion
The right solar system size depends on your daily energy use, roof space and future plans. A suitable solar system paired with a 13–14 kWh battery may help Adelaide households make better use of their solar energy. Contact us today for a solar system designed around your home.
FAQs:
What size solar system do I need for my house?
Divide your average daily usage in kWh by about 4 to estimate the kW of solar needed.
How much power does a 13 kW solar system produce per day?
A 13 kW solar system in Adelaide typically produces around 50 to 58 kWh per day, depending on the season, weather and installation conditions.
How many solar panels do I need for a 13 kW system?
A 13 kW system generally requires around 29 to 33 solar panels, depending on the wattage of each panel.
Should I get a bigger solar system if I add a battery?
Yes. Your system needs enough capacity to power your home during the day and charge the battery.
Can I add more solar panels later?
Often yes, but inverter capacity, roof space and network export rules may limit how easily you can expand.
