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How to size a solar system for your home
Choosing the right solar system size comes down to three things: how much electricity you use, when you use it, and what you plan to add in the future, like a battery or an electric vehicle charger. This guide walks you through the same process our accredited designers use for homes across Newcastle, Lake Macquarie and the Hunter.
How to work out your solar system size in 5 steps
1. Find your average daily electricity use
Grab your last four electricity bills, ideally one from each season. Most bills show your average daily usage in kWh. If yours doesn’t, divide the total kWh used by the number of days in the billing period.
Winter and summer bills are the most important. Heating, cooling and pool pumps can push usage up sharply in those months, and a system sized only on a spring bill will usually come up short.
If you have a smart meter, your retailer’s app or online account will show your usage in 30-minute intervals. This is the most accurate data you can give a solar designer.
2. Work out when you use your power
Solar panels only generate while the sun is up, so the savings depend on how much of that power you use yourself. Energy you use directly replaces power you would otherwise buy from the grid at full retail price. Energy you export earns a feed-in tariff, which in NSW is now only a few cents per kWh. You can compare current feed-in tariffs from different retailers on the government’s Energy Made Easy website.
A household that is home during the day, runs a pool pump or works from home will use far more solar directly than one where everyone is out from 8 am to 6 pm. The more you use during daylight hours, the faster a system pays for itself.
A simple way to shift more use into the day is to run the dishwasher, washing machine, dryer and hot water system on timers between 10 am and 3 pm.
3. Convert your usage into a system size
In the Newcastle and Hunter region, each 1 kW of well-positioned solar panels produces around 4 kWh per day averaged across the year. Output is higher in summer, often above 5 kWh per kW, and drops to around 2.5 to 3 kWh per kW on short winter days.
The basic formula is:
System size (kW) = average daily use (kWh) ÷ 4
This gives you a system that produces roughly as much energy as you use over a full year. It’s a starting point, not a final answer. Steps 4 and 5 adjust it for your plans and your property.
4. Plan for batteries, EVs and future changes
Solar panels are one of the cheapest parts of a system to add at the start and one of the most expensive to add later. It pays to think ahead.
- Adding a battery. A battery needs surplus daytime solar to charge. As a rough guide, add 3 to 4 kW of panels on top of your base size to fill a typical 10 to 13.5 kWh home battery on an average day.
- Buying an electric vehicle. Most EVs use around 15 to 18 kWh per 100 km. If you drive 40 km a day, that’s about 6 to 7 kWh a day, or roughly 1.5 to 2 kW of extra panels.
- Going all-electric. Replacing gas hot water, cooking or heating with electric heat pumps and induction adds to your daily use, but also means more of your solar is used at home.
- A growing family. More people at home usually means more daytime use.
5. Check your roof and network limits
The last step is making sure the system fits your roof and your local grid.
Roof space. A modern 440 W panel is roughly 1.7 m × 1.1 m. Allow about 5 m² of usable, unshaded roof per kW of solar. A 6.6 kW system needs around 30 m², while 13.2 kW needs about 60 m².
Orientation. North-facing panels usually generate the most overall. East and west-facing panels produce slightly less, but can better match morning and afternoon energy use.
Shading. Trees, chimneys, nearby buildings and antennas can reduce output, so shading should be checked before finalising the layout.
Network limits. Newcastle, Lake Macquarie and much of the Central Coast are on Ausgrid, while parts of the Upper Hunter are on Essential Energy. Both networks can limit how much solar you connect and export, especially on single-phase homes.
Inverter sizing. Under federal rebate rules, panel capacity can be up to 133% of inverter capacity. That’s why 6.6 kW of panels is commonly paired with a 5 kW inverter.
Solar system sizes and output in the Hunter
Use this table as a guide to what common system sizes produce in the Newcastle and Hunter region. Figures assume north-facing, unshaded panels and are daily averages.
Output varies with season, roof angle, orientation, shading and weather. Expect roughly 30% less in winter and 25% more in summer than the averages shown.
Two real-world sizing examples
Common solar sizing mistakes to avoid
Sizing from a single bill. One quarter doesn’t show the full picture. Always look at a full year of usage, especially winter.
Going too small to save money upfront. The fixed costs of an installation, like scaffolding, labour, the inverter and connection, are similar whether you install 5 kW or 8 kW. Extra panels at the start are usually the best value you’ll get.
Oversizing without a plan to use the energy. With low feed-in tariffs, a very large system with no battery and little daytime use will export most of its power for a small return. Size for how you’ll actually use it.
Ignoring future plans. If a battery, EV charger or pool is on the cards in the next few years, factor it in now.
Choosing on price per kW alone. A cheap system with poor-quality panels, inverters or workmanship will produce less and fail sooner. We only use CEC-approved equipment and premium electrical components for this reason. Learn more about our team and standards.
