Fast read
Sizing a solar PV array so your battery performs at its best hinges on four variables that work together: daily energy use, usable battery storage, local sunshine, and inverter limits. Across most of Australia, a practical rule of thumb is a solar array that is roughly 1.5–2 times larger (in kW) than the battery’s usable capacity (in kWh). In real terms, a 10 kWh battery generally pairs well with a 6–10 kW solar system. Staying in that band lets the panels cover daytime loads and still charge the battery reliably—even on gloomy winter afternoons—without throwing money at oversizing that never pays back.
The precise balance shifts with your goals—maximising self-consumption, boosting blackout protection, or trimming peak-time bills—and with the amount of sunshine your postcode receives. A modern hybrid inverter teamed with a well-chosen battery, such as Sigenergy’s modular SigenStor or the Sungrow SBR series, turns that guideline into an efficient, future-ready system. Read on to see how each factor shapes the final size your installer will recommend.
Solar + Battery: How to Get the Right System Size
Your electricity bill reveals how many kilowatt-hours (kWh) you use on an average day, and seasonal swings—think air-conditioning during Darwin’s Build-Up or heating through a Tasmanian winter—may nudge the figure higher. Next, clarify why you want storage. If your priority is maximising self-consumption, you will want enough capacity to cover most evening use. If blackout resilience matters more, focus on the appliances you truly need to keep running—fridge, lights, Wi-Fi, maybe the garage door—and size the battery for that shorter duty. Homeowners targeting time-of-use savings may accept a slightly smaller battery so long as it can charge off-peak or on surplus solar, then discharge at the pricey evening rate. These answers dictate your battery size and, by extension, set a minimum generation target for the panels.
For example, an Adelaide household that aims to offset nearly all evening consumption might choose an 11.5 kWh Sigenergy pack. Someone in Brisbane who mainly wants backup for essentials could be comfortable with 5 kWh. Either way, that number becomes the anchor point for solar sizing.
Factor in Australia’s sunshine and the calendar
Australia is blessed with sun, yet Peak Sun Hours (PSH) differ sharply by latitude and season. Perth enjoys roughly 5.5 PSH in summer but slides to about 3 PSH in winter; Hobart enjoys around 5 PSH in January but dips closer to 2 PSH in June. Those figures translate directly into daily output: a 6.6 kW array in Perth might deliver 32 kWh a day on average, while the same array in Hobart can fall below 20 kWh during mid-winter. Where winter sun is scarce—or roof space is limited—opting for ultra-efficient modules such as AIKO’s ABC panels or simply moving to the higher end of the kW-to-kWh ratio bridges the seasonal gap.
Understand battery charge rates and inverter limits
Batteries can only accept energy at a fixed rate. A 10 kWh unit capped at 5 kW cannot harvest more power at once, no matter how hard your panels push. Hybrid inverters also impose boundaries: continuous AC output has to match your household peak, and DC input has a ceiling, even though many modern models, like Sungrow’s SH-RS series, happily accept modest oversizing (for instance, 10 kW of panels on an 8 kW inverter). Brands such as Sigenergy advertise higher-rate charging, which lets bigger arrays capture more sunshine on brilliant days.
Checking these specifications prevents you from paying for solar capacity that ends up idle.
A practical guideline for the solar-to-battery ratio
Most designers land on the 1.5–2 × ratio because it works across Australia’s climate zones, tariff structures, and future-growth plans. Put simply, a 5 kWh battery tends to suit roughly 3–5 kW of panels; a 10 kWh battery needs about 6–10 kW; and a 13.5 kWh battery is happiest with 8–13 kW. Opting for the upper end delivers faster charging, better resilience on overcast days, and room for an electric vehicle down the track. That margin will also position you to make the most of the Federal Cheaper Home Batteries Program that starts on 1 July 2025 and will cover roughly 30 % of a qualifying battery’s upfront cost.
Why “more solar” can still pay
Oversizing within reason brings clear benefits. First, it cushions you against seasonal lows: Northern NSW or southern WA households often add a spare kilowatt or two simply to ride out cloudy weeks. Second, it handles daytime electricity hogs—pool pumps, heat-pump hot-water units, and midday EV charging all thrive on abundant solar. Third, lithium batteries last longer if they are not depth-cycled every night; extra generation keeps the state of charge higher without touching the grid. Finally, even a modest feed-in tariff displaces fossil generation and trims your net carbon footprint.
Modern energy-management software means surplus solar rarely goes to waste: you can schedule a dishwasher cycle, preheat the electric storage tank, or trickle-charge the EV once the battery hits 100 %.
What happens if the balance is off?
When the array is undersized—say a 5 kW system feeding a 13 kWh battery—storage may sit half empty through much of winter. You could add panels if the inverter allows, or shift high-load chores such as laundry into daylight hours. Some households also top up from the grid at low off-peak rates, though that dilutes the renewable share of your consumption.
By contrast, a “too large” array—imagine 10 kW of panels on a 5 kWh battery—is rarely a technical headache because the inverter will export the excess. The real question is economics: with feed-in tariffs hovering around 5–10 c/kWh, oversizing beyond your genuine daytime needs may lengthen payback. Yet if you plan to add an EV or a second battery module—both SigenStor and Sungrow SBR systems are designed for easy expansion—that headroom quickly pays dividends.
Work with a CEC-accredited installer
Armed with your usage data and goals, a Clean Energy Council accredited designer/installer can model year-round output for your specific postcode, match inverter power to battery charge rates, and walk you through incentives—from today’s STCs to state rebates like the NSW Battery Rebate or WA’s upcoming subsidy. They will also ensure compliance with AS/NZS 5139 (battery safety) and AS/NZS 5033 (PV array design) and manage DNSP export-limit approvals. Choosing an installer who regularly works with your shortlisted brands—AIKO, Sungrow, Sigenergy—avoids teething issues and streamlines any warranty claim.
Conclusion: balance today’s needs with tomorrow’s ambitions
Solar-and-battery sizing is never one-size-fits-all, but the 1.5–2 × solar-to-battery guideline is a dependable starting point. Staying in that window generally secures enough solar to charge the battery most days, powers daytime loads without dipping into storage, and keeps options open for future upgrades such as induction cooking, a heat pump, or an EV.
Take clear usage numbers and a firm set of goals to your installer, check equipment charge rates, and confirm which incentives you can claim. Get the match right and you will enjoy lower bills, greater energy independence, and a lighter carbon footprint for decades—exactly the outcome Your Energy Answers was created to help you achieve.
