What size solar system do I need in Perth?
How much solar do Perth households need? This guide matches usage to system size, explains why 6.6kW is the entry-level size and when 8–10kW fits, and covers Western Power's network limits.
The right solar system size for a Perth home depends on how much power you use, when you use it, whether you add a battery, and the network limits at your address. WattMate's free energy audit report works out a size from your own bill and answers, so you can start there before you collect quotes.
Get your free energy audit report for a personalised starting point.
Choosing the right solar system size is one of the most consequential decisions of a solar purchase, and it's judged over the system's life, around 25 years, not on the first year's bill. Too small is the costlier mistake: adding panels or battery capacity later usually means a second installation. Too large for a solar-only home means exporting power that DEBS won't pay for, or running into network limits.
Here's how to think through it for a Perth property.
How much does a solar system generate in Perth?
A bigger system generates more, but how much depends on your roof's direction, shading and where you live. Perth gets strong sun for solar. The table below gives indicative annual generation by system size for north-facing panels, and your installer or WattMate's free energy audit report can estimate yours.
Perth is one of the best locations in Australia for solar. With an average of 5.0 peak sun hours per day (Bureau of Meteorology average for the Perth metro area), a well-installed system generates consistently across the year.
Typical annual generation for north-facing panels in Perth metro:
| System size | Approx annual generation |
|---|---|
| 3kW | 4,500–5,500 kWh |
| 5kW | 7,500–9,000 kWh |
| 6.6kW | 10,000–12,000 kWh |
| 10kW | 15,000–18,000 kWh |
| 13.3kW | 20,000–24,000 kWh |
These are estimates for systems with north-facing panels. East or west-facing systems generate roughly 10–20% less annually. South-facing panels generate significantly less (50–70% of north-facing output) and are generally avoided for main arrays in Perth, though they're sometimes used to maximise roof space on large properties.
How do you match solar system size to your usage?
Start with your annual electricity use from your Synergy bills. Then think about when you use power and whether you will add a battery, because solar you use at home saves more than solar you export. The steps below walk through each one, and the free energy audit report does this from your own bill.
The starting point is your annual electricity consumption, which you can find on your Synergy bills or in My Synergy's usage history.
Step 1: Know your annual usage
A typical Perth household falls into one of these bands:
| Household type | Typical annual usage |
|---|---|
| 1–2 person, no pool, no EV | 3,000–5,000 kWh/yr |
| 3–4 person family, no pool | 5,000–8,000 kWh/yr |
| Family with ducted AC or pool | 7,000–12,000 kWh/yr |
| Large home or home EV charging | 12,000–20,000 kWh/yr |
Step 2: Decide on your target self-consumption
Solar savings come from self-consuming solar generation (avoiding grid purchases at 33.26c/kWh), not from exporting to the grid (paid at 10c peak / 2c off-peak under DEBS).
If you're home during the day, have a heat pump running midday, or have a battery, you might self-consume 60–80% of your solar generation. If you're at work during the day with no battery, self-consumption might be only 20–35%.
A lower self-consumption ratio means more of your solar is exported at the low DEBS rates. That reduces the effective value of each kWh generated. This matters for sizing decisions.
Step 3: Decide whether a battery is part of the plan
Without a battery, going big mostly adds midday export, and the economics push back twice. Within the DEBS cap, midday export earns just 2c/kWh, a fraction of what you save by self-consuming the same energy. And past the cap, export income vanishes entirely: DEBS only pays systems with a solar generating capacity of 5kW or less (the 6.6kW-panels-on-5kW-inverter pairing is deemed 5kW and qualifies), so a bigger system's export earns nothing at all. That's why a solar-only home stays at 6.6kW of panels on a 5kW inverter.
A battery changes that. It stores midday generation for the evening, and with a battery connected the SAA rules allow a hybrid inverter to carry a bigger array, up to the inverter maker's maximum for that model. A 5kW hybrid still keeps DEBS. For a home that uses most of its power in the evening, a bigger array plus a battery often comes out ahead over the system's life.
A practical approach:
- Solar only: 6.6kW of panels on a 5kW inverter is the entry point, and it stays the solar-only size because it keeps DEBS
- An evening-heavy home (ducted AC, a pool, an EV): price a bigger array and a battery together as one job on a hybrid inverter, and check the network limit at your address first. Keep the inverter at 5kW to stay within DEBS; a bigger inverter sits past the DEBS cap, so its value rests entirely on what you use and store. On single phase, a system above the generation limit is still allowed with Western Power approval and a generation-limit setting; it doesn't need a three-phase upgrade
Why is there an entry-level solar size in Perth?
Perth's entry-level size comes from network and scheme rules for panels, inverters and exports, not from what suits every home. Those rules changed in 2026, and an entry-level system is a starting point rather than a target. The section below explains the rules, and the free energy audit report works out the size that fits your home.
You'll hear "6.6kW" a lot in Perth, and there's a specific reason.
For years, Western Power's connection standards limited residential single-phase inverters to 5kW AC output, and the industry standard (AS/NZS 4777) allows panels to be oversized relative to the inverter by up to 1.33x, meaning a 5kW inverter pairs with up to 6.65kW of panels (rounded to 6.6kW in practice). The rules changed on 1 May 2026: the only cap on inverter capacity is now 30kVA in total, battery inverters included. A single-phase home has a generation limit of 10kVA or 15kVA, depending on the connection; above it, Western Power approval and a generation-limit setting apply, but it doesn't require a three-phase upgrade. The 6.6kW configuration remains the entry-level choice anyway, because export is still limited, and generation you can neither use nor export earns nothing.
This "oversized" configuration is deliberate. During the middle of the day on a clear Perth summer day, the inverter would clip some generation, but on average, the extra panel capacity produces more energy in the mornings, evenings, and on partly cloudy days when the inverter isn't at full capacity. Net generation from a 6.6kW array with a 5kW inverter is meaningfully higher than a 5kW array with a 5kW inverter over the year.
Result: 6.6kW of panels + 5kW inverter is still the entry-level size for Perth homes, and it costs only marginally more than a 5kW system because the labour is the same and the extra panels are cheap. Typical new systems nationally are larger, at 8–10kW. Going bigger on single phase is now allowed under the 2026 rules, but it pays off mainly when you can use the extra generation at home or store it in a battery, rather than export it.
If you have three-phase power (common in larger homes and some newer estates), the whole-site aggregate limit is 30kVA of inverter capacity, battery inverters included, the same as on single-phase. The DEBS payment cap doesn't scale with it, though. Two different rules are at work here: the network's export limit, which Western Power sets for your connection, and the DEBS payment cap of 5kW of generating capacity for the whole system. So a three-phase home with a 10kW inverter connects fine and exports within its network limit, but earns nothing for what it sends out.
What network limits apply to a Perth solar system?
Western Power sets limits on inverter capacity and on how much your system can export, and some suburbs have tighter limits. Your installer should check the limits for your address before quoting. The details below cover the standard connection, constrained areas and how to check your address.
Beyond the inverter rules, some Perth properties are subject to additional export constraints from Western Power due to network capacity in specific areas.
Standard connection: A system whose inverter supports remote management can export up to the limit Western Power sets for the connection. Systems without that connectivity are capped at 1.5kW of export. Your installer confirms what your connection allows.
Constrained network areas: In some suburbs where the local network is at capacity, Western Power may limit exports further: sometimes to 1.5kW or even zero export. This is not unusual in parts of outer Perth and high-solar-penetration suburbs.
How to check: Your solar installer should check the network capacity at your property's address before quoting. The Western Power "check my address" tool provides the current connection capacity for residential solar connections. If you're buying a system, ask your installer what export limit applies to your specific address.
Impact on sizing: If your export is limited to 1.5kW, installing a 10kW system is counterproductive: you'd clip heavily during peak solar hours and only export at the constrained rate. In this case, a smaller system sized to your self-consumption (plus battery, if you want to store the excess) makes more economic sense.
Should you add a battery?
A battery stores midday solar for the evening, so a home that uses most of its power in the evening may suit a bigger array with a battery. Size the battery to your evening and overnight use. The points below compare solar only, solar with a battery, and tight export limits.
A battery changes the sizing equation:
Without a battery: Stay at 6.6kW of panels on a 5kW inverter so the system keeps DEBS, within your address's network limits. Some generation will be exported, earning 2c/kWh off-peak if your system is within the DEBS cap, and nothing at all if it sits past it.
With a battery: A bigger array often wins for an evening-heavy home, because the battery stores midday generation for use in the evening. Size the battery to your evening and overnight use. Undersizing is the costlier mistake, because adding capacity later usually means a second installation. A 6.6kW system with a battery is an entry point, not a target.
With tight export limits: A battery is almost essential to make larger systems worthwhile. If you're limited to 1.5kW export, a battery stores the generation that would otherwise be clipped by the export constraint, converting it to usable evening power.
For what a battery unlocks in rebates, see the complete Perth solar rebates guide.
How do roof direction and shading affect solar size?
Panels facing north generate the most in Perth, and other directions generate less. Shading on even one panel can cut a string's output unless you use microinverters or optimisers (small devices that let each panel work on its own). The generation estimates here assume north-facing panels with little shade.
The generation figures above assume north-facing panels in Perth metro with minimal shading. Your situation may differ:
Orientation impact on annual generation:
- North-facing: 100% (benchmark)
- North-east or north-west: approximately 90–95%
- East or west-facing: approximately 80–90%
- South-east or south-west: approximately 60–75%
- South-facing: approximately 50–65%
Many Perth homes split panels across multiple roof faces (for example, north and west). This reduces total generation but smooths the generation profile through the day.
Shading: Even partial shading on one panel can significantly reduce the output of an entire string (in a conventional string inverter system). If your roof has shade from trees, a pergola, or a chimney, ask your installer about micro-inverters or DC optimisers, which allow panels to work independently rather than being limited by the weakest panel.
How do you get your solar sizing right?
Use your last year of Synergy usage, get quotes from SAA-accredited installers who model sizes against that usage, and compare designs over the system's life. WattMate's free energy audit report gives you a personalised starting point before you collect quotes.
The most reliable way to size a system is to:
- Pull your last 12 months of usage from your Synergy bills or My Synergy's usage history
- Get quotes from multiple SAA-accredited installers, sharing that usage data so they can model system sizes against your actual consumption rather than rough estimates. Ask for two designs: solar only at 6.6kW on a 5kW inverter, and a bigger array with a battery sized to your evening and overnight use. Compare them over the system's life, within your address's network limits
Installers with a My Synergy data consent (or access to smart meter data through your permission) can design a system against your actual usage half-hourly data, much more accurate than estimating from bill totals.
Generation estimates are based on Perth metro conditions (5.0 peak sun hours, standard panel orientation and tilt). Actual output varies with specific location, installation quality, shading, and temperature. Western Power's network limits and connection standards are subject to change: check the Western Power website or ask a licensed installer for current limits at your address.