What size solar system do I need in Perth?

Choosing the right solar system size is one of the most consequential decisions of a solar purchase. Too small and you're leaving savings on the table; too large and you're exporting cheap-rate power that you could have self-consumed — or running into network limits.

Here's how to think through it for a Perth property.

Perth solar generation by system size

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.

Matching system size to your usage

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 — reducing the effective value of each kWh generated. This matters for sizing decisions.

Step 3: Size for your usage, not for maximum generation

The common trap is to "go big" to maximise generation. But beyond a certain size, you hit network export limits (discussed below) and export more power at 2c/kWh off-peak DEBS rate. That 2c/kWh exported power is worth very little — sizing above what you can sensibly use or export at peak rates is often not worth the extra panels.

A practical approach:

• If you're a 5,000 kWh/yr household with reasonable daytime usage, a 5–6.6kW system will cover most of your consumption
• If you're a 10,000 kWh/yr household with ducted AC, a 10kW system may be appropriate — but check the three-phase availability and network limit for your property first

The 6.6kW system: why it's Perth's most common choice

You'll hear "6.6kW" more than any other size in Perth, and there's a specific reason.

Western Power's connection standards limit residential single-phase inverters to 5kW AC output. The Clean Energy Council and the industry standard (AS4777) allow panels to be oversized relative to the inverter by up to 1.33× — meaning a 5kW inverter can be paired with up to 6.65kW of panels (rounded to 6.6kW in practice).

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 the maximum practical single-phase system in most Perth suburbs, and it costs only marginally more than a 5kW system because the labour is the same and the extra panels are cheap.

If you have three-phase power (common in larger homes and some newer estates), the limit is higher — up to 30kW inverter capacity in most cases.

Network limits: what Western Power actually allows

Beyond the inverter size limit, some Perth properties are subject to additional export constraints from Western Power due to network capacity in specific areas.

Standard connection: Most Perth properties can export up to 5kW AC (matching the inverter limit). Your system can be sized up to 6.6kW panels as described above.

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 changes the sizing equation:

Without a battery: Size for roughly 80–100% of your annual consumption, but stay within the network limits. Accept that some generation will be exported at 2c/kWh.

With a battery: You can justify a slightly larger system because the battery stores excess midday generation for use in the evening — improving self-consumption. A 6.6kW system + 10kWh battery for a family home is a common combination.

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.

See our solar vs solar + battery comparison for the Perth payback numbers.

Orientation and shading

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.

Getting your sizing right

The most reliable way to size a system is to:

1. Upload your last 12 months of Synergy bills to BillWise — it extracts your actual monthly usage
2. Compare a few scenarios in our solar calculator using your actual usage data
3. Get quotes from multiple CEC-accredited installers for a 6.6kW system (the typical Perth starting point) and discuss whether to go larger or smaller based on your specific address constraints

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.