Right solar system size by household in Perth: 1-person to 6-person homes

Installers often quote a 6.6kW system as a one-size-fits-all answer without checking whether it actually fits your household. A 6.6kW system on a 1-person household generates twice the energy they can use; the same system on a 5-person household with ducted AC and a pool barely covers daytime demand.

6.6kW is an entry point, not a default. Getting the size right matters for two reasons:

1. Without a battery, surplus mostly exports. Midday surplus earns the DEBS off-peak rate instead of avoiding a grid import, so a solar-only home is usually best at up to 6.6kW of panels on a 5kW inverter, which keeps DEBS.
2. Undersizing is the costly mistake. It leaves savings unrealised for the life of the system, and a battery only adds value if the solar is large enough to fill it. Judge the size over the system's life, not the first year.

Here's a Perth-calibrated guide by household size.

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Perth consumption benchmarks by household size

For reference, typical Perth household electricity consumption by size (A1 tariff, air conditioning assumed but not ducted, no pool, no EV):

Large load additions:

• Pool pump (year-round): add approximately +1,500–3,000kWh/year
• Ducted reverse-cycle AC (Perth summer heavy use): add approximately +2,000–5,000kWh/year
• Electric vehicle (10,000km/year average Perth driver): add approximately +2,000–2,500kWh/year
• Electric hot water (replacing gas): add approximately +1,500–2,500kWh/year

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System size recommendations by household

1–2 person household (2,500–6,000kWh/year)

Starting point: up to 6.6kW of panels on a 5kW inverter; a battery if your evening use is significant

A 1-person Perth household consuming 3,000kWh/year will find even a 5kW system generates approximately 8,200kWh/year, far exceeding consumption. The key for small households is maximising self-consumption (pool timer, hot water in solar hours) to avoid the surplus exporting at only 2c off-peak.

For a 2-person household at 5,000kWh/year, a 6.6kW system generates approximately 10,800kWh/year. Self-consumption at 35–45% = 3,780–4,860kWh self-consumed. Most of the rest exports at 2c off-peak, with only a small share landing in the 10c peak window. Without a battery, a bigger array mostly adds export.

Battery case for small households: a battery moves midday surplus into the evening, so you avoid evening imports instead of exporting at the off-peak rate. Size it to your evening and overnight use, and judge it over its life rather than on a first-year payback. If you choose a hybrid inverter, the battery can be added later without an alteration.

3–4 person household (6,000–9,000kWh/year)

Starting point: 6.6kW of panels or more, with a battery sized to your evening and overnight use

This is the mainstream Perth household. A 6.6kW system at 40–50% self-consumption covers approximately 4,300–5,400kWh of a 7,500kWh annual demand, leaving 2,100–3,200kWh/year to import. A bigger array covers more and leaves more surplus to fill a battery.

If the household has a pool, ducted AC or heavy evening use, a bigger array with a battery is a stronger starting point. On a hybrid inverter with a battery attached, the array can go above the usual ratio, up to the inverter maker's own limit, and a 5kW hybrid keeps DEBS. For apartment-style consumption (no pool, minimal AC), 6.6kW of panels on a 5kW inverter can be enough.

Battery: a battery sized to your evening and overnight use is where much of this household's value sits. Undersizing is the costly mistake, because adding capacity later usually means a second installation.

4–5 person household with pool and/or ducted AC (10,000–16,000kWh/year)

Starting point: a large array with a battery

Households in this range are typically Perth's best solar candidates: high consumption, high bills, and sufficient roof space on a standard 4-bedroom home for a 10–13.3kW array.

A 13.3kW array at Perth's 5.0 PSH generates approximately 21,800kWh/year, well above this household's use. Two ways to set that up:

• A 5kW hybrid inverter with a battery: keeps DEBS. The array it can carry is set by the inverter maker's limit for battery systems, which varies by model, so ask whether the array you want fits.
• An inverter above 5kW: carries a larger array, but DEBS pays nothing for export and export is limited at the connection, so the surplus has to go into a battery or your own loads to earn its keep.

Ask your installer to show both, and judge them over the system's life rather than a first-year payback.

5–6 person household or household with EV + pool + ducted AC (14,000–22,000kWh/year)

Starting point: the largest array your roof and connection allow, with a battery sized to evening and overnight use; possibly three-phase connection

For Perth's highest-consumption households, maximising system size (within roof and network capacity limits) is the right strategy. Western Power's 5kW export limit is counted in total across all phases, so three-phase doesn't raise it; a bigger single-phase system above the generation limit needs Western Power approval rather than a three-phase upgrade.

At this size the battery and your evening loads (EV charging, cooling) carry most of the value, because an inverter above 5kW earns no DEBS export payment. Get the design priced both ways and compare the value over the system's life.

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Common sizing mistakes to avoid

Sizing for "average" consumption without checking your bills Before accepting a quote, calculate your actual annual consumption from your last 4 Synergy bills. The numbers on your bills are more accurate than any rule-of-thumb estimate.

Undersizing "to see how it goes" Installing a 5kW system to "test solar" on a 4-person household costs you savings. The incremental cost of going from 5kW to 10kW in a single installation is approximately $3,000–$5,000, far less than doing a second installation later.

Oversizing for an empty nest that won't refill Sizing for 3 kids when 2 have already left home means years of undersized self-consumption and better export returns than saves. Review the next 5-year consumption trajectory, not the last 5.

Ignoring the EV you'll buy in 2 years A planned EV adds 2,000–3,000kWh/year of home-chargeable consumption. If the EV is coming, size for it now: the marginal cost of 2 extra panels at time of installation is $300–$600.

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The right system size in Perth comes from your own usage, especially your evening and overnight use. 6.6kW of panels on a 5kW inverter is the entry point for a solar-only home and keeps DEBS. For evening-heavy homes, a bigger array with a battery often wins. Get your actual annual kWh from your bills before accepting a quote, size the battery to your evenings, and size up rather than down.