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

Installers often quote a "standard 6.6kW system" 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.

Getting the size right matters for two reasons:

1. Oversizing on small households: surplus exports at 10c/kWh instead of avoiding 33.26c/kWh import — less economic
2. Undersizing on large households: leaves significant savings unrealised; battery adds more value but only if the solar is large enough to fill it

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

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):

| Household | Annual kWh | Approximate annual bill (A1 2026) | |---|---|---| | 1 person | 2,500–4,000kWh | $830–$1,330 + supply | | 2 people | 4,000–6,000kWh | $1,330–$2,000 + supply | | 3–4 people | 6,000–9,000kWh | $2,000–$3,000 + supply | | 4–5 people | 8,000–12,000kWh | $2,660–$3,990 + supply | | 5–6 people | 10,000–15,000kWh | $3,326–$4,990 + supply |

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

System size recommendations by household

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

Recommended system: 5–6.6kW solar, no battery immediately

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 10c.

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. The rest exports at 10c. The saving is still meaningful but the return from a larger system is diminishing.

Battery case for small households: Adding a 5kWh battery lifts self-consumption from ~40% to ~70%, capturing an additional 3,000kWh/year at 33.26c savings vs 10c export = approximately $696/year additional value. Payback on the battery: approximately 10–13 years depending on battery cost. Worth considering if backup power is valued, but less compelling on pure economics vs larger households.

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

Recommended system: 6.6kW to 10kW solar; 10kWh battery if budget allows

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 10kW system covers more and leaves more battery-eligible surplus.

If the household has a pool or ducted AC, a 10kW system is a stronger starting point. For apartment-style consumption (no pool, minimal AC), 6.6kW is appropriate.

Battery: A 10kWh battery on a 10kW system for a 4-person Perth household shifts self-sufficiency from approximately 50% to 80%. At Perth tariff rates, this saves approximately $2,800/year vs grid — payback on a $10,000 battery of approximately 7–9 years.

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

Recommended system: 10–13.3kW solar; 10kWh battery recommended

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 system at Perth's 5.0 PSH generates approximately 21,800kWh/year. For a 13,000kWh/year household at 55% self-consumption (with load management): 11,990kWh self-consumed + 9,810kWh exported = savings of $3,985 avoided import + $981 export = $4,966/year.

System cost approximately $17,000–$24,000. Payback approximately 4–5 years.

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

Recommended system: 13.3–20kW solar; 10–20kWh battery; 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 single-phase export limit encourages three-phase connection for systems above approximately 10kW AC output.

A 17kW system generating approximately 27,800kWh/year for a 16,000kWh/year household (at 60% self-consumption with battery): 16,680kWh self-consumed + 11,120kWh exported = savings of $5,546 + $1,112 = $6,658/year. System cost approximately $22,000–$32,000. Payback approximately 4–5 years.

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.

The right system size in Perth is the one that covers 80–95% of your annual consumption when matched with load management and (where budget allows) a 10kWh battery. For most Perth households, that means 6.6kW (small/2-person), 10kW (3–4 person standard), or 13.3kW (4–5 person with large loads). Get your actual annual kWh from your bills before accepting a quote — then size up rather than down.