Home energy audit Perth: find where your electricity bill is going

The average Perth household spends $1,800–$2,800/year on electricity. In most homes, four categories account for over 80% of that: air conditioning, hot water, lighting, and refrigeration. The other 20% is spread across dozens of smaller loads.

Before investing in solar or battery storage, it's worth spending 30 minutes auditing where your electricity actually goes — the cheapest savings come from reducing consumption, not from generating more.

Step 1 — Get your baseline from your bills

Collect your last 12 months of Synergy bills. For each quarter, note:

• Total kWh consumed
• Billing period dates
• Total cost (excl. any credits)

Add up 12 months to get your annual consumption. Divide by 12 for the monthly average.

What this tells you: Your annual spend and seasonal pattern. Households with ducted AC will see a January/February peak. Households without will see a flatter pattern.

If you have solar, look at the import figure (electricity taken from the grid), not just generation. The import figure is what your bill is based on.

Step 2 — Profile your big loads

In Perth, the major consumption categories are:

Air conditioning (30–50% of bill in summer)

Air conditioning is the single largest driver of electricity costs in Perth homes with reverse-cycle systems.

Estimating your AC cost:

• Typical living-area split system: 1.5–2.5kW at mid load
• Running 5 hours/evening × 6 months (Oct–Mar): 5 × 2kW × 180 days = 1,800 kWh/year
• At A1 (33.26c): $598/year for one unit

If you have a ducted system running at 3–5kW instead:

• 5 hours × 4kW × 180 days = 3,600 kWh/year → $1,197/year

Fastest AC savings:

• Raise cooling setpoint from 22°C to 24°C (each degree reduces consumption ~6–10%)
• Use ceiling fans to extend AC comfort at higher temperatures
• Pre-cool during solar hours (Midday Saver: 9am–3pm at 8.85c/kWh) rather than running AC through the evening peak
• Service filters annually — blocked filters reduce efficiency

Hot water (20–30% of bill)

Hot water is the second largest load for most Perth households, and the one with the best energy efficiency opportunity.

Estimating your hot water cost:

• Resistive electric (instantaneous or off-peak storage): 10–15 kWh/day for a family
• At A1: 12 kWh × 33.26c × 365 = $1,458/year
• Heat pump at COP 3.5: same hot water for 3.4 kWh/day → $414/year

Switching from resistive electric to a heat pump saves approximately $1,000/year for a typical family. This is the single largest energy efficiency upgrade available in most Perth homes.

For homes still on gas hot water: the comparison depends on current gas rates. Heat pump at 8.85c/kWh Midday Saver super off-peak costs significantly less than gas at current rates for most households.

Refrigeration (5–10% of bill)

A typical Perth household fridge uses 300–600 kWh/year depending on age and model. Modern 4–5 star fridges use 200–350 kWh/year.

• Old fridge (pre-2010, no energy rating): up to 600–900 kWh/year = $199–$299/year
• Modern efficient fridge (4 star+): 200–300 kWh/year = $66–$100/year

A spare fridge in the garage that's mostly empty costs $100–$200/year to run while contributing nothing. If you have one: consider whether it's earning its keep.

Estimating yours: Your fridge model typically has a kWh/year figure on the energy label, or available from the manufacturer. Alternatively, plug-in power meters ($20–40) measure actual consumption.

Lighting (5–15% of bill)

If you still have halogen downlights (50W per globe), lighting can be 10–15% of your bill. If you've already switched to LED, it drops to 2–5%.

• 24 × 50W halogens, 4hr/day: 1,752 kWh/year = $582/year
• 24 × 8W LED equivalents: 281 kWh/year = $93/year

If you haven't switched to LED yet, do it first. Payback is 6–9 months.

Standby and always-on loads (5–15% of bill)

Standby power across a typical Perth home: 200–500W continuous. At 300W average:

• 300W × 24hr × 365 = 2,628 kWh/year = $874/year

Check your overnight baseline: if your smart meter shows 0.3+ kWh per half-hour interval overnight (6am–6am when no one is active), you have significant standby load.

Common high standby loads:

• Satellite/pay TV box: 15–25W
• Gaming console on rest mode: 10–15W
• Desktop computer in sleep: 5–20W
• Pool pump (if running at night): 750W+ — should be on a timer

Pool pump (if applicable)

A pool pump running 8 hours/day continuously:

• 750W pump × 8hr × 365 = 2,190 kWh/year = $728/year

Running it only during solar hours (10am–2pm, 4 hours):

• 750W × 4hr × 365 = 1,095 kWh/year → saved from solar, not from grid
• Grid cost: near zero if timed with solar

Setting a pool pump timer to run during solar generation is the simplest way to shift a major load.

Step 3 — Prioritise interventions

| Intervention | Typical annual saving | Upfront cost | Payback | |---|---|---|---| | LED lighting (replace halogens) | $400–$500 | $200–$400 | 6–9 months | | Heat pump hot water (from resistive) | $800–$1,100 | $2,500–$4,000 | 3–4 years | | Pool pump timer (solar hours) | $300–$500 | $0–$50 (if timer exists) | Immediate | | Fridge replacement (old unit) | $100–$200 | $600–$1,500 | 4–8 years | | AC setpoint +2°C | $100–$200 | $0 | Immediate | | Ceiling insulation (upgrade to R4.1+) | $200–$400 | $1,000–$2,500 | 4–8 years | | Solar (6.6kW, after efficiency upgrades) | $1,400–$2,200 | $6,000–$9,000 | 4–6 years |

The order matters: do the free/cheap changes first (setpoints, timers, standby elimination), then LED if not done, then hot water, then solar. Solar sized on a reduced consumption load is appropriately sized — buying 6.6kW before switching off your halogen downlights means you're sizing solar against an avoidable load.

Step 4 — Identify tariff mismatch

Review your consumption profile against your tariff:

On A1 flat rate: All consumption costs 33.26c/kWh. Solar generation saves 33.26c on self-consumed electricity and earns 2c on export.

On Midday Saver: Consumption 9am–3pm costs 8.85c/kWh. Consumption 3pm–9pm costs 55.33c/kWh. If your evening consumption is high and you can't shift it, Midday Saver costs more than A1.

Upload your Synergy bills to BillWise to see which tariff suits your usage pattern — the tool models both against your actual data.

Consumption figures and costs are based on Perth conditions (continuous AC use in summer, A1 tariff at 33.26c/kWh effective 1 July 2026, Midday Saver at 8.85c/55.33c/24.34c). Actual savings depend on your specific usage patterns, equipment, and tariff.