Why is my Synergy bill so high? A Perth household diagnostic guide

Getting a Synergy bill that's higher than you expected is one of the most common reasons Perth households reach for the calculator. Before assuming something's broken, most high bills trace back to one of eight causes — and each one has a different fix.

Here's how to work through them.

1. The supply charge is unavoidable

Before looking at consumption, check how much of your bill is the daily supply charge.

From 1 July 2026, the Synergy A1 supply charge is $1.19/day (~$436/year). On Midday Saver it's $1.33/day (~$485/year). This is fixed regardless of how much power you use — even if you have solar and your net import is close to zero, you still pay the supply charge.

For a household that got solar recently and expected their bill to drop dramatically: the supply charge is why it didn't fall all the way to zero.

Fix: Nothing you can do about the supply charge — it's the cost of being grid-connected. Budget for it separately from your consumption cost.

2. Seasonal patterns: summer AC dominates Perth bills

Perth summer is the #1 driver of unexpectedly high electricity bills.

A reverse-cycle split system running on a 39°C day uses:

• Small unit (2.5kW): 800–1,000 Wh/hour
• Medium unit (5kW): 1.5–2.0 kWh/hour
• Large unit (7–10kW): 2.5–3.5 kWh/hour

A household running two medium units for 8 hours on a hot day draws 24–32 kWh of AC alone. At 33.26c/kWh, that's $8–11 in a single day — before the rest of the household's baseline load.

Summer bills 40–80% higher than winter bills are completely normal in Perth metro. If your summer quarterly bill is significantly higher than your spring bill, AC usage is almost certainly the primary cause.

Fix: Pre-cool rooms before the heat peak (get the house to 24°C by 2pm so the AC runs less when it's hottest). Seal gaps and consider block-out curtains — Perth's direct sun loading on west-facing windows is significant. A ceiling fan in each room lets you set the AC 2–3°C warmer and cut consumption by roughly 25%.

3. Your tariff doesn't match your usage pattern

The Synergy A1 flat rate (33.26c/kWh from 1 July 2026) and Midday Saver aren't interchangeable. Households on the wrong tariff consistently overpay.

The break-even point between the two tariffs is 28.8% of usage during the 3pm–9pm peak window.

• More than 28.8% in peak hours: A1 is cheaper
• Less than 28.8% in peak hours: Midday Saver saves money

Households with solar and/or a pool pump that runs midday almost always sit under the 28.8% threshold — and many of them are on A1 by default, quietly overpaying on every bill.

Fix: Check your My Synergy portal for a time-of-use breakdown, or upload your bill to BillWise and we'll calculate which tariff is cheaper for your actual pattern. Switching is free with no lock-in — you can test Midday Saver for one billing period and switch back if it doesn't suit.

4. Hot water systems: the hidden load

Hot water accounts for 20–30% of a typical Perth household's electricity. If you have an electric resistive hot water system (the older style with a simple element), it's one of the most expensive appliances in the house.

| Hot water type | Annual running cost (6-person household) | |---|---| | Gas continuous flow | ~$400–600 (gas prices vary) | | Electric resistive (off-peak tariff) | ~$600–900 | | Electric resistive (general tariff) | ~$900–1,400 | | Heat pump water heater | ~$200–350 |

If your hot water system is set to heat during the day on a general tariff (not a controlled load/off-peak circuit), you're paying full rate for every litre of hot water. Many Perth households have their hot water timer set incorrectly — or it's heating 24/7 because the timer failed.

Fix: Check whether your hot water system is on a separate off-peak or controlled-load circuit (ask an electrician or check your meter configuration). If you have solar, shift the hot water timer to the 10am–2pm window to self-consume daytime generation. If the system is more than 10 years old, a heat pump water heater replacement pays for itself in 3–5 years.

5. Pool pumps: runtime and timing matter

A single-speed pool pump uses 750W–1,500W. Running for 8 hours a day, that's 6–12 kWh/day — $2–4 at A1 rates, or $730–1,460/year just for the pool pump.

Two common mistakes:

1. Running in the afternoon peak (3–9pm) — on Midday Saver, this costs 55.33c/kWh instead of 8.85c/kWh
2. Running longer than needed — many pumps run on factory defaults that exceed what the pool actually needs

Fix: Set the pool pump to run between 9am–3pm if you have Midday Saver or solar. Reduce runtime in cooler months (6 hours instead of 8). Variable-speed pumps use 50–80% less power than single-speed models — the payback period is typically 2–4 years in Perth conditions.

6. Solar underperformance

If you have solar and your bill has crept up over time, the panels may not be generating what they should.

Common causes:

• Shading: trees grown taller since installation, new nearby structures
• Soiling: Perth's dust, pollen, and bird droppings reduce output by 5–15% if panels aren't cleaned
• Panel degradation: panels typically lose 0.5% per year, so a 10-year-old system generates ~5% less than at install
• Inverter issues: a faulty inverter can operate at reduced output without a visible error
• String mismatch: one shaded or degraded panel pulls down the whole string

Fix: Check your inverter's monitoring app (SolarEdge, Fronius, Growatt, Sungrow all have apps) and compare today's output against a similar sunny day from 12 months ago. If output is down more than 5–10%, get an installer to check. Clean the panels annually — a quick rinse with a garden hose on a cool morning works for most soiling.

7. Phantom loads and idle devices

Electronics on standby collectively draw 50–150W in a typical Perth home. Over 24 hours and 365 days, that's 438–1,314 kWh/year — costing $146–437 at A1 rates.

Common phantom-load culprits:

• Old plasma or large LED TVs in standby
• Gaming consoles left on rest mode
• Older computer monitors or desktops
• Microwave clock displays
• Second fridge in the garage (often inefficient older models)

A second fridge running in a hot garage is particularly expensive — garage temperatures in Perth summer can reach 40–50°C, forcing the compressor to work much harder. A second fridge can use 800–1,200 kWh/year.

Fix: Use a smart power strip or individually switched power boards for entertainment systems. Measure the biggest suspect items with a plug-in energy monitor (available at Bunnings). A garage fridge running through a Perth summer is often the single biggest surprise load.

8. Feed-in tariff changes affecting your net bill

If you have solar, your bill is a net of consumption charges minus export credits. The DEBS (Distributed Energy Buyback Scheme) rates are:

• Peak export (3pm–9pm): 10c/kWh
• Off-peak export: 2c/kWh

The off-peak rate has been 2c/kWh since DEBS replaced the old 7.135c net metering arrangement. If your solar system was installed before 2020 and you recently rolled off a legacy tariff, your credits may have dropped significantly — and your net bill increased — for the same usage pattern.

Fix: Log in to My Synergy and confirm your export arrangement — DEBS or a legacy tariff — and its expiry date. If you're exporting a lot of off-peak power at 2c, a battery starts to look financially interesting (shifting that export to evening self-consumption at 33.26c makes each kWh worth ~27c more).

How to actually diagnose your bill

The steps above identify the eight most common causes — but your specific pattern depends on your actual usage data.

The fastest way to diagnose is to look at your usage by time of day. Your My Synergy portal shows hourly intervals for smart meter customers. What you're looking for:

• Flat usage pattern (same kWh/hour all day): hot water system heating constantly, or a large phantom load
• Spike between 3pm–9pm: AC, EV charging, or cooking — all running at peak-rate hours if you're on Midday Saver
• No midday dip on sunny days: solar may not be performing as expected
• High base load overnight (11pm–5am, nobody home): hot water, second fridge, or something left on

Upload your bill to BillWise → and we'll identify which of these patterns is driving your costs and calculate the saving for each fix.

All tariff rates are Synergy A1 from 1 July 2026 (33.26c/kWh consumption, 119.2419c/day supply). DEBS export rates: peak 10c/kWh, off-peak 2c/kWh. Running cost estimates use Perth average conditions (33°C summer average, 15°C winter average). Individual results will vary.