Managing night-time electricity costs in Perth with solar

Solar panels stop generating when the sun goes down. For most Perth households, 3pm–10pm is when significant electricity consumption happens — cooking, air conditioning, lighting, entertainment, and appliances. This evening window is where your electricity costs concentrate, and it's where strategic decisions have the most financial impact.

Why evening electricity is expensive on Midday Saver

On Synergy's Midday Saver tariff, the evening peak (3pm–9pm) is charged at 55.33c/kWh — one of the highest residential electricity rates in Australia.

Without solar or battery storage:

• Cooking (45 min, 2kW oven): 1.5kWh × 55.33c = 83c
• Air conditioning (3hr, 3kW): 9kWh × 55.33c = $4.98
• Dishwasher (1 cycle): 1.2kWh × 55.33c = 66c
• Hot water system (resistive 4kWh): 4kWh × 55.33c = $2.21

Evening total: approximately $8.68 on peak rate Same usage in off-peak (9pm–midnight, 24.34c): approximately $3.81

The difference highlights why timing matters.

Strategy 1: shift loads earlier (pre-sunset)

The simplest approach — run appliances before 3pm when solar is still generating:

Dishwasher: Run the dishwasher after lunch (12–2pm) instead of after dinner. Solar covers the load entirely during summer months.

Washing machine: Morning or lunchtime washes during 9am–3pm consume cheap super off-peak electricity or solar generation.

Slow cooker / Instant Pot: Start cooking the evening meal by 1pm on the slow cooker setting. Finishes by 5–6pm without the oven running at peak rates.

Hot water: Set the hot water system timer to heat in the morning (9am–12pm) using solar or cheap super off-peak power. The insulated tank holds heat for evening showers.

Strategy 2: pre-cool and coast

On summer evenings in Perth, air conditioning is the largest evening electricity load. The pre-cooling strategy reduces or eliminates this:

1. Run air conditioning during 10am–2:30pm to cool the house to 22–23°C
2. Turn off or reduce air conditioning before 3pm
3. Close all blinds and block west-facing windows from the afternoon sun
4. Allow the house temperature to drift from 22°C before peak rates end at 9pm

In well-insulated Perth homes, temperature rise from 22°C might reach 26–27°C by 8–9pm on typical summer days — uncomfortable but manageable with fans. Ceiling fans at 20W are 1/100th the cost of air conditioning at 2,000W.

If the house still needs air conditioning during peak hours, set the setpoint to 26°C rather than 23°C — every degree higher on the thermostat reduces consumption by approximately 10%.

Strategy 3: battery storage

A battery captures surplus daytime solar generation and discharges it during the 3–9pm peak window. This is the most effective technical solution for reducing evening grid import:

Example (10kWh battery, fully charged by 3pm):

• 10kWh discharge during 3–9pm (6 hours at average 1.67kW)
• Covers: lights, cooking, TV, mild air conditioning
• Grid import during peak window: near zero
• Saving vs importing at 55.33c: 10kWh × 55.33c = $5.53/day during summer

Battery limitations: A 10kWh battery discharged at 5kW (heavy air conditioning + cooking simultaneously) lasts only 2 hours. The battery reduces peak grid import significantly; it doesn't eliminate it if multiple high-draw appliances run simultaneously.

Strategy 4: use the off-peak window (9pm onwards)

On Midday Saver, electricity from 9pm–midnight (and midnight–9am) costs 24.34c/kWh — lower than peak but more than super off-peak. Using large appliances after 9pm costs much less than during 3–9pm peak:

• Dishwasher after 9pm: $0.29 instead of $0.66 at peak
• EV charging after 9pm at 7.4kW × 8hr: $14.34 instead of $32.82 at peak

The off-peak window is the practical choice for:

• EV owners who can't charge during the day
• Households whose evening schedule can't shift appliance timing

What doesn't reduce evening electricity costs

Larger solar system: A larger system generates more daytime electricity, but evening solar generation is still zero regardless of system size. More panels = more surplus to export or store; they don't extend the generation window past sunset.

More panels without battery: Additional panels generate more daytime surplus (which you may export at 2c/kWh DEBS off-peak). This doesn't reduce evening import unless the surplus is captured in a battery.

The full strategy combined

For maximum evening cost reduction:

1. Time all shiftable loads to 9am–3pm (dishwasher, washing, hot water, slow cooker)
2. Pre-cool the house before 3pm, close blinds, coast on fans where possible
3. Battery covers residual evening load (lighting, TV, moderate appliance use)
4. Defer heavy appliances (EV, second wash load, second dishwasher cycle) to after 9pm off-peak if needed

This combination can reduce evening peak electricity import by 60–80% for a typical Perth household on Midday Saver with a 6.6kW solar system and 10kWh battery.

Evening usage patterns vary significantly by household. Run your own analysis using BillWise by uploading your Synergy bill — we break down your consumption by time window to identify where your biggest evening cost opportunities are.