Maximising solar self-consumption in Perth without a battery

Without a battery, every kilowatt-hour of solar you self-consume is worth 33.26c (the A1 rate you avoid importing). Every kilowatt-hour you export earns only 2c under DEBS off-peak (outside 3pm–9pm). The ratio is 16:1. Maximising self-consumption is therefore the highest-return strategy for a no-battery solar household.

When does your solar generate?

Perth solar generation (6.6kW north-facing) typically:

• Starts generating useful output from approximately 8am (summer) or 9am (winter)
• Peaks around solar noon (12pm–1pm)
• Falls below 1kW from approximately 4pm–5pm (summer) or 3pm (winter)
• Zero generation after approximately 5:30pm (summer) or 4:30pm (winter)

The prime self-consumption window is 10am–2pm — this is when generation is high and household base load is often low (occupants at work, minimal AC).

The fundamental challenge

For most Perth working households, the natural timing is wrong:

• Morning peak (7am–9am): High household load (breakfast, hot water, AC pre-cool) — but solar is only starting to ramp up
• Solar peak (10am–2pm): Generation at maximum — but household occupancy often low, loads small
• Evening peak (5pm–8pm): Return home, cooking, cooling, high loads — but solar is at zero or minimal output

The result: without intervention, a typical household self-consumes only 25–40% of their solar generation. The rest exports at 2c/kWh.

Strategy 1: dishwasher and laundry timing

The simplest, most impactful change: shift washing machine, dryer (if you have one), and dishwasher to midday solar hours.

Most effective approach:

• Set appliances on a delay-start timer to finish around 11am–12pm
• Or run them manually after morning departure (10am start for a 1.5-hour wash)
• Dishwasher after lunch rather than after dinner

Electricity saving:

• Washing machine (1kW): 1 load/day, shifted from 7pm to 11am = 1kWh × (33.26c − 2c) = 31.26c/day saved = $114/year
• Dishwasher (1.2kW for 1.5hr): shifted from 8pm to 12pm = 1.8kWh × 31.26c = $20.50/year

Strategy 2: pool pump timing

If you have a pool, the pump is typically one of the largest daytime loads. A single-speed pool pump (1kW) running 8 hours/day at peak grid times costs approximately $970/year.

Solar-timed pool pump: Shift filtration hours to 9am–3pm. If your pump is on a basic timer, this is a 5-minute timer adjustment.

With Midday Saver: Pool pump in the super off-peak window (9am–3pm) at 8.85c/kWh costs approximately $260/year — even without self-consuming solar. Combining Midday Saver with solar self-consumption reduces the cost to near-zero.

Strategy 3: hot water timing

Electric storage hot water (off-peak controlled load): Most Perth households with electric storage hot water have it on Synergy's controlled load tariff (overnight at a discounted rate). To shift to solar:

• Ask your electrician to switch the hot water timer from overnight to a 10am–2pm daytime window
• Your hot water will heat during peak solar generation
• At A1 tariff, midday self-consumed solar offsets 33.26c/kWh you'd otherwise pay on controlled load

Heat pump hot water: Heat pumps run most efficiently during warm Perth afternoons. Scheduling to run 10am–2pm maximises both solar self-consumption and heat pump COP (coefficient of performance — higher COP in warmer ambient temperatures).

Strategy 4: air conditioning pre-cooling

The pre-cooling strategy: On Midday Saver or A1 with solar, run AC harder during 10am–2pm to cool the house to 22–23°C. After 2pm, switch AC to maintain mode (25–26°C). The thermal mass of the house retains coolness through the evening without AC running.

Energy saved: A 10kW ducted AC running at full cooling (4kW draw) from 10am–2pm, then switching to maintain mode (1.5kW) from 2pm–8pm:

• Full cooling 4 hours × 4kW = 16kWh (solar covered: 12kWh; small import: 4kWh)
• Maintain mode 6 hours × 1.5kW = 9kWh (mostly grid after 2pm)
• vs running at 3kW continuously 7am–9pm = 42kWh × 33.26c = $13.97/day

Pre-cooling shifts consumption earlier, increasing solar self-consumption during peak generation hours.

Strategy 5: smart plugs and automation

Smart plugs (e.g. TP-Link Kasa, Shelly, or Matter-compatible devices) allow scheduling appliances to specific time windows.

High-value smart plug targets:

• Water features / pond pumps
• Pool lights or garden lighting (if on non-timer circuits)
• Dehumidifiers
• Electric blanket pre-warming (winter: warm the bed 10am–11am, switch off — the blanket retains warmth)

Monitoring-triggered automation: Some inverter brands (Fronius, Sungrow, Enphase) offer APIs or smart home integrations that trigger loads when solar export exceeds a threshold. This is a more sophisticated setup but gives the closest thing to battery-like self-consumption without the battery cost.

What to expect from active load shifting

A Perth household that actively shifts loads to solar hours typically improves self-consumption ratio from 30–35% to 45–60%. For a 6.6kW system generating 10,000kWh/year:

• 30% self-consumption: 3,000kWh × 33.26c = $998/year avoided import + 7,000kWh × 2c = $140 export = $1,138/year total
• 55% self-consumption: 5,500kWh × 33.26c = $1,829/year avoided import + 4,500kWh × 2c = $90 export = $1,919/year total
• Difference from load shifting alone: approximately $780/year

For the cost of changing some timer settings, this is one of the highest-return adjustments available.

Midday Saver and self-consumption

If you're on Midday Saver, the super off-peak rate (8.85c/kWh, 9am–3pm) applies to grid imports during that window even when your solar isn't covering all loads. This means:

• Self-consumed solar during 9am–3pm: avoids 8.85c/kWh import (a smaller saving than A1)
• Grid import during 9am–3pm: only costs 8.85c/kWh (cheap anyway)
• Peak window (3pm–9pm) at 55.33c/kWh: the period to minimise grid imports

On Midday Saver, the focus shifts to keeping loads away from the peak window rather than purely maximising solar self-consumption. AC during 9am–3pm (self-consumed solar + cheap grid) beats AC at 3pm–9pm at peak rates.

Your monitoring app shows your self-consumption ratio (or you can calculate it: self-consumed kWh = generated kWh − exported kWh). Upload your Synergy bill to BillWise to see how much you could save by shifting specific loads to solar hours.