Solar and bore pump irrigation in Perth: saving on garden watering costs

Perth sits on the Superficial Aquifer — a vast shallow groundwater system that makes bore water access practical for a large proportion of suburban properties. Thousands of Perth homes use bore pumps for garden irrigation, particularly in summer when reticulation demand is high.

Bore pumps run on electricity. For households watering large gardens through Perth's long dry summer, bore pump electricity consumption is a meaningful bill component. Solar generation timed to irrigation hours can substantially reduce or eliminate this cost.

How much electricity does a bore pump use?

Typical residential bore pump specs:

• Most Perth suburban bore pumps draw 750W–2.5kW
• Common operation: 30–90 minutes per irrigation cycle
• Typical summer irrigation schedule: 3–5 days per week, 2–3 cycles per day (multiple zones)

Annual electricity estimate:

| Pump size | Run time | Annual kWh (summer heavy) | |---|---|---| | 750W | 60 min/day × 120 days | ~90kWh | | 1.1kW | 90 min/day × 150 days | ~248kWh | | 1.5kW | 90 min/day × 150 days | ~338kWh | | 2.0kW | 2hr/day × 120 days | ~480kWh |

Actual consumption varies by garden size, zone count, reticulation controller schedule, and bore yield.

Cost at A1 tariff (33.26c/kWh):

• Light bore use: ~$30/yr
• Moderate suburban: ~$80–$115/yr
• Heavy irrigation (large blocks): ~$160/yr+

These are modest amounts compared to air conditioning or hot water — bore pump electricity is rarely the dominant bill driver. But for households already adding solar, optimal timing of bore pump operation can shift this cost entirely to solar generation.

When bore pumps and solar align naturally

Perth's irrigation season (September–April, peaking November–March) coincides closely with maximum solar generation. Summer days when the garden needs water are also the days of maximum solar output.

Daytime irrigation scheduling: Most Perth bore reticulation controllers can schedule irrigation for morning hours. Setting irrigation cycles to run between 7am–10am or 9am–12pm means:

• The bore pump runs during solar generation hours
• On a 6.6kW solar system, even a 2kW bore pump represents a modest fraction of available generation
• The self-consumption benefit: bore pump power comes from solar rather than grid

Existing controller compatibility: Standard reticulation controllers (Rain Bird, Hunter, Orbit, Holman) all support timed scheduling — no special hardware needed. Change the irrigation start time to align with solar generation.

The value of self-consuming bore pump electricity

At A1 tariff (33.26c/kWh), bore pump electricity costs approximately 33c per kWh. The same kWh from solar self-consumption is "free" (having displaced grid import). At DEBS off-peak export (2c/kWh), that same kWh would have earned only 2c if exported.

Self-consumption vs export value:

• 1kWh to bore pump (A1): saves 33.26c
• 1kWh exported at DEBS off-peak: earns 2c
• Difference: 31.26c per kWh

For bore pump loads running during solar generation hours, the self-consumption saving is approximately 16× better than exporting the same energy. This is the core logic for timing irrigation to solar hours regardless of system size.

Dedicated off-grid bore pump systems

For properties without mains solar systems — rural lots, hobby farms, large properties on the rural fringe of Perth — a dedicated off-grid solar bore pump is an alternative to running mains electrical connection to the bore.

How it works: A small dedicated solar panel (300–500W) and DC pump replaces the AC pump and mains connection. The pump only runs when the sun is shining, which aligns with daytime irrigation needs.

Cost:

• Small solar pump kit (100W panel + DC pump): $500–$1,500
• Professional installation with wiring and pressure tank: $2,000–$5,000

Suitable for:

• New bores where running mains to the pump is expensive
• Hobby farms with irrigation timing flexibility
• Bore locations distant from the house switchboard

Not suitable for:

• Established systems with existing AC pumps (replacing a functioning pump with a solar DC system rarely pencils out financially)
• High-demand irrigation requiring consistent flow regardless of solar availability

Bore yield and pump sizing considerations

Perth's Superficial Aquifer yield varies by suburb and depth:

• Many Perth suburban bores yield 2,000–4,000L/hr (typical for garden use)
• Deeper Leederville Aquifer bores have higher yields but require deeper drilling and higher pump head

Bore failure and solar: Bore pumps can fail from:

• Pump wear (impellers, seals)
• Motor burnout from low bore yield (running dry)
• Bore contamination (sediment, algae)

These failure modes are independent of whether the pump runs on solar or grid power. Solar timing doesn't affect pump reliability.

Running costs on Midday Saver

On Synergy's Midday Saver tariff, the super off-peak window (9am–3pm) costs 8.85c/kWh. Running a 1.5kW bore pump for 90 minutes during this window costs approximately 20c — compared to 83c at peak rates (3–9pm).

Even without rooftop solar, Midday Saver households should schedule bore irrigation during the super off-peak window to minimise electricity cost.

Practical steps

For existing solar + bore pump:

1. Check your bore controller's current irrigation schedule
2. Identify irrigation start times and adjust to begin no earlier than 8am and finish by 1pm (leaving solar headroom for other loads)
3. Verify the schedule in your solar monitoring app — confirm the pump draw appears during solar generation periods
4. No additional equipment is required

For households without solar: If you're adding solar primarily for reasons other than bore pump costs, bore pump alignment is a free benefit. If bore pump cost is a significant motivator, note that the annual saving from solar covering bore pump electricity ($30–$160/year) is unlikely to materially affect the solar payback calculation — it's a bonus, not a primary driver.

Bore pump electricity is rarely the largest component of a Perth electricity bill, but timing irrigation to solar generation hours captures the maximum self-consumption benefit at no additional cost. Upload your Synergy bill to BillWise to see where your electricity spending concentrates.