Solar Water Pump Calculator

How to use this calculator

Enter six values and the calculator returns the hydraulic energy your application needs each day, the electrical energy the pump will draw, the PV array size in watts-peak, how many panels you need at the wattage you choose, the pump’s operating power during sunlight hours, and the average flow rate it will deliver.

1. Daily water demand (litres/day) — total volume you need each day. Common Australian targets: 50–80 L/day per beef breeder, 70–110 L/day per lactating dairy cow, 6–10 L/day per sheep, 4–6 L/m²/week for irrigated horticulture in summer.
2. Total dynamic head (m) — pumping water level in your bore in metres, plus any rising main elevation gain to a tank stand. Use the driller’s pumping level, allowing for seasonal drawdown.
3. Peak sun hours/day — annual-average daily irradiance. Typical Australian figures: Brisbane 4.6, Perth 5.5, Sydney 4.5, Melbourne 3.9, Adelaide 4.4, Darwin 5.5, Alice Springs 5.9, Mount Isa 5.7, Broken Hill 5.0, Hobart 3.7. Bureau of Meteorology long-term monthly data give precise figures by latitude.
4. Pump wire-to-water efficiency (%) — overall pump efficiency. 45% is a fair default for a Mono Sun-Sub or Lorentz PS2 submersible.
5. System derate (%) — losses from controller (3–5%), wiring (2–4%), and panel soiling/temperature (5–10%). 85% is a sound default; drop to 80% in dusty pastoral country where soiling is heavy.
6. Panel wattage (W) — your chosen panel. The 2026 standard CEC-listed module is 400–440 W; 540 W bifacial modules dominate ground-mount rural installs.

How solar water pumping works

A solar water pumping system has three components: the photovoltaic array, the pump controller, and the pump. Unlike a grid-connected solar electric system, there is no battery and no inverter — the controller takes raw DC from the panels and feeds the pump directly with whatever power the sun is currently producing.

The controller does two important jobs. First, it implements maximum power point tracking (MPPT) so the panels run at their peak even as light levels change. Second, it varies the pump speed throughout the day — fastest at noon, slower at sunrise and sunset, and clean shutdown at low irradiance. Variable-speed operation is why solar bore pumps keep running through patchy cloud while a fixed-speed mains pump would short-cycle.

The pump itself is typically a brushless DC submersible (for bores) or a surface-mounted DC centrifugal pump (for dam transfer and shallow installations). Lorentz PS2, Grundfos SQFlex, Mono Sun-Sub, and Davey are the dominant brands in the Australian rural water market. Mono helical-rotor and Lorentz PS2 with the helical-rotor cartridge are preferred for high-head, low-flow bore applications — moving 1,000–5,000 L/day from 60–200 m bores.

The physics, derived from first principles

The hydraulic energy needed to lift a volume V of water through a vertical height H is fixed by physics: water density (about 1,000 kg per cubic metre), gravity (9.81 m/s²), volume, and height.

E_hydraulic_Wh = ρ × g × V_m3 × H_m / 3600
              = 1000 × 9.81 × V_m3 × H_m / 3600
              ≈ V_m3 × H_m × 2.725

Electrical energy is hydraulic energy divided by pump and system efficiencies:

E_electrical_Wh = E_hydraulic_Wh / (η_pump × η_system)

PV array in watts-peak:

PV_Wp = E_electrical_Wh / PSH

Worked example

A 5,000 L/day stock-water system at 40 m of head on a New South Wales cattle property (PSH 5.0), with a Mono Sun-Sub pump (45% wire-to-water), 85% system efficiency, 400 W panels:

• V_m3 = 5 m³
• H_m = 40 m
• E_hyd = 5 × 40 × 2.725 = 545 Wh
• E_elec = 545 / (0.45 × 0.85) = 1,425 Wh
• PV needed = 1,425 / 5.0 = 285 Wp
• Panels = ceil(285 / 400) = 1 panel

A single 400 W panel gives 40% headroom for cloudy days. Most installers run two panels (800 Wp) on this size duty so the pump still meets demand on a 50%-irradiance day.

Australian sizing rules of thumb

For solar-direct pumping with no batteries and a tank, in Australian conditions:

• Design the storage tank to hold 5–7 days of livestock demand. The Bureau of Meteorology long-term cloud records support this for most pastoral country.
• Size the array for the worst sun month at your latitude (typically June or July in the southern states, December in northern Australia).
• Add 30–50% PV oversizing to the worst-month calculation.
• For typical southern Australian bore pumping at 40 m head, expect 0.4–0.6 Wp per litre-per-day at annual mean PSH, or 0.8–1.2 Wp per litre-per-day if you size to the worst winter month alone.
• The Future Drought Fund’s Farm Business Resilience Program has published recommended margins for stock-water resilience that closely match these numbers.

Pump types compared

For most graziering applications under 10,000 L/day from a bore under 60 m, a Mono Sun-Sub or Grundfos SQFlex submersible is the standard pick. For deeper bores (100 m+), a Mono helical-rotor or Lorentz PS2 with the helical-rotor cartridge maintains flow at low input power where a centrifugal would stall.

Australian state-level incentives

• Future Drought Fund (Farm Business Resilience Program) — Commonwealth co-funded program through state delivery partners; solar pumping has been funded in pastoral electorates as part of drought-resilience infrastructure.
• NSW Department of Primary Industries — On-Farm Emergency Water Infrastructure Rebate Scheme — has funded solar pumping in past drought cycles; check current eligibility.
• Queensland Drought and Climate Adaptation Program — funds water infrastructure for drought resilience including solar-direct pumping.
• Victoria’s On-Farm Drought Infrastructure Support Grants — covers off-grid pumping where it reduces dependence on shared reticulated supply.
• CEC-accredited installer requirement — for grid-connected solar at the homestead, CEC accreditation is mandatory. For stand-alone solar bore pumping, CEC accreditation isn’t required but most state grant programs prefer accredited installers.
• Smart Apprentice Scheme and Drought Loans — interest-free or low-interest finance from RIC (Regional Investment Corporation) covers water infrastructure including solar pumping.

Common mistakes that hurt performance

• Using standing water level instead of pumping level. Murray Basin and Great Artesian Basin bores can drawdown 10–30 m at typical pumping rates; sizing to standing under-sizes the array badly.
• Assuming a centrifugal will work at 150 m of head. Above 80–100 m, centrifugal output collapses; Mono or Lorentz helical-rotor is the correct choice.
• Pumping straight to trough with no tank. A solar-direct system without storage runs dry on cloudy days. A 22,000 L Bushman tank on a tank stand is the standard pattern.
• Long cable runs without proper sizing. Bore caps to panel array distances of 50–100 m are common; voltage drop above 3% causes nuisance trips during low-irradiance starts. Size cable to AS/NZS 3008 with margin.
• Roof-mounting the array on the homestead. A ground-mount frame at the bore avoids long cable runs and lets the array be tilted to the bore latitude rather than the homestead roof pitch.

Sources

• Clean Energy Council — Solar PV systems — installer accreditation and module data
• Bureau of Meteorology — Solar radiation data — peak sun hour data by location
• Australian Renewable Energy Agency (ARENA) — solar pumping case studies
• Future Drought Fund — Farm Business Resilience Program — funded solar pumping projects
• SunWiz — Australian solar market data — agricultural PV installation statistics
• Mono Pumps Australia — Sun-Sub sizing guide — pump curves and selection charts referenced for efficiency defaults