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Solar water pump sizing calculator

Daily water, sun hours for your state, lift and pipe friction in; flow rate, total dynamic head, pump and panel watts and storage out. Every step is printed so you can check it. New to the terms? Start with how to size a solar pump.

By the editors of SolarPoweredWaterPumps.comLast reviewed October 2026

1. Water needed per day

Beef cattle (cow or finishing steer) (head)Milking dairy cows (head)Horses (head)Sheep or goats (head)Finishing pigs (head)People in the house (people)Garden or orchard under drip (sq ft)Anything else (gal/day)

Hot-weather planning figures, per day: beef cattle (cow or finishing steer) 20 gal per head; milking dairy cows 35 gal per head; horses 15 gal per head; sheep or goats 2.5 gal per head; finishing pigs 3 gal per head; people in the house 50 gal per person; garden or orchard under drip 0.089 gal per sq ft. Sources on the methodology page.

2. Sun where the panels go

StateWhen you need the water

Houston, south-facing at 20 degrees. Annual average 5.21, darkest month Dec at 3.66 peak sun hours. Design value used: 3.66.

3. Lift and pipe

Pump typeDepth to pumping water level (ft)Rise from wellhead or pump to the tank (ft, negative if downhill)Total pipe length (ft, including drop pipe)PipePipe sizePressure wanted at the outlet (psi, 0 for a tank)Fittings allowance (% of pipe friction)

4. System

PowerWire-to-water efficiency (%)

Small DC pumps typically turn 25 to 50% of their electrical input into lifted water. 35% is a cautious middle; use the figure from your pump's curve if you have it.

1.82 gpm · 91 ft · 120 WSee results

SolarPoweredWaterPumps.com: pump sizing spec sheetOct 19, 2026

Water per day	400 gal	Location	Texas (Houston)
Design sun	3.66 h (Year-round (size for the darkest month))	Pump	Submersible
Lift / rise	80 ft / 10 ft	Pipe	300 ft of 1 in Polyethylene (PE, SIDR)
Outlet pressure	0 psi	Efficiency	35% wire-to-water
Power	Direct drive to a tank

Your system, drawnnot to scale

Water per day

400gal

Flow rate needed

1.82gpm

Total dynamic head

91ft

Pump input

89W

Solar array

120W

Storage tank

1,200gal

The working

Pumping hours. A direct-drive pump runs on sunlight, so it gets the equivalent of 3.66 full-sun hours a day in the design month.
Flow. 400 gal ÷ (3.66 h × 60) = 1.82 gpm.
Static head. 80 ft lift + 10 ft rise = 90 ft.
Friction. 1 in Polyethylene at 1.82 gpm loses 0.34 ft per 100 ft (Hazen-Williams, C=140). × 300 ft ÷ 100 × (1 + 10% fittings) = 1.1 ft. Velocity 0.7 ft/s.
Total dynamic head = 91.1 ft.
Hydraulic power. 1.82 gpm × 91.1 ft ÷ 3,960 × 745.7 = 31.3 W of water work. ÷ 35% efficiency = 89 W at the pump.
Daily energy. 400 gal × 91.1 ft × 0.00314 Wh = 114 Wh of lifting, or 327 Wh of electricity.
Array. 89 W ÷ 0.75 (heat, dust, wiring and the weak hours either side of noon) = 119 W of panels.
Storage. Three days of water, 400 × 3 = 1,200 gal. The tank is the battery in a direct-drive system.

Pumps worth checking against this duty

Affiliate links: we may earn a commission at no extra cost to you. That doesn't change what we recommend. Disclosure.

VEVOR 12V 120W (rated up to 3.2 gpm and 230 ft, 12V class)
VEVOR 24V 277W (rated up to 9.25 gpm and 272 ft, 24V class)
VEVOR 48V 369W (rated up to 8.4 gpm and 273 ft, 48V class)

Shown because their rated maximums clear your flow and head with margin. Maximum flow and maximum head never happen together: read the manufacturer's curve at 91 ft before buying. We have not tested these pumps.

Runs entirely in your browser. Nothing you type is sent anywhere. A planning estimate, not engineering: have electrical work checked against NEC Article 690 and use a licensed well contractor where your state requires one.

Assumptions

Sun hours are NREL NSRDB data via PVGIS, for a south-facing panel at 20 degrees at the largest city in each state. See sun hours by state.
A direct-drive pump is assumed to pump at full rate for the design month's peak sun hours. Real pumps start slowly in the morning; the 0.75 array factor allows for it.
Friction uses Hazen-Williams with C = 140 for polyethylene and 150 for PVC. The friction tables use the same formula.
Battery mode assumes LiFePO4 at 80% usable capacity and 90% round-trip efficiency.
Full detail on the methodology page.