Pumping water is one of the most practical and rewarding uses of solar power — especially for irrigation, livestock, and off-grid homes where running a grid line to a well is expensive or impossible. Because a solar pump usually runs during the day and fills a tank, it often needs no batteries at all, which keeps the system simple and affordable. The key to a system that actually delivers the water you need is sizing it correctly, and that comes down to two numbers: how much water you need per hour, and how high you have to lift it.
The two numbers that decide everything
Every pump sizing calculation starts here:
- Flow rate — how much water you need per hour, in cubic meters (m³/h) or liters. This is driven by your use: irrigation area, number of animals, or household demand.
- Total head — the total vertical distance the pump lifts water, in meters, plus friction losses in the pipe. A deep borehole with an elevated tank has high head; moving water across flat ground has low head.
Multiply these together (with gravity and water density) and you get the hydraulic power — the pure physical work of lifting that water. Everything else is about how much electrical power it takes to deliver that work.
The formula
The hydraulic power in watts is:
Hydraulic power (W) = Flow (m³/h) × Head (m) × 1000 × 9.81 ÷ 3600
That's the ideal power. A real pump and motor aren't 100% efficient, so the actual electrical power the pump draws is higher:
Pump power (W) = Hydraulic power ÷ Pump efficiency
And because the solar side has its own losses (controller, wiring, heat, panel derating), the solar array is sized a step larger again, with a safety margin so the pump reaches full flow even in less-than-perfect sun:
Array size (W) = Pump power ÷ System efficiency × safety margin
A worked example
Say a small farm needs 5 m³ of water per hour, lifted a total head of 30 meters:
- Hydraulic power = 5 × 30 × 1000 × 9.81 ÷ 3600 ≈ 409 W
- At 45% pump efficiency: 409 ÷ 0.45 ≈ 908 W of pump power
- With system losses and margin, the solar array needed is roughly 1,300-1,400 W
So this farm would need around 1.3-1.4 kW of panels — about three to four modern panels — running direct into the pump during daylight, filling a tank for use through the day.
Why head matters more than people expect
Flow and head both increase the power needed, but head is the one people underestimate. Doubling the lift height doubles the power required, and every meter of pipe friction adds to it. Deep boreholes are the classic case: a pump moving a modest flow from 80 meters down needs far more power than one moving the same flow from a shallow well. The chart above shows this relationship directly for your own numbers.
Do you need batteries?
Usually not. The most common and cost-effective approach is direct solar pumping: the panels drive the pump whenever the sun is out, and water is stored in a tank rather than storing energy in batteries. A day or two of tank storage is far cheaper than a battery bank. You only need batteries if you must pump at night or need a guaranteed constant flow regardless of weather.
Turning the array size into panels
Once you have the array size in watts, our solar panel calculator converts it into a panel count for the wattage you plan to use, and the energy production calculator shows how much energy that array delivers across the day. If you decide you do want battery backup for night pumping, the battery calculator will size the bank.
Frequently asked questions
How do I size a solar water pump?
Start with the flow rate you need and the total head the pump lifts against. These give the hydraulic power. Divide by pump efficiency to get the pump's electrical power, then divide by system efficiency and apply a safety margin to get the solar array size. This calculator does all of that for you.
What is total head in a water pumping system?
Total head is the total resistance the pump works against, in meters — the vertical lift from water source to discharge, plus pipe friction losses. As a starting point, add about 5 to 10 percent to the static height for friction, more for long or narrow pipe runs.
How many solar panels do I need to run a water pump?
It depends on the pump power and your sunlight. A small pump lifting a modest flow a few meters might need only 300 to 600 watts of panels, while a deep borehole pump can need several kilowatts. Enter your flow and head above and the calculator estimates the array size, which you can convert to a panel count with our panel calculator.
Can a solar pump work without batteries?
Yes. Many solar pumping systems run direct — panels power the pump during daylight and water is stored in a tank instead of storing energy in batteries. This is cheaper and simpler for irrigation and livestock. Batteries are only needed if you must pump at night.