Last updated
Four example water supplies, calculated
All use 5 sun hours, a typical 40% pump system, direct solar with a two-day tank, and 10% pipe friction.
| Supply | Water per day | Total head | Pump power | Solar panels | Flow | Tank |
|---|---|---|---|---|---|---|
| Village garden tap | 1,500 L | 19.8 m | 40 W | 60 W | 5.0 L/min | 3,000 L |
| Cattle trough | 2,000 L | 29.7 m | 81 W | 110 W | 6.7 L/min | 4,000 L |
| Drip irrigation plot | 10,000 L | 49.7 m | 677 W | 850 W | 33.3 L/min | 20,000 L |
| Deep borehole household | 6,000 L | 93.5 m | 637 W | 800 W | 16.7 L/min | 12,000 L |
- The drip plot includes 1 bar (about 10 m of head) of outlet pressure. Pressure counts as lift, and it is a big share of the total.
- The deep borehole lifts less water than the drip plot, but from 80 m down, so it needs almost as much solar.
How the sizes are calculated
- Total dynamic head (m) = (depth to water while pumping + height to the tank + outlet pressure as meters of water) × (1 + friction allowance). One bar is about 10.2 m of head and one psi is about 0.703 m.
- Water energy per day (Wh) = 2.725 × cubic meters per day × total head in meters. The 2.725 comes from 1,000 kg per m³ × 9.81 ÷ 3,600.
- Electrical energy (Wh) = water energy ÷ pump system efficiency. Typical solar pump sets are around 30–50% efficient from panel to water.
- Pump power (W) = electrical energy ÷ peak sun hours, and flow = daily water ÷ peak sun hours.
- Solar panels (W) = electrical energy ÷ (peak sun hours × 0.8) when pumping direct, and × 0.75 through batteries. The factor covers heat, dust, wiring and controller losses.
- Tank = daily water × days of storage. Battery = electrical energy × days ÷ usable capacity.
- Panels you already have: water per day = panel watts × sun hours × 0.8 × efficiency ÷ (2.725 × head).
The warning for very large jobs appears when daily water in m³ times head in meters is above about 2,000, a common rule of thumb for what a single solar pump set can do. The calculator does not model seasonal sun changes, panel tilt or a specific pump’s curve.
Typical daily water use
| Use | Rough planning value |
|---|---|
| People, drinking and basic household use | 50 L (13 US gal) each |
| Dairy cow | 100 L (26 gal) |
| Beef cattle | 45 L (12 gal) |
| Horse | 40 L (11 gal) |
| Pig | 15 L (4 gal) |
| Sheep or goat | 6 L (1.6 gal) |
| Chicken or duck | 0.3 L (0.08 gal) |
| Garden or crop | about 5 mm of water per day in summer, which is 5 L per m² |
These are rough values. Climate, animal size, feed and milk production change them, so use local agricultural advice for your area.
Using it anywhere in the world
- Daily water can be entered in liters, cubic meters or US gallons, and lift in meters or feet. The page picks defaults from your browser language.
- Outlet pressure can be in bar or psi.
- Flow is shown in both liters per minute and US gallons per minute.
- Choose the sun level for the month when you need the most water, not the best month.
Why solar pumps fall short
- Using the static water level. Use the level while pumping, which is lower because the water table drops as you draw water.
- Forgetting friction and pressure. Long pipes and drip systems add real head.
- Sizing for the best month. Water use often peaks when sun hours are not at their highest.
- Skipping the tank. Storing water is far cheaper than storing electricity.
- Choosing the wrong pump type. A pump has to deliver the flow you need at your head. Check its curve, not only its watts.
- No dry-run protection. A float switch or level probe stops the pump when the well or tank is empty.
Common questions
How many solar panels do I need for a water pump?
Three things set it: how much water you need, how high it must be lifted, and your sun hours. Pumping 10,000 L a day from 30 m down to a tank 5 m above ground needs about 660 W of panels with 5 sun hours. Pumping 2,000 L a day to a trough from 25 m down needs only about 110 W.
What is total dynamic head (TDH)?
Total dynamic head is the total effort the pump has to make, expressed as a height of water. It is the depth to the water while pumping, plus the height to the tank or outlet, plus any outlet pressure, plus an allowance for pipe friction. As a guide, 10.2 m of head equals 1 bar, and 2.31 ft of head equals 1 psi.
Do I need batteries for a solar water pump?
Usually not. A water tank is much cheaper than a battery, and the pump simply runs when the sun shines. Batteries make sense when you need to pump at night or run a pressurised household supply. Use the “Through batteries” option to see the battery size for those cases.
How much water can a 300 W solar pump set deliver?
With 5 sun hours and a typical pump, 300 W of panels pumps about 17.6 m³ (17,600 L) a day from 10 m of head, about 5.9 m³ from 30 m and about 2.9 m³ from 60 m. Output falls in proportion to the head. Enter your panel watts in the calculator to see your own figure.
Does solar pumping work on cloudy days?
A solar pump delivers less water in weak light, and it may not run at all in heavy overcast. That is why a storage tank matters. Size the system using the sun level for the month when you need the most water, and keep one to three days of water in the tank.
How do I find the depth to water?
Use the water level while the pump is running, not the level when it is idle. The difference is called drawdown, and it can add several meters. A well driller’s record or a water level probe gives you the number. If you only know the idle level, add a safety margin.
Related calculators
For battery storage, use the battery runtime calculator. To size cable and fuses for the pump circuit, use the wire gauge and fuse calculator, and for a whole system see the solar and battery calculator.
Fencing animals on a solar farm? Try the electric fence solar calculator.