Pump motors are sold in horsepower, but solar arrays are sized in kilowatts. This guide converts one to the other and shows the minimum array for each common motor size. The water pump sizer does the same sums for any value from 0.5 to 200 hp.
One mechanical horsepower is 0.7457 kW. A metric horsepower (PS) is slightly smaller, 0.7355 kW. The horsepower on a motor nameplate is the power at the shaft, not the electricity it draws.
| Pump motor (hp) | Shaft power (kW) | Motor input (kW) | Minimum solar array (kW) |
|---|---|---|---|
| 1 | 0.7 | 0.8 | 1.1 |
| 2 | 1.5 | 1.7 | 2.1 |
| 3 | 2.2 | 2.5 | 3.2 |
| 5 | 3.7 | 4.1 | 5.3 |
| 7.5 | 5.6 | 6.2 | 8.0 |
| 10 | 7.5 | 8.3 | 10.7 |
| 15 | 11.2 | 12.4 | 16.0 |
| 20 | 14.9 | 16.6 | 21.4 |
| 30 | 22.4 | 24.9 | 32.0 |
| 50 | 37.3 | 41.4 | 53.4 |
| 75 | 55.9 | 62.1 | 80.1 |
| 100 | 74.6 | 82.9 | 106.8 |
| 150 | 111.9 | 124.3 | 160.2 |
| 200 | 149.1 | 165.7 | 213.5 |
Round up to a whole number of panels. A 10 hp pump needs at least 10.7 kW, which is 20 panels of 550 W (11 kW).
Example: a 10 hp pump with 60 percent pump efficiency lifting 60 m. Hydraulic power is 7.46 × 0.6 = 4.47 kW, so flow is 4.47 × 367 ÷ 60 = 27.4 m³/h. With 5.5 sun hours that is about 151 m³ a day.
Next step: size your pump, then see the matching parts.
