Solar pump inverter power ratings, kW and HP
22 kW and 30 HP are the same drive. So are 30 kW and 40 HP, and 37 kW and 50 HP. One horsepower is 0.746 kW, and the two sets of numbers are one product range described in two habits.
This page maps them against each other, gives the cabinet footprint at each band, and explains why picking a drive by power alone gets you a correctly sized box around a possibly wrong pump.
1 HP = 0.746 kW
Convert before you compare. Half the confusion in this category is two names for the same thing.
37 kW is the step
Below it, a wall-standing frame. At and above it, floor-standing and much bigger. Plan the room accordingly.
The motor sets the drive
And the duty point set the motor. Start at the water, not at the power rating.
The conversion, with the cabinet size
| Metric | Imperial | Cabinet W × H × D | Notes |
|---|---|---|---|
| 5.5 kW | 7.5 HP | 600 × 1000 × 350 mm | Wall space; small borehole or a surface set |
| 7.5 kW | 10 HP | 600 × 1000 × 350 mm | Wall space |
| 11 kW | 15 HP | 600 × 1000 × 350 mm | Top of the compact frame |
| 15 kW | 20 HP | 800 × 1000 × 350 mm | Wider frame, same depth |
| 18.5 kW | 25 HP | 800 × 1000 × 350 mm | Wider frame |
| 22 kW | 30 HP | 800 × 1000 × 350 mm | The most common agricultural size |
| 30 kW | 40 HP | 800 × 1000 × 350 mm | Still on the wall-standing frame |
| 37 kW | 50 HP | 800 × 2000–2200 × 600–800 mm | Floor-standing. Plan the room around it |
| 45 kW | 60 HP | 800 × 2000–2200 × 600–800 mm | Floor-standing |
| 55 kW | 75 HP | 800 × 2000–2200 × 600–800 mm | Floor-standing |
Horsepower figures are the trade rounding of the exact conversion: 22 kW is 29.5 HP, 30 kW is 40.2 HP, 37 kW is 49.6 HP. Cabinet dimensions are the standard enclosure for each band; a higher enclosure rating or extra devices change them.
Why the power rating is only half the specification
A drive has to cover the motor: nameplate power, voltage and phase. That part is simple and it is what the power rating answers. What it does not answer is whether the motor is the right motor.
| The duty point chose the pump | Flow at total dynamic head. Get that wrong and you have a correctly rated drive around a pump that cannot reach your tank. |
| The pump chose the motor | Same power covers very different pumps. At 1500 W one model reaches 160 m and another stops at 70 m. |
| The motor chose the drive | Only at this point does the kW or HP number become the question, and by then it is the easy one. |
| The site chose the array | String length comes from the module and the site temperature extremes, not from the drive rating. |
The order matters
Enquiries that open with “I need a 30 HP solar pump inverter” are common and perfectly answerable, but the useful first question back is always about the well. If you already have the pump, the nameplate settles it in one photograph. Why power tells you nothing about head.
Electrical window, all bands
| PV input window | Two ranges. Low window 150 – 450 V, high window 350 – 780 V. Which suits you depends on how the array is strung. |
| Where to put the string Voc | Aim for 360 – 430 V on the low window and 620 – 750 V on the high one, checked at your record low module temperature. |
| AC input | 110 V, 220 V or 380 V, 50 or 60 Hz, for sites that also have grid or a generator. |
| Motor output | 0 – 599 Hz, so the pump speed follows whatever the array can give. |
| Power range | 0.75 kW to 55 kW single or three phase, and 37 kW to 200 kW on the larger three-phase frame. |
What settles it in one message
If you already have the pump, this is the fastest route to a price:
- •A photograph of the pump nameplate. Motor power, voltage, phase and frequency are all on it.
- •The site city or coordinates, for the temperature extremes.
- •What is on site now: solar only, grid, or a generator, and what it has to do.
Send the nameplate
One photograph and a location is enough to quote a drive cabinet. If you do not have a pump yet, start from the well instead and we will work forward.
Inverter power rating FAQ
How many HP is a 22 kW solar pump inverter?
About 30 HP. One horsepower is 0.746 kW, so 22 kW is 29.5 HP and the trade rounds it to 30. The same equipment is sold as a 22 kW drive in metric markets and a 30 HP drive where horsepower is the habit; it is one product with two names.
What is a 30 kW solar pump inverter in horsepower?
40 HP. 30 kW divided by 0.746 is 40.2, rounded to 40. Likewise 37 kW is 50 HP and 11 kW is 15 HP. If an offer quotes one unit and your specification is in the other, converting is the first thing to do before comparing anything else.
Do I choose a solar pump inverter by its kW rating?
You match it to the motor, not to the water. The drive rating has to cover the pump motor nameplate power, voltage and phase. But the motor size itself came from the duty point, and if the duty point was wrong the drive will be the right size for the wrong pump. Get the head and flow settled first.
Can a bigger inverter drive a smaller pump?
Generally yes, and it is sometimes done deliberately to leave room for a future larger pump. It costs more, takes more space and does not make the pump deliver more water. What does not work is the other way round: a drive rated below the motor will trip on overload.
Why does the cabinet get so much bigger at 37 kW?
Because it changes from a wall-standing frame to a floor-standing one: roughly 800 × 1000 × 350 mm up to 30 kW, against 800 × 2000 to 2200 × 600 to 800 mm at 37 kW and above. It is worth checking early because it changes what kind of room or shelter the site needs.
What PV array voltage do these drives need?
Two input windows are available: a low window of 150 to 450 V and a high window of 350 to 780 V. Aim for a string open-circuit voltage of 360 to 430 V on the low window and 620 to 750 V on the high one, checked at your record low module temperature so a cold morning does not push the array over the limit.
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