4-5
300W Panels
1,200W
Minimum Array
1,500+
Gallons/Day
If you're looking to run a 1HP well pump on solar panels, you need to get the sizing right. Too few panels and the pump won't start. Too many and you've wasted money. The answer depends on your pump type, well depth, and whether you're going direct-drive or through batteries.
This guide gives you the exact panel count for every common setup, explains why a "1HP" pump actually draws more than 746W, and helps you choose between the two main approaches to solar well pumping.
01
Quick Answer: Solar Panels for a 1HP Pump
| Setup | Total Watts | 300W Panels | 100W Panels |
|---|---|---|---|
| 3-phase DC solar pump (direct drive) | 1,200W | 4 | 12 |
| Single-phase AC pump + inverter | 1,500-1,800W | 5-6 | 15-18 |
| AC pump + battery bank + inverter | 1,500-2,000W | 5-7 | 15-20 |
If you're installing a new solar pump system from scratch, a 3-phase DC pump with direct-drive controller is the most efficient option: fewer panels, no batteries, no inverter. If you're retrofitting an existing AC well pump, you'll need more panels to cover the inverter and startup losses.
02
The Sizing Math
The formula seems simple, but there's a critical detail most people miss: a "1HP" pump does not draw exactly 746W.
Why 1HP is Not 746W
1 HP equals 746W of mechanical output. But electric motors aren't 100% efficient. A typical submersible well pump motor runs at 60-75% efficiency, meaning it draws more electrical watts to produce 746W of mechanical work:
Electrical Draw = HP × 746 ÷ Motor Efficiency
Then add 20-30% for the oversizing margin (panels don't produce rated watts in real conditions):
Solar Array Size = Actual Draw × 1.25 (safety factor)
03
Sizing by Pump Type
3-Phase DC Solar Pump (Best for New Installs)
Brands like RPS, Grundfos SQFlex, and Lorentz make pumps designed specifically for solar. They use a DC controller that converts panel power to 3-phase AC for the motor. Three-phase motors are more efficient and have a lower startup surge.
| Pump HP | Running W | Startup W | Solar Array | 300W Panels |
|---|---|---|---|---|
| 1/2 HP | 400-500W | 500-650W | 600W | 2 |
| 3/4 HP | 600-750W | 750-950W | 900W | 3 |
| 1 HP | 800-1,000W | 950-1,200W | 1,200W | 4 |
| 1.5 HP | 1,100-1,400W | 1,400-1,800W | 1,800W | 6 |
| 2 HP | 1,500-1,800W | 1,800-2,200W | 2,400W | 8 |
Single-Phase AC Pump (Retrofitting Existing)
If you already have a standard 120V or 240V well pump and want to run it from solar, you'll need an inverter between the panels/batteries and the pump. This adds losses and means dealing with the higher startup surge of single-phase motors.
| Pump HP | Running W | Startup Surge | Solar Array* | 300W Panels |
|---|---|---|---|---|
| 1/2 HP | 500-600W | 1,000-1,500W | 900W | 3 |
| 3/4 HP | 750-900W | 1,500-2,000W | 1,200W | 4 |
| 1 HP | 1,000-1,200W | 2,000-2,500W | 1,500-1,800W | 5-6 |
| 1.5 HP | 1,500-1,800W | 3,000-3,500W | 2,400W | 8 |
| 2 HP | 1,800-2,400W | 3,500-4,500W | 3,000W | 10 |
*Array size assumes battery bank handles startup surge. If running direct from panels through an inverter, add 30-50% more panels for surge capacity.
04
How Well Depth Changes Everything
A 1HP pump works harder to lift water from deeper wells, which increases power draw and reduces flow rate. Here's what to expect at different depths:
| Well Depth | 1HP Flow Rate | Power Draw | Daily Output* |
|---|---|---|---|
| 50-100 ft | 10-15 GPM | 700-850W | 2,000-3,000 gal |
| 100-200 ft | 7-12 GPM | 850-1,000W | 1,500-2,500 gal |
| 200-300 ft | 4-8 GPM | 1,000-1,100W | 800-1,500 gal |
| 300-400 ft | 2-5 GPM | 1,100W+ | 400-800 gal |
| 400+ ft | <3 GPM | Overloaded | <500 gal |
*Daily output assumes 5 peak sun hours and a 3-phase DC solar pump. Single-phase AC pumps produce about 20% less due to efficiency losses.
05
Direct Solar vs Battery Backup
There are two ways to run a well pump on solar. Your choice affects panel count, cost, and when you have water access.
| Feature | Direct-Drive Solar | Battery + Inverter |
|---|---|---|
| How it works | Panels → controller → pump | Panels → batteries → inverter → pump |
| Panels needed (1HP) | 4 x 300W (1,200W) | 5-7 x 300W (1,500-2,100W) |
| Batteries needed | None | 200-400Ah LiFePO4 |
| Inverter needed | No (controller included) | Yes (3,000W+ pure sine) |
| Pumps at night? | No - daytime only | Yes - anytime |
| Total system cost | $2,000-3,500 | $4,000-7,000+ |
| Complexity | Simple | Complex |
| Best for | Filling a storage tank | On-demand pressurized water |
06
Which Solar Panels to Use
For well pump applications, panel selection is straightforward. Here's what matters:
Use 300-400W Panels
Larger panels mean fewer connections, less racking, and lower cost per watt. Four 300W panels are cheaper and simpler than twelve 100W panels for the same 1,200W array. The only reason to use 100W panels is if you need portability.
Match Voltage to Your Controller
Solar pump controllers have specific voltage input ranges. Check your controller specs before buying panels. Most 1HP solar pump controllers accept 100-400V DC input (panels wired in series). Standard MPPT charge controllers for battery systems typically accept up to 150V.
Ground Mount Near the Well
Panels for well pumps are usually ground-mounted near the wellhead, not on a roof. This minimizes wire runs (which cause voltage drop) and makes maintenance easier. Use a tilt-adjustable frame to optimize angle seasonally.
07
Frequently Asked Questions
How many solar panels do I need for a 1HP water pump?
For a 3-phase DC solar pump: 4 x 300W panels (1,200W total). For a single-phase AC pump through an inverter: 5-6 x 300W panels (1,500-1,800W). The extra panels cover inverter losses and the higher startup surge of single-phase motors. Always size 20-30% above the pump rating.
Can I run a well pump directly from solar panels without batteries?
Yes, with a dedicated solar pump controller. DC solar pumps (like RPS Pro or Grundfos SQFlex) connect panels directly to a controller that drives the pump. No batteries needed. The pump runs when the sun shines and stops at night. Water is stored in a tank instead of batteries, which is cheaper and simpler.
How many watts does a 1HP well pump use?
A 1HP pump is rated at 746W (1 HP = 746W). But real-world draw is higher: expect 800-1,100W running depending on efficiency, well depth, and pump age. Startup surge can hit 1,500-2,200W for single-phase motors. Three-phase pumps have a lower surge of about 900-1,200W.
What size inverter do I need for a 1HP well pump?
For a single-phase 1HP pump, you need at least a 3,000W inverter (pure sine wave) to handle the 2,000-2,200W startup surge. A 2,000W inverter will likely trip on startup. For 3-phase solar pumps with a dedicated controller, no inverter is needed.
How much water can a 1HP solar pump produce per day?
A 1HP solar pump produces 1,000-2,500 gallons per day depending on well depth, pipe diameter, and sun hours. At 100 feet depth with 5 peak sun hours, expect about 1,500-2,000 gallons. At 300 feet depth, output drops to 500-800 gallons per day. Deeper wells need more powerful pumps.
Sources
- Pump specifications: RPS Solar Pumps - Panel count and configuration for 1HP 3-phase pumps
- Motor efficiency: NEMA MG-1 motor standards for submersible pump motor efficiency ratings
- Flow rate data: Grundfos SQFlex and RPS Pro Series pump curve documentation
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