How to Size a Submersible Well Pump for Your Needs？

November 01, 2025

1. Key Factors That Affect Pump Sizing
2. Step-by-Step Guide to Sizing a Submersible Well Pump

When it comes to building a reliable water supply system from wells—whether for residential use, irrigation, or off-grid living—sizing a submersible well pump correctly is paramount. A solar well pump is a specialized type of submersible well pump, engineered to run on solar energy while retaining all the core advantages of submersion: quiet operation, corrosion resistance, and efficient water lifting. Proper sizing ensures your solar well pump meets water demands without wasting energy, extending its lifespan and protecting your investment. The following sections explain the key factors and step-by-step process for sizing, with a focus on the role of solar well pumps within the submersible well pump category.

1. Key Factors That Affect Pump Sizing

Sizing a submersible well pump—including solar well pumps—relies on four critical parameters that directly impact performance and efficiency. Ignoring any of these can lead to inadequate water flow, premature failure, or unnecessary energy costs.

1.1 Well Depth and Static Water Level

The physical characteristics of your well are the foundation for choosing the right submersible well pump. Well depth (total distance from the surface to the bottom of the well) and static water level (depth of water when the well is at rest) determine the pump’s required lifting capacity.

For deep wells (typically 100 feet or more), a submersible well pump is the only practical choice, as surface pumps struggle with suction limitations. The solar well pump must be installed below the pumping water level (the lowest water level during operation) to avoid dry running—a leading cause of motor burnout. This is especially important for solar well pumps, which often operate in remote areas where maintenance is less accessible.

Well casing diameter also matters: most residential wells use 3-inch or 4-inch casings, and submersible well pumps (including solar well pumps) are designed to fit these standard sizes. A pump that’s too large for the casing will jam, while one that’s too small may not efficiently draw water.

1.2 Flow Rate Requirements (GPM)

Flow rate, measured in gallons per minute (GPM), is the volume of water your submersible well pump needs to deliver to meet daily demands. Calculating this accurately ensures you don’t end up with a pump that’s underpowered or oversized.

Start by estimating usage from all sources: a 4-person household typically requires 6–8 GPM for fixtures (showers, sinks, toilets, washing machines), while small gardens need 2–4 GPM for irrigation. For livestock, allocate 1–2 GPM per 10 animals. Add a 15–20% safety margin to account for peak usage (e.g., morning showers combined with laundry).

For solar well pumps, flow rate sizing has an extra layer: since solar power is only available during daylight hours, distribute water usage accordingly. A solar well pump sized to handle peak demand during the day avoids the need for large, costly batteries.

Additionally, match the pump’s flow rate to the well’s natural recovery rate (how quickly water refills the well) to prevent depleting the water source.

1.3 Total Dynamic Head (TDH) Explained

Total Dynamic Head (TDH) is the total resistance your submersible well pump must overcome to deliver water to its final destination. It’s the most critical calculation for sizing, as even a small error can render the pump ineffective.

TDH combines three key components:

Vertical Lift: The vertical distance from the pumping water level to the highest discharge point (e.g., a roof-mounted water tank or second-floor bathroom).
Friction Loss: Pressure lost as water flows through pipes, fittings, valves, and filters. Smaller pipe diameters or longer pipe runs increase friction loss.
Pressure Head: The pressure required at the outlet to ensure proper operation of fixtures—most homes need 40–60 PSI (pounds per square inch), which converts to 93–139 feet of head (1 PSI = 2.31 feet of head).

For example, if your pumping water level is 50 feet deep, the discharge point is 20 feet above ground, friction loss is 5 feet, and pressure head is 93 feet, your TDH is 50 + 20 + 5 + 93 = 168 feet. Your submersible well pump—whether traditional or a solar well pump—must be rated for at least 168 feet of TDH at your required flow rate.

1.4 Power Supply: Voltage and Phase

The power supply determines the type of submersible well pump you can use, with distinct considerations for traditional AC models and solar PV water pumping systems.

Traditional submersible well pumps typically operate on 115V (single-phase) or 230V (single-phase) for residential applications, while commercial or agricultural pumps may require three-phase power (208V, 230V, or 460V). It is essential to match the pump’s voltage and phase to your electrical service—using a 230V pump with a 115V supply can result in poor performance or motor damage.

Solar PV water pumping systems are generally composed of three main components: solar PV modules, a solar pump inverter or controller, and a submersible water pump. The solar PV array, formed by multiple modules connected in series and parallel, absorbs sunlight and converts it into electrical energy to power the system.

The solar pump controller performs control and regulation of system operation, regulating DC for direct-drive DC pumps. It also continuously adjusts the output frequency according to solar irradiance, implementing Maximum Power Point Tracking (MPPT) to maximize energy utilizatio

The water pump, whether AC or DC, draws water from wells and delivers it to storage tanks, reservoirs, or irrigation systems. For solar water pumping systems using our pumps, the configuration—including inverter or controller rating and pump type—should be selected according to actual operational requirements and installation conditions to ensure reliable and efficient performance.

2. Step-by-Step Guide to Sizing a Submersible Well Pump

Follow this structured process to size your submersible well pump—whether you’re choosing a traditional AC model or a solar well pump—with confidence.

2.1 Gather Well Information

Start by collecting detailed data about your well to eliminate guesswork. The most valuable resource is your well driller’s log, which includes total well depth, casing diameter, static water level, and well yield (recovery rate). If you don’t have a log, hire a professional to measure these parameters.

Key details to confirm:

Casing diameter (3-inch or 4-inch is standard) to ensure the submersible well pump fits.
Static and pumping water levels to calculate drawdown (static level minus pumping level) and vertical lift.
Well yield (GPM) to match the pump’s flow rate.
Water quality: If the well has high sediment or minerals, choose a submersible well pump (including solar well pumps) with a sediment filter or helical rotor design to prevent clogging.

2.2 Calculate Required Flow and Head

With well information in hand, calculate your required flow rate and TDH—the two numbers that will guide your pump selection.

For flow rate:

List all water uses and their GPM requirements.
Add them to get peak demand.
Multiply by 1.15–1.20 to add the safety margin.
For solar well pumps, ensure the system can deliver required flow during daylight hours (e.g., if peak demand is 10 GPM, select a solar well pump that maintains 10 GPM output under typical sunlight to avoid battery dependency).

For TDH:

Calculate vertical lift (pumping water level + height to discharge point).
Estimate friction loss using a pipe friction chart (available online) or consult a professional.
Convert desired outlet pressure (PSI) to feet of head (PSI × 2.31).
Add the three values to get total TDH.

2.3 Choose the Correct Horsepower

Horsepower (HP) represents the submersible well pump’s motor power and must align with your calculated flow rate and TDH. Use the pump’s performance curve (provided by the manufacturer) to find the right HP—this chart plots flow rate (GPM) against TDH (feet) for each HP rating.

Ideal HP recommendations based on common scenarios:

Shallow wells (≤50 feet TDH) and low flow (≤5 GPM): 0.5 HP submersible well pump.
Medium wells (50–150 feet TDH) and moderate flow (5–10 GPM): 1 HP model (suitable for most 4-person homes).
Deep wells (150–250 feet TDH) and high flow (10–15 GPM): 1.5 HP pump.
Very deep wells (>250 feet TDH) or commercial use: 2+ HP.

2.4 Match Pump Voltage to Power Source

When comparing AC and solar models, ensure the pump’s voltage rating matches the power source:

AC pumps typically operate at 110V or 220V single-phase, or 380V three-phase for larger systems.
The solar well pump uses DC power of 24V, 48V, 72V, or 90V, which is transformed into AC by an inverter to drive the pump efficiently.
The total voltage from the solar array (panels wired in series) should match the pump’s rated voltage to ensure stable performance and protect the controller.

For solar well pumps, prioritize high-efficiency DC motors (brushless or permanent magnet types) that deliver more water per watt of solar energy. A slightly oversized solar well pump (e.g., 1.5 HP instead of 1 HP) can help maintain flow in low-light conditions, but avoid excessive oversizing to prevent wasted energy and higher costs.

Sizing a submersible well pump—whether traditional or a specialized solar well pump—hinges on balancing well traits, water demand, and power supply. A solar well pump, as a purpose-built submersible well pump, offers energy independence and sustainability, ideal for off-grid or eco-focused setups. For personalized guidance or further support, feel free to contact us.