This solar pump sizing calculator takes the four numbers that matter (daily water need, well depth, distance to tank, and US region) and tells you the pump size, panel wattage, and specific model that will actually work for your property. Built by a working borehole driller, not a software engineer guessing.

Most online solar pump calculators ignore winter sun hours and skip pump efficiency in the wattage math. The result: people buy a pump sized for July and watch their cattle go thirsty in November. This one does it correctly.

How This Solar Pump Sizing Calculator Works

The calculator runs three real world physics formulas behind the inputs you see. Total Dynamic Head (TDH) accounts for vertical lift, outlet pressure, and pipe friction. Required GPM divides your daily water need by the actual sun hours your region delivers in winter, with a 30 percent safety margin applied.

Solar array size comes from the hydraulic power formula divided by typical pump efficiency for solar submersibles, multiplied by 1.5 to cover losses from cloud cover, panel angle, and dust. The pump recommendation matches your computed TDH and GPM to the right product family. Helical rotor for very deep wells, multi stage centrifugal for everything else, surface kits for ponds.

If you want the engineering depth behind every number, the full math is explained in our solar submersible water pumps guide. This calculator is the short version.

What Each Result Means

Total Dynamic Head (TDH)

TDH is the total vertical distance a pump must move water, measured in feet. It includes the pumping water level in your well, the height of your storage tank above ground, the equivalent height of any pressure you need at the outlet (1 PSI equals 2.31 feet of head), and friction losses through the pipe.

This is the most misunderstood spec in solar pump sizing. Most people see “200 foot well” and assume TDH is 200 feet, when the actual figure is often 280 to 350 feet once tank height, pressure, and friction are added.

Required GPM (Gallons Per Minute)

GPM is how fast the pump must move water during sun hours to meet your daily need. The calculator computes it from your daily gallon target divided by available pumping time, with a margin for cloudy days and growing demand.

Note that the calculator returns “minimum GPM at your TDH.” Pump specifications are usually quoted at zero head. A pump rated at 5 GPM might only deliver 3 GPM at 200 feet of head, so always check the manufacturer’s flow chart at your specific TDH before buying.

Solar Array Wattage

This is the total wattage of solar panels you need to power the pump under typical conditions. The calculator sizes the array at 1.5 times pump wattage in normal sun regions, 1.8 times in low sun regions like the Pacific Northwest.

You can split the wattage across any number of panels. For example, 600 watts of capacity could be three 200 watt panels or two 300 watt panels. Match the panel voltage to your pump and use an MPPT controller for 25 to 30 percent more output than direct connection.

Pump Recommendation

The pump suggestion routes you to one of six pumps reviewed in our solar pumps article, based on which one best matches your computed TDH and GPM. Grundfos for the deepest wells, PWS or BACOENG for mid range residential, Eco-Worthy for shallow or budget setups, SHYLIYU for high flow operations, and Solariver for surface water below 30 feet of lift.

Five Mistakes That Kill Solar Pump Systems

These are the sizing errors I see most often on service calls. Each one is easy to avoid before buying.

1. Sizing for summer sun hours. The pump runs great in July, then delivers 40 percent less in January when you need it most. Always size on winter peak sun hours for the location.
2. Forgetting outlet pressure in the TDH calculation. Pressurizing a tank to 40 PSI adds 92 feet of head. A pump that handles 200 feet of vertical lift does not necessarily handle 200 feet plus 40 PSI of pressurization.
3. Skipping the MPPT controller. Direct connection wastes 25 to 30 percent of panel output. An MPPT controller pays for itself in under two months.
4. Using vinyl tape on underwater splices. The splice will fail within 18 months. Use heat shrink with epoxy resin or a manufactured splice kit.
5. No dry run protection. A solar pump that runs in air when the well draws down will destroy its bearings in days. Any system without dry run protection is on borrowed time.

When You Should Not Use This Solar Pump Sizing Calculator

This calculator is built for residential, livestock, and small homestead applications in the United States. It gives a strong starting point for most installations, but a few situations deserve a professional sizing study.

Wells over 400 feet deep need calculations that account for cable voltage drop, motor cooling, and pump submergence depth. These are critical and best handled by a pump dealer with software like Grundfos GoFlow or Lorentz Compass. The cost of a bad pick at this depth runs into thousands of dollars.

Commercial irrigation systems delivering over 5,000 gallons per day usually justify multiple pumps or AC inverter driven systems. A single DC solar submersible is the wrong architecture above that threshold.

Hybrid solar plus grid systems also need a real sizing study, because the architecture affects pump selection, controller choice, and panel orientation. Use the NREL PVWatts Calculator for the solar production half of the design, then consult a dealer.

Frequently Asked Questions

Is this solar pump sizing calculator accurate enough to buy from?

For standard residential and homestead applications in the US, yes. The calculator uses real physics formulas and conservative safety margins. For deep wells over 300 feet, commercial systems, or critical municipal style installs, treat the output as a starting estimate and verify with a pump dealer.

How do I figure out my pumping water level?

If you have a well log from when the well was drilled, the static water level is on it. Subtract about 10 to 20 feet for drawdown during pumping in a typical residential well. If you do not have a log, drop a weighted string with a knot every 10 feet down the well and feel where it gets wet, then estimate drawdown from there.

Why does the calculator use winter sun hours instead of annual average?

If your system is sized for the annual average, it underperforms half the year. Sizing for winter ensures the pump still delivers when sun hours are at their lowest. The system will produce excess water in summer, which is fine since the storage tank simply fills earlier in the day.

Can I use this calculator for AC powered well pumps?

No, this calculator is specifically for DC solar submersible pumps. For grid powered AC pumps, sizing depends on your pressure tank capacity and pump duty cycle, not sun hours. See our pressure tank sizing guide for the AC equivalent.

What if my actual GPM result is between two pumps?

Always size up. A pump running below its rated capacity lasts longer than one running at maximum output every day. The extra cost of the larger pump is usually small compared to replacing an undersized pump in three years.

Do I need batteries with a solar submersible pump?

Most installs do not need them, because the storage tank acts as your “battery” by holding pumped water for nighttime use. Add batteries only if you need to pump on demand outside of sun hours, which is rare for residential or livestock applications.

How many solar panels do I need for the recommended wattage?

Divide the total array wattage by your panel wattage. A 600 watt array could be three 200 watt panels or two 300 watt panels. Match the panel voltage to your pump’s input voltage (typically 24V, 48V, or 72V DC for solar submersibles).

Will the calculator work for wind powered pumps too?

Not exactly, because wind output is more variable than solar. The Grundfos SQFlex line accepts both solar and wind input on the same controller; if you go that route, see our wind powered water pump guide for the complementary sizing.

Read Next

• The Best Solar Submersible Water Pumps of 2026
• The Best Well Pressure Tanks of 2026
• The Best Automatic Pump Controller
• How to Build a Wind Powered Water Pump
• The Best Water Pressure Booster Pump