Solar water pumps for wells and irrigation

A well 200 ft deep and a pond 10 ft down the slope ask completely different things of a solar pump, even if both households want the same 300 gallons a day. The pump does not size to how much water exists; it sizes to how hard it must work to lift and push that water — a single figure called total dynamic head. Get that number right and the panel count, the pump type, and the kit fall into place. This guide walks the 2 sizing numbers, the submersible-versus-surface choice, a worked panel-wattage example, and what a real solar well pump kit contains. It pairs naturally with the power side: how you store and route that energy lives in our guide to an off-grid or hybrid solar system.

The two numbers that size everything

Every solar pump decision starts with flow rate and total dynamic head. Flow rate is the gallons per minute (GPM) you need; the New Mexico State University Extension guide warns it “should be slightly lower than the well’s sustainable flow” so you never pump the well dry. Total dynamic head (TDH) is the harder concept — and the one that governs the rest.

NMSU defines TDH as “how hard a pump must work to move water from the well, through the total length of piping and all fittings, and to a discharge level.” AltE reduces it to a formula: Total Dynamic Head = Vertical Head + Effective Additional Head Due to Pipe Friction. Friction is not trivial — at 2 GPM through 3/4-inch pipe, AltE notes it adds “1 ft vertical head per 100 ft” of run, and most field guides budget 15% to 25% of well depth for it.

These two numbers fight each other, which is the single most important thing to understand. As NMSU puts it bluntly, “for bigger TDH values, the pump will move less water per minute.” A pump rated 10 GPM at 50 ft of head might deliver only 3 GPM at 200 ft. Read pump curves at your head, not at the headline number.

Submersible or surface: the depth decision

Once you know your lift, the pump type nearly picks itself, and the dividing line is 25 ft. The Green Watt states the rule cleanly: a submersible is “the standard choice for wells deeper than 25 feet,” while a surface pump suits “shallow wells (under 25 feet to water) or pumping from ponds, springs, and cisterns.”

The reason is physics, not preference. A surface pump sits above ground and sucks water up, and suction has a hard ceiling: “most surface pumps can lift water a maximum of 20 to 25 ft vertically,” per The Green Watt. A submersible sits down in the water and pushes, so it can lift from 600 ft or more. NMSU, focusing on the common case, limits its own analysis to submersible centrifugal pumps running “up to 2000 watts of DC power at 30 to 180 V.”

Sizing the panel array to the lift

Panel wattage scales with both flow and head, so a deep well is a power problem long before it is a plumbing one. The Green Watt gives the underlying relation: pump power (watts) = GPM × TDH (ft) ÷ (5.308 × pump efficiency). Push more gallons or lift them higher and the wattage climbs in lockstep.

A worked example at 4 GPM

NMSU’s worked submersible case shows the numbers directly: at its design point the pump “can only pump up to 4 GPM and requires 257 W of power to operate.” You then size the array above that draw. AltE’s rule of thumb is explicit: oversize the panel wattage 30% above the pump rating — its example runs “116 W × 1.3 oversizing = 151 W of solar panels or greater.” The 30% cushion covers dust, heat, wiring loss, and off-angle sun.

The depth-to-panel jump is steep: The Green Watt notes “a shallow well at 25 ft needs only 2 panels, while a very deep well at 800 ft needs 18.” That is a 9-fold difference in array for the same household — which is exactly why you measure head before you price panels.

Direct-drive or battery: how to run it

With the pump and array sized, one choice remains: run solar-direct or add a battery. Most homestead systems should run direct. RPS Solar Pumps describes the standard DC path: “DC power is routed from the solar panels, down through a charge controller (usually MPPT) which directs the DC power directly to the DC pump.” No inverter, no battery, fewer failure points.

The trick that replaces the battery is storage in a tank, not in cells. The Green Watt describes it plainly: “the pump runs only when the sun shines. Water is pumped into a storage tank during daylight hours and available on demand at any time through gravity or a pressure tank.” A 1,500-gallon cistern is a cheaper, longer-lived battery than any lithium bank when what you are storing is water.

DC also wins on efficiency at this scale. RPS notes DC pumps “are more efficient than running on solar with an inverter,” and they start in weak light. AC pumps earn their keep at the big end — RPS reserves them for “higher head (like deep wells, faraway tanks or high pressure irrigation), high volume flow rates (up to 400 GPM).” For a homestead well feeding a drip irrigation system, DC-direct into a tank is almost always the right call.

What is in a solar well pump kit

A packaged solar well pump kit bundles the matched parts so the DC voltages line up, but the 5 core pieces are the same whether you buy a kit or assemble them. Below is the checklist to vet any kit against before you buy.

1. The pump — submersible or surface, rated for your flow at your TDH, not at zero head.
2. The solar array — sized 30% above the pump’s wattage, from roughly 2 panels at 25 ft to 18 at 800 ft.
3. The pump controller — usually MPPT, which matches panel output to the motor and adds dry-run and low-light protection.
4. Storage — a tank or cistern sized to your days of autonomy, the water-side replacement for a battery.
5. Wire, a disconnect, and a well seal — the balance-of-system parts kits most often skimp on.

Size storage by your daily need and local weather. NMSU recommends “a normal storage value for sunny regions like New Mexico is 3 days of water, but it may be up to 10 depending on various factors.” At AltE’s domestic figure of “75 gallons per day per person,” a family of 4 wanting 3 days holds about 900 gallons; wanting 7 days, about 2,100. For the wider self-reliant water picture, our guide to off-grid living sets the pump in context.

Irrigation changes the duty cycle

A pump that comfortably serves a house can fail an irrigation block, because irrigation is a different duty cycle. Domestic demand is small and spread across the day; irrigation is a large draw concentrated into a short window, often the same midday hours when the panels make the most power. That alignment is an advantage if you design for it.

The cleanest pattern is to pump to a tank, then irrigate from the tank. The solar-direct pump fills an elevated cistern through the sunny hours; gravity or a small pressure pump then feeds the field on your schedule. This decouples the pump’s solar-bound output from the crop’s watering window, and it lets a modest 4-GPM pump service a block that would need a far bigger pump if fed live. Match the tank to a full irrigation set plus a day of household use.

The takeaway

A solar water pump is a sizing problem with a clear order of operations. Start with total dynamic head — the lift plus friction — because it sets the flow you can expect and the wattage you must supply. Let the 25-ft line pick submersible versus surface. Size the array about 30% over the pump, from 2 panels at a shallow well to 18 at 800 ft. Then store water in a tank, not a battery, and run DC-direct through an MPPT controller unless you genuinely must pump after dark. Anchor the whole design to a real daily number — near 75 gallons per person, plus livestock and the irrigation set — and the kit, the panels, and the pump all follow from there.