Solar water pumping does not follow the rules of the rest of your solar system. A house PV array can be oversized, undersized, cloudy-day-tolerant, or seasonally lopsided and still keep the fridge cold. A solar water pump has to lift a specific volume of water against a specific column of pressure, from a specific depth, at a specific flow rate — and if any one of those numbers is wrong, the pump either does not deliver, burns out its brushless motor, or the well runs dry.

PES Supply stocks 89 solar-pump SKUs from three direct-distributor lines: Grundfos SQFlex submersible AC/DC-compatible pumps (28 kits and controllers in the catalog), Shurflo 9300 series diaphragm pumps for shallow-well and cistern-fill duty (20 SKUs), and Dankoff SolarForce, Slowpump, and Flowlight booster pumps for pressure-boost and rainwater applications. This guide shows contractors and self-installers which line fits which application and how to bundle the pump, controller, PV, and tank into one PO.

The three variables that determine your system are total dynamic head (TDH — the vertical lift plus friction loss plus pressure requirement), daily gallon requirement (livestock, household, irrigation), and peak solar hours at your site. Every pump curve is TDH × flow rate at a given PV wattage; every bundle is priced by the intersection of your three numbers with those curves.

Unlike a house PV system, a solar pump is a hydraulic machine driven by an electrical system. The design starts with the water requirements — not the wattage. If you approach it "watts first" you either over-buy PV or under-deliver water. If you approach it "water first," the electrical system sizes itself based on the hydraulic answer.

1. 1

   Calculate daily gallon requirement

   Household: 50–80 gal/person/day off-grid. Livestock: cattle 12–20 gal/head, horses 8–12 gal/head, sheep 2–3 gal/head, poultry 0.05–0.1 gal/bird. Garden irrigation: 620 gal per 1000 ft² per week in summer, or 90 gal/day. Add 25% for hot-week peaks. A 4-person homestead with 10 cattle and a 3,000 ft² garden totals: 320 + 180 + 270 = 770 gal/day peak-week.

2. 2

   Measure total dynamic head (TDH)

   TDH = pumping level (static water depth + drawdown at flow) + vertical lift above ground to tank + pressure at tank (30 psi = 69 ft head) + pipe friction loss (calculate at pump flow, typical 5-15 ft per 100 ft of 1-inch pipe). For a 200-ft-deep well with 40 ft static, 20 ft drawdown, 40 ft rise to tank, 30 psi tank pressure, and 60 ft of pipe: 60 + 40 + 69 + 5 = 174 ft TDH.

3. 3

   Determine peak solar hours

   Use NREL PVWatts or a simpler chart. Winter months: 2.5–4 kWh/kW/day depending on latitude. For a stock tank that fills daily, size to 4 hours of usable solar. For a cistern that fills 3× per week, size to 6 hours. Solar pumps run only during daylight — no batteries in most kits — so if you need water at night, size the storage tank, not the pump.

4. 4

   Match pump to TDH and gallons/day

   Consult the manufacturer flow-vs-head chart at rated wattage. Grundfos 25 SQF-7 at 174 ft TDH delivers ~700 gph on a 900-1200 W array — 5,600 gal in 8 solar hours. Shurflo 9300 at same head delivers ~90 gph on a 100 W array — 720 gal/day, only adequate for the household portion. In this case the Grundfos wins by a factor of eight, and its bundle price ($5,196) is roughly 3× the Shurflo, so cost per gallon-day is lower.

5. 5

   Size the PV array and controller

   Grundfos SQFlex pumps come with a matched CU 200 controller and specify PV wattage per model. A 25 SQF-7 wants 900–1500 W nominal. Two 400-450W bifacial modules on a Grundfos-approved rack meet the minimum; three modules give buffer for cloudy days. Wire modules per the controller's input voltage window (typically 60–300 VDC). Shurflo 9300 runs on 24 or 48 VDC, needs 100–160 W minimum, and pairs with a Shurflo PV controller or a linear-current booster (LCB).

6. 6

   Size the storage tank

   Storage buys autonomy through the night and through cloudy days. Rule of thumb: 3–5 days of daily consumption. For our 770 gal/day homestead: 2,300–3,850 gallons. That is one 2,500-gallon polyethylene cistern (Norwesco, Snyder, or Bushman brands, $1,800–$3,000 typical) plus a pressure tank at the point of use. A gravity-fed tank at 40 ft elevation delivers 17 psi to the house without any second pump; a cistern in the basement needs a Dankoff booster or Shurflo pressure pump.

Before you can size a solar pump you have to speak the well driller's language. Six terms carry the sizing math:

Total well depth. Measured from ground level to the bottom of the well casing. A 400-foot well has 400 feet of casing installed. The pump does not necessarily sit at the bottom — it sits above the well screen and above the highest anticipated drawdown level.

Static water level. The depth from ground level to the top of the water column when the pump is off. This is your baseline; when the pump has been idle for hours, this is where the water sits.

Drawdown. The additional depth the water drops when the pump is running at a given flow rate. A well with 40 ft static level and 20 ft drawdown at 6 gpm has a pumping level of 60 ft. Drawdown grows as flow rate grows and shrinks as the aquifer recovers.

Recovery rate (yield). Gallons per minute the well can supply sustainably. A "5 gpm well" recovers 5 gpm indefinitely without dropping the pumping level below the pump. Your solar pump must not draw faster than yield, or the well runs dry.

Vertical lift. Height from ground level to the top of the storage tank. Adds directly to TDH.

Friction loss. Pressure drop across pipe length caused by fluid moving against pipe wall. Calculated per 100 ft of pipe at the flow rate. A 1-inch schedule-40 poly pipe at 6 gpm has 4.5 ft of friction loss per 100 ft. Ask your driller for a well log — it will state total depth, static level, and measured yield. Those three numbers plus your tank elevation give you TDH.

Livestock is the classic solar-pumping application. A stock tank sits at a well, the pump runs on sunny hours, the tank fills, animals drink through the day, and the system needs zero attention. The reason solar wins here economically is that running utility power to a remote pasture well is $8–$15 per foot of trench for direct-bury conduit, plus a service upgrade and a subpanel. A 1,000-ft trench is $12,000 minimum. A Grundfos 6 SQF-3 kit at $4,737 with a 700-gallon steel stock tank at $1,200 is 40% of the trenching bill and requires zero utility interconnect.

Sizing math. Ten Angus cattle at 15 gal/head/day plus 6 sheep at 3 gal each = 168 gal/day baseline, 250 gal peak-week. Well is 220 ft deep with 60 ft static water level and 15 ft drawdown at 5 gpm. Vertical lift to stock tank at ground level = 60 + 15 = 75 ft TDH plus a few feet of horizontal friction. Grundfos 6 SQF-3 at 75 ft TDH delivers roughly 850 gph on the rated 720 W PV. Six sunny hours produces 5,100 gallons — 20× the daily need, so you drain-back-fill the tank once every four days. Or, more accurately, the tank float switch cycles the controller on/off and you get automatic operation.

Bundle recommendation. Grundfos 6 SQF-3 pump ($3,200 pump-only) + CU 200 controller + 3× 400W bifacial modules + IronRidge XR-100 top-of-pole mount + 100 ft of stainless drop pipe + torque arrestor + splice kit + safety rope + float switch. PES ships this as the "Grundfos 6 sqf-3 Pre-designed SQFlex Solar Water Pumping Kit" at $4,737 all-in. Add a 700-gallon galvanized stock tank and you are livestock-ready for 20+ years.

Winter operation. In cold country, freeze protection is the whole game. Bury the water line below frost line (5–7 ft in most of the northern US and southern Canada). Install a stock-tank de-icer — a thermostatic 5–15 W element sits in the tank and keeps a hole open in the ice. A submersible thermostatic heater from Farm Innovators or K&H Pet ($55–$120) is the standard. Wire it to your house AC via a low-voltage lead or on a small dedicated solar+battery loop with a 30 W panel and a marine battery.

Whole-house solar water pumping is the demanding case. The pump has to run every day, all year, with sufficient reserve to handle irrigation and laundry on peak days, and the water pressure at the fixture has to feel like grid-supplied water. That means a pressurized system with a bladder tank, a cistern, and either a solar pump feeding the cistern (two-stage) or a submersible pump running direct-off-grid (one-stage).

Two-stage design (preferred). A Grundfos 11 SQF-2 or 25 SQF-7 sits in the well and pumps to a 2,500-gallon cistern at the house — either above ground for gravity feed or in a heated basement/crawlspace. From the cistern, a small AC pressure pump (running off your house PV/battery inverter) draws through a 20-gallon bladder tank at 40–60 psi. The solar well pump runs on sunny days only; the pressure pump runs on demand. No battery bank required on the well pump side, and the pressure pump uses less than 0.5 kWh/day.

One-stage design. A traditional 3-wire submersible well pump (Franklin Electric or Grundfos SP series) driven by your house off-grid inverter (Sol-Ark 15K, OutBack Radian, EG4). The pump only runs when the pressure tank calls, so battery draw is spiky but total energy is small. Downside: the pump has a 4–7× locked-rotor amps (LRA) surge on start, which forces you to size the inverter for that surge (a 3/4 HP pump at 240 V has ~40 A LRA = 9.6 kVA momentary). For homes with a Sol-Ark 15K or EG4 18kPV, this is not a problem. For smaller inverters it is.

PES bundle recommendation for whole-house. Grundfos 25 SQF-7 pumping kit ($5,196) + 2,500-gallon Norwesco vertical cistern (~$2,400 from freight partner) + Grundfos MQ 3-45 pressure pump ($850) + WellMate WM-9 well-x-trol tank ($480) + all valves, fittings, and low-water cutoff. All-in bundle: $9,500–$12,000, delivers full-pressure whole-house water at 4 gal/min drawdown to two showers running simultaneously.

Water quality. Rural wells often have iron, hardness, sulfur, or nitrate issues. Plan your treatment train after the pump: sediment filter (5 micron), water softener if hardness exceeds 7 gpg, iron filter (Terminox ISM, Katalox Light, or air-injection oxidation) if iron exceeds 0.3 mg/L, and a whole-house UV sterilizer (Viqua or Sterilight) if the well is under 100 ft or open-source (spring, cistern). Test with a certified lab (National Testing Laboratories, LaMotte) — do not rely on retailer test strips.

Irrigation is high-volume, low-pressure. Drip-irrigation systems run at 10–20 psi; sprinkler zones run at 30–45 psi. Both are lower than household pressure requirements, which means the pump can be larger flow / lower pressure — a "high flow at moderate head" pump. The Dankoff SolarForce series and Grundfos SP-series pumps fill this niche. Or, for pressurized irrigation from a cistern, the Dankoff Slowpump 2500 series booster.

A 3,000 ft² garden needs about 90 gal/day in summer. Three raised beds and a small orchard push this to 200–300 gal/day. A drip-irrigation manifold with 12 zones and 1 gph emitters uses roughly 200 gal per full-manifold hour. That is well within any solar-pump budget.

Bundle: Shurflo 9325 Submersible Solar Water Well Pump (12V/24V) at $1,062 — for a shallow well up to 230 ft, feeding a raised cistern that gravity-drips to the garden. Add 2× 200W monocrystalline panels ($600), a Genasun GV-10 MPPT controller ($150), and 100 ft of poly drop pipe ($120). Complete garden-irrigation solar pump for under $2,000, delivering roughly 300 gallons per solar day to a 500-gallon rain barrel or cistern.

Larger orchard or field irrigation: Grundfos 40 SQF-3 or Lorentz PS2 for 20+ gpm flow rates. Direct-to-drip lines rather than to cistern. Solar-only operation follows sunny weather — which for growing-season irrigation is exactly what you want. In arid climates like eastern Washington, western Colorado, and southern Utah, solar-direct field irrigation is a mature technology used commercially at 5–200 acre scale.

Grundfos SQFlex is the class-defining product for deep-well solar pumping. It is a submersible, brushless-DC / AC-compatible, 316L stainless-steel pump that accepts either 30–300 VDC directly from a PV array or 90–240 VAC from a generator or house inverter — the same pump, no separate DC-only or AC-only version. The CU 200 matched controller runs dry-run protection, soft-start, and float-switch integration. The pump body has a wet-end designed for sand and abrasives — real well water, not laboratory water.

The SQFlex lineup covers depth from 5 ft (SQFlex 25 SQF-3 at low head, 25 gpm) to 700 ft (SQFlex 3 SQF-2 at high head, 3 gpm). The model numbering is flow @ head — a "6 SQF-3" is 6 gpm at a design head, with a 3-inch pump body diameter that fits any well casing 4 inches and larger. A "25 SQF-7" is a 25-gpm-class pump with 7 stages for higher pressure. PES ships pre-designed kits with the pump, matched controller, PV modules, top-of-pole mount, drop pipe, safety rope, splice kit, and torque arrestor. Everything a well driller needs on a single PO with a single freight quote.

Real-world reliability. Grundfos SQFlex is used by USAID, UNICEF, and NGO water-supply programs across Africa, Central Asia, and Latin America because it is the pump that keeps working in 130°F ambient, high-sand well water, and 12+ hours daily duty cycle with zero maintenance. In North American rural installs, we routinely see 15-year service life. The end-suction wet-end and impeller can be rebuilt at year 10–12 for ~$800 in parts; the motor typically outlasts the well.

SQFlex model selection at a glance. 25 SQF-3: shallow-to-medium wells (100–300 ft), high flow (up to 25 gpm at low head). 11 SQF-2: medium wells (150–500 ft), medium flow (11 gpm at mid head). 6 SQF-2 and 6 SQF-3: medium-to-deep wells (200–500 ft), 6 gpm class. 3 SQF-2: deep wells (400–700 ft), 3 gpm high pressure. Match your yield to the pump's flow class; do not oversize flow beyond well recovery or you draw down the well.

Shurflo 9300 is the opposite of the SQFlex — it is small, cheap, diaphragm-driven, and best suited to shallow-well and cistern-lift duty up to about 230 feet. It runs on 12 or 24 VDC directly from a small PV array (100–160 W), draws 3–6 A while pumping, and delivers roughly 90 gph at 150 ft TDH. It is the correct pump for hunting cabins, off-grid tiny homes, and small livestock water where daily volume is 300–800 gallons and total dynamic head is under 200 feet.

The wet-end is a diaphragm rather than a centrifugal impeller. That means it self-primes, tolerates air entrainment, and can run dry briefly without immediate damage (though it dislikes it and should have a low-water cutoff regardless). The tradeoff is that diaphragms wear — plan on a rebuild kit every 4–6 years at $80 in parts. This is a $1,000-class pump, not a $5,000-class pump, and it fills that price-point niche well.

Common bundle: Shurflo 9300 pump + Shurflo controller + one 200 W solar panel + a linear-current-booster (LCB) so the pump starts at lower irradiance + drop pipe + fittings. PES ships the "Shurflo 9300 Solar Water Pumping Kit (to 230 ft)" at $1,687 as a complete package. Add a 100-gallon polyethylene tank for surge storage and you have a complete cabin water supply for under $2,200.

Almost all solar pump systems can be built as direct-coupled (PV panels → controller → pump, no battery) or battery-assisted (PV → charge controller → battery → pump on demand). Direct-coupled is cheaper by $1,500–$3,000 and simpler. Battery-assisted delivers water at night and on cloudy days without any PV production, at the cost of the battery bank.

Choose direct-coupled when: you have adequate tank storage (3+ days of demand), your peak-demand hours match sunny hours (livestock drink most in the afternoon; garden irrigation is generally daytime), and you can accept the pump not running on heavy-overcast days. This is the correct answer for 80% of solar-pump installations.

Choose battery-assisted when: your home already has an off-grid battery bank (Sol-Ark + Fortress/SimpliPhi/EG4), so the pump is just another load on the inverter, or you need on-demand pressure delivery to fixtures rather than tank storage. In this case the pump is a standard AC submersible on the inverter's output, and the well pump is not really a "solar pump" — it is an AC pump on a solar-powered house.

Even the right pump fails when the accessories are wrong. Here is a distributor's tight-list of the details that separate a 15-year installation from a 3-year failure.

Drop pipe. Use stainless-steel-reinforced polyethylene drop pipe or stainless flex pipe for deep wells. Cheap PVC or standard poly fails at the female-thread coupling under thermal cycling. Grundfos recommends 316 stainless for all SQFlex installs over 300 ft, and PES packages that upgrade automatically in the deep-well kits.

Torque arrestor. A rubber-and-metal ring that sits above the pump and prevents the pump body from spinning against the well casing when the motor starts. Every SQFlex kit should include one; without it, the drop pipe can unscrew itself over 3–5 years.

Safety rope. A stainless or polypropylene rope from the well cap down to the pump, tied off, so if a coupling fails the pump does not drop 300 ft to the well bottom (retrieval cost: $4,000–$8,000).

Splice kit. The pump's motor lead is spliced to the surface wire inside the well. Use only submersible-rated heat-shrink or resin-filled splice kits. Wire-nuts do not work — they corrode and short-circuit within a year.

Well cap. Sanitary well cap with rubber gasket, screened vent, and conduit for the wire. Local codes typically require it; the SQFlex kits include a compatible cap.

Low-water cutoff. Non-negotiable. Grundfos CU 200 has integrated dry-run protection. For Shurflo installations add a WellChek or a mechanical float switch mounted at the pump-drop level.

Surge protection on the controller AC/DC input. A $60 DPS device from MidNite or Delta protects the controller board from nearby lightning strikes. In lightning-prone regions (Southeast, Great Plains) this is not optional.

Grounding. All exposed metal (pump body, drop pipe, casing) tied to a single ground rod system per NEC 250. Ground rod at the well head. This prevents corrosion from stray currents and protects the pump from lightning-induced surges.