Solar Pump Systems for Multiple Boreholes: Hydraulic and Control Design

A multiple-borehole solar pump system is not one pump calculation repeated twice. Each borehole is a separate water source with its own drawdown, sustainable abstraction rate, total dynamic head, water chemistry, recovery time, cable run, and failure modes. The sound design method is to qualify every source independently, select a hydraulic and electrical duty for each pump, and then coordinate the sources at a common tank or distribution main.

The central design question is therefore not simply whether one photovoltaic array can produce enough watts. It is whether the complete arrangement can deliver the required daily water volume without over-pumping a borehole, operating a pump outside its curve, back-feeding a stopped source, or switching a motor while a controller remains energized. This guide gives EPC teams, irrigation contractors, distributors, and OEM buyers a calculation method, control sequence, and commissioning record that can be placed directly into a request for quotation.

1. Begin with a separate source data sheet for every borehole

Two nearby wells can behave differently even when their drilled depths look similar. The static water level describes the resting condition, while the pumping or dynamic level must be measured at a stated flow and after a stated pumping period. Drawdown is the difference between those levels. The U.S. Geological Survey explanation of aquifers and groundwater notes that excessive pumping can lower the aquifer level, reduce well yield, and even affect neighboring wells. A pump quotation cannot replace an aquifer or step-drawdown test.

• Record borehole ID, coordinates, casing inside diameter, drilled depth, pump setting depth, static level, and measured dynamic level.

• State the test flow, test duration, recovery time, sustainable abstraction limit, seasonal observations, and any regulatory abstraction limit.

• Record sand content, temperature, pH, conductivity, chlorides, iron, and other water-quality values relevant to pump materials and downstream use.

• Define the independent pipe route, elevation profile, cable length, isolation point, check valve, flow meter, pressure gauge, and dry-run sensing method.

• Keep assumptions visibly marked. Do not silently copy a water level, yield, or water analysis from one borehole to another.

USGS aquifer-test methods model pumping-induced drawdown from measured observations; the practical lesson for procurement is that each borehole needs traceable test evidence. The USGS WTAQ technical report describes analysis of drawdown in confined and water-table aquifers and accounts for effects such as well-bore storage and delayed response. The project engineer should set allowable operating flow and minimum water level from site evidence and local requirements, not from a generic pump label.

2. Calculate total dynamic head for each source

Total dynamic head, or TDH, is the head the pump must overcome at the specified flow. For a borehole feeding an open storage tank, a useful design form is: TDH = vertical head from pumping water level to tank inlet + pipe and fitting losses + required residual head at the inlet. If the destination is pressurized, convert the required outlet pressure to head and include it. Calculate friction at the design flow for the actual pipe diameter, length, material, valves, meter, and manifold; do not use one percentage allowance for every branch.

Worked two-borehole example

Assume Borehole A has a measured pumping level 28 m below ground. The tank inlet is 12 m above ground, calculated branch and manifold loss is 6 m at the design flow, and 2 m residual head is required at the inlet. Its duty is therefore 28 + 12 + 6 + 2 = 48 m TDH. Borehole B has a pumping level of 42 m, the same 12 m elevation, 8 m loss through its longer branch, and 2 m residual. Its duty is 42 + 12 + 8 + 2 = 64 m TDH.

The 16 m difference means that a single pump model may not operate efficiently at both sources. Plot 48 m and 64 m on the candidate pump curves at the required flow, then check motor current, controller output range, PV voltage window, cable voltage drop, and minimum-sun behavior for each duty. The U.S. Department of Energy pumping systems sourcebook explains the interaction between system curves, pump operation, and multiple-pump arrangements. Its system-level principle applies here: equipment must be evaluated at the actual operating point, not only by nominal power.

Now test daily yield. If demand is 120 m3/day, Borehole A may sustainably provide 8 m3/h for six permitted hours, or 48 m3/day. Borehole B may provide 6 m3/h for eight hours, also 48 m3/day. Combined planned production is only 96 m3/day, leaving a 24 m3/day deficit. Increasing pump size does not create aquifer yield. The design must reduce demand, increase storage and pumping opportunity within the sustainable limits, confirm a higher permitted yield through testing, or add another qualified source.

3. Choose an architecture that can fail safely

The most serviceable arrangement usually gives every borehole its own pump, solar pump controller, protection settings, disconnect, check valve, isolation valve, and flow measurement, with both lines discharging into a common storage tank. The tank level controller requests water, while local controls decide whether each source is healthy and permitted to run. Separate PV arrays simplify electrical independence; a shared DC field may be possible only when the controller manufacturer and switching design explicitly support it.

A shared controller that alternates between two motors demands engineered interlocking. Both motors must be stopped before changeover; the controller DC bus must reach the manufacturer's safe state; output contactors must be rated for the motor duty; electrical and mechanical interlocks must prevent simultaneous connection; and each motor's parameters and protection thresholds must be loaded correctly. Never open or transfer a motor circuit on the live output of a variable-speed solar pump controller unless the equipment manufacturer has approved the exact method.

Where uninterrupted service matters, the RUTANPUMP duty-standby solar pump changeover guide provides a useful control baseline. Multiple boreholes add another constraint: the sources may have different safe yields, so alternation cannot be based only on equal run hours. Source priority should combine tank demand, available solar power, recent abstraction, recovery time, water level, flow confirmation, and maintenance status.

4. Prevent crossflow and false protection

Every borehole branch should have an accessible isolation valve and a non-return valve selected for the water quality, pipe velocity, installation orientation, and surge condition. A stopped branch must not receive pressure from an operating branch. Crossflow can spin a stopped pump backward, contaminate one source from another, distort flow totals, and hide a leaking valve. Locate pressure and flow measurement so the commissioning team can prove zero reverse flow while the other source is running.

Dry-run protection must also be source-specific. A power-based threshold learned on Borehole A may nuisance-trip or fail to protect Borehole B because their heads, motor loads, cable lengths, and drawdown patterns differ. Prefer direct water-level evidence where practical, then combine it with minimum-flow, underload, restart delay, and maximum starts per hour. Log why each threshold was chosen and test it without allowing the pump to remain unwatered.

• High tank level: stop all pumps and block automatic restart until the defined lower level is reached.

• Low tank level: request the preferred healthy source, then add or alternate a second source only within its daily abstraction and recovery limits.

• Low flow with motor running: stop the affected source, verify valve position and water level, alarm, and apply a controlled restart delay.

• Stopped-source reverse pressure or flow: isolate the branch and inspect the non-return valve before returning it to automatic service.

• Controller, sensor, or communication fault: move the affected source to a defined safe state; telemetry loss must not defeat local protection.

5. Build a commissioning matrix with measured acceptance values

Commissioning should create a baseline that future service teams can compare against. Record the calibrated instrument ID, date, irradiance or PV input, tank level, source water level, flow, discharge pressure, motor current, controller frequency, DC voltage, alarm state, and valve lineup. A pass statement without measured values is weak evidence. The FAO solar-powered irrigation systems sourcebook treats solar pumping as a complete design, operation, and maintenance system; that approach is particularly important when several sources share storage and distribution.

• Standalone test A: operate only Borehole A at representative solar input; record stable flow, TDH evidence, current, dynamic water level, and protection margin.

• Standalone test B: repeat with Borehole B using its own expected operating point and thresholds.

• Changeover test: command A-to-B and B-to-A transfers; verify break-before-make logic, safe controller state, correct settings, and no unintended restart.

• Crossflow test: close or stop one source while the other runs; confirm no reverse flow, abnormal pressure, or backward pump rotation.

• Low-water test: simulate or safely induce each source's low-level condition; confirm trip, alarm, restart delay, and recovery logic independently.

• Low-sun and recovery test: observe ramp-down, stop, morning restart, and behavior after power restoration without contactor chatter or rapid cycling.

• Failure test: disconnect a flow sensor, tank level input, and communications path one at a time; record the defined local safe response.

• Twenty-four-hour water balance: compare each branch meter, tank level change, delivered volume, and allowed abstraction; investigate unexplained variance.

Acceptance limits belong in the purchase specification before testing. Examples include maximum allowed deviation between reference and installed flow meters, minimum insulation resistance under the applicable procedure, maximum cable voltage drop, maximum starts per hour, permitted pressure surge, and the time allowed for a failed source to be isolated. Values must come from the approved equipment documents and project standards; this article intentionally does not invent universal limits.

6. Procurement package and supplier review

A comparable request for quotation should include the two source data sheets, hydraulic profile, daily demand curve, tank geometry, desired control narrative, PV climate basis, cable routes, water analysis, ambient conditions, destination standards, and commissioning matrix. Ask the supplier to return a pump curve with each duty point marked, array string layout, controller voltage/current limits, cable recommendation, valve and meter schedule, wiring diagram, control sequence, alarm list, installation manual, spare-parts list, and deviations.

For a shared-controller proposal, require the controller manufacturer to approve the switching topology in writing. Identify the contactor utilization category, interlock arrangement, safe discharge time, motor parameter selection, and failure response. For independent controllers, verify whether simultaneous operation can overload the common pipe or exceed the tank inlet capacity. The center-pivot solar water pump design guide shows how downstream pressure and flow requirements can dominate source selection.

Supplier review should distinguish documented model capability from optional customization. Check that drawings, bill of materials, firmware or parameter files, labels, packaging, and manuals have revision identifiers. A production-representative sample should pass the agreed matrix before the approved configuration is frozen. Incoming inspection can then verify identity, workmanship, markings, key dimensions, accessories, basic operation, and risk-based performance without pretending that a brief receiving test replaces hydraulic qualification.

Frequently asked questions

Can one solar pump controller run pumps in two boreholes?

Only when the controller manufacturer approves the exact arrangement and the design provides stop-before-transfer logic, a safe DC-bus state, correctly rated output switching, mechanical and electrical interlocks, and separate motor parameters and protection settings. Independent controllers are usually simpler to protect and service.

How do you prevent crossflow between boreholes?

Install a correctly selected non-return valve and an accessible isolation valve on every borehole branch. Commission the system by running each source alone and proving that the stopped branch has no reverse flow, abnormal pressure, or backward pump rotation. Add per-branch flow and pressure measurement where the risk justifies it.

Should multiple boreholes use the same dry-run setting?

No. Set and validate protection for each source using its measured water level, drawdown, flow, head, motor load, cable, and recovery behavior. A threshold copied from another borehole can cause nuisance trips or fail to protect the pump.

Contact RUTANPUMP

For hydraulic selection, OEM requirements, drawings, samples, controller coordination, and project quotations, send the source data sheets, daily demand, pipe profile, quantity, destination market, and expected schedule to RUTANPUMP / Wenling Jingzhan Mechanical & Electrical Co., Ltd.

Email: [sales@rutanpump.com](mailto:sales@rutanpump.com). WhatsApp / WeChat: +86 18267835331. Tel: +86 (0576) 86322398. Website: www.rutanpump.com.