Solar Borehole Pump Installation Depth: Submergence, Well Yield, Cable, and Pipe Constraints
Solar borehole pump installation depth is not simply “near the bottom” or “a few metres below the water.” The pump setting must stay submerged during the lowest credible pumping water level, remain above sediment and the well bottom, respect motor-cooling requirements, fit the screened interval and casing geometry, and stay within cable, pipe, lifting, and controller limits.
The design starts with measured elevations and a pumping test. The U.S. Geological Survey groundwater-well overview explains that pumping lowers the water level and that a well begins to pump air when the level falls below the intake. The NREL guide to water pumping with renewable energy notes that borehole yield and total pumping head are design inputs for selecting the motor-pump subsystem. A product-specific installation manual is also essential. Franklin Electric's current Application, Installation and Maintenance resources illustrate why submersible-motor cooling, cable, electrical, and installation rules must be taken from the selected equipment, not copied from a generic article.
This guide provides a field method and a calculation framework. Example numbers are hypothetical. They are not RUTANPUMP model specifications.
Establish one elevation datum
Choose a fixed measuring point, usually the top of the casing or a surveyed wellhead reference. Record every depth from that point. Do not mix depths measured from ground level, casing top, pump support plate, and water-level access port.
At minimum, record:
total measured well depth;
top and bottom of the screened or open interval;
inside casing diameter and restrictions;
static water level after adequate recovery;
pumping water level at each tested flow;
test duration and whether the level stabilized;
recovery level and recovery time after stopping;
sediment depth or evidence of sand production;
intended discharge elevation and required terminal pressure;
pipe, cable, and safety-line lengths.
The USGS publication on measuring water levels and pumping rates emphasizes a fixed measuring point and reliable water-level measurement. Use a suitable electric tape, air line, pressure transducer, or other approved method, and document its accuracy and datum.
Distinguish static level, dynamic level, and drawdown
Static water level is measured after the well has recovered and before pumping. Dynamic, or pumping, water level is measured while the pump delivers a stated flow. Drawdown is the difference between those two levels.
If the static level is 18 m below the measuring point and the stabilized pumping level is 31 m at 4.0 m3/h, drawdown at that test condition is 13 m. A pump set only 2 m below the static level would not remain submerged during that duty.
Do not design from a single short test if seasonal decline, nearby pumping, or demand variability can lower the water level further. Record the design low-water level separately from the test level and explain the allowance used. When evidence is incomplete, use monitoring or a conservative operating limit rather than inventing a permanent yield.
Build the depth-elevation worksheet
Use a table that keeps water, equipment, and structure on the same datum.
Item: Static water level; Depth below datum: measured; Source and condition: after documented recovery; Design use: reference only
Item: Stabilized pumping level; Depth below datum: measured; Source and condition: flow and test duration stated; Design use: hydraulic head and submergence
Item: Seasonal low-water allowance; Depth below datum: justified estimate or monitoring record; Source and condition: drought, nearby wells, historical range; Design use: design low level
Item: Pump discharge position; Depth below datum: proposed; Source and condition: from installation drawing; Design use: pipe and cable length
Item: Pump intake position; Depth below datum: proposed; Source and condition: from pump drawing; Design use: available submergence
Item: Top of screen; Depth below datum: measured record; Source and condition: well log; Design use: placement review
Item: Bottom of screen; Depth below datum: measured record; Source and condition: well log; Design use: placement and sediment review
Item: Sediment or well bottom; Depth below datum: measured; Source and condition: method and date stated; Design use: bottom clearance
Item: Required water outlet elevation; Depth below datum: surveyed; Source and condition: tank inlet or pressure point; Design use: static head
Attach the well log, pumping-test curve, pump outline, and final as-installed record. A depth value without its datum and date is not traceable.
Calculate available submergence
Available submergence is the vertical distance from the design low pumping water level to the pump's applicable reference point, normally defined by the manufacturer as the intake, top of motor, or another location.
For a hypothetical installation:
stabilized pumping water level during the test: 31 m;
additional seasonal and uncertainty allowance: 4 m;
design low pumping water level: 35 m;
proposed pump intake depth: 43 m.
Available intake submergence is 43 - 35 = 8 m.
Eight metres is not automatically acceptable. Compare it with the selected pump and motor manufacturer's minimum submergence, cooling-flow requirement, installation orientation, and permitted operating envelope. Some installations need a flow sleeve to provide motor cooling when the casing is oversized, the water enters above the motor, or natural velocity past the motor is insufficient.
The setting must also remain above the well bottom and sediment zone. If the bottom is 47 m and the pump assembly extends below the intake, the hypothetical 43 m intake position may leave inadequate clearance. Use the actual pump drawing, not the intake depth alone.
Check well yield against solar pumping behaviour
A solar pump may ramp with irradiance, operate for long daytime periods, and restart after cloud transients. The well must support the instantaneous and cumulative pumping profile, not only the daily water volume.
Plot pumping rate against dynamic water level during a step test or suitable pumping test. Select an operating flow that the well can sustain with the required water-level margin. If the controller can run the pump faster than the sustainable well yield under strong sun, configure a verified flow limit, level protection, or duty cycle.
Dry-run protection is a safeguard, not a substitute for setting-depth design. A sensor or controller may stop the pump after water falls, but repeated air ingestion, rapid cycling, delayed detection, or inaccurate restart timing can still reduce reliability. The article on solar pump dry-run protection explains how to validate detection and recovery logic.
Add total dynamic head at the design water level
Pump selection and setting depth are connected through total dynamic head. Calculate static lift from the pumping water level, not from the pump depth. Lowering the pump farther below the same water surface does not add equivalent discharge head, although it does change pipe length, cable length, submergence, and mechanical loads.
For a discharge to an elevated tank, include vertical lift from the design pumping water level to the tank inlet, required terminal pressure, pipe friction, fittings, valves, and other losses. Evaluate the pump curve at expected PV/controller operating conditions.
Keep the head calculation separate from the installation-depth worksheet, then cross-check the common inputs. The RUTANPUMP guide on solar water pump and storage tank sizing shows how daily demand and effective solar pumping hours become a required flow and duty point.
Verify cable, pipe, and lifting limits
Increasing setting depth increases suspended mass, cable voltage drop, riser friction, joint count, lifting difficulty, and service risk. Check:
motor cable conductor size for current, length, voltage drop, temperature, and starting or controller waveform;
splice type, water resistance, strain relief, and separation from sharp edges;
riser-pipe pressure rating, tensile load, joint method, torque, corrosion, and thermal movement;
cable-support interval and compatibility with the pipe;
safety line only where the manufacturer and site procedure permit it;
wellhead support capacity and lifting equipment rating;
maximum assembly length that can be safely installed and withdrawn;
controller limits for motor cable length, filters, insulation stress, and grounding.
Do not hang the pump from the electrical cable. The wellhead must carry the intended mechanical load through the approved riser or support arrangement. Review the wellhead cable support and entry-sealing guide before freezing the installation detail.
Commission with measured evidence
Commissioning should confirm the design assumptions under representative sunlight or a controlled power source allowed by the manufacturer.
Confirm pump model, motor, controller, PV array, cable, riser, valves, sensors, and protection settings against the approved bill of materials.
Measure the as-installed pump reference depth from the fixed datum.
Record static water level before starting.
Start at a controlled condition and verify rotation or flow direction as applicable.
Measure flow, discharge pressure, PV voltage and current, controller output, and pumping water level at defined intervals.
Continue until the water level and flow reach the required test endpoint or stabilization criterion.
Calculate actual drawdown and available submergence.
Verify cable support, wellhead sealing, pipe movement, leaks, vibration, and abnormal noise.
Test dry-run or low-water protection using the approved non-damaging method.
Record shutdown, restart delay, recovery water level, and final acceptance disposition.
If the measured pumping level is lower than the design assumption, do not simply lower the pump. Recheck well yield, bottom clearance, screen location, motor cooling, cable and pipe limits, and the sustainable flow.
Installation-depth decision matrix
Observation: Pump loses submergence during peak sun; Engineering response: Reduce sustainable flow, improve level protection, reassess setting and seasonal allowance
Observation: Adequate water above pump but motor cooling is uncertain; Engineering response: Apply manufacturer cooling-flow criteria; assess flow sleeve or different location
Observation: Sand increases when pump is lowered; Engineering response: Review screen, intake velocity, bottom clearance, well condition, and flow rate
Observation: Cable drop exceeds controller/motor allowance; Engineering response: Increase conductor size, shorten run, or change system architecture using approved limits
Observation: Dynamic level does not stabilize during test; Engineering response: Extend or redesign the test and avoid treating the observed flow as permanent yield
Observation: Pump fits hydraulically but cannot be safely withdrawn; Engineering response: Redesign riser sections, lifting method, wellhead, and service procedure before release
Frequently asked questions
How far below the water level should a solar submersible pump be installed?
Use the selected manufacturer’s minimum submergence and cooling requirements, applied to the lowest credible pumping water level. Add evidence for seasonal decline and uncertainty, while preserving bottom, sediment, screen, cable, pipe, and service clearances.
Should pump depth be measured from static or pumping water level?
Record both. Static level describes the recovered well, while pumping level at a stated flow is used for available submergence and hydraulic head. Design should also consider seasonal or long-term low-water conditions.
Does lowering the pump increase total dynamic head?
Static lift is measured from the pumping water surface to the discharge point, not from the pump depth. A deeper setting mainly changes submergence, pipe and cable length, friction, suspended load, and service conditions.
Can dry-run protection compensate for uncertain well yield?
No. It limits damage after a low-water condition is detected. The system still needs a pumping test, sustainable flow decision, installation-depth margin, verified detection logic, and controlled restart behaviour.
Contact RUTANPUMP
For solar borehole pump selection, installation-depth review, controller matching, OEM supply, and distributor support, send the well log, water-level test, required flow, discharge elevation, pipe and cable lengths, PV data, operating environment, quantity, and destination through the RUTANPUMP contact page.
RUTANPUMP / Wenling Jingzhan Mechanical & Electrical Co., Ltd.
Email: sales@rutanpump.com
WhatsApp / WeChat: +86 18267835331
Telephone: +86 (0576) 86322398
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