Solar Well Pump Float Switches, Ultrasonic Tank Sensors, Dry-Run Probes & Pressure Tank Automation
An unmonitored solar well pump without automation will either overflow your 5,000-gallon cistern into the yard all afternoon or pump a slow-recovering borehole dry and burn up the motor bearings. Properly wiring Normally-Closed (NC) vs. Normally-Open (NO) cistern float switches, down-hole 24V conductivity dry-run probes, and long-distance LoRa wireless tank level transmitters turns a solar well into a zero-maintenance utility.
Conventional Grid/Generator Pumping vs. Solar Hydraulic Engineering
| Hydraulic Parameter | Conventional AC / Generator Mistake | Solar Hydraulic Engineering Spec | Ranch & Homestead Advantage |
|---|---|---|---|
| Cistern Full Shutoff Logic (NC vs. NO Float Switch) | Buying a standard "Pump-Down / Sump" float switch by mistake (Turns well pump ON when tank is full and OFF when empty!) | Check Controller Logic: Grundfos CU200 / Lorentz PS2 use a Low-Voltage Dry-Contact Float Loop (Wire for Tank-Fill / Pump-Up operation) | Wide-angle tether weight gives 400–600 gallons of hysteresis so the pump doesn’t short-cycle every 2 minutes |
| Cistern 1,500+ Feet Away Up a Mountain (No Trench Wire) | Trenching 1,500 feet of 14/2 wire up a rocky cliff just for a float switch | Option A: LoRa 915 MHz Solar Wireless Float Transmitter (2-mile line-of-sight range) | Option B: Pressure-Transducer Backpressure Cutoff at Wellhead! | Using a brass mechanical float valve in the hilltop tank + a pressure switch at the wellhead stops the pump with ZERO wires between well and tank! |
| Down-Hole Well Dry-Run Protection | Pump sucks air and sand for 3 hours when water table drops in August | Two-Conductor Encapsulated Water Level Probe taped 10 ft above pump + 20-minute auto-recovery timer | Saves $2,500+ in burned-up helical stators and melted centrifugal impellers |
| Direct-to-Pressure-Tank Solar Pumping (No Cistern) | Standard 30/50 PSI Square D mechanical switch chatters rapidly when clouds pass | Oversized 86–119 Gallon Well-X-Trol Bladder Tank + Solar Controller Anti-Chatter Minimum Run Timer + Check Valve | Stores pressurized water during sunny hours for evening dishes and morning showers |
Total Dynamic Head (TDH), Solar Array Wattage & Daily Gallon Flow Schedule
| Well Depth / Design Scenario | Solar Array (Watts) | Pump / Hardware Spec | Peak Flow / Setting | Daily Output / Result |
|---|---|---|---|---|
| Wired Cistern Float Switch (<500 Ft from Wellhead) | 5V / 12V / 24V Dry-Contact Signal Loop (Zero Shock Hazard) | 16/2 or 14/2 Direct-Burial UF-B / Shielded Tray Cable in 3/4" PVC | Tether Length = 12" to 18" (400-Gal Differential) | Most reliable hardwired shutoff method |
| Wire-Free Hydraulic Backpressure Cutoff (Tank up to 5,000 Ft Away) | Zero Comms Wires Required Between Well and Hilltop Tank | Hudson/Jobe Mechanical Float Valve in Tank + Reverse-Acting Pressure Switch at Wellhead (+15 PSI above pumping head) | When tank fills, mechanical float closes -> line pressure spikes +15 PSI -> wellhead switch stops pump! | Includes 6-hour solar delay timer or bleed orifice to reset pressure after tank drawdown |
| Long-Range LoRa Wireless Tank Level Telemetry (Up to 3 Miles) | Mini 5W Solar Panel on Cistern Lid + Ultrasonic/Float Sensor | 915 MHz LoRa Transceiver Pair (Ranch Systems / RPS / Lorentz Connected) | Closes Relay at Wellhead Controller + Smartphone Tank % App | Built-in fail-safe stops pump if radio heartbeat is lost |
| Direct Bladder Pressure Tank Setup (Cabin / Small Home) | 800W – 1,600W DC Array | Two 86-Gallon Bladder Tanks in Parallel + Square D FSG2 Reverse-Contact / Standard Switch | 40/60 PSI Setpoint (38 PSI Air Pre-Charge) | Provides 55–70 gallons of pressurized night drawdown without batteries |
3-Step Borehole & Ranch Commissioning Checklist
Set Float Switch Counterweight for a 12-to-18 Inch Vertical Swing
Never clamp a float switch tether short (2 inches), which causes the solar pump to cycle ON and OFF every 60 seconds as waves ripple in the tank. Clamp the counterweight 12 to 18 inches from the float body so the tank drops 300–500 gallons before calling for the pump.
Verify Normal-Open (NO) vs. Normal-Closed (NC) Controller Jumper
Check your pump manual before burying the wire: Lorentz PS2 Remote Tank Switch inputs pause the pump when the circuit OPENS when full, whereas some Grundfos/Square D pressure loops pause when the circuit CLOSES. Use a 3-wire SPDT (Single-Pole Double-Throw) float switch (Black/White/Red wires) so you have BOTH NO and NC contacts available at the wellhead!
Protect Float & Dry-Run Sensor Terminals Against Lightning Surges
Long 400-foot float switch wires act as antennas during summer thunderstorms, sending induced voltage spikes straight into the pump controller logic board. Use shielded twisted-pair cable grounded at ONE end only (at the wellhead ground rod).
Solar Well Pump & USDA NRCS Engineering Specification Sheet
Copy and customize this hydraulic specification for your well driller quote or USDA NRCS EQIP Practice Code 533 application.
SOLAR WELL AUTOMATION, FLOAT SWITCH & DRY-RUN CONTROL SCHEDULE: 1. Down-Hole Dry-Run Cutoff: Encapsulated 2-wire water-sensing probe installed 10 ft above pump intake wired to Controller Dry-Run terminal with 20-minute aquifer recovery restart delay. 2. Cistern Level Control: 3-Wire SPDT Mechanical Float Switch with 15-inch tether differential (or [WIRELESS_LORA_OR_BACKPRESSURE_SWITCH]) halting pump operation at 95% tank capacity.
Frequently Asked Solar Well Pumping Questions
How can I stop my solar well pump when a stock tank 2,000 feet away is full WITHOUT running a wire or radio?
Use the "Hydraulic Backpressure Switch" trick! Install a heavy-duty mechanical float valve (like a Jobe Topaz or Hudson valve) inside the stock tank 2,000 feet away. At the wellhead, install a small 2-gallon mini expansion tank, a pressure gauge, and a pressure switch wired to the solar controller’s float input. Watch the pressure gauge while the pump is filling the tank (say it reads 35 PSI). Set the wellhead pressure switch to open at 50 PSI. The moment the distant stock tank fills up and the mechanical float valve closes, pipe pressure at the wellhead rises to 50 PSI and clicks the solar pump off!
Why should I always buy a 3-wire (SPDT) float switch instead of a 2-wire float switch?
A 2-wire float switch is permanently locked at the factory as either "Pump Up (Fill)" or "Pump Down (Empty)." A 3-wire SPDT float switch has a Common wire, a Normally Open wire, and a Normally Closed wire—meaning it works with 100% of solar pump controllers on the market simply by choosing which two wires you land on the terminal block.