Geothermal Well Water Level Monitoring: Wireless Level Transmitter Case with 4G and Solar Power
2026/10/27
This case describes a production geothermal well used for district heating. The wellhead water temperature runs 60–95 °C, the static water level sits 20–80 m below the wellhead, the submersible pump is set at 80–200 m, and there is no reliable low-voltage power at the wellhead — the nearest usable supply is several hundred metres away across an access road. The water carries dissolved gas, fine sand and a strong carbonate scaling tendency. Winter ambient drops to −15 °C, and the wellhead pit floods after rain.
| Field parameter | Typical value on site | Why it changes the instrument choice |
|---|---|---|
| Wellhead water temperature | 60–95 °C | Standard PVC or PE cables soften; the sensor cable and diaphragm must be rated for continuous hot water |
| Static level below wellhead | 20–80 m | Measurement span is large, so accuracy must be specified as a percentage of span, not of full scale |
| Wellhead power supply | None (off-grid) | Loop-powered 4–20 mA cannot drive a remote link; a battery/solar wireless node is required |
| Water quality | Dissolved gas, sand, scale | Diaphragm fouling and gas pockets cause drift on pressure-type sensors |
| Ambient conditions | −15 °C in winter, flooded pit | Enclosure and antenna must be IP67 or better with frost protection |
- Manual dip measurement once a week could not detect a falling water level caused by pump drawdown, so the pump occasionally ran dry and tripped on overload.
- A standard submersible transmitter with a PVC cable hardened and cracked at the wellhead gland within one heating season.
- No data path to the control room: the heating station only learned about a well problem when a resident called about cold radiators.
The requirement was a continuous reading of dynamic water level in a hot, scaling, off-grid well, delivered to a heating control room 1.2 km away. The chosen configuration was a high-temperature submersible level transmitter with a vented, heat-resistant cable, mounted inside a 1.5-inch sounding pipe strapped to the pump riser, connected to a battery-powered remote terminal unit with a 4G module and a 40 W solar panel.
| Selection item | Specified value | Reason |
|---|---|---|
| Sensor type | Submersible pressure transmitter, vented gauge | Radar from the wellhead was rejected: steam, foam and a narrow casing create false echoes at this depth |
| Wetted material | 316L diaphragm with PTFE facing | Limits carbonate scale adhesion and allows acid cleaning without damaging the diaphragm |
| Temperature rating | Continuous 90 °C, cable 105 °C | Matches measured wellhead temperature with margin |
| Measuring range | 0–150 m H₂O | Covers pump setting depth plus drawdown |
| Accuracy | ±0.5 % of span | Gives roughly ±0.75 m at full span, adequate for pump protection |
| Output and link | RS485 Modbus to RTU; 4G to server; local 4–20 mA | Local loop for the station PLC, wireless for the remote control room |
| Power | 3.6 V lithium pack plus 40 W solar, 12 V buffer | Keeps the node alive through 10 cloudy winter days |
| Protection | IP68 sensor, IP67 enclosure | Flooded pit and hose-down conditions |
- The sounding pipe is fixed to the pump riser at 3 m intervals, with the open bottom 2 m above the pump intake so sand and gas stay out of the sensing zone.
- The vent tube is routed upward with a desiccant cartridge and a drip loop; a blocked vent is the most common cause of reading error on vented sensors.
- The cable gland is sealed with a high-temperature gasket rated above 100 °C, and a 30 cm service loop is left outside the wellhead for future re-termination.
- The solar panel faces south at 45° with a lightning arrester on the DC side and a separate earth electrode at the wellhead.
- Alarm thresholds are set at the control room: low-low level stops the pump, low level raises a warning, and a rate-of-fall alarm flags a sudden drop.
- Water level is refreshed every 60 seconds and displayed on the heating station screen and on a mobile page, replacing the weekly manual dip.
- Dry-run trips stopped, because the low-low threshold now acts on a live level signal instead of a delayed current-based protection.
Can I use a radar gauge instead? For an open wellhead with a wide casing, yes; for a narrow casing with steam and foam, a submersible pressure sensor is more stable.
- Confirm continuous temperature at the wellhead, not the average, and require a cable rating above it.
- Confirm the sounding pipe diameter and the distance from the wellhead to the lowest dynamic level.
- Ask for the Modbus register map and alarm logic in writing before shipment.
- Order one spare transmitter and one spare cable gland — the cable gland is the part that fails first.
