This is data showing water level and volume for a reservoir. Reservoir devices are off the grid (no power, wifi) and use ESP32 (NodeMCU-32S)/Moteino Mega with JSN-SR04T sensors and Lora (Reyax RYLC896) to send results. Solar + 18650 LiPo bat for power
Uber Solar Water Heater, Complete High Pressure System 18 EVT 100 Litres Close Coupled Thermosiphon. Collector is facing South West at 7 deg slope to horz, with a slight tilt towards North West to aid the thermosiphon.
Solar water heating system. Direct coupled separate vac tube array connected to a well insulted 150 litre Geyser using natural thermo-siphon for heat transfer. Electric element backup is connected with timer set on from 18h00 to 20h00.