As part of a USAID Powering Agriculture grant I have been working
on smart irrigation at The Sustainable Engineering Lab. Three solar
systems, 4.8 to 6.8kW, have been installed in Gabar, Senegal to provide
irrigation water to twenty one smallholder farmers.
The diagram above shows the basic design. One criterion was to
avoid battery storage as much as possible. There is no large battery array
or water tower. Water is distributed directly by means of drip or stored
at ground level in basins for hand distribution. The motivation behind
this design decision is purely economical.
The system is controlled by a Raspberry Pi. The chip above is a "hat"
that integrates all the sensors and switches. A pyranometer and a
temperature sensor are used to approximate shortwave radiation and
cell temperature. Power available is estimated based on those readings.
Some of the other elements of the PCB are a real-time clock for more
accurate logs, an RS-485 to USB converter for reading an array of smart
meters, and a transistor array for signaling the relays on the power