  Underground infrastructure networks form the backbone of vital supply and
disposal systems. However, they are under-monitored in comparison to their
value. This is due, in large part, to the lack of energy supply for monitoring
and data transmission. In this paper, we investigate a novel, energy harvesting
system used to power underground sewer infrastructure monitoring networks. The
system collects the required energy from ambient sources, such as temperature
differences or residual light in sewer networks. A prototype was developed that
could use either a thermoelectric generator (TEG) or a solar cell to capture
the energy needed to acquire and transmit ultrasonic water level data via
LoRaWAN. Real-world field trials were satisfactory and showed the potential
power output, as well as, possibilities to improve the system. Using an
extrapolation model, we proved that the developed solution could work reliably
throughout the year.
