Shepherd Nova: A Public Testbed for Rigorous Experiments Under Repeatable Energy-Harvesting Conditions

Public testbeds are essential for replicable experiments and meaningful comparisons on shared physical infrastructure. While many testbeds exist for battery-powered Internet of Things (IoT) systems, there is a lack of public testbeds for observing and profiling the distributed operation of energy-harvesting IoT systems, including battery-free devices. We fill this gap and present Shepherd Nova, the first public testbed designed to support experiments under repeatable energy-harvesting conditions. Shepherd Nova uses field-recorded harvesting data to supply power to devices, consistently replicating real-world spatio-temporal energy availability across multiple experiments. Its virtual power source supports diverse ambient energy sources, harvesting circuitry, and energy storage devices. Moreover, Shepherd Nova provides services like general-purpose input/output (GPIO) tracing, power profiling, and serial output logging, all of which can run synchronously and with high resolution. Sub-microsecond synchronization enables precise correlation between these observations and emulated energy-harvesting conditions, offering unprecedented insights into distributed energy-harvesting IoT systems. In this paper, we describe Shepherd Nova's design, characterize its performance, and demonstrate its capabilities through controlled experiments and an example test case. To access the testbed, documentation as well as open-source harvesting data, hardware designs, and code, visit https://testbed.nes-lab.org/.