Highly Responsive Batteryless System for Indoor Light Energy Harvesting Environments

Energy-neutral operation (ENO) aims to provide near-perpetual device operation using energy harvested from ambient environments. Existing ENO techniques, however, have two key problems. The batteries used in harvesting devices have inherently limited lifespans, and the device experiences a long cold-start time when charging the battery. In this paper, we propose a long-lasting and highly responsive batteryless system, called RENO, to solve the problems that occur in energy harvesting devices. Using a supercapacitor to store energy, RENO maximizes the responsiveness in ENO especially running in dynamic harvesting environments such as indoor light energy harvesting. Combining the intermittent characteristics of power-neutral operation (PNO), RENO allows dual-mode operation of PNO and ENO, depending on the current harvesting capability. The device works as a PNO device when charging the energy storage, solving the ENO cold-start issue, while the harvested energy is efficiently managed with ENO. For this dual-mode operation, RENO provides hardware and software that handle the switch between PNO and ENO effectively. Application developers are provided with a well-defined API, which enables energy-efficient development of applications without detailed knowledge of the target hardware. Using the API, developers simply declare a task to be executed as either PNO or ENO, and the rest is handled by the system. The prototype system is implemented, and its functionality is evaluated in controlled environments. We also validate the proposed system with two real-world applications, proving the efficacy of dual-mode batteryless operation.