Exploring the effect of energy storage sizing on intermittent computing system performance

Batteryless energy-harvesting devices promise to deliver a sustainable Internet of Things. Intermittent computing is an emerging area, where application forward progress, i.e. computation beneficial to the progress of the active application, is maintained by saving volatile computing state into non-volatile memory before power interruptions, and restored afterwards. Conventional intermittent computing approaches typically minimize energy storage to reduce device dimensions and interruption periods, but this can result in high state-saving and -restoring overheads and impede forward progress. In this paper, we argue that adding a small amount of energy storage can significantly improve forward progress. We develop an intermittent computing model that accurately estimates forward progress, with an experimentally validated mean error of 0.5%. Using this model, we show that sizing energy storage can improve forward progress by up to 65% with a constant current supply, and 43% with real-world photovoltaic sources. An extension to this approach, which uses a cost function to trade-off the energy storage size against forward progress, can save 83% of capacitor volume and 91% of interruption periods while maintaining 93% of the maximum forward progress.