Alternative Energy Sources for Sensor Nodes: Rationalized Design for Long-Term Deployment

Energy harvesting is a means of extending the lifetimes of wireless sensor nodes. Here, we describe the current state-of-the-art in energy harvesting technologies, and compare them against long-life primary batteries in terms of their total energy, economic cost and environmental impact. Issues affecting the lifetimes of energy harvesting devices, which are often overlooked, are described. We discuss the requirements for energy-awareness by wireless sensor network management algorithms, and how to deliver it for systems using batteries or energy harvesting devices and supercapacitors. A novel approach to monitoring state-of-charge, and an embedded software architecture for energy management (which has been deployed on battery-powered and energy-harvesting nodes), are introduced. This new 'energy stack' structures the node's energy-related operations, while hiding their complexity from the application layer, and providing a straightforward interface. We present a complete approach to designing the energy-related aspects of a node for long-term deployment, including hardware choices and embedded software design.