Implications of solar energy harvesting on sensor networks design

The design of wireless sensor networks presents a host of challenges like power management, ensuring coverage of an area with sensor nodes, providing fault tolerance in case of node failures and localization of nodes. But managing the power of a sensor node given the energy constraints, such that the lifetime of the node, the network and the application’s performance are maximized, still continues to be most dominant challenge. Energy harvesting has a good potential to solve the problem of energy constraint of nodes, as nodes can harvest more energy from the environment. Specifically, harvesting solar energy is ideal for outdoor sensor networks due to the omnipresent nature of sun light. In this report, we study the various challenges involved, in the design of a sensor network that uses solar energy harvesting. Solar panels and batteries are the most important components in a sensor node that uses solar energy harvesting. A study of issues of a solar panel and the trade offs in using the various battery chemistries is discussed. Power management has both node level and network level implications. Node level power management can be done by changing the duty cycles of nodes, to match the power consumption profile to the energy harvesting profile, as a way to increase the lifetime of the node and the application performance. Two approaches in this direction are discussed along with a relative comparison of both of them. Managing power at the network level involves “effective energy”, a parameter that is indicative of both the harvesting opportunity of a node and its current battery status. Approaches to find this parameter, and use it as a cost-metric in flat-routing schemes like Bellman-Ford, and to elect nodes as cluster-heads in cluster-based routing schemes like LEACH, is discussed. Another direction is to adapt data based routing schemes like Directed Diffusion, to preferably route data via solar powered nodes when both types of nodes are present. An approach in this direction has been studied.