Power management is an important concern in sensor networks, because a tethered energy infrastructure
is usually not available and an obvious concern is to use the available battery energy
efficiently. However, in some of the sensor networking applications, an additional facility is available
to ameliorate the energy problem: harvesting energy from the environment. Certain considerations
in using an energy harvesting source are fundamentally different from that in using a battery, because,
rather than a limit on the maximum energy, it has a limit on the maximum rate at which
the energy can be used. Further, the harvested energy availability typically varies with time in a
nondeterministic manner.While a deterministic metric, such as residual battery, suffices to characterize
the energy availability in the case of batteries, a more sophisticated characterization may be
required for a harvesting source. Another issue that becomes important in networked systems with
multiple harvesting nodes is that different nodes may have different harvesting opportunity. In a
distributed application, the same end-user performance may be achieved using different workload
allocations, and resultant energy consumptions at multiple nodes. In this case, it is important to
align the workload allocation with the energy availability at the harvesting nodes.We consider the
above issues in power management for energy-harvesting sensor networks.We develop abstractions
to characterize the complex time varying nature of such sources with analytically tractable models
and use them to address key design issues. We also develop distributed methods to efficiently use
harvested energy and test these both in simulation and experimentally on an energy-harvesting
sensor network, prototyped for this work.
