Design of Energy Harvesting Technology: Feasibility for Low- Power Wireless Sensor Networks

In designing for a system’s lifecycle considerations, longterm energy needs often become an important limiting factor. Shifting from conventional energy sources (e.g. fossil fuels) toward renewable sources (e.g. wind and solar) has become a popular means for focusing on the lifecycle of large-scale systems like automobiles and the national electrical grid. This same shift in small, low-power systems such as sensors has the additional advantage of potentially increasing the operational life of the systems. This paper introduces a methodology for determining the feasibility of in situ energy harvesting as a viable power source for a given low-power system. The method is demonstrated by considering a wireless sensor node and the specific application of monitoring the fatigue life of highway bridges, with a target operational life of ten years for the sensor node. Peak and average power requirements for wireless sensor nodes are calculated and compared to the power density available from solar, wind, and vibration energy. Energy storage is also discussed, including both disposable batteries (as the status quo with which to compare energy harvesting) and rechargeable systems (as a necessary component of the energy harvesting system). Solar, wind, and vibration energy are all found to be feasible sources of power for this particular application. Vibration harvesting has lower power density than solar and wind harvesting, but has the advantage of being less dependent on location, more self-contained, and largely maintenance free. Energy harvesting in general only becomes attractive for projected life cycles exceeding the life of disposable batteries, which for this particular application is estimated at 4-6 years. Thus, energy harvesting is an excellent way to extend the lifespan of low-power systems where power availability is the limiting factor.