Energy Harvesting for Bridge Monitoring Applications

Photo of Duncan McFarland, Michael Mullis, Benjamin Riley Students: Duncan McFarland, Michael Mullis, Benjamin Riley

Sponsor: The University of Texas at Austin

Date: Spring 2010

Requirements:
The harvester must reliably and autonomously operate for ten years after installation with no maintenance while capturing enough energy to power the communication end node of the sensor network. Though the power consumption of the end node was not fully defined, it was assumed to be the power consumption of its main component: the 10 Watt National Instruments CompactRIO. The harvester also needs an energy storage device to store excess energy and use it to power the load when the harvester does not produce power. It must be resistant to the elements, wildlife, and vandalism. Finally, as a non-invasive installation it must not permanently alter the bridge or interrupt traffic flow.

Problem:
Wireless sensor networks are being installed on fracture-critical bridges to allow engineers to monitor their health without the need to send a team out on site to visually inspect each bridge. Because many bridges are in remote locations it is not feasible to have these sensor networks powered by the electrical grid. The UT Mechanical Engineering department has been tasked with developing energy harvesting systems to capture ambient energy from the environment and use it to power the sensor networks.

Solution:
The team decided to use solar energy to power the load because of its high energy density. A large lithium phosphate battery provides the energy storage element because of its many characteristics that suggest it can operate 10 years without maintenance. Also, a maximum power point tracking charge controller and a battery protection circuit allow the solar panel to charge the battery and to regulate the energy flow in the system. For the attachment method the team decided to clamp to the bridge so that the bridge is not altered. Two struts, clamped to the bottom of the bridge, extend out into the sunlight where they stabilize a vertical pipe that holds the solar panel. Wires run from the panel back under the bridge where the end node and the battery system are located. Wind load, fatigue, and stress calculations were performed to ensure the attachment was rugged enough to last 10 years.

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