raghunathan-ipsn2005

raghunathan-ipsn2005 - Design Considerations for Solar...

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Design Considerations for Solar Energy Harvesting Wireless Embedded Systems Vijay Raghunathan, Aman Kansal, Jason Hsu, Jonathan Friedman, and Mani Srivastava Networked and Embedded Systems Lab (NESL) Department of Electrical Engineering University of California, Los Angeles, CA 90095 Email: { vijay, kansal, jasonh, jf, mbs } @ee.ucla.edu Abstract — Sustainable operation of battery powered wireless embed- ded systems (such as sensor nodes) is a key challenge, and considerable research effort has been devoted to energy optimization of such systems. Environmental energy harvesting, in particular solar based, has emerged as a viable technique to supplement battery supplies. However, designing an efficient solar harvesting system to realize the potential benefits of energy harvesting requires an in-depth understanding of several factors. For example, solar energy supply is highly time varying and may not always be sufficient to power the embedded system. Harvesting compo- nents, such as solar panels, and energy storage elements, such as batteries or ultracapacitors, have different voltage-current characteristics, which must be matched to each other as well as the energy requirements of the system to maximize harvesting efficiency. Further, battery non- idealities, such as self-discharge and round trip efficiency, directly affect energy usage and storage decisions. The ability of the system to modulate its power consumption by selectively deactivating its sub-components also impacts the overall power management architecture. This paper describes key issues and tradeoffs which arise in the design of solar energy harvesting, wireless embedded systems and presents the design, implementation, and performance evaluation of Heliomote, our prototype that addresses several of these issues. Experimental results demonstrate that Heliomote, which behaves as a plug-in to the Berkeley/Crossbow motes and autonomously manages energy harvesting and storage, enables near-perpetual, harvesting aware operation of the sensor node. I. INTRODUCTION The application space for wireless sensor networks is dominated by the longevity constraint, since the cost of physically deploying the sensor nodes often outweighs the cost of the nodes themselves. Energy is the limiting factor in achieving extreme (months to years) systemwide lifetime. Fortunately, a promising technique to forestall this network energy crisis is emerging – environmental energy harvesting. Exploiting energy sources ubiquitous to the operating space of the sensor nodes raises the possibility of infinite lifetime. Achieving this (through harvesting aware design) represents a new frontier in the natural progression of energy optimization techniques, which started from low power design [1], evolved into power aware design [2], and recently, battery aware design [3].
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raghunathan-ipsn2005 - Design Considerations for Solar...

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