Design Considerations for Solar Energy Harvesting Wireless
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
vijay, kansal, jasonh, jf, mbs
— 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.
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 , evolved into power aware
design , and recently, battery aware design .