  Field sensor networks have important applications in environmental
monitoring, particularly climate change, air, water and soil quality, in
disaster monitoring and in border security. The reduced cost of electronics,
sensors and actuators make it possible to deploy hundreds if not thousands of
these sensor modules. However power technology have not kept up. Current power
supply technologies such as batteries limit many applications due to their low
specific energy. Photovoltaics typically requires large bulky panels and is
dependent on varying solar insolation and therefore requires backup power
sources. Polymer Electrolyte Membrane (PEM) fuel cells are a promising
alternative, because they are clean, quiet and operate at high efficiency.
However challenges remain in achieving long lives due to factors such as
catalyst degradation and hydrogen storage. In this work, we devise a framework
for designing fuel cells power supplies for field sensor networks to achieve
long lives and utilize lithium hydride hydrogen storage technology that offers
high energy density of up to 5,000 Wh/kg. Using this design framework, we
identify operating conditions to maximize the life of the power supply, meet
the required power output and minimize fuel consumption. We devise a series of
controllers to achieve this capability and demonstrate it using a bench-top
experiment that operated for 5,000 hours. The laboratory experiments point
towards a pathway to design and scale these fuel cell power supplies for
various field applications. Our studies show the proposed PEM fuel cell hybrid
system fueled using lithium hydride offers at least a 3 fold reduction in mass
compared to state of the art batteries and 3-5 fold reduction in mass compared
to current fuel cell technologies.
