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Investigation of a Nanogrid Concept for Personal, Energy Harvesting-Based Power Systems
Audrey D. Porter, George V. Kondraske, Ph.D., Advisor
Department of Electrical Engineering, The University of Texas at Arlington, Arlington, Texas 76019
Abstract
Summary of COTS-EH Device Survey
Materials & Methods
A microgrid is a stationary power system of certain capacity (<1 MW) that often
integrates more than one energy source. We propose extension to a nanogrid concept,
with smaller capacity (<10W) and scale to realize portable, personal energy harvesting
(EH) systems. Objectives were to identify: 1) Personal NanoGrid System (PNGS)
architectures, 2) availability of commercial-off-the-shelf (COTS) components for
practical PNGSs, and 3) challenges for future research. Microgrid implementations and
various low power, single modality EH systems were studied in the context of two
implementations: body-worn and small stand-alone systems. A survey of COTS EH
devices of suitable size, configuration, and performance was initiated.
We have determined that some modalities (e.g., radio-frequency) are not yet useful,
while others have merit for one or both implementations considered. Issues with
quiescent power of electronics (maximum power point tracking, combining EH
sources), as well as energy storage (ultracapacitors vs. rechargeable batteries), were
identified. While technical and packaging challenges remain, practical PNGSs are
feasible and open new possibilities to power systems independently of traditional
sources.
Microgrid system architectures and various low power, single modality EH
systems reported in the literature were studied in the context of the two PNGS
types considered. A survey of COTS-EH devices from technical datasheets
was initiated and a database formed. The database incorporated the physical
size as well as analyses of power output performance to determine efficacy in
a PNGS. Photovoltaic, thermoelectric, cantilever-type piezoelectric, and wind
generators are included thus far. Emphasis was placed on those devices of
appropriate dimensions for PNGSs. Various estimates of power output
expected under typical exposure conditions were calculated. Literature
research was also conducted to identify components for integrating multiple
energy sources and development of a testbed to support future work.
Figure 5. Cybmet EnerChip CBC-EVAL-09, 127 x 51 (mm), evaluation module, a
COTS device identified to support future energy harvesting research and development.
Conclusions & Recommendations
 Current COTS-EH devices are available to support development of PNGSs
with capacities sufficient to power devices of interest (medical and sport
related monitoring systems and common consumer products).
 For some EH modalities, there are a wide range of COTS devices available.
Available options and performance are anticipated to increase.
 For very low power applications, allowing for the smallest PNGS, special
technical challenges relate to optimizing support electronics (power
consumed by switching and control subsystems vs. power available for end
applications).
 Challenges and opportunities for innovation exist with regard to size vs.
power/energy tradeoffs, clever packaging, and PNGS design optimization.
Results
We have determined that some modalities (e.g., radio-frequency) are not yet
useful, while others have merit for one or both implementations
considered. Issues with quiescent power of electronics (maximum power point
tracking, combining EH sources), as well as energy storage (ultracapacitors
vs. rechargeable batteries), were identified. Examples of findings associated
with stated objectives are provided in the figures and table that follow.
Personal NanoGrid Systems
Stand-alone
Body-worn
Heat Flow
Energy
Solar
Energy
Literature Cited
Bowden, S. & Honsberg, C. (2013). Solar Cell Operation. In PV CDROM. Retrieved from
http://pveducation.org/pvcdrom/solar-cell-operation/
Haralson, P., Montoya, M., Neal, R., Sherick, R., & Yinger, R. (2013, June 19). Islands in the
Storm: Integrating Microgrids into the Larger Grid. IEEE Power & Energy Magazine, 11,
4, 33-39.
Tan, Y. K. (2013). Energy Harvesting Autonomous Sensor Systems. Boca Raton, FL: CRC
Press.
Wilson, S. (2013). Energy Harvesting & Art. Retrieved from
http://userwww.sfsu.edu/swilson/emerging/artre375.energyharvesting.html
Human
Motion
Energy
Solar
Energy
Wind
Energy
Figure 2. A block diagram of a nanogrid system.
Figure 1. Schematic examples of the two types of PNGSs considered.
Typical Photovoltaic COTS Cell
Introduction
A microgrid is “a group of interconnected loads and distributed energy resources that
acts as a single controllable entity”. Both renewable and non-renewable energy
resources can be included. Two recent trends inspired the concept of a nanogrid.
Specifically, these trends are the increased availability of: 1) very low power electronic
systems in integrated circuit form (microcontrollers, analog components, wireless
communications, etc.) and 2) the number and types of small energy harvesting (EH)
devices. A nanogrid is similar to microgrid in terms of structure and function, but has
a smaller physical scale, less power generation capacity (10W or less) and is
envisioned to be portable and include only renewable energy resources. It is not
connected to other grids, always operating in the so-called island mode. The objectives
of the present effort were to identify: 1) Personal NanoGrid System (PNGS)
architectures, 2) availability of commercial-off-the-shelf (COTS) components for
practical PNGSs, and 3) challenges for future PNGS research and development.
Acknowledgments
Maximum
Power Point
Short Circuit Current
Photovoltaic COTS System
IV Curve
Power
Curve
I would like to thank Dr. George V. Kondraske for being a mentor and guide to
me during the research. I would also like to thank Dr. Kambiz Alavi, Dr.
Jonathan W. Bredow, and Mr. Mohammadreza Jahangir Moghadam for
providing me with the opportunity to be in the REU program during summer
2013. Funding for this program was provided by the National Science
Foundation (NSF grant #EEC-1156801, REU Site: Research Experiences for
Undergraduates in Sensors and Applications).
For further information
Open Circuit Voltage
Please contact me, Audrey D. Porter, at [email protected].
Voltage (V)
Figure 3. Maximum Power Point Tracking (MPPT) is necessary for optimized
nanogrid performance.
Figure 4. Estimated power output performance (left) and energy harvested (right)
for three series-connected IXYS SolarBITS KXOB22-01X8s.
G. Kondraske, Ph.D. (advisor)
Human Performance Institute
Univ. of Texas at Arlington
PO Box 19180
Arlington, TX 76019-0180
E-mail: [email protected]