Introduction

1. 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 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. Materials &Methods 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. Summary of COTS-EH Device Survey 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. Acknowledgments Iwould 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). 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. Maximum Power Point Short Circuit Current Photovoltaic COTS System IV Curve For further information Please contact me, Audrey D. Porter, at audrey.porter@mavs.uta.edu. Power Curve Open Circuit Voltage G. Kondraske, Ph.D. (advisor) Human Performance Institute Univ. of Texas at Arlington PO Box 19180 Arlington, TX 76019-0180 E-mail: kondraske@uta.edu 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.