Autonomy and Battery Utilization within Microgrids and Solar-Battery Applications

Distributed Energy Resources (DER) have increased penetration into the electric grid in recent years due to the growth of many renewable energy technologies as well as more efficient small conventional generation sources. Microgrids have grown in popularity along with the increased usage of DERs as a way to manage the multiple DERs on a local level.¹Microgrids contain energy storage devices to store and distribute the intermittent energy provided by DERs (see figure 1).

Coupling a solar energy resource with a Li-ion battery energy storage, we study the autonomy (the percentage of time the system meets demand) and utilization (amount of capacity used) during yearly operation.²By including a demand schedule with the coupled solar and battery system, we study both how different demands, system sizes and solar insolation patterns will affect the autonomy and utilization of the system. Both islanded and grid-tied demand structures will be discussed.

The battery model involved in this study is an electrochemical and transport based Li-ion battery model.³For the solar portion of the model we will assess both ideal insolation curves as well as site based insolation data. For the real-site data, several solar monitoring sites within the US will be employed.  The real data will offer a contrasting look at how much the coupled system can be affected on a daily and seasonal basis.   In addition, using real data will allow for a greater assessment about the stability of a coupled system in areas with strong insolation, but high variability against areas of weaker insolation, but low variability. A balance between a high level of both autonomy and utilization will be studied in conjunction with preferable demand structures. This balance will affect the structure and operation of a microgrid with both solar and battery systems.

Acknowledgements

The authors acknowledge financial support from the U.S. Department of Energy’s Advanced Research Projects Agency- Energy (ARPA-E), and the Solar Energy Research Institute in India and the United States (SERIIUS), as well as, Washington University in St. Louis’ McDonnell Academy Global Energy and Environmental Partnership (MAGEEP).

References

1.             R. H. Lasseter,  Journal of Energy Engineering-Asce, 133, (2007)

2.             C. Protogeropoulos, B. J. Brinkworth, and R. H. Marshall,  International Journal of Energy Research, 21, (1997)

3.             S. Santhanagopalan, Q. Z. Guo, P. Ramadass, and R. E. White,  Journal of Power Sources, 156, (2006)