Modeling and Lifetime Assessment of Lithium-Ion Batteries Used for Solar Firming Applications and Grid Storage

The intermittent nature of many renewable power sources inhibits their implementation in the electric grid (1). Consumers demand an uninterrupted power supply and the unpredictable nature of renewables means that only a portion of the electric grid’s energy portfolio can come from these sources.  However adding an energy storage device to renewable power sources can stabilize the source’s intermittency.

A coupled system can supply a constant level of power to the grid (below the system’s peak generation rating) by storing part of the energy created during peak generation hours and releasing that energy during periods of low or no power generation (see figure 1).

Our study utilizes a model of a photovoltaic solar cell coupled with a Lithium-ion battery.  The system charges the battery anytime power generation exceeds the goal constant output and discharges the battery when the solar power output falls below the goal output. This protocol will control the system with the goal of generating the highest constant power output while still protecting the battery from degradation.  Stabilizing the power source inevitably leads to sub-optimal charging and discharging patterns for the Li-ion battery and additionally can lead to intermittent cycling (small depth of discharge or small charging percentages).  Our control strategy will seek to optimize both systems for single cycle and lifetime results.

The hybrid system will involve an electrochemical and transport based Li-ion battery model (2-5). Intermittent charging patterns obtained from solar insolation variations will be studied and their effects on capacity fade will be analyzed. The study will focus on the lifetime benefit that can be obtained from a battery during implementation into a solar firming application and seeks to understand the dynamics associated with coupled solar-battery system.

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

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4. Fuller, T. F., Doyle, M., and Newman, J. J. of the Electrochemical Society., 141,1 (1994).

5. Northrop, P. W. C., Ramadesigan, V., De, S., and Subramanian, V. R. J. of the Electrochemical Society., 158, A1461 (2011).