Lithium-ion batteries routinely undergo charge-discharge cycles
and their performance degrades with use. Storage and cycling are
the main causes of performance degradation.

BESS
Performance
Degradation

Unified
Physics-based
Model

The main indicators of battery performance are charge capacity andresistance. For lithium-ion batteries, performance decline can be
attributed to loss of cyclable lithium, electrode fracture, anddegradation of electrolyte.
Southwest Research Institute® (SwRI®) has launched the Battery
Energy Storage System (BESS) for Electric Grid Joint Industry
Program (JIP). Our investigations will include:Preventive
maintenanceGrid-connected Battery Energy
Storage Systems

Physical Asset
Battery Energy
Storage System(BESS)

StatisticalModel• Developing new test cycles for batteries used in grid applications• Estimating the life span of batteries and their potential for failure• Reducing the likelihood of battery fires

SwRI is involved in various
aspects of BESS for electric
grid including modeling ofperformance degradation,safety, and economics.

JIP Goal

The main goal of the Joint Industry Program is to discover more about howa battery degrades and the likelihood of its failure. SwRI plans to accomplish
this by developing a physical model-based method to estimate performancedegradation in grid-connected batteries and establish a correlation with battery
fires. Program outcomes could be used in a revenue maximization model and forpreventive maintenance to reduce occurrence of battery fires.

Statistical Model of Battery Degradation

As an alternative or redundancy to the physical model-based method above,
battery performance degradation could be estimated by statistical means.
SwRI has developed and verified a hierarchical method that uses characteristic
timescales of a battery and a representation of any arbitrary duty as acomposition of “simple” cycles.
The main uses of this model are:

• Off-line calculation to meet expected battery life
• Estimation of warranty costs using uncertainty bounds on battery life
• Real-time estimation of degradation
The degradation from the fundamental components was determined using
SwRI’s proprietary hierarchical cyclic degradation model. The charts show good
agreement between the estimated and measured degradation.

BESS Safety(Fire)Es
de tima
gra teda oftionBESS
Dispatch
Strategy

Operator
RevenueTargets

Bid inenergy
marketrgyEne emyrt
te sBat age SyroSt

Energy Management Unit

Through the SPARKS program, Southern Methodist Universityonlatiu(SMU) and Southwest Research Institute collaboratedgRe
ncy
on research to manage variability of distributedeuqFre
renewable energy sources such as wind and solar,
ingmforwith simultaneous consideration of grid stability
Peralign
Sand operator revenue.
trkeMaWe focused on how to maximize longterm revenue generation of a typicalsolar farm and its connected batteryenergy storage providing stackedservices including:• Direct power sale to the grid from solargeneration• Fast frequency regulation (quicklymPVteSysntmegeana
Mrgy
Ene dicted
Pre owerPPV

linger
Powdi
Grl
tro
ConnalSigtgenALDRl
tro
ConnalSig

Sel

itUntem
Sys tusaStgrgin

haVCPge )itra tricity
brc
A e
rgy g elEnebuyin/lingerPowPVElectricity Flowl(seresponding to deviation in the gridfrequency) from the battery

Information Flow

Agent-based machine learning is made to maximize
revenue from grid service provided by a BESS.

• Energy arbitrage (buy low and sell high) using the battery asintermediate storage

SMU and SwRI built a machine learning model with a PPO (proximalpolicy optimization)-based agent, a cutting-edge method in deep
reinforcement learning (DRL agent).
Using data from SwRI’s Energy Storage Technology Center and public
sources, we demonstrated that our model is flexible, quick to learn,
and beats comparative models at maximizing profit by more than20%. The BESS life-cycle cost needed for this model could be obtained
from our physically- and statistically-based degradation methods.

Benefits of JIP Membership

Participants can guide the research to keep it true to industry
needs. They also can license the IP before SwRI offers it to JIP nonparticipants, which may provide a competitive advantage by reducing
life-cycle costs.

This new JIP will utilize grid-connected energy
storage at SwRI's San Antonio location.

We welcome your inquiries.
For more information, please contact:

Jayant V. Sarlashkar
Institute Engineer
210.522.5506
jsarlashkar@swri.org

Southwest Research Institute is a premier independent, nonprofit research and development
organization using multidisciplinary services to provide solutions to some of the world’s mostchallenging scientific and engineering problems. Headquartered in San Antonio, Texas, ourclient-focused, client-funded organization occupies 1,500 acres, providing more than 2.3 million
square feet of laboratories, test facilities, workshops, and offices for more than 2,600 employees
who perform contract work for government and industry clients.
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Race/Color/Religion/Sex/Sexual Orientation/Gender Identity/National Origin/Disabled/VeteranCommitted to Diversity in the Workplace

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