Defining CPS Challenges in a
Sustainable Electricity Grid
AUTHORS:
Jay Taneja, Randy Katz, and David Culler
Computer Science Division
University of California, Berkeley
Presenting by:
Phanindar Reddy Tati
Contents:
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Abstract
Introduction
The California Electricity Grid
Towards A Sustainable Grid
Opportunities for Cyber Physical Systems
Conclusion
Abstract:
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Cyber-Physical Systems (CPS) are characterized as complex distributed systems exhibiting
substantial uncertainty due to interactions with the physical world. Today’s electric grids are often
described as CPS because a portfolio of distributed supplies must be dispatched in real-time to
match uncontrolled, uncertain demand while adhering to constraints imposed by the intervening
transmission and distribution network. With the increased control complexity required by deep
penetration of fluctuating renewable supplies, the grid becomes more profoundly a CPS and needs
to be addressed as a system. In this evolving CPS, a large fraction of supply is under-actuated, a
substantial portion of demand needs to become dispatchable, interactions among distributed
elements are no longer unidirectional, and operating requirements of elements are more dynamic.
To more sharply define these CPS challenges, we obtain a yearlong, detailed measurement of the
real-time blend of supplies on the primary California grid dispatched to meet current demand and
then scale the solar and wind assets, preserving uncontrolled weather effects, to a level of
penetration associated with California’s 2050 GHG targets. In this representation of a future
sustainable grid, we assess the impact of demand shaping, storage, and agility on the reconstituted
supply portfolio, characterize resulting duration curves and ramping, and investigate the distributed
control and management regime. We articulate new operational and market opportunities and
challenges that may materialize from intermittent periods of abundance and scarcity in the overall
energy network. We find that in a sustainable grid, lulls in renewable production during winter are
more critical than peaks in demand during summer, capacity for load shifting and energy storage
are more valuable as renewables penetration increases, and that grid balancing requires integrated
management of supply and demand resources.
Continued…
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How Electricity Grid is a CPS?
As renewable resources increases, Grid gets more complex
Interaction among distributed elements are no longer unidirectional
System needs to be more dynamic
To discuss more sharply in real time, California Electricity Grid
considered
 In this paper, Authors discusses about
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Sustainable Grid
Impact of demand shaping, storage
Investigated Distributed control and Management
New operational and Market opportunities, Challenges
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ABSTRACT
Introduction:
 A portfolio of electric power generation resources must be
managed dynamically to meet an uncontrolled time-varying demand
 Primary control loop is managed by an operator to avoid iterative
unit commitment problem; based on a prediction of load,
generation capacity
 Matching of generation to load is refined through hour-ahead and 5minute ahead markets based on recently observed demand
 Generators to manage mismatches
 Utilizing Information Technology- ‘SMART METERS’
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ABSTRACT
INTRODUCTION
Continued…
 Smart Meters
 Monitors loads
 Delivery of signal to trigger response from demand
 Checks power quality at intermediate points
Information Planes
Physical Planes
Classic Grid
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ABSTRACT
INTRODUCTION
Continued…
 Integration of large amounts of renewable resources makes the
Electricity Grid more challenging
 To achieve deep penetration of renewable resources
LOAD-FOLLOWING-SUPPLY
SUPPLY-FOLLOWING LOAD
model
 Zero-Emissions Load Balancing
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ABSTRACT
INTRODUCTION
Continued…
 PROBLEM: Maintaining the dynamic match between supply and
demand in a grid with a deep penetration of Renewables
 Methods:
 Pervasive monitoring, modeling
 Mitigation employing a rich information plane
 Distributed intelligence
 Basis for this Study:
 Data released by California Independent System Operator (CA ISO)
 Authors performed a scaling study if much larger array of renewable
assets were deployed
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ABSTRACT
INTRODUCTION
Continued…
 Authors answering a question
 What would the grid be like with a deep penetration of renewables today?
 Not considering changes in Demand
 Dynamics are not universal but Methodology is similar
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ABSTRACT
INTRODUCTION
The California Electricity Grid
 CA ISO:
 Independent, non-profit corporation that monitors, controls electric power
 Has 25,865 mile network
 Released hourly supply data for it’s 10 different types of generation sources
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INTRODUCTION
THE CALIFORNIA ELECTRICITY GRID
Continued…
 Here, Overall demand is defined as the sum of these generation
sources.
 Electricity demand varies on multiple timescales:
 Daily: Peaks in late afternoon
 Weekly: Weekends 9.6% less than week days
 Seasonally: Winter 15.8% less than summer
 CHALLENGE: Matching highly-variable electricity demand with a
portfolio of generation resources
 33% of power should be produced from Renewable resources by
2020 (wind, solar, geothermal, biomass, biogas, hydroelectric)
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INTRODUCTION
THE CALIFORNIA ELECTRICITY GRID
Continued…
 Temporal Variations:
 Nuclear resources- Stable base load
 Hydroelectric- More power in summer
 Thermal- To meet day-to-day variations
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INTRODUCTION
THE CALIFORNIA ELECTRICITY GRID
Continued…
Solar and Wind Power in
California:
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Solar -403MW
Wind -2.8GW
Day Time- More Solar power
Night- More Wind power
Combination could do better
Unpredictable resources
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INTRODUCTION
THE CALIFORNIA ELECTRICITY GRID
Towards A Sustainable Grid:
 Scaling Methodology: To model a sustainable grid of scale CA ISO
with a large fraction of renewable energy
 Scale solar and wind each by constant factor
 Reduce imports, thermal power until demand equals generation
 Energy produced beyond present-day energy is Excess
 Assumptions:
 Proportional scaling of wind and solar hourly through yearly
 Estimated solar based on distribution of length of the day
 Geographic diversity of both wind and solar is similar in future
 Authors selected 60% renewables threshold
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THE CALIFORNIA ELECTRICITY GRID
TOWARDS A SUSTAINABLE GRID
Continued…
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THE CALIFORNIA ELECTRICITY GRID
TOWARDS A SUSTAINABLE GRID
Continued…
 Characterization of a grid with 60% renewables
 Summer, Excess power  Exported or used to enable new energy-agile
practices
 Winter, less power
 Still has to meet day-to-day demand
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THE CALIFORNIA ELECTRICITY GRID
TOWARDS A SUSTAINABLE GRID
Opportunities for Cyber Physical Systems
 A grid with deep renewables as predicted in the sustainable grid,
presents a family of CPS challenges and opportunities
 Cooperative portfolio Management:
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THE CALIFORNIA ELECTRICITY GRID
TOWARDS A SUSTAINABLE GRID
Continued…
Loads-Following Supply
 Operators controls supply to
match the demand
 Existing grids works on this
Supply-Following Loads:
 Shifts the part of burden of
maintaining the match onto
demand
 From periods of deficit to
excess
 Shifts to thermal at points of
deficit
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THE CALIFORNIA ELECTRICITY GRID
TOWARDS A SUSTAINABLE GRID
Continued…
 Use of Storage:
 128GW storage/ worldwide
 99.9% hydroelectric (Stores water)
 Allows shaping of supply rather than demand and is substitutable
for any type of power generation
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THE CALIFORNIA ELECTRICITY GRID
TOWARDS A SUSTAINABLE GRID
Continued…
 Load curtailment and Energy Efficiency:
 From Summer to Winter, Operator targets the critical hours (where power
generation is costly)
 Reduction of energy consumption at any hour of the day becomes more
valuable
 More energy-efficient demand improves performance
 Energy-storage is more valuable
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THE CALIFORNIA ELECTRICITY GRID
TOWARDS A SUSTAINABLE GRID
Conclusion:
 Modern electric grids are CPS
 Build a model of what the grid would look like with sufficient
sources to provide 60% of the electricity consumed
 Introduced Supply-following loads
 Discussed energy storage, demand curtailment
 This study is preliminary step
 These CPS efforts will move us a step closer to the sustainable grid
design
 As resources are being consumed rapidly, sustainable grid is
necessary
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TOWARDS A SUSTAINABLE GRID
• CONCLUSION