Distributed Generation for
Power Resiliency to
Disasters
Alexis Kwasinski, PhD
The University of Texas at Austin
© Alexis Kwasinski, 2012
Overview
•  Power Grids Vulnerabilities
•  Performance During Natural Disasters
•  Case studies
•  Proposed Technological Solutions
• Microgrids
•  Planning
•  Residential microgrids
Note: Most of the photos and information are from field damage assessments
and research work supported by NSF
© Alexis Kwasinski, 2013
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Issues in Conventional Power Grids
•  Weaknesses
•  Predominant centralized architecture and control as seen by users.
•  Passive transmission and distribution.
•  Very extensive network (long paths and many components).
•  Need for continuous balance of generation and demand.
•  Difficulties in integrating meaningful levels of electric energy storage.
•  Stability and power quality issues when integrating significant levels of
renewable energy sources.
•  Difficulties in integrating new loads
•  Aging infrastructure
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Power grids performance during natural
disasters
•  Practical observations after disasters - vulnerabilities
•  Sub-transmission and distribution portions of the grid lack redundancy
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Power grids performance during natural
disasters
•  Practical observations after disasters - Vulnerabilities
•  E.g. Hurricane Isaac
•  Severe damage is limited to relatively small areas.
•  Only one damaged pole among many undamaged causing most of the
island to loose power.
Grand Isle, about 1 week after the hurricane
Entergy Louisiana
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Power grids performance during natural
disasters
•  Restoration logistics
•  Effective management of logistics is key to reduce outage time.
Irene
Isaac
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Power grids performance during natural
disasters
•  Natural disasters as real test-beds to evaluate
power grids vulnerabilities
•  Some relevant recent hurricanes: Katrina, Gustav, Ike, Irene (2011),
Isaac (2012) and Sandy.
•  All of these hurricanes caused at least one million power outages.
•  Power outages extended over large areas and lasted from several
days to weeks.
•  Extensive damage was mainly
observed in part of the areas
affected by the storm surge.
•  Noticeable short and long-term
drop in power demand with Katrina
and Ike.
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Power grids performance during natural
disasters
•  Natural disasters as real test-beds to evaluate
power grids vulnerabilities
•  Some relevant recent earthquakes: Chile (2010), Christchurch
(2/2011), and Japan (3/2011).
•  Power outages extended over large areas.
•  Noticeable short and long-term drop in power demand
•  Except in Japan, power generation issues were minor.
•  Issues in New Zealand with soil liquefaction.
•  In all of these events strong shaking
damaged some substation components.
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Power grids performance during natural
disasters
•  Case study: Hurricane Ike
•  Most of the area affected by a large disaster
shows little damage to the power grid, yet,
power outages are significant and long.
Cat. 2 Hurricane Ike
Photo courtesy of NOAA
Outage Incidence (Peak % of
customers without power)
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Power grids performance during natural
disasters
•  Case Study: Hurricane Sandy
•  Little damage to the power grid but outages were severe
•  Longer restoration times than usual observed in areas with underground
power facilities.
•  A short circuit in the substation of a power plant in Manhattan caused a
significant portion of the power outages in that island.
98% restoration
time
Outage Incidence
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Power grids performance during natural
disasters
•  Case Study: Hurricane Sandy
•  Often, damage to power grids is less severe than for residences.
•  Important damage to several substations
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Power grids performance during natural
disasters
•  Case studies: Hurricane Sandy
•  Only observed cases of damage in PV systems.
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Power grids performance during natural
disasters
•  Practical observations after disasters
•  Severe damage is limited to relatively small areas.
< 10 % of the affected area
> 90 % of the affected area
•  Bolivar Peninsula after Hurricane Ike
vs.
•  Baton Rouge, Louisiana,
after Hurricane Gustav
(only 1 pole damaged
among many undamaged)
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Power grids performance during natural
disasters
•  Key observation that leads to microgrid-based solutions:
•  During disasters damage distribution is inhomogeneous
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Technical Solutions
•  Utility domain
•  Some solutions:
•  Infrastructure hardening
•  Buried infrastructure
•  Mobile transformers
•  Community energy storage
•  Advanced distribution automation
•  These solutions are limited because they do not address inherent
problems in power grids.
•  Smart meters and related other smart grid technologies facilitate
detecting a fault but they provide very limited improvement to avoid
faults or to mitigate their effects.
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Technical Solutions
•  Utility hardening approaches
•  Approaches:
•  Tree trimming
•  Reinforced poles
•  Buried infrastructure
•  Not necessarily effective
•  Very costly
•  May reduce the probability of failures during some type of
disasters but it adds complexity (e.g. conductors cooling)
and increases repair times under all operating conditions.
•  Conventional hardening approaches do not address inherent
vulnerabilities in power grids.
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Technical Solutions
•  User domain
•  Stand by power systems (i.e. systems with local energy storage
often in batteries and/or diesel).
•  Microgrids
Fuel cell-based microgrid in Garden City,
NY after Hurricane Irene (and Sandy)
Cell site with a standby diesel genset
after Hurricane Ike
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Technical Solutions
•  Microgrids (mostly fixed ones, but also applicable to
portable system)
•  What is a microgrid?
•  Microgrids are considered to be locally confined and independently
controlled electric power grids in which a distribution architecture integrates
loads and distributed energy resources—i.e. local distributed generators
and energy storage devices—which allows the microgrid to operate
connected or isolated to a main grid
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Power grids performance during natural
disasters
•  Ad-hoc microgrids
•  Ad-hoc microgrids using diesel
generators connected to the power
distribution grid has been used in the
past but it presents issues (e.g. safety,
reliability, power quality….)
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Power grids performance during natural
disasters
•  Some lessons from Japan s earthquake and tsunami.
•  Natural disasters are not single events. They are complex events with 4
distinct phases: pre-disaster, during the disaster, immediate aftermath and
long-term aftermath (when power generation, transmission and/or
distribution capacity may be lacking).
Onagawa nuclear power plant: Offline
since the earthquake. Currently, almost all
nuclear power plants in Japan are offline
•  As a result of Fukushima #1 Nuclear Power plant event electric power
utilization in Japan has been affected, particularly during the summer when
rotating outages are likely.
•  Microgrids may also help to limit these and other
effects during the long term aftermath.
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Microgrids Operation in Disasters
•  Case study: NTT s/NEDO microgrid in Sendai
•  This microgrid was designed to provide different power quality levels to part
of an university campus, including a clinic. Operational on 3/11/11
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Microgrids Operation in Disasters
•  Case study: NTT s/NEDO microgrid in Sendai
•  Performance during the March 11, 2011 earthquake
2x350 kW
50 kW
•  1) Earthquake happens. Natural gas generators fail to start.
•  2) Manual disconnection of all operating circuits except the dc one
•  3) and 4) Natural gas generators are brought back into service by
maintenance personnel. A few minutes later, the circuits that were
intentionally disconnected are powered again.
•  5) Power supply from the main grid is restored.
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Microgrids Operation in Disasters
•  Case study: NTT s/NEDO microgrid in Sendai
•  Performance during the March 11, 2011 earthquake
•  Natural gas infrastructure in Sendai: contrary to most of the city that relied
on natural gas supply from a damaged facility in the port, the microgrid
natural gas was stored inland and was not damaged.
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Microgrids Operation in Disasters
•  Lessons from the operation of NTT-Facilities/NEDO
microgrid in Sendai.
•  Local energy storage in batteries were a key asset to keep at
least the most critical circuit operating.
•  PV power only played a complementary role.
•  Natural gas supply did not fail thanks to an almost exclusive design
for the distribution pipelines for this site.
•  Flexible remote operation is very important during extreme events
conditions.
•  Connection of generators or their components through ac buses
seem to increase failure to start probability.
•  Source diversification is important.
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Microgrids
•  Some open questions both for permanent and mobile
microgrids
•  Control for stable operation (contrary to conventional power grids,
individual loads ratings are a significant portion of the power
generation capacity; microgrids have low inertia).
•  Power electronics for integration of diverse power sources and
energy storage.
•  Optimal system control.
•  Autonomous controllers (droop) in cases with constant-power loads.
•  Planning (e.g. energy storage sizing, design for enhanced reliability
and flexibility)
•  Grid interconnection and coordinated operation.
•  Safety
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Microgrids Planning
•  Goal: Maximize power availability with minimal cost
(e.g. without oversizing the microgrid)
•  Availability is ratio between the expected time that the microgrid power its
load and the total operational time.
U µG = U NB e
Total unavailability
⎡
⎤
⎢
−
µMCS ,i TBAT )⎥
(
⎢ µ ∈Μ
⎥
⎣ i mcs
⎦
Base unavailability
(without batteries)
∑
Total availability
= 1 − AµG
Repair rate from a
minimal cut state to
an operational state
Batteries
autonomy
•  Base unavailability is heavily dependent on the unavailabilities of the
microgrid sources, which, in turn, may be dependent on lifelines performance.
•  Local energy storage in batteries may contribute significantly to reduce
microgrid unavailability.
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Microgrids Planning
•  Power sources dependent on a lifeline
•  There are two types of sources: those that depend on a lifeline and those
that do not depend on lifelines (e.g. renewable energy sources).
•  Lifelines are infrastructures used by local power generators to receive
energy. Lifelines are affected differently by various natural disasters.
Transportation and fuel
delivery
Electric grid
© Alexis Kwasinski, 2013
Natural gas
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Microgrids Planning
•  Lifeline dependency. E.g. Hurricane Isaac
•  Electric service interruption
Port Sulfur,
Oct. 2010
(Diesel
supply need)
• Flooded roads made impossible to deliver fuel for
permanent diesel gensets
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Microgrids Planning
•  Power sources dependent on a lifeline
•  Approaches to limit the negative impact of lifeline dependencies on
microgrid availability:
•  Use of diverse power source technologies (e.g. combine natural gas
and diesel, or natural gas and renewable energy sources)
•  Local energy storage
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Microgrids Planning
•  Power sources dependent on a lifeline
•  Continuous fuel supply
uCOFS =
uSB =
λf
Continuous
operation
µ f + λf
λMG (λGen + ρGen µMG )
µMG (µMG + µGen )
Standby
•  Discontinuous fuel supply (with local energy storage… e.g. diesel storage)
PE = 1 − PE* = P{td > TTC } = 1 − ∫
td =TTC
td = 0
f d (td )dtd
Triangular fd(t) u =
f
© Alexis Kwasinski, 2013
TM − TTC
PE*
3 TUf + 3TTC + TM − TTC
PE
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Microgrids Planning
•  Renewable energy sources
•  Most renewable energy sources do not require lifelines, but…..
•  Issues with PV systems: large footprints. Solution:
•  Size PV arrays for less than the required load and use it to support
another power source rated at full capacity.
•  Renewable energy sources have, typically, variable output. Solutions:
•  Local energy storage (e.g. batteries)
•  Source diversification (combine wind and PV)
2x350 kW
natural gas
generators
50 kW
PV array
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Microgrids Planning
•  Renewable energy sources
•  Modeling of renewable energy sources and combined energy storage
based on Markov chains
PV
PV (75%)
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Microgrids Planning
•  Microgrids cost
•  Microgrids capital cost may be considered to be high.
•  Objective evaluation tool: risk assessment.
Risk = (Probability of an event to happen) x (Impact of the event)
Event: loss of power as a result of a given disaster
Impact: cost of not having electric power during and after a disaster
•  Basic decision approach to choose a microgrid:
Risk > (Microgrid lifetime cost)
•  Initially the decision inequality may benefit the microgrid option for
critical loads in which the impact is high.
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Microgrids Planning
•  Planning for disaster resistance – Risk Assessments
•  What is the optimum level of protection?
•  Issue with risk assessment: Before the event, human
perception is biased towards probability whereas after the
event is biased towards impact.
•  Demand drop affects risk equation.
•  Unknowns: disaster intensity vs. damage to power grids
Added portion of the seawall
Onagawa nuclear power plant
Otsuchi. Was it a sufficient level
of protection?
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Residential Microgrids
•  Residential grid-tied PV systems
•  Conventional grid-tied system (utility centered approach) are
not a microgrid.
•  Most widely used PV integration approach in the U.S.
•  PV and home operation subject to grid operation: Due to IEEE
Standard 1547, the inverter cannot power the home when the
grid is not present.
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Residential Microgrids
•  Case study of grid tied inverters: Lower 9th Ward
after Isaac
•  The sun was shinning but
no grid = no power
(even with PV arrays).
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Residential Microgrids
•  PV power generation in disasters
•  This solution is not intended for these relatively very few cases:
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Residential Microgrids
•  PV power generation in disasters
•  The focus is on these many cases
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Residential Microgrids
•  Alternative residential grid-tied PV systems
•  Alternatives for power sources:
•  PV
•  Wind
•  Natural gas (generators, fuel cells…)
•  Example of an alternative for power distribution architectures:
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Residential Microgrids
•  Controller (emergency operation module in HEMS)
•  Hybrid: grid connected and
grid isolated modes
•  Key functions:
•  Load management
•  Resource management
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Residential Microgrids
•  The value of the load
•  Evolving loads: more intelligence and more controllable. More
residential critical loads requiring local power (e.g. phones and
electric vehicles) may increase the value of alternative power during
disasters for residential users.
•  Load management objectives:
•  Improved efficiency
•  Load prioritization
•  Electric vehicles duality
•  A critical load
•  A valuable resource
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Microgrids for Disaster Resiliency
•  Pecan Street s value
•  Power generation and consumption data can be used to
•  understand users needs and realize load prioritization algorithms for different
times during the day (and different seasons and conditions).
•  coordinate (and integrate) electrical and natural gas use.
•  understand benefits, roles and requirements of electric vehicles during
disaster conditions.
•  optimize residential microgrids asset planning
•  anticipate coordinated load and local resources management during disasters
•  understand the combined effect of dispersed PV power generation within a
constraint area and anticipate potential microgrid performance and sizing
needs.
•  improve PV generation and power distribution models in a constraint area
•  Use
of community level energy storage during disasters (?)
•  Future: Microgrid test-bed at Pike Powers Lab or at another
location (?)
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Microgrids for Disaster Resiliency
•  UT s research capabilities and expertise
•  Microgrids modeling:
•
•
•
•
•
Power distribution
Power electronic interfaces
Loads
Energy storage
Sources
•  Stability analysis
•  Optimal microgrid resource management
•  Analysis and realization of controllers
•  Design of power electronic circuits to facilitate integration of
diverse power sources and energy storage
•  Energy storage technologies
•  Microgrid test-bed at the Center for Electromechanics.
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Thank you very much
akwasins@utexas.edu
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