utility wind integration state of the art
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Utilit y Wind Integration
State of the Ar t
Prepared By:
Utility Wind Integration Group
in cooperation with
American Public Power Association
Edison Electric Institute
National Rural ElectricCooperative Association
May 2006
UWIG • P.O. Box 2787 • Reston, VA 20195 • 703-860-5160 • Fax: 703-860-1544 • www.uwig.org
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In just ive years rom
2000-2005, wind energy
has become a signiicant
resource on many electric utility systems,
with over 50,000 MW
o nameplate capacity
installed worldwide at the
end o 2005. Wind energy
is now “utility scale” and
can aect utility system
planning and operationsor both generation and
transmission. he utility
industry in general, and
transmission system
operators in particular, are
beginning to take note.
At the end o 2005, thePower Engineering Society
(PES) o the Institute o
Electrical and Electronic
Engineers (IEEE)
published a special issue
o its Power & Energy
Magazine (Volume 3,
Number 6, November/
December 2005) ocused
on integrating wind into
the power system. his
document provides a brie
summary o many o the
salient points rom that
special issue about the
current state o knowledge
regarding utility wind
integration issues. It does
not support or recommend
any particular course
1hese conclusions wil l need to be reexamined as results o higher-wind-penetrat ion studies — in the range o 25% to
30% o peak bal ancing-area load—become available . However, achieving such penetrat ions is l ikely to require one or twodecades. During that t ime, other signiicant changes are l ikely to occur in both the makeup and the operating strategies o the nation’s power systems. Depending on the evolution o public policies , technological capabil it ies , and uti l ity strategicplans, these changes can be either more or less accommodating to the natural characterist ics o wind power plants.
o action or advocateany particular policy or
position on the part o the
cooperating organizations.
he discussion below
ocuses on wind’s impacts
on the operating costs
o the non-wind portion
o the power system and
on wind’s impacts on the
electrical integrity o the
system. hese impacts
should be viewed in the
context o wind’s total
impact on reliable system
operation and electricity
costs to consumers. he
case studies summarized in
the magazine address early
concerns about the impact
Overview & Summary of Wind Integration
o wind power’s variability and uncertainty on power
system reliability and costs.
Wind resources have
impacts that can be
managed through proper
plant interconnection,
integration, transmission
planning and system and
market operations.
On the cost side, at wind
penetrations o up to 20%
o system peak demand,
system operating cost
increases arising rom wind
variability and uncertainty
amounted to about 10%
or less o the wholesale
value o the wind energy.1
Photos courtesy of Endless Energy, GE Energy and NREL.
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hese incremental costs,
which can be assigned to
wind-power generators,
are substantially lessthan imbalance penalties
generally imposed through
Open Access ransmission
aris under FERC Order
No. 888. A variety o means
– such as commercially
available wind orecasting
and others discussedbelow – can be employed
to reduce these costs. In
many cases, customer
payments or electricity can
be decreased when wind
is added to the system,
because the operating-cost
increases could be osetby savings rom displacing
ossil uel generation.
Further, there is evidence
that with new equipment
designs and proper plant
engineering, system
stability in response to a
major plant or line outage
can actually be improved
by the addition o wind
generation. Since wind
is primarily an energy
– not a capacity – source,
no additional generation
needs to be added to
provide back-up capability
provided that wind capacity
is properly discounted
in the determination
o generation capacity
adequacy. However, wind
generation penetration may
aect the mix and dispatch
o other generation on the
system over time, sincenon-wind generation is
needed to maintain system
reliability when winds are
low.
Wind generation will also
provide some additional
load carrying capability tomeet orecasted increases
in system demand. his
contribution is likely to
be up to 40% o a typical
project’s nameplate
rating, depending on
local wind characteristics
and coincidence with thesystem load proile. Wind
generation may require
system operators to carry
additional
operating
reserves.
Given the
existing
uncertainties
in load
orecasts,
the studies
indicate
that the
requirement
or additional
reserves
will likely
be modest
or broadly
distributed
wind plants.
he actual impact o
adding wind generation in
dierent balancing areas
can vary depending onlocal actors. For instance,
dealing with large wind
output variations and
steep ramps over a short
period o time could be
challenging or smaller
balancing areas, depending
on the speciic situation.
he remainder o this
document touches on wind
plant interconnection
and integration,
transmission planning and
market operations and
accommodating more windin the uture.
Overview & Summary of Wind Integration
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the dispatchable generating
resources available, market
and regulatory environment,
and characteristics o thewind generation resources as
compared to the load. Dealing
with large output variations
and steep ramps over a short
period o time (e.g., within the
hour) could be challenging
or smaller balancing areas,
depending on their specicsituation.
Wind’s variability cannot be
treated in isolation rom the
load variability inherent in
the system. Because wind and
load variability are statistically
uncorrelated, the net increaseo variability due to the
addition o wind is less than
the variability o the wind
generation alone.
Commercially available wind
orecasting capability can
reduce the costs associatedwith day-ahead uncertainty
substantially. In one major
study, state-o-the-art
orecasting was shown to
provide 80% o the benets
that would result rom perect
orecasting.
Implementation o wind-
plant-output orecasting in
both power market operation
and system operations
planning in the control room
environment is a critical
next step in accommodating
increasing amounts o windpenetration in power systems.
Utility planners traditionally view new generation
primarily in terms o its
capacity to serve peak demand. But wind is
primarily an energy resource.
Its primary value lies
in its ability to displace
energy produced rom the
combustion o ossil uels and
to serve as a hedge against
uel price risk and uturerestrictions on emissions.
Te addition o a wind
plant to a power system
does not require the
addition o any backup
conventional generation
since wind is used primarily as an energy resource. In
this case, when the wind
is not blowing, the system
must rely on existing
dispatchable generation to
meet the system demand.
Wind plants provideadditional planning
reserves to a system, but
only to the extent o their
capacity value. Capacity
or day-to-day reliability
purposes must be provided
through existing market
mechanisms and utility unitcommitment processes.
Te capacity value o wind
generation is typically up
to 40% o nameplate rating
and depends heavily on the
correlation between the
system load prole and thewind plant output.
Te addition o a wind
plant to a power system
increases the amount o
variability and uncertainty o the net load. Tis may
introduce measurable
changes in the amount o
operating reserves required
or regulation, ramping and
load-ollowing. Operating
reserves may consist o both
spinning and non-spinningreserves. In two major
recent studies, the addition
o 1,500 MW and 3,300
MW o wind (15% and 10%,
respectively, o system peak
load) increased regulation
requirements by 8 MW and
36 MW, respectively, tomaintain the same level o
NERC control perormance
standards.
Fluctuations in the net load
(load minus wind) caused
by greater variability and
uncertainty introducedby wind plants have been
shown to increase system
operating costs by up to
about $5/MWH at wind
penetration levels up to 20%.
Te greatest part o this
cost is associated with the
uncertainty introduced intoday-ahead unit commitment
due to the uncertainty
in day-ahead orecasts
o real-time wind energy
production.
Te impact o adding
wind generation can vary depending on the nature o
Wind Plant Integration
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Understanding and quantiying
the impacts o wind plants on
utility systems is a critical irst
step in identiying and solving
problems.
A number o steps can be taken
to improve the ability to integrate
increasing amounts o wind
capacity on power systems. hese
include:
– Improvements in wind-turbine
and wind-plant models
– Improvements in wind-plant
operating characteristics
– Careully evaluating wind-
integration operating impacts
– Incorporating wind-plantorecasting into utility
control-room operations
– Making better use o
physically (in contrast with
contractually) available
transmission capacity
– Upgrading and expanding
transmission systems
– Developing well-unctioning
hour-ahead and day-ahead
markets, and expanding access
to those markets
– Adopting market rules andtari provisions that are more
appropriate to weather-driven
resources
– Consolidating balancing areas
into larger entities or accessing
a larger resource base through
the use o dynamic scheduling
Wind power plant terminal behavior is dierent
rom that o conventional power plants, but can
be compatible with existing power systems. With
current technology, wind-power plants can be
designed to meet industry expectations such as
riding through a three-phase ault, supplying
reactive power to the system, controlling
terminal voltage and participating in SCADA
system operation.
Increased demands will be placed on wind plant
perormance in the uture. Recent requirements
include low voltage ride-through capability,
reactive power control, voltage control,
output control, and ramp rate control. Future
requirements are likely to include post-ault
machine response characteristics more similar
to those o conventional generators (e.g., inertial
response and governor response).
Better dynamic models o wind turbines and
aggregate models o wind plants are needed toperorm more accurate studies o transmission
planning and system operation.
In areas with limited penetration, modern wind
plants can be added without degrading system
perormance. System stability studies have shown
that modern wind plants equipped with power
electronic controls and dynamic voltage support
capability can improve system perormance by
damping power swings and supporting post-ault
voltage recovery.
Because o spatial variations o wind rom
turbine to turbine in a wind plant – and to a
greater degree rom plant to plant – a sudden loss
o all wind power on a system simultaneously
due to a loss o wind is not a credible event.
Wind PlantInterconnection
Accommodating MoreWind in the Future
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Upgrades or additions to transmission
acilities may be needed to access locations
with large wind-energy potential.
Current transmission planning
processes are able to identiy solutionsto transmission
problems, but the
time required or
implementation
o solutions oten
exceeds wind-
plant permitting
and constructiontimes by several
years.
Well-
unctioning
hour-ahead and
day-ahead markets
provide the best means o addressing the variability in wind
plant output.
Energy imbalance charges based
on actual costs or market prices provide appropriate incentives
or accurate wind orecasting. Since wind plant operators have no
control over the wind, penalty charges applied to wind imbalances do
not improve system reliability. Market products and tari instrumentsshould properly allocate actual costs o generation energy imbalance.
Wind turbine output or ramp rates may need to be curtailed or limited
periods o time to meet system reliability requirements economically.
Consolidation o balancing areas or the use o dynamic scheduling can
improve system reliability and reduce the cost o integrating additional wind
generation into electric system operation.
Transmission Planning & Market Operations
P O B 2787 R VA 20195 703 860 5160 F 703 860 1544 i
Te Power & Energy Magazine articles summarized in this document are available to IEEE PES members at theollowing link:http://www.ieee.org/portal/site/pes/menuitem.bd2bc5a5608058f2275875bac26c8/index.jsp?&pName=pes_home and to UWIG members at www.uwig.org through the Members link
Inormation on a number o integration studies can be ound at:http://www.uwig.org/opimpactsdocs.html