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

http://www.uwig.org/




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.



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



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



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



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


http://www.ieee.org/portal/site/pes/menuitem.bfd2bcf5a5608058fb2275875bac26c8/index.jsp?&pName=pes_h









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Utility Wind Integration State of the Art

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