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An Analysis of the Impact of Balancing Area 

Cooperation on the Operation of the Western 

Interconnection with Wind and Solar Generation

Michael Milligan and Debbie 

Lew, NREL

Gary Jordan and Richard 

Piwko, GE

Brendan Kirby and Jack King, 

Consultants, NREL

Stephen Beuning, Xcel Energy

National Renewable Energy Laboratory

WINDPOWER 2011

May 22-25, 2011

NREL/PR-5500-51546
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Outline

• Overview/Objective

• Operating Reserves

• Ramping

• Production Simulation

• Conclusions

Photo by Pat Corkery, NREL/PIX16571
National Renewable Energy Laboratory Innovation for Our Energy Future

Objective

• Analysis of alternative BA configurations in the 

Western Interconnection

• Proposed Energy Imbalance Market

• Flexibility reserve analysis utilizing method from 

Eastern Wind Integration and Transmission 

Study (EWITS)

• Production simulations using GE-MAPS

– Alternative levels of transactional “friction” for

• Unit commitment

• Economic dispatch.
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Imbalance Market Overview

EIM Footprint

EIM Tool: 

SCED

Intra-hour variability is captured and allocated 

in real-time within the entire region, limited by 

Diversity benefit the physical capability of the wires.

reduces operating 

costs for balancing.
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Imbalance Market Overview

Schedule Day-Ahead & 

Up-to 30 minutes prior to

Operating Hour 

Real-time 

Dispatch Post-Operating 

time

Forecast and

unit Commit

Generators

self-schedule

Generators 

voluntary submit

offers

DSM resources 

voluntary submit

offers

Prepare and 

finalize predispatch schedules

Perform securityconstrained 

economic dispatch 

to keep balance

Provide redispatch

if any congestion

occurs

Send dispatch

set points to

generators

Coordinate any

contingency

reserve deployments

With EIS dispatch

Market Participant: WECC EIM Market Operator:

Gather meter

data to support

settlements

Provide 

settlement statement

and invoices

Transmission Provider:

Provide meter

data to support

settlements
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Imbalance Market Is Not Full Coordination

• Does not include framework for unit 

commitment coordination

• Voluntary participation at the BA level

• All generators may not choose to participate

• Will some level of coordination of unit 

commitment evolve over time?
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Data

• Data from the Western Wind and Solar 

Integration Study (WWSIS)

• Wind data developed by 3Tier and described in 

Development of Regional Wind Resource and 

Wind Plant Output Datasets available at 

http://www.nrel.gov/wind/integrationdatasets/pdf

s/western/2010/3tier_final_report.pdf

• Generation and transmission data from WWSIS 

as described in 

http://www.nrel.gov/wind/systemsintegration/pdf

s/2010/wwsis_final_report.pdf
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Flexibility Reserve/Operating Reserve

• Wide-area pooling of variability analyzed using 

extension of EWITS approach

• Described in prior work

– Milligan, M.; Kirby, B.; King, J.; Beuning, S. (2010). Benefit of Regional Energy Balancing 

Service on Wind Integration in the Western Interconnection of the United States: Preprint. 10 

pp.; NREL Report No. CP-5500-49076.

• Contingency reserve not affected

• Wind and solar increase the dispatch range and 

ramping speed required from conventional 

generationfocus of part 1 of the analysis.
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Full Footprint EIM

0

1000

2000

3000

4000

5000

6000

7000

8000

Total Reg Spin Supplemental

BAU 2440 2096 4192

EIM 1198 969 1938

Reserve Requirement (MW)

Reserve Savings for Footprint EIM 

BAU

EIM
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Ramping Requirements Are Reduced, with 

and without Wind/Solar
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Ramp Duration for 1 Year
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GE-MAPS Analysis: Map of WECC Areas
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Alternative Levels of Transactional Friction

Company-Level Operation

Commitment 

hurdle rate

Dispatch 

hurdle rate

Low 

renewable 

penetration

Medium 

renewable 

penetration

$5/MWh $5/MWh X X

$25/MWh $5/MWh X X

$25/MWh $25/MWh X X
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Total Operating Costs

16,000

16,500

17,000

17,500

18,000

18,500

19,000

19,500

20,000

20,500

21,000

Region (low renewables) Region (medium renewables)

Total Operating Costs ($M)

Total Operating Costs ($M)

Full

Dispatch

BAU
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Operating Cost Reductions with Increased 

Coordination

0

100

200

300

400

500

600

700

Company (low renewables) Company (medium renewables)

Operating Cost Reduction ($M)

Full

Dispatch
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Conclusions

• Significant reserve reductions are possible.

• Ramping needs are reduced, even without 

wind/solar energy.

• Existing uncoordinated unit commitment will 

capture 20%-40% of total operating cost 

savings potential compared to full coordination.
Questions?

18

Photo by Michael Milligan, NREL/PIX13367

The National 

Renewable Energy 

Laboratory’s Wind 

Systems 

Interconnection 

Analysis work is 

funded by the Wind 

and Water Power 

Program, Office of 

Energy Efficiency and 

Renewable Energy of 

the U.S. Department 

of Energy under 

Contract No. DEAC02-05CH11231.