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Flexibility and Control of Power Generation in Coal Plants:

Solutions from the Dispatch Floor

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AGENDA

• Xcel Energy: An Introduction • Loads & Resources: The Problem • Coal as a Flexible Resource: A

Solution

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Keith Parks Senior Trading Analyst Xcel Energy 1800 Larimer Street Suite 1000 Denver CO 80202 USA W: +1 303 571 2831 C: +1 303 859 2280 E: keith.parks@xcelenergy.com

Please contact me w/ questions & commentary

X C E L E N E R G Y

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XCEL ENERGY

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Northern States Power

Southwestern Public Service

Company

Public Service Company of

Colorado

• No. 1 utility wind provider • Top-ten utility for solar

capacity • Leader in emission

reductions • Nationally recognized in

energy efficiency • Member of the Dow Jones

Sustainability Index

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0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016

Cap

acity

MW

Xcel Energy Wind Generation Growth (current)PSCo (2343) NSP (1867) SPS (1527)

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XCEL ENERGY

Ave Capacity Factor: 38%

Renewable Energy Leadership Reduce Carbon

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6.000

9.000

2010 2016 2021

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awat

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Xcel Energy Wind Energy

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1.000

2.000

3.000

2010 2016 2021

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awat

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Xcel Energy Solar Energy

Our Changing Energy Mix

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37%

25%

13%

19%

6%

56% 23%

12%

3% 6%

35%

12% 12%

34%

7%

Coal Natural Gas Nuclear Wind Other Renewable

2021 2005 2016

Reduce Carbon

Carbon Reduction Goals Xcel Energy reductions on pace to surpass international climate goals

Reduce Carbon

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60% by 2030 with the right policy and technology

L O A D S & R E S O U R C E S

LOADS AND RESOURCES

• Obligations and resources are maintained in balance at all times

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Traditional Utility Paradigm

Mid-Merit

Baseload

Peakers

LOADS AND RESOURCES (APR/OCT)

• Expand focus to all hours of the year to manage uncertainty (Apr/Oct).

Traditional Utility Paradigm

Mid-Merit

Baseload

Peakers Renewables

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LOADS AND RESOURCES (2017)

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Traditional Utility Paradigm

Mid-Merit

Baseload

Peakers Renewables

• Spread between daily high/low loads increase. Timing of ramps uncertain.

LOADS AND RESOURCES (2024)

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High Penetration Portfolio

Balance Portfolio

Variable

• New paradigm: Flexible and Informed Grid

LOADS AND RESOURCES – A NEW PARADIGM

High Penetration Portfolio

Balance Portfolio

Variable

Traditional Utility Paradigm (w/ some RE)

Mid-Merit

Baseload

Peakers Renewables

VER forecasts ignored in commitment VERs are must-take in dispatch VERs penalized for deviations Current reserves are sufficient

VER forecasts integrated into planning VERs are dispatchable VERs married with flexible resources Reserve products tailored for VERs

C O A L A S A F L E X I B L E R E S O U R C E

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PAWNEE POWER PLANT

• 1 x 500MW Capacity • Year Built: 1981 • Subbituminous Coal (aka brown

coal; black lignite) • 6 coal mills • NOx and SO2 emission controls

I use the Pawnee Power Plant as an example. Though, the following slides are indicative of ALL our coal facilities.

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PAWNEE – TYPICAL DUTY

The duty of our coal plants has changed significantly from pure baseload generation to heavy load following

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PAWNEE – TYPICAL DUTY

The duty of our coal plants has changed significantly from pure baseload generation to heavy load following

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PAWNEE – TYPICAL DUTY

AGC – Regulation

Econ Max

Econ Min

• Pawnee has three primary modes of operation – ECON MAX – AGC – Economic Dispatch – ECON MIN

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PAWNEE – TYPICAL DUTY

Econ Max

• Traditional model of operation • Requires 5 of 6 mills to be in operation

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PAWNEE – TYPICAL DUTY

AGC - Regulation

• Dispatch signal sent electronically every 4-seconds from EMS • Dynamic econ max/min and ramp rate limits • Economically dispatched relative to peers • Variable speed coal feeders and some overpressure enables dispatch

STEPS 1. EMS calculates economic set-point based on a set of peers (peers selected by

operator) 2. Set-point honors ramp rates and economic limits set by the power plant 3. Set-point sent automatically and electronically

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PAWNEE – TYPICAL DUTY

Econ Min

• Coal mills dynamically decommitted (3 to 4 mills in operation) • 30 minutes to remove a mill; 20 minutes to replace • Enables lower loads without decommitment • Working to enable AGC through economic min operation

STEPS 1. Shut off coal feeder 2. Grind out coal in mill 3. Shut down mill 4. Close slide gates in air duct 5. Reverse to commit coal mill

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IMPACTS

• Thermal Stresses on the Boiler Tubes – Load Following has minor long-term impact – Decommitment can have major cost implications

long-term. • Coal Mill Cycling

– Roller makes contact with the coal mill table during the grind out process. Increases wear and tear.

• Flame Stability – Can be a concern at low loads. Streaming of natural

gas into the flame helps provide stability. • Emission Controls

– NOx removal can be compromised at low loads as the temperature of the flue gas is reduced.

– SO2 removal requires greater management of ammonia concentration.

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WIND PLANT ON AGC

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• 70% of Xcel Energy wind capacity is AGC capable – All wind farms with SCADA systems post-2007 are enabled

• Allows for real-time curtailment with incredible precision • Wind farms provide the fastest ramping capability of all XE

resources

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CONCLUSION

• Coordinated system dispatch via Automatic Generation Control (or other automatic econ dispatch system) enables huge efficiencies

• Coal plants are able to respond in real-time. • Lower loads are possible through coal mill cycling. • Coal plants are able to dispatch with variable speed

feeders and moderate use of boiler over-pressure (within strict limits)

• Wind plants are capable of fast and precise generation control.

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PSCO WIND PENETRATION PERCENT OF OBLIGATION LOAD

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APRIL - COLORADO

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