© copyright 2013, first solar, inc....2 . key messages •pv power plant has become a...

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Key Messages

• PV power plant has become a cost-effective energy resource

• Well designed “Grid Friendly” PV plant actively stabilizes grid and enhances its reliability

• Resource diversity and grid flexibility are necessary to manage solar variability

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Years

Power Systems Planning & Design Grid Stability & Reliability

Milliseconds to Minutes Hours to Days

Load Balancing

Key Learning

• Add Grid Controls to Support Reliability & Grid Security

• Integrate forecasting into daily operation

• Update operating procedures - balancing area, frequent updates, ramping support

• Adopt diverse resource portfolio to reduce risks and increase flexibility

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Utility Scale PV Power Plant Overview

PV Module Arrays Inverters

Transformers

Combiner Boxes

Photovoltaic Combining Switchgear

34.5kV (AC) Typical

300 to 690V (AC)

1000V (DC) Substation

Gen Tie-line Power Grid

69 to 525kV (AC)

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TOPAZ SOLAR FARM

Largest utility scale solar plant in the world

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NERC Task Force on Intermittent Resources Impact to the Grid

Voltage, VAR control and/or power factor regulation

Fault ride through

Real power control, ramping, and curtailment

Frequency control

“Modern solar plants can now contribute to the

reliability and efficiency of grid operation by offering

the following capabilities:”

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Power Grid

Grid Integration and Plant Control System

Real-time Controllers Satellite Imagery

Transformer

Inverters

PV Module Arrays

Combiner Boxes

Power Conversion Station (PCS) Photovoltaic Combining

Switchgear (PVCS) Substation

Plant SCADA system

• Checks grid’s actual conditions and required set points

• Sends individual instructions to each inverter based on location, losses, and performance

• Controls quality of power coming out of the PV plant

All every 100 milliseconds! Short Term Forecasting

Set Points

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Benefit of Plant Level Control System

Plant Output Limit Plant Output Limit

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Dynamic Power Factor Regulation

Source: Agua Caliente PV Plant in Yuma, Arizona, USA May 23, 2012. ~212MW on-line.

Command Power Factor

Power Factor Set Point Changed from 0.98 to 1.0

Reaches 90% Steady State Value in ~ 3.2 seconds

Inverters Change VAr Output

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Power Curtailment at Different Levels

Source: Agua Caliente PV Plant in Yuma, Arizona, USA March 13, 2012. ~90MW on-line.

Plant Curtailment Test

Set Point Reduced

Set Point Increased

Ramp rates between set point changes are controlled

Inverters are Turned Down/ OFF to curtail output

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Stopping and Starting One Block (30MW)

Source: Agua Caliente PV Plant in Yuma, Arizona, USA March 13, 2012. ~90MW on-line.

Ramp Rate Controls

Plant Stop Command

Plant Start Command

Inverters are Started in Sequence Inverters are

Turned Off in Sequence; Ramp Rates are Controlled

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Frequency Droop Control

Plant Controls Support Frequency Droop

• Ability to reduce active power in case grid is overloaded (i.e., high frequency)

When grid needs more generation (i.e., low frequency) renewable plant cannot increase active power … unless plant is already curtailed then it can increase power

Decrease Active Power In Case of High Frequency

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Agua Caliente 290MW (AC)

California

Arizona

Palo Verde Nuclear

Generating Station

North Gila

Substation

Hoodoo Wash

Substation

Agua Caliente

500kV Palo Verde-Hassayampa

Transmission Line

Hassayampa

Substation

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Agua Caliente - Typical Plant Operating Day (March 19, 2014)

90%

95%

100%

105%

110%

-0.6

-0.3

0.0

0.3

0.6

0.9

1.2

4:00 8:00 12:00 16:00 20:00

Vo

ltag

e (P

U)

and

Po

wer

Fac

tor

Po

wer

(P

U)

and

Re

acti

ve P

ow

er

(PU

)

Time of Day

Power (PU)

Voltage (PU) Power Factor

Reactive Power (PU)

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Agua Caliente Voltage Support – Event on March 21, 2014

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90%

95%

100%

105%

110%

-0.3

0.0

0.3

0.6

0.9

1.2

4:00 8:00 12:00 16:00

Vo

ltag

e (P

U)

Po

wer

(P

U)

and

Re

acti

ve P

ow

er

(PU

)

Time of Day

Power (PU)

Reactive Power (PU)

Voltage (PU)

The PV plant is asked to support voltage by APS

Operators.

Night Shutdown

500kV Palo Verde -Hassayampa line

taken out of service

Agua Caliente Voltage Support – Event on March 21, 2014

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Single Location

20 Bundled Locations

One-minute Global Irradiance (W/sq.m)

One-minute Global Irradiance (W/sq.m)

Aggregation Effect Between Plants Reduces Variability

Spatial diversity of solar plants reduces aggregated variability… minimizing grid impact as the number of solar plants increase

Source: “Implications of Wide-Area Geographic Diversity for Short-Term Variability of Solar Power”; Andrew Mills and Ryan Wiser, Lawrence Berkeley National Laboratory, September 2010

Source: Hoff et al. 2008

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Impact of Cloud Passage on Plant Output

As plants become larger… high frequency variability reduces.

Average Irradiance

Total Power

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ERCOT Daily Load – Typical Summer Day

Solar reduces peak load

0

10

20

30

40

50

60

70

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 0

Load

(G

W)

Time (Hours)

Typical Summer Day Load Profile (July 31, 2012)

Solar 10GW

7/31/2012

Net Load

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Years

Power Systems Planning & Design

Variable Generation Integration Topics

Grid Stability & Reliability

Msec to Minutes Hours to Days

Load Balancing

Years

Power Systems Planning & Design

• Variable generation requires grid flexibility

CONCERN

• Adopt diverse resource portfolio to increase flexibility and reduce risks

LEARNING

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Complementing the Power Portfolio

Solar is a hedge against fuel price volatility

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Study needed to determine shape of Flexibility Supply Curve and Quantify Costs Flexibility Supply Curve

Sources of Flexibility

Low Cost

High Cost

Batteries Flywheels CAES PHEV

Markets

Flexible Generation

Traditional Storage

Wind/Solar Curtailment

Storage

In Range of 1 or 2%

Hydro with Dams Pumped Hydro Gas Storage

Simple Cycle GT Combined Cycle Some Coal Plants Real-Time

Hour Ahead Day-Ahead Price Responsive Load Ancillary Service

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Key Messages -- Summary

• PV power plant has become a cost-effective energy resource

• Well designed “Grid Friendly” PV plant actively stabilizes grid and enhances its reliability

• Resource diversity and grid flexibility are necessary to manage solar variability

© copyright 2013, first solar, inc....2 . key messages •pv power plant has become a...

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