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Key Messages
• PV power plant is a cost-effective energy resource

• Well designed “Grid Friendly” PV plant actively stabilizes grid and enhances its reliability
• PV variability can be managed with existing grid infrastructure through forecasting and site diversity with minimum impact
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First Solar — Utility Scale PV Plant Leader
Over 3GW Completed or In Development (10MW AC – 550MW AC Plants)

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Utility Scale PV Power Plant Overview
PV Module Arrays Combiner Boxes
300 to 690V (AC) 1000V (DC)

Inverters Transformers Photovoltaic Combining Switchgear Substation

34.5kV (AC) Typical 69 to 525kV (AC)

Gen Tie-line

Power Grid

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PV Module
PV Module Arrays

1000V (DC)

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Combiner Box
Combiner Boxes
• Aggregates DC wiring from multiple strings

(80KW-160KW)
• Provides single dc output to inverter

1000V (DC)

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Utility Scale Solar Plant Inverters
Inverters
• Converts DC power to AC (low voltage) • Grid Management Functions (LVRT,

Reactive Power, etc.)
300 to 690V (AC) 1000V (DC)

• UL1741 and IEEE1547 compliant

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Transformer
• Increases low AC voltage to medium

Transformers
300 to 690V (AC)

AC voltage for Collection System

34.5kV (AC) Typical
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Power Conversion Station (PCS) – Inverter & Step-up Transformer

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Photovoltaic Combining Switchgear (PVCS)

Photovoltaic Combining Switchgear

• Aggregates AC power from multiple

transformers (up to 40MW)

34.5kV (AC) Typical

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Substation and Generator Tie-line
• Provides plant controls, disconnects, and

step up transformer • Delivers electricity to the grid

Substation

69 to 525kV (AC)

Gen Tie-line

Power Grid

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TOPAZ SOLAR FARM

Largest utility scale solar plant in the world

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AGUA CALIENTE

Reliable bulk power generation utilizing advanced plant controls and forecasting

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COPPER MOUNTAIN 1

Co-located with existing gas combined cycle power plant

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GREENOUGH RIVER

Displacing the energy requirements of a desalination plant

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Nakorn Ratchasima, Thailand – 7.5 MW(DC)

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PHALODI

Providing energy security to India and displacing 1 million tons of coal

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DEWA SOLAR PLANT

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PV Plant Variability … Agua Caliente – July 2013

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Grid Integration and Plant Control Systems

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Typical Convention Generation, Transmission and Distribution System

Power Flow

Conventional Centralized Generation

Power Flow

 top down power flow  high voltage lines to low voltage lines
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Source: U.S. Department of Energy. "Benefits of Using Mobile Transformers and Mobile Substations for Rapidly Restoring Electric Service: A Report to the United States Congress

What happens when load changes? …. Generator has to change output
Generation Increase 100kW Load Increase 100kW

 As load changes, the generators have to

respond instantly to change its output  Bulk electricity storage is not common
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Source: U.S. Department of Energy. "Benefits of Using Mobile Transformers and Mobile Substations for Rapidly Restoring Electric Service: A Report to the United States Congress

In Practice … Aggregated load matters …
Generator Decrease 400kW Load Increase 100kW

 What really matters is the changes to aggregated load … not individual load

Load Decrease 500kW

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Source: U.S. Department of Energy. "Benefits of Using Mobile Transformers and Mobile Substations for Rapidly Restoring Electric Service: A Report to the United States Congress

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Multiple Generators and Control Areas
Multiple Generators

 In grid of reasonable size, multiple generators are present … and are scheduled for daily

Multiple Loads

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Source: Bernd Engel, SMA

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operation  Total Generation = Aggregated Load + Losses in a Control Area  Must maintain regulating and contingency reserves to meet control performance and reliability standards

Daily Load Forecasting and Generator Dispatch
 Economic Dispatch …
Day Ahead Forecast Load

use load forecast to commit units (hours to day ahead)

0

6

12

18

24

Time of Day

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Grid Operators Deal with Variability & Uncertainty
 Use load forecast and
Day Ahead Forecast Load

Actual Load

uncertainty in load and generation through regulation and dispatch operation

0

6

12

18

24

Time of Day

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Load Following and Regulation Reserves
 Load Following:
Adjust set point (10 min to hours)

 Regulation:
Automatically adjusts generator
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output (secs to minutes)
Regulation = Actual Load – Real-time Forecast Load Load Following = Real-time Forecast Load – Hourly Schedule

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Key Topics – Impact of PV Solar on Power Grid
Grid Stability & Reliability
Load Balancing Power Systems Planning & Design

Milliseconds to Minutes

Hours to Days

Years

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• PV solar intermittency raises grid stability and reliability concerns

• PV Variability increases operational complexity

• Higher PV penetration requires increased grid flexibility

Variable Generation Integration Topics
Grid Stability & Reliability Load Balancing

Power Systems Planning & Design

CONCERN
Msec to Minutes Hours to Days Years

Grid Stability & Reliability

• Solar PV generation does not contribute to the reliability of bulk generation

LEARNING
• Add grid controls to support reliability and grid security Milliseconds to Minutes
Source: Pacific North West Laboratory, Grid Stability; The Challenges of power grid stability. http://eioc.pnnl.gov/research/gridstability.stm
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NERC Task Force on Intermittent Resources Impact to the Grid
“Modern solar plants can now contribute to the reliability and efficiency of grid operation by offering the following capabilities:”
 Voltage, VAR control and/or power factor regulation  Fault ride through  Real power control, ramping, and curtailment

 Primary frequency regulation
 Frequency droop response  Short circuit duty control

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Voltage Support – Power Flow Reversal
PV

Substation
House 2

MV Grid

20 kV

0,4 kV

Conductor

House 1

P
Q
P Last 2

IEEE 1547 prohibits voltage control

Transformer P

Distance

Allowable Range

Voltage

High Feed-in Low Load High Feed-in Low Load + Reactive Power
Source: Bernd Engel, SMA

Normal Flow Voltage Drop

Maximum Load

PV With Reactive Power Capability Avoids Costly Network Upgrades

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Reverse Flow with PV Reactive Power Voltage Drop

Reverse Flow Voltage Violation

P Last 1

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Voltage Regulation

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“Utility Scale” Active Power Control

Reduced Power
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Grid Integration and Plant Control System
PV Module Arrays
Power Conversion Station (PCS) Photovoltaic Combining Switchgear (PVCS) Substation Power Grid

Combiner Boxes

Inverters

Transformer
• Checks grid’s actual conditions and required set points

Satellite Imagery

Plant SCADA system

Real-time Controllers

• Sends individual instructions to each inverter based on location, losses, and performance
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• Controls quality of power coming out of the PV plant

Short Term Forecasting

Set Points

All every 100 milliseconds!

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Without a Plant Control System

Plant Output Limit

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Inverter Curtailed Locally

Benefit of Plant Level Control System

Plant Plant Output Limit Output Limit

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Proprietary plant controller
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Dynamic Power Factor Regulation
Power Factor Set Point Changed from 0.98 to 1.0

Command Power Factor

Reaches 90% Steady State Value in ~ 3.2 seconds

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

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Inverters Change VAr Output

Power Curtailment at Different Levels
Inverters are Turned Down/ OFF to curtail output Set Point Increased

Plant Curtailment Test

Set Point Reduced

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

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Ramp rates between set point changes are controlled

Stopping and Starting One Block (30MW)
Plant Stop Command

Ramp Rate Controls

Plant Start Command

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

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Inverters are Turned Off in Sequence; Ramp Rates are Controlled

Inverters are Started in Sequence

Frequency Droop Control
• 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

Plant Controls Support Frequency Droop

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Power Plant Fault Ride-Through Behavior

(Source: SMA)

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PV Plants are designed to support both voltage and frequency ride-through capability leveraging utility scale inverters and best practices

What Makes a PV Plant “Grid Friendly”?

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© Copyright 2013, First Solar, Inc.

Variable Generation Integration Topics
Grid Stability & Reliability Load Balancing

Power Systems Planning & Design

CONCERN
Msec to Minutes Hours to Days Years

• Solar Generation is not fully dispatchable

Load Balancing

• Adds variability and uncertainty . . . complicates daily dispatch .

LEARNING
• Integrate forecasting into daily operation • Improved operating procedures – balancing area, frequent updates, ramping support
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Hours to Days

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Net Demand
Load (MW) Net Load Curve (MW)
PV Solar

Daily Load

0

12 Time of Day (Hours)

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Source: SEC Data. 2020 Load and Generation Mix Projected @5.6% annually for illustration purposes only. FS estimate on PV contribution. Actual resource distribution likely to be different.

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© Copyright 2013, First Solar, Inc.

Aggregation Effect Between Plants Reduces Variability
One-minute Global Irradiance (W/sq.m)

Single Location

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

20 Bundled Locations

Source: Hoff et al. 2008

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

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Impact of Cloud Passage on Plant Output
Total Power Average Irradiance

As plants become larger… high frequency variability reduces.

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NRG/MidAmerican – Agua Caliente 290MWac
North America Largest PV Plant Enbridge – Sarnia 80 MW
• • • • • • Yuma County Dateland, Arizona USA 2,400 Acres 39,000 Tons Steel PPA: PG&E EPC/O&M: NRG

3.0 Miles

First 2008 EPC Project Sempra – El Dorado 10MW
2.0 Miles

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NextEra / GE – Desert Sunlight – 550MWac

3.1 Miles

NRG — Agua 290MW ac

3.9 Miles

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© Copyright 2013, First Solar, Inc.

Variable Generation Integration Topics
Grid Stability & Reliability Load Balancing Power Systems Planning & Design

CONCERN
Msec to Minutes Hours to Days Years

• Variable generation requires grid flexibility

Power Systems Planning & Design

LEARNING
• Adopt diverse resource portfolio to increase flexibility and reduce risks Years
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Complementing the Power Portfolio

Solar is a hedge against fuel price volatility

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Power System Planning and Design
Requires a generation mix with more operational flexibility to serve the net load
Solar generation reduces peak load Addition of varaible generation: Net Load Duration Curve becomes more steep Gas GT

Hydro

Peaking
System Load Generation Mid-Merit Generation

Peaking
Generation Gas CCGT Generation
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Mid-Merit

Base Load Generation Base Load Generation Hours of Operation / Year System Load Net System Load with VG Variable generation has impact on low and minimum load conditions

Less Base Load and more Mid-Merit and Peaking Generation

(Source: Nick Miller at GE)
Coal

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California—20% Renewables and Growing to 33%
GWh
25000

20000
15000 10000 5000 0 2006 (~10%) 2012 (20%) 2020 E (33%)

• Successfully integrated 20% renewables today
• Building toward 33% renewable energy

Operators have managed high penetration. Others can leverage this learning.
CAISO Testimony in 2010 CPUC LTPP Docket No. R.10-05-006; July 1, 2011; Exhibit 1, slide 5; trajectory scenario

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Dispatchable Renewables Wind Solar

Typical Load, Solar and Wind Generating March 2020

Source: CAISO

Matt Burkhart SDGE, Sempra Feb 13,2013 Solar Power Gen San Diego

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Net Load and Flexible Capacity Needs

Source: CAISO

Matt Burkhart SDGE, Sempra Feb 13,2013 Solar Power Gen San Diego

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

Flexibility Supply Curve

Storage
High Cost

Wind/Solar Curtailment
Traditional Storage
Batteries Flywheels CAES PHEV

Flexible Generation
Markets
Low Cost
Simple Cycle GT Combined Cycle Some Coal Plants

In Range of 1 or 2%

Real-Time Hour Ahead Day-Ahead Price Responsive Load Ancillary Service

Sources of Flexibility

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Hydro with Dams Pumped Hydro Gas Storage

Conclusions
• Modern PV plants can contribute actively to grid stability and reliability • PV variability can be managed without significant impact to existing grid infrastructure through site diversity and forecasting

• PV power plants offer a cost-effective energy resource
• Lessons learned to date on Renewable Integration
© Copyright 2013, First Solar, Inc.

— Large-scale PV has been successfully integrated into grids worldwide — No reported issues due to often cited barriers: PV variability, harmonics, DC current injection, anti-islanding failure or protection coordination — Bulk energy storage has not been necessary for variable generation integration

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