Advances in Utility- Scale PV Plants: Key Lessons Learned · 2017-11-07 · Advances in Utility-Scale PV Plants: Key Lessons Learned Mahesh Morjaria, Ph.D. VP, PV Systems Enabling

Advances in Utility-Scale PV Plants:

Key Lessons Learned

Mahesh Morjaria, Ph.D.VP, PV Systems

Enabling a world powered by reliable, affordable

solar electricity.

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Key Messages – Advances in Utility-Scale PV Plants

Sources: 1 Lazard Levelized Cost of Energy Analysis – Version 10; GTM Research Global Solar PV Demand Monitor Q2017. . 2. Beyond 33% Renewables: Grid Integration Policy for a Low-‐Carbon Future, CPUC White Paper

• Utility-scale solar electricity now costs less than conventional generation in many markets1

– Cheaper than rooftop PV by a factor of 2-3

• Need to address grid challenges to grow solar substantially2

— Maintain grid stability and reliability while integrating large-scale solar into electricity grid system

— Increase grid flexibility to increase solar penetration and reduce

curtailment

• Key cost reduction drivers include:– Module cost reduction & efficiency improvement

– BOS & Plant design innovations

– Improved Investment Climate

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Utility-Scale Solar Energy is Competitive Today … Eliminates Fuel Price Volatility

Source: Lazard Levelized Cost of Energy Analysis – Version 10;

$-

$0.05

$0.10

$0.15

$0.20

$0.25

$0.30

Coal Nuclear Gas CC Gas Peaking Diesel First Solar

LevelizedCost of Energy

($/kWh)

Unsubsidized

Eliminates FuelPrice Risk

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PV Module Experience Curve – Key Driver for Low-Cost Solar

“Terawatt-scale photovoltaics: Trajectories and challenges”, Haegel et al, , Science Mag, 14 APRIL 2017, VOL 356 ISSUE 6334

2016$0.35/w310 GW

~3 TW by ‘30

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BOS Has Been Critical As Well In Reducing Utility-Scale PV Plant Cost

Module Module

ModuleModule Module

BOS

BOS

BOS

BOSBOS

Other

Other

Other

OtherOther

2012 2014 2016 2018E 2020E

< $1/WSource: Data from GTM Research and SEIA Report

BOS: Balance of Systems

• Inverter

• Electrical BOS

• Structural BOS

• Labor

Other

• Design & Engineering

• Permitting & Interconnection

• Civil

• Supply Chain, Logistics & Misc

• Taxes

• Overhead & Margin

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PV Plant Schematic

Power Grid

•

•

•

Solar ArraysCombiner

Boxes

DC

•••

Solar ArraysCombiner

Boxes

DC

•••

Power Conversion Station

Switchgear

AC

Substation

Sunlight to DC Power DC Power to AC Power AC Power to Grid

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Lower Cost PV Plant Architecture … Moving from 1kV to 1.5kV DC Design

Cost savings from

Larger, more cost-effective inverters

Fewer PCS (Inverters, Transformers, DAS Panel)

DC & AC Wiring Impact

O&M

1000VDC 1500VDC

1.5kV 4 MVA INVERTERAC POWER BLOCK

34.5kVAC

1000VDC

PV Arrays

Power Conversion Stations

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Typical DC Wiring for S4 Modules

4 String Harness 4 String Harness

15 S4 Modules per 1500VDC String- +

Female MC4

Male MC4

MC4

Connectors

Sunny Side

S4 Module

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DC Wiring Improvement– Trunk Bus Solution

Combiner

Box

4 String Harnesses DC Trunk BusesIPC

Connection

Combiner

Box

4 String Harness WhipsJumpers

● ● ● ●

● ● ● ●

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3-Phase PV Inverter Price Have Continued to Fall …and Converge

Source: The Global PV Inverter and MLPE Landscape H1 2017, GTM Research

$0.00

$0.05

$0.10

$0.15

$0.20

$0.25

$0.30

2013 2014 2015 2016 2017E 2018E 2019E 2020E 2021E 2022E

String vs Central Inverter Cost ($/Wac)

Three-Phase String Inverter

Central Inverter

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PV Plant Schematic – Central vs String Inverters

Power GridSolar ArraysCombiner

Boxes

DC

•••

Power Conversion Station

Switchgear

AC

Substation


Central Inverter Architecture

Solar ArraysString

Inverter

AC

•••

Power GridSubstation

DC

Switchgear

AC

PCS (Transformer)

String Inverter Architecture Cost savings from No Combiner Box Improved O&M

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COMBINER BOXES

POWER GRIDSUBSTATION

INVERTER TRANSFORMER

PCS1500V DC

INVERTER TRANSFORMER

1500V DC

34.5kV AC

DC/DC CONVERTER

POWER GRIDINVERTER

MVDC AC

1500V DC

TRANSFORMER SUBSTATION

Yet Another PV Architecture: Medium Voltage DC Plant (MVDC)

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DC/DC CONVERTER

POWER GRIDINVERTER

MVDC AC

1500V DC

TRANSFORMER SUBSTATION

Storage Ready

Medium Voltage DC Plant Architecture (MVDC) – BOS Simplification

Potential Benfits

Fewer Components/Reduced Wiring

Higher Plant Efficiency

Reduced O&M

Robust Grid Capability

Ready for Storage Architecture

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Reducing Energy Storage Costs … Opportunities for Fully Dispatchable Solar

Rack-level battery price

history and projections

($/kWh of storage)

Levelized Cost of Storage

(LCOS) ($/MWh)

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PV + Storage (PVS): Fully Dispatchable Clean Energy Plant

Increase the PV array size

Store excess energy in Energy Storage

ESS provides flexibility to generate desired profile

Amount of battery capacity is set by desired dispatch profile and solar irradiance

Shared Infrastructure costs (interconnect, development, O&M)

Interconnection limit

Charging

Game Changer: Clean energy plantMore cost-effective than conventional generation?

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Game Changer: Clean Energy PlantLess Costly than New Conventional Generation

Shifting Energy to Increase Output During Target Period (~10 MWdc PV)

Without Storage Will Get 48% Firm Capacity During Target Period (TPCF)

1 hr Storage Will Get 68% Firm

Capacity During Target Period

(TPCF)

2 hr Storage Will Get 87% Firm


(TPCF)

4 Hr Storage Will Get 98% Firm


(TPCF)

Storage (hrs) TPCF

0 48%

1 68%

2 87%

4 98%

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Introducing Larger Format Series 6 Module … reduces BOS Cost

Physical Dimensions for Equal Efficiency

c-Si

350 W

1m

2m S6

420 W

1.2m

2m

Large FormatMORE WATTS PER INSTALL OPERATION

FramedSIMPLIFIED MOUNTING TO COMMON INDUSTRY STRUCTURES

19

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Site: San Luis Obispo, CA USA

Owner: MidAmerican EnergyHoldings Company

Size 550MW

Const. Time: 2011—2015

Acres: ~7,500 site

Modules: ~9 million

TOPAZ SOLAR PLANT

One of the largest utility scale solar plant in the world

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Grid Stability & Reliability

Milliseconds to Minutes Years

Power Systems Planning & Design

Hours to Days

Load Balancing

Solar PV Impact on Power Grid – Key Topics

Two Key Conditions for Grid Stability

• Voltage is maintained within Normal Range

• Frequency is maintained within Normal Range

i.e., Generated Power = Loads ( + Grid Losses)

at every instant

Typical PV Plant Output

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Plant Control System Enables Grid Friendly Features

Patent No. 8,774,974. Real-time photovoltaic power plant control system

POWER GRIDSUBSTATION

DC

•••


SWITCHGEAR

AC

SOLAR ARRAYS COMBINERBOX

DC

POWER CONVERSION STATION

Typical DC Voltage 1kV or 1.5kV Typical AC Collection Voltage 34.5kV

(Alternatives 4.16kV to 27.6kV)

69 to 765kV

(AC)

• 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

Closed-loop controls at 100 milliseconds!

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Passage of Clouds at a 290 MW PV Plant

~20 minutes

Large Plant Size Attenuates Impact of Cloud Passages on Power Output

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AGUA CALIENTE 290MW AC | CONNECTING ON 500 KV TRANSMISSION LINE

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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TYPICAL PLANT OPERATION (UNITY POWER FACTOR)

Plant Is Maintained At Constant Power Factor as Required

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

Volt

age

(P

U)

an

d P

ow

er F

act

or

Po

we

r (P

U) a

nd

Rea

ctiv

e P

ow

er (

PU

)

Time of Day

Typical Operating Day

Reactive Power (PU)

Voltage (PU)

Power (PU)

Power Factor

Normalization ValuesActive Power: 300MWReactive Power: 20MVARVoltage: 530kV

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MARCH 21ST 2014 EVENT

Palo Verde Nuclear

Generating Station

North Gila

Substation

Hoodoo Wash

Substation

Agua Caliente

500kV Palo Verde-Hassayampa

Transmission Line

Hassayampa

SubstationO

Line Taken

Out of

Service

26Maintain Voltage Even Under Changing Power Conditions

Power (PU)

Reactive Power (PU)

Voltage (PU)

Voltage (PU)

Power (PU)

Voltage (PU)

VOLTAGE SUPPORT FROM PV PLANT

Grid Operator

Seeks Voltage

Support

Voltage Control

Started

Night

Shutdown

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Role of Utility-Scale PV Plants In Grid Stability & Reliability

• NERC identified essential reliability services to integrate higher levels of solar resources

• Utility-Scale PV Plants Provides

Grid Friendly Features Required by NERC Voltage regulation Real power control, ramping, and curtailment Primary frequency regulation Frequency droop response Short circuit duty control Fault ride through

Utility-Scale PV Plant Contributes to Grid Stability & Reliability Like Conventional Generation

Source: NERC: 2012 Special Assessment Interconnection Requirements for Variable Generation

Demonstration of Essential Reliability Services by a 300-MW Solar PV Power Plant

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TESTS SUCCESSFULLY CONDUCTED ON 300 MW SOLAR PV PLANT

• Power Ramping Ramp its real-power output at a specified ramp-rate Provide regulation up/down service

• Voltage Control Control a specified voltage schedule Operate at a constant power factor Produce a constant level of MVAR Provide controllable reactive support (droop setting) Provide reactive support at night

• Frequency Provide frequency response for low frequency &

high frequency events Control the speed of frequency response Provide fast frequency response to arrest frequency decline

Utility-Scale PV Plant Contributes to Grid Stability & Reliability Like Conventional Generation

Can variable energy resources provide essential reliability services

to operate the grid?

• NERC identified three essential reliability services (ERS) to integrate higher levels of

renewable resources1. Frequency Control

2. Voltage Control

3. Ramping capability or Flexible Capacity

• Test results demonstrated utility-scale PV plant has the capability to provide these

essential reliability services

• Advancement in smart controls technology allows these plants to provide services similar

to conventional resources

• VERs (Variable Energy Resources) with the right operating characteristics are necessary

to decarbonize the grid

Page 30

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• First Solar PV modules

• 4 MVA PV inverters

• 8 x 40 MVA blocks

• 34.5 kV collector system

• Two 170 MVA transformers

• Tie with 230 kV transmission line

• PMUs collecting data on 230 kV side

PV Power Plant Description

40 MVA Block

34.5 kV

Collection

170 MVA

Transformer

230 kV

Transmission

PMU4MVA Inverter

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170

180

190

200

210

220

230

0 200 400 600 800 1000 1200 1400

RELATIVE TIME (sec)

Available MW Min allowed MW Commanded MW Measured MW

• 30MW headroom

• 4-sec AGC signal provided to Plant Controller

• Tests were conducted for

— Sunrise

— Middle of the day

— Sunset240

245

250

255

260

265

270

275

280

285

0 200 400 600 800 1000 1200 1400

RELATIVE TIME (sec)

Avaliable MW Min Allowed MW Commanded MW Measured (MW)

AGC Participation Tests – 300 MW Utility-Scale PV PlantP

OW

ER

(M

W)

PO

WE

R (

MW

)

MORNING

MIDDAY

30MW Headroom

30MW Headroom

Available MW

Available MW

MinimumAllowed MW

MinimumAllowed MW

Measured MW

Measured MW

Commanded MW

Commanded MW

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SteamTurbine

PumpTurbine

Hydro CombinedCycle

LimitedEnergyStorage

GasTurbine

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

PV Plants Outperform Conventional Resources in Frequency Regulation

http://www.caiso.com/Documents/TestsShowRenewablePlantsCanBalanceLow-CarbonGrid.pdf

Blue bars taken from the ISO’s informational submittal to FERC on the performance ofresources providing regulation services between January 1, 2015 and March 31, 2016

Solar PV(Middle ofthe Day)

Solar PV(Sunset)

Solar PV(Sunrise

Regulation accuracy by PV Plant is about 24-30% points better than fast gas turbines

40%

63%

87-93%


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• 3% and 5% under and over-frequency tests

• 20% headroom

• ±36 mHz dead band

• Used actual frequency event time series measured in the U.S. Western Interconnection

Frequency Droop Tests

𝐷𝑟𝑜𝑜𝑝 =∆𝑃/𝑃𝑟𝑎𝑡𝑒𝑑∆𝑓/60𝐻𝑧

Example of 3% droop

test (under-frequency)

PowerFrequency

35

“Grid Friendly Utility-Scale PV Plants are Essential for Large-Scale PV Integration”— CAISO

Reality: Utility-scale PV Solar is a Flexible Resource that can enhance grid reliability


Dispatchable PV Plant

• Solar can provide NERC-identified essential reliability

services to integrate higher levels of renewable resources,

including: — Frequency Control

— Voltage Control

— Ramping capability or flexible capacity

• Automated Generation Control regulation accuracy of 24-

30% points better than fast gas turbines

• Reduces need for services from conventional generation

— Goes beyond simple PV energy value

— Enables additional solar

— Reduces need for expensive storage


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Solar Curtailment is to be Expected with Higher Penetration

Perception of solar saturation/over-

generationTo get to the lowest cost/best fit option,

some saturation is to be expected

Perception

Reality

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• The “duck” chart elegantly captures oversupply misperception

• Two Concerns:

— Low Net Load: flexibility to reduce must-run generation resources is limited

— High Ramp Rates in Evening: flexibility of other generation to ramp up is limited

ramp need~13GWin three hours

TYPICAL SPRING DAY

2018

2012 (actual)

2013 (actual)

201420152016

20172019

2020over generation risk

The Perception of Solar Saturation

Actual 3-hour ramp

of 13GW on December

18, 2016

Net Load of 8.5GW on

May 14, 2017

Steeper Ramps

Deeper Belly

Not a Reliability Issue!

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0

10

20

30

40

50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Pro

du

cti

on

(G

W)

Time of Day

Production By Resource Type

May 14, 2017

Solar

Hydro

Thermal

Imports

Imports

Other Renewables

Nuclear

Source: CAISO Data. BTM Solar: Behind the Meter Solar: Estimated Based on CEC Data

The Perception of Solar Saturation

LOW LOAD DAYTYPICAL SPRING DAY

“Solar Overgen” is an Economics Issue Not Reliability

Minimum Must Run Generation

8.5 GWNuclear, Imports Thermal & Hydro

LoadBTM Solar

Curtailment

Grid Solar BTM (Behind the Meter) Solar

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39Source: CAISO Data. BTM Solar: Behind the Meter Solar: Estimated Based on CEC Data

Comparing Generation Low Load and High Load Days

HIGH LOAD DAY

BTM Solar

Nuclear

Solar Generation During High Load Days (Summer) is More Valuable

LOW LOAD DAY

Load


0

10

20

30

40

50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Pro

du

cti

on

(G

W)

Time of Day


May 14, 2017

Solar

Hydro

Thermal

Imports

Imports

Other Renewables

Nuclear


8.5 GWNuclear, Imports Thermal & Hydro

LoadBTM Solar

Curtailment


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40

0

10

20

30

40

50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Pro

du

cti

on

(G

W)

Time of Day


May 14, 2017

Solar

Hydro

Thermal

Imports

Imports

Curtailment

Other Renewables

Nuclear

BTM Solar

Source: CAISO Data. BTM Solar: Behind the Meter Solar: Estimated Based on CEC Data

Increasing Solar While Maintaining Minimum Must Run Constraint (Hypothetical!)

HIGH LOAD DAY

0

10

20

30

40

50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Pro

du

cti

on

(G

W)

Time of Day


Summer Day

Add 10GW New Grid Solar

Hydro

Thermal

Imports

BTM Solar


Nuclear

Load

LOW LOAD DAY


8.5 GWNuclear, Imports, Thermal & Hydro

Load

It is Economical to Add Flexible & Controllable Solar

… Even If It Leads To More Curtailment During Low Load Days


42

Optimal portfolio balances solutions with overbuild (conceptual!)

All Overbuild All StorageMix of Overbuild and Storage

Some curtailment is necessary to achieve the least

cost/ best fit solution

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Solar is the New Hydro!

Source: E3 – Solar is the New Hydro

“Solar is the New Hydro”

Renewable

Clean

Affordable

Abundant

Occasional Spill is Routine

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Here Comes Solar … “Every One Else Make Way For It?”, Not a Sustainable Approach

• Solar today is like a privileged vehicle without any controls that all other vehicles have to make room for on the highway

• As solar penetration goes up … congestion increase, solar must be controllable and flexible to achieve sustainable growth

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Curtailment is Indeed Growing … In Frequency & Magnitude

Energy Imbalance Market (EIM) has

helped CAISO avoid renewable

curtailments this year, although avoided

curtailments are down from previous

years. | CAISO

Source: ”Spring Oversupply Lifts CAISO Curtailments”, April 2017, RTO Insider. https://www.rtoinsider.com/caiso-duck-curve-curtailments-42004/

Total solar output was reduced by about 1.6% due toreal-time economic dispatch instructions and curtailments in 2016

EIM Avoided Curtailment

Renewable Curtailment

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Increasing Grid Flexibility to Meet Challenges of High Renewable Penetration

Generation Storage

Demand Response

Dispatchable

Quick StartLoad Shift

Over

Generation

Mitigation

Peak Load Reduction

Off-Peak Load consumption

Dispatchable Solar/WindFast Ramping

Regulation

Frequency

Response

Fast & Flexible Generation

Transmission

Plus

Operational & Market

Flexibility• Faster electricity markets

• Larger balancing areas

• Control center decision support

tools

• Probabilistic & scenario

methods

• Look-ahead simulation

Sources: M. Ahlstrom, “Operations and Integrating Variable Generation”, UVIG A Short Course on the Integration and Interconnection of Variable Generation into Electric Power

Systems, June 2014. And Clyde Loutan, CAISO, “Demonstration of Essential Reliability Services by a 300-MW Photovoltaic Power Plant”

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Key Summary – Advances in Utility-Scale PV Plants

Sources: 1 Lazard Levelized Cost of Energy Analysis – Version 10; GTM Research Global Solar PV Demand Monitor Q2017. . 2. Beyond 33% Renewables: Grid Integration Policy for a Low-‐Carbon Future, CPUC White Paper

• Utility-scale solar electricity now costs less than conventional generation in many markets1

– Cheaper than rooftop PV by a factor of 2-3

• Need to address grid challenges to grow solar substantially2

— Maintain grid stability and reliability while integrating large-scale solar into electricity grid system

— Increase grid flexibility to increase solar penetration and reduce

curtailment

• Key cost reduction drivers include:– Module cost reduction & efficiency improvement

– BOS & Plant design innovations

– Improved Investment Climate