essential reliability services from pv...

Essential Reliability Services From

PV Plants

Mahesh Morjaria, Ph. D.VP, PV Systems

Enabling a world powered by reliable, affordable

solar electricity.

2

Utility-Scale PV Plants Contribute to Grid Stability & Reliability Like Conventional Generation

Utility-Scale PV Plants Support Grid Stability & Reliability

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

Utility-Scale PV Plants Provide 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

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PV Plant Schematic

POWER GRIDSUBSTATION

DC

•••

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

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)

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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

•••

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

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

9Maintain 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

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

Can variable energy resources provide essential reliability services

to reliably operate the grid?

• NERC identified three essential reliability services to reliably 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

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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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Reactive power capability of a typical synchronous generator

compared to a PV Inverter

Proposed CAISO Reactive Capability for Asynchronous Resources

Q (MVAR)

P (

MW

)

Reactive Power Capability – PV Plant vs Synchronous Generator

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Typical Grid Requirement (e.g. ERCOT in Texas)

Reactive Power (Q)

Rea

l Po

wer

(P)

Inductive (Q-I) Capacitive (Q-C)

(Pn,Qn)

0.95 pf Line

Grid POI Requirement

• Provide leading and lagging reactive power at Point of Interconnection (POI/POC) for all real power ranges from 10% to 100%

• Example: − Real Power: Pn = 300 MW

− Reactive Power: Qn = ~100 MVAr

− Apparent Power: Sn = ~315 MVA

− Power Factor pf = 0.95

• The PV plant must be capable of either producing or absorbing up to 100 MVAr when real power is from 30 MW to 300 MW

0.95 pf Line

Pn

QnQn

Sn

Pmax

Q = S2 − P2

pf =𝑃

𝑆

Corner Point driving design

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Demonstrated the Capability to Change System Voltage

By changing the reactive

output of the plant from +100

MVAR to -100 MVAR, the

voltage at the POI changed

from 242 kV to 227 kV

Voltage

MVAR Output

MVAR Set Point

Demonstrated the ability of the plant to produce or absorb reactive power

(±100 MVAR) even at nearly zero power output

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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

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Examples of Over-Frequency Droop Tests

Example of 5% droop test (over-frequency)

Measured droop

response – 5%

Measured droop

response – 3%

PowerFrequency

Measured droop

response – 5%

Measured droop

response – 3%

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• Reactive power tests at high and low power production levels

• The plant meets the proposed CAISO reactive power requirements

Measured Reactive Power Capability and Voltages at POI

The plant is capable of providing +/- 100MVAR of dynamic reactive power

response at any point when operating on this P-Q plane

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Active Power Curtailment Test

Active Power

Active Power

Set Point

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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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—Regulation-up and regulation-down, or AGC tests during

sunrise, middle of the day, and sunset

—Frequency response tests with 3% and 5% droop settings

for over- frequency and under- frequency conditions

—Curtailment and APC tests to verify plant performance to

decrease or increase its output while maintaining specific

ramp rates

—Voltage and reactive power control tests

—Voltage control at near zero active power levels (nighttime

control)

Summary of Conducted Tests

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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

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Utility-scale PV solar is a flexible resource that can enhance grid reliability

Dispatchable PV Plant

• Solar can provide NERC-identified essential services to reliably

integrate higher levels of renewable resources, including: — Frequency Control

— Voltage Control

— Ramping capability or flexible capacity

• Automated Generation Control (AGC) 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

CAISO: “Grid Friendly Utility-Scale PV Plants are

Essential for Large-Scale PV Integration”

