distributed pv monitoring · chris trueblood, pe . sr. project engineer . 14 november 2012 ....

Chris Trueblood, PE Sr. Project Engineer

14 November 2012

Distributed PV Monitoring PV System Performance, Variability, and Observations

Using High Resolution Field Data

2 © 2012 Electric Power Research Institute, Inc. All rights reserved.

Distributed Photovoltaic (PV) Monitoring Today’s presentation outline

1. Overview

2. Solar Resource

3. Energy Performance

4. Output Variability

5. Voltage Observations

HD

HD

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Our History…

• Founded in 1972

• Independent, nonprofit center for public interest energy and environmental research

• Collaborative resource for the electricity sector

• Major offices in Palo Alto, CA; Charlotte, NC; Knoxville, TN – Laboratories in Knoxville,

Charlotte and Lenox, MA Chauncey Starr EPRI Founder


Our Members…

• 450+ participants in more than 40 countries

• EPRI members generate more than 90% of the electricity in the United States

• International funding of nearly 21% of EPRI’s research, development and demonstrations

• Programs funded by more than 1,000 energy organizations


High Resolution Field Data & Geospatial Analytics Distributed PV Monitoring supports EPRI’s core PV research areas

Bulk System

Distribution System

Distributed PV

Monitoring

Renewable Generation

Operations & Maintenance

Utilities & System

Operators

PV System Owners &

Stakeholders


PV systems small and large are monitored High definition monitoring captures 1-sec data on any size PV system

2kW tracker in TX

1MW ground in TN

0.2kW pole in AL

200kW roof in CA


High-resolution PV monitoring is nationwide Concentrated areas include Southeast, Atlantic Coast, and California

Cluster PV Plant

Planned

Installed

Main map: © 2012 Microsoft Corporation. Imagery © Microsoft – available exclusively by DigitalGlobe (Bing Maps Terms of Use: http://go.microsoft.com/?linkid=9710837). Inset map: Map data © 2012 Google

Site Locations, September 2012

Recent Install


Monitoring for Central Inverter PV Systems Instrumentation for solar resource, selected dc points, and ac output

Solar Resource • Irradiance: plane-of-array,

global horizontal • Weather: temperature,

humidity, wind, rain

PV Array • Module: dc voltage,

current, back temperature • Combiner box: dc voltage,

string currents

Inverter • Input: dc voltage, current • Output: ac power, energy

totals (real & reactive), voltage, current

Data acquisition: up to 1-second recording, automatic data transfers, internet time synchronization, remote login

Instrumentation designed, assembled, configured, and tested by EPRI for field installation


1MW PV System in Tennessee Solar resource and AC output recorded at 1-sec resolution

Imagery ©2011 DigitalGlobe, GeoEye, U.S. Geological Survey, USDA Farm Service Agency, Map data ©2011 Google

8 Pyranometers • 7 on PV system • 1 on single-module • Plane-of-array • 25° fixed tilt, south

1.0 MWdc • 3.5 acre property • 4,608 PV modules • Four 260kW inverters • Installed Aug 2010 • Data began Oct 2011

Pyranometer Single Module & Data Logger


2. Solar Resource

Know your sun


Monthly Solar Insolation: Simulated & Measured At 1MW plant in TN, measured in plane-of-array

Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct0

1

2

3

4

5

6

7

Inso

latio

n (k

Wh/

m²/d

ay)

Month

PVWatts Simulated Output1MW Plant in TN Measured (Monthly)1MW Plant in TN Measured (Avg)

20122011

Avg = 4.55 kWh/m2/day


Solar Resource Calendar – August 2012 Measured plane-of-array irradiance, 1-minute averages, daytime only

21 3 4

111098765

12 13 14 15 16 17 18

25242322212019

26 27 28 29 30 31

Sun Mon Tue Wed Thu Fri Sat


Categories for Daily Variability Conditions Sandia’s variability index (VI) and clearness index (CI) to classify days

High

Moderate

Mild Overcast

Clear

VI < 2 CI ≥ 0.5

VI < 2 CI ≤ 0.5

2 ≤ VI < 5

5 ≤ VI < 10

VI > 10

Clear Sky POA IrradianceMeasured POA Irradiance


Variability Conditions

Variability Conditions: Arizona

Variability Conditions: Tennessee

Annual Insolation

Latitude Tilt


3. Energy Performance

The report card


0

5

10

15

20

25

Avg

Day

time

Hou

rs

Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct0.00

0.05

0.10

0.15

0.20

0.25

Cap

acity

Fac

tor

Month

1MW PV SystemSingle Module PV SystemAverage for 1MW PV SystemAverage for Single Module System

Average Daytime Hours

20122011

Capacity Factor: 1MW vs. Single Module Based on actual energy generated relative to nameplate dc rating

Avg = 0.176

Avg = 0.158


Performance Factor Definition Quantifies how well a system performs given the available solar resource

( )( )

( )( )2

2

1000 mWh mWhlation Solar Inso

kWing System RatkWhput Energy Out

e FactorPerformanc =

• Represents how well a PV system performed given the available solar resource

• Useful metric to compare the total energy output of different PV systems

• A factor of 1.0 indicates optimum PV system performance

• Typical values range between 0.7 and 1.0


Performance Factor: 1MW vs. Single Module Offers balance-of-system insight and likely effect of module temperature

Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct0

10

20

30

40

50

60

Tem

pera

ture

(°C

)

Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct0.6

0.7

0.8

0.9

1.0

1.1

Perf

orm

ance

Fac

tor

Month

Weighted Average Module Temperature1MW PV SystemSingle Module PV System

2011 2012


Power Duration: 1MW vs. Single Module Normalized to dc nameplate rating, irradiance normalized to 1000 W/m2

0 10 20 30 40 50 60 70 80 90 1000

20

40

60

80

100

120

Mea

sure

d Va

lue

(% o

f Rat

ing)

Percentage of 4455 Daytime Hours (%)

IrradiancePower - Single ModulePower - 1MW Plant

Data spans 1 year Nov 2011 – Oct 2012


Seasonal Daily Generation Profile By Hour Shows max, min, median, and inner quartile ranges for 1MW PV system

6 8 10 12 14 16 18 200

0.2

0.4

0.6

0.8

1

Hour of Day

Nor

mal

ized

Gen

erat

ion

Winter (Jan-Mar)

6 8 10 12 14 16 18 200

0.2

0.4

0.6

0.8

1

Hour of Day

Spring (Apr-Jun)

0.50 span

0.25 span


4. Output Variability

Solar is on the move…


Output Variability Analysis

• Benefit – How often and when

significant ramping events occur

• Time intervals – 10 & 30 seconds – 1 & 10 minutes – 1 hour

• Scope

– Single site: PV plant or representative single module

– Aggregated single modules

(Sep 29, 2011)... 12:00 15:00 18:000

200

400

600

800

1000

AC

Pow

er (k

W)

(Sep 29, 2011)... 13:10 13:11 13:12 13:130

200

400

600

800

1000

X: 29-Sep-2011 13:11:15Y: 157.9

AC

Pow

er (k

W)

Local Date & Time (Eastern)

X: 29-Sep-2011 13:11:40Y: 927.6

X: 29-Sep-2011 13:09:55Y: 908.6

X: 29-Sep-2011 13:10:20Y: 165.6

–743kW in 25 sec

(2.9% per sec)

+770kW in 25 sec

(3.0% per sec)


Output Variability is all about Changes in Power Sequential differences between instantaneous or averaged measurements

0

0.2

0.4

0.6

0.8

Nor

mal

ized

Pow

er

AC Power

09:00 12:00 15:00 18:00-0.6

-0.3

0

0.3

0.6

Nor

mal

ized

Cha

nge

Local Time

10-Second Interval1-Minute Interval


The Histogram: Changes in Power at 1MW site Relative frequency of changes for 4 ramp rate intervals: 10s, 1m, 10m, 1h

-100 -80 -60 -40 -20 0 20 40 60 80 1000

1

2

3

4

5

Rel

ativ

e Fr

eque

ncy

(%)

Change in Power (% of System Rating)

1 hour10 min1 min10 sec


Changes in Power at Selected Percentiles Focus is the extremes, both up and down directions (1MW PV system)

Fa Wi Sp Su Fa Wi Sp Su Fa Wi Sp Su Fa Wi Sp Su-100

-50

0

50

100

Cha

nge

in P

ower

(% o

f Rat

ing)

Season

99.99th99.9th99th95th90th

10 sec 1 min 10 min 1 hourRamp Rate Interval


Changes in Power at Selected Percentiles Focus is the time of day when extreme changes occur (1MW PV system)

6 8 10 12 14 16 18 200

20

40

60

80

100

Cha

nge

in P

ower

(% o

f Rat

ed O

utpu

t)

Hour of Day (Local Time)

99.99th99.9th99th95th90th

Q3 2012 (July-September)

Magnitudes only, for 1-minute ramp rate interval only


Exceedance of Change: Total Duration Useful to visualize extreme changes and their total time of occurrence

0.01 0.1 1.0 10 1000

20

40

60

80

100

Cha

nge

in P

ower

(% o

f Rat

ing)

Percentage of 1236 Daytime Hours (%)

10 sec1 min10 min1 hour

Magnitudes only, for 1 season (Q3 2012 Jul-Sep)

Showing 4 ramp rate intervals: 10s, 1m, 10m, 1h


5. Voltage Observations

What is happening to voltage?


Sample Distribution Circuits with Existing PV J1 is in northeast, K1 is in southeast, both serve rural communities

Characteristic J1 K1 Voltage (kV) 12.5 13.8

Peak Load, Approx (MW) 6.0 6.0

Existing PV (MW) 1.7 1.0

Substation LTC Yes Yes

Feeder Regulators 3 0

Capacitor Banks 2 fixed and 3 voltage controlled 1 fixed

Total Circuit Miles 58 28

Feeder “Footprint” (mi2) 35 7


Secondary Service Voltage, 10-Second Average 1MW plant in TN (K1), May 2012 voltages plotted against ac power

+5.0% limit

May 2012

267,864 points


Circuit J1: Voltage Exceeds Planning Limit 10-second average PV plant service voltage often above +5% at midday

+5.0% limit

May 2012 (267,864 points) • 3.0% of points exceed +5% limit • 5.5% exceed limit when Power > 0.01


No More Solar Allowed Utility has closed circuit J1 for new PV systems

• Concerns or complaints of overvoltage • 1.7MW PV plants on rural circuit (small town + farms) • At 6 MW max load, 28% masked by PV with full sun • Utility asked customer to lower power factor on PV inverters

1 mi Imagery ©2011 DigitalGlobe, GeoEye, U.S. Geological Survey, USDA Farm Service Agency, Map data ©2011 Google

0.5MW

1.2MW


Together…Shaping the Future of Electricity

distributed pv monitoring · chris trueblood, pe . sr. project engineer . 14 november 2012 ....

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