2014 PV Reliability, Operations & Maintenance Workshop: Commissioning PV Systems with an O&M Focus Solmetric, Paul Hernday

1. Commissioning PV Systems
with an O&M Focus
Paul Hernday
Senior Applications Engineer
paul@solmetric.com
cell 707-217-3094
May 7, 2014
Sandia/EPRI 2014 PV Systems Symposium

2. Topics
• Guide to Performance and Safety Measurements
• Guidelines for interpreting I-V curves
• Techniques for visualizing I-V data from large arrays
• Complementary use of I-V curve tracing and IR imaging
• Enriching the value of zone monitoring with manual I-V curve testing

3. Reduced O&M
burden & improved
project ROI
Reduced risk, cost
of capital, & LCOE
for future projects
Cost of capital ~ risk ~ 1/knowledge
Roger Hill, Sandia
Earlier exposure &
resolution of issues
Improved
commissioning
measurement
practices
More detailed
assessment of
performance
Improved design &
construction practices


Guide to Performance & Safety Measurements for
Commercial PV System Commissioning

4. Context / Opportunity
for commissioning measurements
• Rigorous commissioning ( + resolution of issues) results in higher early
and long term production and reduced maintenance burden.
• Larger systems have tended to receive more rigorous commissioning.
• In commercial systems, there is wide variation in which measurements are
performed and how the data is evaluated.
• Formal commissioning standards such as IEC-62446 are very relevant to
the commercial space but are not firmly embedded in US practice.
• What appears to be lacking is awareness of:
• The business case for effective commissioning
• The reasons for including particular measurements
• Guidance on performing the measurements, including environmental
conditions, so that the measurements are a useful reference for
ongoing maintenance work.
• How to interpret the data and what to report

5. • Introduction
• System Performance
• Array Performance
• Insulation Resistance
• IR Measurement
• Solar Access
Chapters
Goal
Reduce the Levelized Cost of Energy (LCOE) of commercial scale
PV generation by advancing the use of best measurement practices
in the commissioning of new systems.
In Scope Out of Scope
Commercial systems Residential & utility
Commissioning, re-, retro- Detailed troubleshooting
Performance and safety
measurements
Testing of monitoring,
comm’s & other systems
Measurement practice Specific electronic tools
Weather conditions Required conditions
Example test limits Required test limits
What to report Reporting format
Guide to Performance & Safety Measurements for
Commercial PV System Commissioning

6. Guide to Performance & Safety Measurements for
Commercial PV System Commissioning
SECONDARY COMMISSIONING – ENERGY TEST – ENERGY PERFORMANCE INDEX (EPI)
Method 1 – Use commissioning test measurements of actual hourly weather for input to PV System Model 1 to
calculate hourly and monthly Expected Energy output kWh. Compare Measured to Expected using EPI.
Commissioning Data
Excerpt from draft of
system performance chapter

7. Guide to Performance & Safety Measurements for
Commercial PV System Commissioning
Method 2 – Use Regression model developed from measured data from
as-built system to Expected Energy output during first month (Month 1)
of system operation during commissioning tests.
Commissioning Data
Excerpt from draft of
system performance chapter

8. Topics
• Guide to Performance and Safety Measurements
• Guidelines for interpreting I-V curves
• Techniques for visualizing I-V data from large arrays
• Complementary use of I-V curve tracing and IR imaging
• Enriching the value of zone monitoring with manual I-V curve testing

9. Example I-V Curve Measurement Setup
Curve tracer connected to combiner buss bars
Courtesy Chevron Energy Solutions © 2011

10. Fastest
• One measurement per string at the combiner box
• No need to return to clamp-meter the strings
Most complete
I-V curve plus Isc, Voc, Imp, Vmp, Pmax, Performance
Factor and Fill Factor
Most specific
Results are independent of inverter performance and
issues with shading or soiling elsewhere in the array.
Best troubleshooting clues
• I-V curve shape suggests possible causes
• Selective shading method reduces troubleshooting time
Safest
Combiner is isolated from the inverter and other sub-
arrays, reducing arc flash hazard.
Benefits of I-V Curve Tracing
For PV source performance testing

11. • Classification system for
how I-V curves deviate
from expectations.
• Descriptive, not physical.
• When coupled with likely
causes, it becomes a
powerful troubleshooting
aid.
Deviations from Normal I-V Curve Shape

12. Measuring Actual String Performance
• Actual hardware performance is often
obscured by issues related to weather,
obstructions, or measurement technique.
• Peeling away the external effects is easy
once a few simple concepts are mastered.
• The benefits should include:
Measurement Issues
• Irradiance sensor not in POA
• Thermocouple not attached
• Thermocouple location
• Resistive losses
Actual
string
performance
Weather Issues
• Low irradiance
• Variable irradiance
• Wind
Obstruction
Issues
• Shade
• Soiling
Hmm…
 Deeper understanding of
commissioning data
 Less costly troubleshooting
 Reliable basis for module
warranty claims.
 Understanding of module
degradation rates

14. Using Selective Shading
to troubleshooting underperforming strings
Courtesy Dave Bell &
Harmony Farm Supply
• Finds the bad module with wiring intact,
based on repeated string I-V curve
measurements with modules electrically
removed one at a time by bypass diodes.
• Blocking light to 2+ rows of cells forces the
bypass diodes ON.
• If one module in a string of N modules is
bad, (N-1) I-V curves will show its effects
and one I-V curve will be normal. The one
normal curve = shading the bad module:

15. Topics
• Guide to Performance and Safety Measurements
• Guidelines for interpreting I-V curves
• Techniques for visualizing I-V data from large arrays
• Complementary use of I-V curve tracing and IR imaging
• Enriching the value of zone monitoring with manual I-V curve testing

16. Fill Factor
The underutilized performance metric
Isc
VocVoltage
Voltage
Ratio
(Vmp/Voc)
Imp
Vmp
Max
Power
Point
Current Ratio (Imp/Isc)
Current
Imp x Vmp
Isc x Voc
Fill Factor ==
Green area
Blue area
• FF (0….1) is a measure
of the squareness of the
I-V curve
• Higher FF means more
output for a given Isc and
Voc:
• Relatively independent
of irradiance under high
light conditions
• Excellent screen for
comparing curve shapes
• I-ratio and V-ratio provide
valuable hints about
series or shunt
resistance

17. Useful Data Analysis Tools
1950
2000
2050
2100
7
6
5
4
3
2
1
0
Frequency
Pmax (Watts)
Pmax (W)
Count

18. Fill Factor Histogram
Example: Broad bell curve with single outlier

19. Fill Factor and Voc Histograms
From I-V curves of strings with PID issues
Voc (Volts)
Inverter 1 Inverter 1

20. FillFactor
Date
Performance Trends
Example: Trends for a particular string
Performance
Factor
0 0
100 1.0
2014 2015 2016 2017
Array Navigator

21. Performance Trends
Example: Population trends
Standard
Deviation%
Date
Performance
Factor%
0 0
100 5.0
2014 2015 2016 2017
Array Navigator

22. Topics
• Guide to Performance and Safety Measurements
• Guidelines for interpreting I-V curves
• Techniques for visualizing I-V data from large arrays
• Complementary use of I-V curve tracing and IR imaging
• Enriching the value of zone monitoring with manual I-V curve testing

23. Infrared Imaging
Image 383
22 C 45 C
One
shaded
cell
Global Solar & Alternative Energies
Solmetric
Solmetric
• A PV system is a thermal
system too, but we need eyes
to see these processes.
• In addition to finding areas of
localized power dissipation,
IR imaging finds sections of
the array that are not
producing (far left, top and
bottom).
• Natural companion tool to I-V
curve tracing (see quote).
“We find that our I-V curve tracers and our infrared cameras are
very often used together to diagnose array performance issues.
For example, if we see an I-V curve with an irregular shape we
immediately view the string with the IR camera to look for
anomalies. Likewise, if we see hot spots on an array or in the
wiring, we use the I-V curve tracer to record and document the
actual performance”.
Jeff Gilbert, Dir. O&M Services, Vigilant Energy Management

24. Aerial Thermography
Portland Habilitation Center, PV by Dynalectric
Image courtesy of Oregon Infrared
http://www.oregoninfrared.com/
Open strings
Module issues

25. Topics
• Guide to Performance and Safety Measurements
• Guidelines for interpreting I-V curves
• Techniques for visualizing I-V data from large arrays
• Complementary use of I-V curve tracing and IR imaging
• Enriching the value of zone monitoring with manual I-V curve testing

26. Granularity & blind spots
Graphics from:
Determining Optimal PV System
Monitoring Granularity
SolarPro, Issue 6.5, Aug/Sep '13
Casey Miller & Todd Miklos
• Zone monitoring provides useful
granularity with lower up-front and
maintenance costs and lower
operational complexity than string
level monitoring.
• How can manual array measurements
supplement zone monitoring to make
it even more economically attractive?

27. ‘Curve Into the Zone’
Complementing zone monitoring with I-V curve tracing
• Supplementing zone monitoring
with periodic manual string I-V
curve tracing and IR imaging
boosts sensitivity to performance
issues.
• Curve tracing can be performed
programmatically and in response
to zone alarms.
• All of the I-V curve data adds to
the detailed array performance
database.
• It is likely that the zone alarm
levels can be further optimized
based on I-V curve tracing data.

28. Commissioning PV Systems
with an O&M Focus
Paul Hernday
Senior Applications Engineer
paul@solmetric.com
cell 707-217-3094
May 7, 2014
Sandia/EPRI 2014 PV Systems Symposium