How to assess PV technical risks and ensure your project is bankable by DNV GL

1. DNV GL © 2018 SAFER, SMARTER, GREENERDNV GL © 2018
How to assess PV technical risks and ensure your project
is bankable
Jackson Moore (Head of Section - Solar, Asia Pacific)
ENERGY - RENEWABLES ADVISORY
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PUBLIC

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PV Technical Risks
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Project Lifecycle – Ensuring performance starts in development
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Feasibility
Feasibility Studies
Site Screening
EIA
Planning
Market Studies
Development
Resource Monitoring
Site Conditions
Technology Selection
Site Layout
Energy Assessment(s)
Grid Connection
EIA
Geotech and Hydrology
FEED / BoP Design
Contracts & Specifications
Pre-Construction
Geotechncial Support
Technology Assessment
EPC Tender & Bid Evaluation
BoP Design & Review
(Final) Energy Assessment
Project Due Diligence
Construction
Owner’s Engineering
Lenders Engineer
Technical Support
Commissioning/Testing
Warranty + O&M
EoW Inspections
Forecasting
O&M Strategy
Operations Monitoring
Due Diligence (Sale / Refinance)
Optimisation
Refurbishment & Decommissioning
1-3 months
Decision to Proceed
1-3 years
Planning Approval
Grid Connection
PPA
6-12 months
Sign Contracts
Financial Close
12-18 months
Practical Completion
Take-Over
2, 5, 10, 20+ years

4. DNV GL © 2018
2. Underperformance of PV modules: labelled power is
higher than real power (most frequent)
3. No or low quality monitoring system (most frequent)
4. Larger than expected module degradation (e.g. due to
manufacturing problems, cracks in solar cells, by-pass
diodes)
5. Interrupted strings due to broken connectors (may be
quality issue of connectors or improper installation)
6. Installation of modules with cracked cells due to
improper manufacturing, transport or installation
7. Potential-Induced degradation of PV modules
8. Structural weakening/failures due to improper structural
design
9. Losses due to shading (in complex terrain)
10.Bad grounding of PV modules frames
Typical failures in PV Installations
#1: Inaccurate system model which makes
determining future performance always wrong.
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Risks and Recommendations
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• Satellite and ground-based measurements are
often needed to provide bankable assessments
• EPC contractors often set guarantee levels below
p50 levels in order to ensure they pass
• Energy models are rarely updated based on as-
built conditions
• Solar measurement stations are often poorly
maintained after COD
Risk – Solar Resource and Energy Assessments
As a result, when a client asks us to
evaluate how a system is performing, it
often requires that we develop the
energy model from scratch
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Data sources &
uncertainty
•Synthetic/
database
(measured or
interpolated)
•Satellite for long-
term correlation
•Nearby ground
measured data (d)
•Site measurements
(reduced to 1-5%,
instead of 5-15%)
Sources of
uncertainty
•Spatial uncertainty
•Year-to-year
variability GHI
(Global Horizontal
Irradiation)
•Irradiation data
(equipment
quality)
•Correlation
uncertainty
•Future variability
Risk – Solar Resource and Energy Assessments
0
0.0001
0.0002
0.0003
0.0004
0.0005
0.0006
0.0007
0.0008
0.0009
ProbabilityDensity
P10P50P90
Shaded sensor
discovered in
data QA/QC
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▪ How to mitigate the risks:
– Capture on-site measurements if not
near available ground-based
measurements
– Utilize redundant secondary
standard pyranometers
– Clean the sensors regularly during
the measurement campaign
– Ensure measurements are not
impacted by shading
– QC data weekly
Recommendation – Solar Resource and Energy Assessments
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Risk – equipment failures
JBox Arcing Solder Joint Degradation Solder Joint Degradation
Encapsulant Browning Backsheet Yellowing Bubbles
QUALITY CONTROL
MATERIALS
QUALITY CONTROL
MATERIALSMATERIALS
DESIGN FLAW
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Risk – equipment failures
Unsoldered joint
▪ DNV GL test labs have tested 100s of modules from
dozens of manufacturers
▪ Use accelerated/stress testing to identify failure
modes and/or quality control
▪ Safety/performance standards do NOT indicate
product quality
– And only test a FEW samples
▪ Difficult to correlate accelerated testing to field
failure rates
▪ Example
– Failures in solder joints identified during a routine visit of a
“Tier 1” supplier
– This is not a 10+ year product due to solder joint
degradation
– This is a UL/IEC certified product, but product quality is
not being adequately controlled
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Risk – equipment failures
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Damp Heat Stress Testing
Thermal Cycle Stress Testing

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Risk – module failure timeline
▪ Review of Failures of Photovoltaic Modules, IEA PVPS 2014
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Risk – equipment failures or degradation?
0
50
100
150
200
250
Dr. Jordan, EUPVSEC, 9/2012
-0.2
0.2
0.6
1.0
1.4
1.8
2.2
2.6
Degradation Rate [% / year]
#ofProjects(2,128Total)
3.0
3.4
3.8
National Renewable Energy Lab (NREL)
Median (P50) 0.5% / year
Average 0.8% / year
P90 1.3 % / year
NREL data shows large spread
Much of the tail is actually
defects that hadn’t been
identified, not actually
degradation.
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14. DNV GL © 2018
Recommendations – equipment failures
▪ No substitute for product qualification testing
▪ PV Evolution Labs (now a DNV GL company) is the
test lab for the GTM “PV Reliability Scorecard”
▪ Developers and lenders can access module test
reports from the DNV GL Product Qualification
Program at no charge
▪ Best mitigation is a combination of:
– 3rd party accelerated life/stress testing
– Review of field history and warranty claim rate
– Manufacturing audit (before and during
manufacture)
– Reviewing results of manufacturer’s ongoing
reliability test program
– Strong warranty/serial defect language
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https://www.dnvgl.com/publications/pv-
module-reliability-scorecard-2017-93448

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Recommendations – product qualification and verification
1. Product Qualification Program:
– Paid for by manufacturers
– Downstream partners obtain data / reports at zero cost by signing simple engagement
letter
2. Statistical Batch Testing: Statistical testing at the project by project level to
screen for defects and to verify that you got what you paid for
PV Modules PV Inverters Rooftop Racking
• Testing per BOM
• Extended Reliability Testing
• Performance Testing
o PAN Files
o IAM coefficients
o LID
o NOCT
• Reliability Testing
• Envelope Characterization
• Transient Response
• Low Light Performance
• Efficiency
• Arc / ground fault
• Micro, string, and utility
scale
• AFCI nuisance trip
• Installation time
o Man*hours per module
• Installer notes
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Risk – improper structural design
▪ Classic wind load analysis that considers only
static loads is often insufficient for solar
▪ Dynamic effects and vortex shedding can lead
to considerably higher-than-expected wind
loading on modules
▪ Few solar-specific standards related to
foundations and racking
▪ We have seen failures in 100-110 kmph winds
(3-second gust; well below the design
requirements) caused by improper application
of wind load calculations
– Risk that insurance may not cover if it can be
proven that design was not sufficient
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Risk – improper structural design
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▪ Geotechnical studies may not fully address
anticipated foundation types, corrosivity
▪ Civil preparation to ensure adequate soil
compaction is difficult to QA
▪ Hydrology and impact of scour/erosion
often overlooked
▪ Structural inadequacies may not be
evident during the warranty period without
thorough review of the structural
calculations and visual inspection of the
structural components

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Recommendations – improper structural design
▪ Pre-construction
– Require post/foundation testing to determine lateral and uplift resistance
▪ EPC Contract
– Racking/tracker supplier should have appropriate wind tunnel test reports to establish design parameters
and structural coefficients (using Boundary Layer Wind Tunnel testing, not aerospace wind tunnels)
– Structural adequacy analysis to be performed by 3rd party engineer that considers the dynamic effects of
wind. Recommend > 4 Hz for all natural frequencies for most PV geometries and locations. Lower natural
frequencies may be acceptable if damping ratios are high (higher than 1-2%) – must be engineered.
– Contractor should be responsible for the geotechnical study to be sure they have reliance on the results
– Contractor should perform a comprehensive drainage analysis that includes specific recommendations for
stormwater depth and scour/erosion potential
▪ Construction
– Geotechnical consultant should oversee civil work and site preparation
– Provide owner-representatives on-site to QA construction
– Check of all structural steel to repair (as needed) galvanizing/epoxy coating damage
▪ Post Construction
– Annual inspections and end-of-warranty inspections should include excavations around foundations
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Risk – incomplete commissioning
▪ Exhaustive and thorough inspections, commissioning and testing can identify
most workmanship issues and many equipment problems
▪ Critical to identify problems prior to project turnover
▪ Standards exist – use them
▪ Common mistakes
– Following procedures for commercial roof-top systems (rather than procedures
appropriate for power generation projects)
– Not testing all strings for Voc/Isc (or Imp)
– Not using IV-curve testing and thermography to diagnose small levels of
underperformance
– Not performing insulation resistance testing on all conductors
– Incomplete records of soil compaction and concrete testing
– Not performing a thermographic survey
– Relying on Performance Ratio (PR)
– Rushing through commissioning and deferring portions to the operational period
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Yes! Test every string.
PR > 10%
uncertainty.
Good enough?

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Risk – incomplete commissioning
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Thermography –
Hot Spot
Insulation Resistance – Ground Fault
0
0.003
0.006
0.009
0.012
0.015
02/07/2012 16/07/2012 30/07/2012 13/08/2012 27/08/2012 10/09/2012
Dailymodulecurrent/DailyIrradiance(A/(W(m2))
Date
String1
String2
String3
String4
String5
String6
Dailymodulecurrent/
DailyIrradiance[A/(Wh/m2)]
String Testing Results

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Recommendations – incomplete commissioning
▪ Standards exist – use them:
– IEC 62446 – Grid connected photovoltaic systems – Minimum requirements for
system documentation, commissioning tests and inspection
– IEC 60891 - Photovoltaic devices - Procedures for temperature and irradiance
corrections to measured I-V characteristics
– IEC 60904 – Photovoltaic devices - Measurement of photovoltaic current-
voltage characteristics
– ASTM E2848 - Standard Test Method for Reporting Photovoltaic Non-
Concentrator System Performance
– ANSI/NETA ATS – Standard for Acceptance Testing Specifications
▪ Yes, test every string and every conductor
▪ Repeat as part of a multi-year “re-commissioning” process
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Yes! You should perform insulation
resistance testing on all conductors –
including the string conductors (and
preferably with modules in circuit).

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Risks and recommendations – performance ratio
▪ PVsyst energy model uncertainty can be > 10% over short periods
▪ Performance ratio is easy to calculate but ignores differences in temperature and
near shading
▪ Performance ratios can be a useful metric, if used appropriately
– Most appropriate when comparing the performance of a system to ITSELF over
the same time period (e.g. July 2013 to July 2014)
▪ Otherwise, for short periods (days to
weeks):
– Incorporate a temperature-corrected
PR analysis
– Utilize regression-based testing (e.g.
ASTM E2848 or similar)
▪ For longer periods (>= 1 year), utilize
PVsyst to compare actual generation to
expected generation (using the on-site
measured weather conditions)
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Risks and recommendations – performance ratio
▪ Advanced PR-based analytics can be useful if:
– Temperature corrected, OR
– Evaluated over comparable weather periods, AND
– Statistical methods used to reduce uncertainty, AND
– High quality (secondary standard) pyranometers are used
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▪ Example string analysis:
- Select hours that ensure highest
linearity in current measurement
devices
- Compute group average combiner-
level current
- Exclude underperformers and re-
compute average
- Utilize linear regression to establish
variance over a range of irradiance
levels
- Establish pass/fail thresholds and
priority of investigation based on
statistical variance
Risks and recommendations – performance ratio
▪ Simple PR-based threshold alarms
don’t work (typical of many popular
DAS systems)
– Either ignored because of nuisance
tripping, OR
– Thresholds set too low to be valuable
▪ O&M providers are using smarter
algorithms (and improving
performance guarantees!)
Utilize statistical methods
to evaluate data
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Risks - Potential Induced Degradation (PID)
▪ PID is caused by sodium ion migration in the glass when
there is a sufficiently high voltage between the cells and
the grounded module frame
▪ PID is largely reversible and easily mitigated in new
system designs
▪ Primarily affects systems using a “floating” array (typical
of transformer-less inverter configurations) or a bi-polar
array
▪ First reports of PID began around 2007; by 2010 most
module manufacturers were aware of and providing
some guidance to customers
▪ However, we still encounter projects experiencing PID
and/or not properly mitigating for it
▪ “PID-resistance” is claimed by many suppliers, but there
are competing standards in the market (some which
allow 10% degradation)
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Recommendations - Potential Induced Degradation (PID)
▪ Utilize a negatively-grounded system (for typical cSi modules)
▪ Some inverter suppliers utilize a topology that manages the string voltage in a
manner to avoid PID; other inverter suppliers provide “charge equalizer”
options
▪ Seek modules with some level of PID-resistance testing (improved designs
using anti-reflective coatings and highly resistive encapsulants have shown
some PID resistance, though testing is on-going)
▪ Difficult to determine that underperformance in the field is attributable to PID
– Underperformance can be masked by soiling
– Initial indications are usually low Voc, but must be tested at the module
level.
– PID is likely if module Voc is low only at one end of the strings
– Module level IV curves will show reduced fill factor
– Electroluminescent imaging can provide further proof (but is impractical in
the field)
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Concluding Remarks
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Recommendations for upcoming projects
▪ Pre-construction
– Select products with accelerated test data from a 3rd party lab
– Insist on strong warranty language/protection – it’s a competitive market
– Require wind tunnel testing of racking and 3rd party structural analysis as part of the
design requirements
– Incorporate appropriate PID mitigation into the design
– Commission a grid outage study (if necessary)
▪ Construction
– Geotechnical engineer should oversee civil work and site preparation
– Owner should have adequate QA representation on-site
– Thorough commissioning and pass/fail criteria (test every string/conductor)
– Acceptance testing should be based on better metrics than PR
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Recommendations for existing projects
▪ This week:
– Confirm your energy model is based on accurate as-built conditions
– Confirm your pyranometers are secondary standard or equivalent and are being cleaned
regularly
▪ Over the next month:
– Perform a thorough analytical review of the project performance (using linear
regression or other statistical methods to confirm expected performance)
– Should be reviewed on a monthly and quarterly basis
– If your project is at risk for PID (e.g. floating configuration), investigate now before the
degradation becomes significant (and while it is still reversible)
▪ At the next annual/semi-annual O&M inspection:
– Perform careful inspection for corrosion
– Excavate around foundations to assess health
– Incorporate a multi-year “re-commissioning” process (if not already in place)
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30. DNV GL © 2018
SAFER, SMARTER, GREENER
www.dnvgl.com
Public
Thank you
31
Jackson Moore (Head of Section – Solar, Asia Pacific)
Jackson.moore@dnvgl.com

31. DNV GL © 2018
Recommended Reading – Structural Analysis
▪ Wind tunnel testing of PV systems: Kopp, G., Maffei, J., Tilley, C., SunLink website “Rooftop Solar Arrays and
Wind Loading A Primer on Using Wind Tunnel Testing as a Basis for Code Compliant Design per ASCE 7,”
http://www.sunlink.com/uploadedFiles/Sunlink/Content/Files/WindPrimer_07-2011.pdf
▪ Low-profile roof mounted PV arrays (flat roofs): “Wind Loads on Low Profile Solar Photovoltaic Systems on
Flat Roofs,” Structural Engineers Association of California (SEAOC) PV2,
http://www.documents.dgs.ca.gov/dsa/dsaab/csc04-12-12_agenda-Item-5B_SEAOC-WindLoad.pdf
▪ High-profile roof mounted PV arrays (flat roofs): O’Brien, C. Banks, D. - Solar Pro, July 2012 “Wind Load
Analysis for Commercial Roof-Mounted Arrays,” http://solarprofessional.com/articles/design-
installation/wind-load-analysis-for-commercial-roof-mounted-arrays;
▪ High-profile or flush mount roof mounted PV arrays (flat and sloped roofs): Banks, D. – CPP Website, “How to
Calculate Wind Loads on Roof Mounted Solar Panels in the US,” ivy.cppwind.com/wp-
content/uploads/2014/03/HowToCalculateWindLoads.pdf
▪ Ground-mounted systems: Banks, D. ASES 2012, “How Wind Loads Will Impact the Solar Industry”
https://ases.conference-services.net/resources/252/2859/pdf/SOLAR2012_0419_full paper.pdf`
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