Real-time series resistance monitoring in PV systems · 2015-06-04 · Real-time Series Resistance...
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NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC. NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.
Real-time series resistance monitoring in PV systems
Michael G. Deceglie Timothy J Silverman
Bill Marion Sarah R. Kurtz
IEEE Photovoltaic Specialists Conference June 14-19, 2015 New Orleans, Louisiana
NREL/PR-5J00-63998
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Benefits of Rs monitoring
• Beyond performance indices - automated diagnostic alerts
• Increases in Rs associated with fire risks
Wohlgemuth and Kurtz, PVSC 2012
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Automated Rs monitoring
• Avoid hands-on, equipment-intensive measurements
• Automatically adapt to other changes in the module o e.g. change in shunt resistance
NREL Image 6326716
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Background: Suns-Voc
• Measure intensity dependent Voc values
• Construct an Rs free IV curve
• Rs from Ohm’s law
• Most often used for measuring cells
• Recently demonstrated outdoors on modules and systems1
1Forsyth et al. PVSC 2014 p1928
Rs-free curve
Actual curve
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Operating principles
Irradiance E0
Irradiance Eʹ
Isc,0
Translate Voc from low irradiance to:
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Operating principles
Translate Voc from low irradiance to:
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Real-time series resistance (RTSR)
• Record operating I and V
• Record Voc at low irradiances
• Compare operating V to recent Voc at target irradiance:
Irradiance E0
Irradiance Eʹ
Isc,0
I0
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Handling temperature
• Module will generally be cooler at Eʹ
• Temperature coefficient depends on irradiance
• Goal: adaptive, calibration-free
Irradiance E0
Irradiance Eʹ
Isc,0
I0
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Handling temperature
• Look at recent Voc measurements near Eʹ o Recent = 1 week o Eʹ ± 10%,
• Regress Voc vs. T • Extrapolate
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Handling temperature
• Look at recent Voc measurements near Eʹ o Recent = 1 week o Eʹ ± 10%,
• Regress Voc vs. T • Extrapolate
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Handling temperature
• Capture Voc vs. T at relevant irradiance • Automatically adapt to changes in the module
• Look at recent Voc measurements near Eʹ o Recent = 1 week o Eʹ ± 10%,
• Regress Voc vs. T • Extrapolate
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Example application
• Various modules deployed in Cocoa FL, Eugene OR, and Golden CO
• IV curves measured at 5-minute intervals
• Meteorological monitoring • Publically available dataset • RTSR: Use subset of data,
not full IV curve
Marion et al. NREL Report: TP-5200-61610 Contact: [email protected]
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Rs time series
Weekly fractional ohmic loss Fractional ohmic loss
Beginning End Can identify increases in Rs
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Rs time series
Weekly fractional ohmic loss IV curves
Beginning End
CIGS1
Si
Can identify increases in Rs
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Rs time series
Weekly fractional ohmic loss
Adapts to other changes in module
IV curves
Beginning End
CIGS1
CIGS2
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Implementation - review
• Collect: o Operating I, V o Low irradiance Voc
o Irradiance and temperature
• Regress recent low irradiance Voc vs. T
• Calculate Rs from Ohm’s law
Irradiance E0
Irradiance Eʹ
Isc,0
I0
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Implementation
• Readily applicable at module level o Integrated electronics o Power optimizers
• Possible at string-level o Challenges:
– Variation in mounting angle
– Partial shading
NREL Image 6326716
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Conclusion – real time series resistance
• Automated, module/array integrated
• Adaptive, calibration-free
• Benefits o Beyond performance
indices o Diagnostic o Early alert for fire
risks This work was supported by the U.S. Department of Energy under Contract No. DE-AC36-08GO28308 with the National Renewable Energy Laboratory.