Accurately Measuring PV Soiling Losses Using Module Power Measurements M. Gostein and B. Stueve, Atonometrics, Inc. Non-uniform PV soiling can’t be measured by short-circuit current alone. ' Example of edge soiling Examples on ground and 0.700 0.750 0.800 0.850 0.900 0.950 1.000 0% 5% 10% 15% 20% 25% 30% 35% Soiling Ratio Edge Cells Soiling Level SR Isc (12 cells) SR Pmax (12 cells) SR Pmax (6 cells) SR Isc (6 cells) From: Gostein, Littmann, Caron, Dunn, Proceedings of the 39th IEEE Photovoltaic Specialists Conference (PVSC), Tampa, FL, June 2013. • In some conditions, soiling may accumulate non- uniformly on PV modules • Wind, rain, condensation, temperature, and gravity all affect soiling distribution • Often, soiling is concentrated at module edges • “Soiling Ratio” (SR) metric can be based on losses in measured current (Isc) or power (Pmax) • Isc measurement simpler, but only approximates true power loss in case of uniform soiling • Experiment shows Isc measurements can severely over- or under-estimate true power loss for non-uniform soiling on c-Si PV modules • Soiling measurement: use “soiled” module and “clean” control • “Clean” control: may use automatically cleaned reference cell • For “soiled module” use actual PV module representative of site, to capture module-specific effects and non-uniformities • Should measure both module current and power Non-Uniform PV Soiling Pmax vs. Isc as Soiling Metric Soiling Measurement System Soiling Underestimated Results Experiment with Simulated Soiling 72-cell c-Si module, two orientations Soiling Ratio Metrics Explanation: Module has 3 internal bypass diodes. Shaded 12-cell string on long edge is bypassed by internal diode, so Isc is not limited by shading; but shading 6 cells across all strings results in the shaded cells controlling and limiting Isc. Soiled Reference Module Washed Ref Cell Measurement Electronics Wash Unit Stand-alone system Utility plant monitoring system Washed Ref Cell Measurement Electronics Wash Unit From: F. Brill, “EnviroPolitics Blog: PSEG building solar farms--and not just in New Jersey,” 16-Nov-2012. [Online]. From: E. Lorenzo, R. Moretón, and I. Luque, “Dust effects on PV array performance: in-field observations with non-uniform patterns,” Progress in Photovoltaics: Research and Applications, 2013. on utility-scale tracking system: roof-mount systems: This poster contains no confidential information. '

Accurately Measuring PV Soiling Losses Using Module Power ... · Accurately Measuring PV Soiling Losses Using Module Power Measurements M. Gostein and B. Stueve, Atonometrics, Inc

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Page 1: Accurately Measuring PV Soiling Losses Using Module Power ... · Accurately Measuring PV Soiling Losses Using Module Power Measurements M. Gostein and B. Stueve, Atonometrics, Inc

Accurately Measuring PV Soiling Losses Using Module Power Measurements M. Gostein and B. Stueve, Atonometrics, Inc.

Non-uniform PV soiling can’t be measured by short-circuit current alone.'

Example of edge soiling Examples on ground and

0.700

0.750

0.800

0.850

0.900

0.950

1.000

0% 5% 10% 15% 20% 25% 30% 35%

Soil

ing

Rat

Edge Cells Soiling Level

SRIsc (12 cells)

SRPmax (12 cells)

SRPmax (6 cells)

SRIsc (6 cells)

From: Gostein, Littmann, Caron, Dunn, Proceedings of the 39th IEEE Photovoltaic Specialists Conference (PVSC), Tampa, FL, June 2013.

• In some conditions, soiling may accumulate non-uniformly on PV modules

• Wind, rain, condensation, temperature, and gravity all affect soiling distribution

• Often, soiling is concentrated at module edges

• “Soiling Ratio” (SR) metriccan be based on losses in measured current (Isc) or power (Pmax)

• Isc measurement simpler, but only approximates true power loss in case of uniform soiling

• Experiment shows Isc measurements can severely over- or under-estimate true power loss for non-uniform soiling on c-Si PV modules

• Soiling measurement: use “soiled” module and “clean” control

• “Clean” control: may useautomatically cleaned reference cell

• For “soiled module” useactual PV module representative of site, to capture module-specific effects and non-uniformities

• Should measure both module current and power

Non-Uniform PV Soiling

Pmax vs. Isc as Soiling Metric

Soiling Measurement System

Soiling Underestimated

Results Experiment with Simulated Soiling

72-cell c-Si module, two orientations

Soiling Ratio Metrics

Explanation: Module has 3 internal bypass diodes. Shaded 12-cell string on long edge is bypassed by internal diode, so Isc is not limited by shading; but shading 6 cells across all strings results in the shaded cells controlling and limiting Isc.

Soiled Reference Module

Washed Ref Cell

Measurement Electronics

Wash Unit

Stand-alone system Utility plant monitoring system

Washed Ref Cell

Measurement Electronics

Wash Unit

From: F. Brill, “EnviroPolitics Blog: PSEG building solar farms--and not just in New Jersey,” 16-Nov-2012. [Online].

From: E. Lorenzo, R. Moretón, and I. Luque, “Dust effects on PV array performance: in-field observations with non-uniform patterns,” Progress in Photovoltaics: Research and Applications, 2013.

on utility-scale tracking system: roof-mount systems:

This poster contains no confidential information.'