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Process for the measurement of performance loss due to series resistance in photovoltaic devices under field conditions

National Renewable Energy Laboratory

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Technology Marketing Summary

An unexpected increase in the series resistance in a photovoltaic module can be a serious problem; not only does the increased resistance reduce current flow  - and hence power generation – from the cell, it can also be an indication of a component failure or other systemic flaw in the device. These failure mechanisms, including broken ribbons, failed solder bonds, or junction box contact issues, can be associated with excess heat and can pose a safety hazard in the device vicinity, making the planning and development of devices that monitor or analyze series resistance critical. One widely used method of measuring series resistance is the Suns-VOC method. The Suns-VOC method analyzes cells under controlled lab conditions and does not, unlike other series-resistance calculation methods, rely on the assumption of device uniformity to generate and analyze the series resistance-free current-voltage (I-V) curve. While there have been some applications of the Suns-VOC method in the analysis of systems and modules outdoors, this analysis does not provide a real-time calculation of the series resistance in an installed module in the field. Therefore, there is still a need for the real-time measurement of series-resistance in outdoor modules without the collection or construction of full series-resistance-free I-V curves.

Description

Scientists at the National Renewable Energy Laboratory (NREL) have developed a novel physics-based method for the measurement of series resistance of a PV device that relies on the same principles as the Suns-VOC method. Like the Suns-VOC method, this novel real-time series resistance (RTSR) method is designed to monitor series resistance under field operating conditions. However, the RTSR method does not require the construction of full series-resistance-free I-V curves and bases its calculations of series resistance on the comparison between high-irradiance operating points and low irradiance open-circuit voltage (VOC) points. Monitoring series-resistance through this method allows for the early detection of changes within the PV modules or systems that are associated with common failures (e.g. broken ribbons, failed solder bonds, or junction box contact issues), does not interrupt the generation of electricity, and can benefit system operators by reducing the system soft costs associated with hands-on inspection, maintenance, and fault-identification.

Benefits
  • Implementable under field operating conditions
  • Doesn’t interrupt electricity generation
  • Does not require the measurement of the full I-V curve
  • Reduces costs
Applications and Industries
  • Photovoltaic Cells
  • Series Resistance Measurement
Technology Status
Technology IDDevelopment StageAvailabilityPublishedLast Updated
NREL ROI 15-34PrototypeAvailable08/23/201608/23/2016

Contact NREL About This Technology

To: Bill Hadley<bill.hadley@nrel.gov>