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18 deceglie modeling and monitoring rtsr

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8th PVPMC Workshop, May 9-10 2017

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18 deceglie modeling and monitoring rtsr

  1. 1. 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. Applying the principles of suns-Voc to PV system monitoring Michael G. Deceglie Timothy J Silverman Sarah R. Kurtz
  2. 2. 2NREL M. Deceglie PV Performance Modeling and Monitoring Workshop 2017 Goal: Rs monitoring • Beyond performance indices - automated diagnostic alerts • Provides actionable intelligence about incipient problems such as failing contacts or connections • Increases in Rs associated with fire risks opped by opening the series circuit in which they are curring. rallel arcs occur when two different dc polarities me in close proximity. In a PV module, a parallel arc n occur due to a ground fault. Parallel arcs are more fficult to detect and much more difficult to stop, as e current flow is either directly from plus to minus or rough a ground loop. terial selection or module design is going to prevent a rom catching fire once an arc is sustained because of mely high temperatures within an arc. Resistive heating of solder bonds connecting two ribbons ame cell. Fig. 6. An arc across the broken interconnect on a cell. The most likely place for an open circuit to occur module is at the output leads because: • These connections are usually not protected by by diodes; No material selection or module design is going to prevent a module from catching fire once an arc is sustained because of the extremely high temperatures within an arc. Fig. 4. Resistive heating of solder bonds connecting two ribbons from the same cell. Fig. 5. An arc caused by failure of the solder bond that attached an output lead to the module circuitry. IV. IMPROVING MODULE DESIGN AND CONSTRUCTION Wohlgemuth and Kurtz, PVSC 2012
  3. 3. 3NREL M. Deceglie PV Performance Modeling and Monitoring Workshop 2017 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
  4. 4. 4NREL M. Deceglie PV Performance Modeling and Monitoring Workshop 2017 Background: Suns-Voc • Measure irradiance dependent Voc values • Construct an Rs free IV curve • Rs from Ohm’s law: • More accurate than diode model curve fitting1 • Most often used for measuring cells • Recently demonstrated outdoors on modules and systems2 1Bowden and Rohatgi, PVSEC 2001 v.2 p.1802 2Forsyth et al., PVSC 2014, p.1928 Rs-free curve Actual curve ΔV
  5. 5. 5NREL M. Deceglie PV Performance Modeling and Monitoring Workshop 2017 Operating principles Irradiance E0 Irradiance Eʹ Isc,0 Translate Voc from low irradiance to:
  6. 6. 6NREL M. Deceglie PV Performance Modeling and Monitoring Workshop 2017 Operating principles Translate Voc from low irradiance to:
  7. 7. 7NREL M. Deceglie PV Performance Modeling and Monitoring Workshop 2017 Real-time series resistance (RTSR) • Observe: o Operating point current I0 and voltage V0 at irradiance E0 o Low-irradiance Voc values • Calculate target irradiance, Eʹ Irradiance E0 Isc,0 (V0, I0)
  8. 8. 8NREL M. Deceglie PV Performance Modeling and Monitoring Workshop 2017 Real-time series resistance (RTSR) • Observe: o Operating point current I0 and voltage V0 at irradiance E0 o Low-irradiance Voc values • Calculate target irradiance, Eʹ • Find recent Vʹoc at Eʹ • Calculate series resistance: Irradiance E0 Isc,0 (V0, I0) Irradiance Eʹ
  9. 9. 9NREL M. Deceglie PV Performance Modeling and Monitoring Workshop 2017 Real-time series resistance (RTSR) • Module will generally be cooler at Eʹ • Temperature coefficient depends on irradiance • Goal: adaptive, calibration-free Irradiance E0 Isc,0 (V0, I0) Irradiance Eʹ
  10. 10. 10NREL M. Deceglie PV Performance Modeling and Monitoring Workshop 2017 Handling temperature 10 20 30 40 17 18 19 20 21 Module temperature (°C) V'oc(V)
  11. 11. 11NREL M. Deceglie PV Performance Modeling and Monitoring Workshop 2017 Handling temperature • Look at recent Voc measurements near Eʹ o Here, recent = 1 week • Regress Voc vs. T • Extrapolate
  12. 12. 12NREL M. Deceglie PV Performance Modeling and Monitoring Workshop 2017 Handling temperature • Capture Voc vs. T at relevant irradiance • Automatically adapt to changes in the module • Look at recent Voc measurements near Eʹ o Here, recent = 1 week • Regress Voc vs. T • Extrapolate Deceglie et al. IEEE J. PV 5:6 p1706 (2015)
  13. 13. 13NREL M. Deceglie PV Performance Modeling and Monitoring Workshop 2017 Irradiance dependence of Voc vs T • Voc temperature coefficient depends on irradiance • Important to extract the correct value for the target irradiance • Using the 1-sun value causes ~20% error in series resistance NREL field data for Si module showing Voc temperature coefficient for varying irradiance
  14. 14. 14NREL M. Deceglie PV Performance Modeling and Monitoring Workshop 2017 Typical target irradiance • For 1-sun operation, typically comparing Voc points from 50–80 W/m2 • Most of the time, irradiance is all diffuse at these times, limiting effects of shade NREL field data for Si module target irradiance for Voc values for given operating irradiance
  15. 15. 15NREL M. Deceglie PV Performance Modeling and Monitoring Workshop 2017 Example application • Public dataset • IV curves collected on modules deployed in Cocoa FL, Eugene OR, and Golden CO • IV curves measured at 5- minute intervals • Meteorological monitoring • RTSR: Use subset of data, not full IV curve Marion et al. NREL Report: TP-5200-61610 Contact: bill.marion@nrel.gov
  16. 16. 16NREL M. Deceglie PV Performance Modeling and Monitoring Workshop 2017 Generating an Rs time series For each operating point: • Calculate target irradiance • Regress Voc vs. T (at target irradiance) for prior week • Calculate Rs → Time series of Rs
  17. 17. 17NREL M. Deceglie PV Performance Modeling and Monitoring Workshop 2017 Generating an Rs time series For each operating point: • Calculate target irradiance • Regress Voc vs. T (at target irradiance) for prior week • Calculate Rs → Time series of Rs Rs losses, aggregated weekly CIGS1 CIGS2 Si
  18. 18. 18NREL M. Deceglie PV Performance Modeling and Monitoring Workshop 2017 Rs time series CIGS1 CIGS2 Si Ohmic loss CIGS2 Si First and final 4 weeks of Rs losses Beginning End Can identify increases in Rs Rs losses, aggregated weekly CIGS1 CIGS2 Si Deceglie et al. IEEE J. PV 5:6 p1706 (2015)
  19. 19. 19NREL M. Deceglie PV Performance Modeling and Monitoring Workshop 2017 Validation with IV curves Weekly fractional ohmic loss IV curves CIGS1 Can identify increases in Rs Beginning End Si Deceglie et al. IEEE J. PV 5:6 p1706 (2015)
  20. 20. 20NREL M. Deceglie PV Performance Modeling and Monitoring Workshop 2017 Adaptive capability Weekly fractional ohmic loss Adapts to other changes in module IV curves CIGS1 CIGS1 CIGS2 Si CIGS2 Beginning End Deceglie et al. IEEE J. PV 5:6 p1706 (2015)
  21. 21. 21NREL M. Deceglie PV Performance Modeling and Monitoring Workshop 2017 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
  22. 22. 22NREL M. Deceglie PV Performance Modeling and Monitoring Workshop 2017 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 / connection problems CIGS1 CIGS2 Si stopped by opening the series circuit in which they are occurring. 2. Parallel arcs occur when two different dc polarities come in close proximity. In a PV module, a parallel arc can occur due to a ground fault. Parallel arcs are more difficult to detect and much more difficult to stop, as the current flow is either directly from plus to minus or through a ground loop. No material selection or module design is going to prevent a module from catching fire once an arc is sustained because of the extremely high temperatures within an arc. Fig. 4. Resistive heating of solder bonds connecting two ribbons from the same cell.
  23. 23. 23NREL M. Deceglie PV Performance Modeling and Monitoring Workshop 2017 Acknowledgements • Thank you for insightful discussion: o Ron Sinton (Sinton Instruments) o Chris Deline (NREL) o Bill Marion (NREL) • Contact: michael.deceglie@nrel.gov • Further reading: o Deceglie et al. IEEE J. PV 5:6 p1706 (2015) • This work was supported by the U.S. Department of Energy under Contract No. DE-AC36-08GO28308 with the National Renewable Energy Laboratory. Funding provided U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Solar Energy Technologies Office.

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