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10 ashwini pavgi_pvpmc

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8th PVPMC Workshop, May 9-10 2017

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10 ashwini pavgi_pvpmc

  1. 1. Temperature Coefficients and Thermal Uniformity Mapping of PV Modules and Plants Ashwini Pavgi, Joseph Kuitche, Jaewon Oh and GovindaSamy TamizhMani 8th PV Performance Modeling and Monitoring Workshop Albuquerque, New Mexico May 9, 2017
  2. 2. PART 1 PART 2 AZ 3 AZ 5 Mapping of thermal uniformity of PV cells in a module Mapping of thermal uniformity of PV modules in PV plants Determination of climate- specific (Phoenix/AZ) thermal model coefficients, specifically for PVsyst 2 This is a two-part presentation:
  3. 3. 3 Part 1 Mapping of Thermal Uniformity in a Module
  4. 4. How to obtain accurate temperature coefficients outdoor? Thermocouple locations T1: Center T2: Corner T3: Short edge T4: Long edge 2. Electrical conditions before taking I-V curves • Maximum power point tracking condition 1. Test modules Various PV technologies: c-Si, CdTe, CIGS and a-Si Approaches to reduce the temperature difference: • Frame and back sheet insulated • Frame-insulated • Black-frame • Aluminum tape on white backsheet 4 This work attempts to answer the following question: How to reduce the temperature difference between T1, T2, T3 and T4? 3. Weather data Wind speed, irradiance etc.
  5. 5. Approaches attempted to reduce the temperature difference in a module 5 Code Insulation Type Technology Code Insulation Type Technology 1 Non-insulated mono-Si 5 Frame and backsheet insulated poly-Si 2 Aluminum tape covered backsheet mono-Si 6 Non-insulated a-Si 3 Frame insulated Poly-Si 7 Non-insulated CIGS 4 Non-insulated (frameless) CdTe 8 Non-insulated (black frame) mono-Si
  6. 6. 0 1 2 3 4 5 6 7 8 9 10 10:00:00 11:00:00 12:00:00 13:00:00 14:00:00 ΔT(oC) Temperature monitoring at Pmax at one minute interval from 10am-2pm cSi CdTe CIGS ΔTmax between four thermocouples @ MPPT 6
  7. 7. -2.8 -5.7 -1.7 -1.4 -5.9 -5.7 -2.6 -4.8 -6.9 -5.4 -3.2 -6.1 4.8 4.5 2.2 1.1 7.4 4.6 2.6 5.4 7.7 4.2 2.9 7.1 -8.0 -6.0 -4.0 -2.0 0.0 2.0 4.0 6.0 8.0 10.0 No insulation Black frame Frame insulation F & BS insulation Percentchange Percentage change in temperature coefficients with respect to different temperature sensors Iscmin Vocmin Pmaxmin Iscmax Vocmax Pmaxmax Thermal variation based on various thermal insulation configurations Variation in c-Si PV module with frame insulation ±3 percent Variation in c-Si PV module with black frame ±6 percent LEAST 7
  8. 8. Maximum temperature difference (ΔTmax) between the thermocouples depends on the insulation configuration 8  c-Si module with black frame experienced the least ΔTmax  The variability in ΔTmax is the highest in no insulated module  ΔTmax value for module backsheet with aluminum cover is highest, but the variability is lower Weather condition: Irradiance= 1007-1015 W/m2 Wind speed = 0.7-0.8 m/s Ambient temperature = 22-24 oC c-Si
  9. 9. Temperature difference between two identical modules (use of thermocouples): White backsheet vs. White backsheet with aluminum cover Backsheet with Al cover: Blocking radiative loss causes higher operating temperature 15 25 35 45 55 65 75 38 39 40 41 42 43 44 10:00AM 11:00AM 12:00PM 1:00PM 2:00PM 3:00PM 4:00PM 5:00PM Temperature(oC) Voc(volts) Temperature and voltage values on a clear sunny day 10am-5pm Sensor A Voc: No insulation Sensor B Voc: Aluminum tape covered BS No insulation: temperature Al tape covered BS: temperature -3 -2.5 -2 -1.5 -1 -0.5 0 0 2 4 6 8 10 12 14 16 18 10:00AM 11:00AM 12:00PM 1:00PM 2:00PM 3:00PM 4:00PM 5:00PM Voc(volts) Temperature(oC) Impact of aluminum covered back sheet on temperature and voltage on a clear sunny day ∆T ∆V Average ΔT= 8oC Highest= 15oC 9
  10. 10. Weather conditions: Irradiance= 1019 W/m2, Wind speed= 1.2 m/s, Ambient temperature= 24.9 oC 61.8-29.4 = 32.4 oC Blockage of radiative loss Since IR imaging captures only the surface radiation (not the cell temperature) of the substrate, IR image shows that the white backsheet with aluminum cover is about 32oC cooler but the cell is actually hotter as can be seen by the attached thermocouples (see the previous slide)! 10 With Al cover on white back sheet White back sheet only With Al cover on white backsheet White backsheet Front Imaging Back Imaging Backsheet with Al cover: Blocking radiative loss causes higher operating temperature Temperature difference between two identical modules (use of IR imaging): White backsheet vs. White backsheet with aluminum cover IR Imaging: Misleading
  11. 11. 11 Part 1 Mapping of Thermal Uniformity in a Plant
  12. 12. Data collected from 04/17/2015 to 09/30/2015 Thermal Mapping of Modules in PV Power Plants System Tilt/ orientation Years fielded Year Commissioned Model Type Number of modules Site 4a Horizontal fixed 19 1997 AZ3 1512 Site 4c One-axis tracking 7 2009 AZ5 1280 Location of thermocouples on each of five modules per plant T1 = Center cell temperature T2 = Corner cell temperature T3 = Bottom cell temperature T4 = Left cell temperature Location of each HOBO under an array 12 AZ3 AZ5 Temperatures of five modules (four corners and center) of each plant monitored Horizontal fixed 1-Axis Tracking AZ5 plant is about 4 feet lower than AZ3 plant & 15 foot high wall to south of AZ5 plant
  13. 13. AZ3 PLANT LEVEL TEMPERATURE DISTRIBUTION: SOLAR NOON (12-1PM) Installation type: Fixed horizontal system Module: Siemens SP75 frameless PV technology: Monocrystalline silicon Years of field exposure: 19 NW SW NE SE Date: July 15, 2015 Weather conditions: Clear sunny day Average irradiance (GHI, SolarAnywhere): 971 W/m2 Average wind speed: 3m/s 13
  14. 14. NW NE SW SE AZ5 PLANT LEVEL TEMPERATURE DISTRIBUTION SOLAR NOON (12-1PM) Installation type: One-axistracking system Module: Sanyo HIP190 framed PV technology: Monocrystalline silicon heterojunction Years of field exposure: 7 Date: July 15, 2015 Weather conditions: Clear sunny day Average irradiance (GHI, SolarAnywhere) : 971 W/m2 Average wind speed: 3m/s 14
  15. 15. Thermal representation for AZ3 and AZ5 9am-5pm data Daily average data Solar noon data AZ3 100% 100% 100% AZ5 109% 107% 103% 30 40 50 60 70 AZ3 and AZ5 : Plant level 9am-5pm temperature (averaged) data AZ3 9-5 AZ5 9-5 30 40 50 60 70 AZ3 and AZ5 : Plant level solar noon temperature (averaged) data AZ3 solar noon AZ5 solar noon 15
  16. 16. 47 48 49 50 51 52 53 Center Corner Bottom Left AZ3 Center Module level temperature variation from 9am – 5pm ∆T = 3.036649 47 48 49 50 51 52 53 Center Corner Bottom Left AZ3 SE ∆T = 0.848 Cell temperature difference within a module: 0.8-3.0oC 47 48 49 50 51 52 53 Center Corner Bottom Left AZ3 SW ∆T = 1.778 47 48 49 50 51 52 53 Center Corner Bottom Left AZ3 NW ∆T = 2.485 47 48 49 50 51 52 53 Center Corner Bottom Left AZ3 NE ∆T = 2.373 Fixed horizontal (AZ3) Average temperature: 50.4oC 16
  17. 17. Module level temperature variation from 9am – 5pm 49 51 53 55 57 59 Center Corner Bottom Left AZ5 Center49 51 53 55 57 59 Center Corner Bottom Left AZ5 NW 49 51 53 55 57 59 Center Corner Bottom Left AZ5 NE 49 51 53 55 57 59 Center Corner Bottom Left AZ5 SE ∆T = 2.010 ∆T = 4.008 ∆T = 0.837∆T = 2.181 ∆T = 2.453 Cell temperature difference within a module: 0.8-4.0oC 1-axis (AZ5) Average temperature: 54.9oC Higher degradation rate & Lower lifetime expected 17 49 51 53 55 57 59 Center Corner Bottom Left AZ5 SW
  18. 18. CONCLUSION • Mapping of thermal uniformity of PV cells in a module • c-Si module with black frame experienced the least ΔTmax • Temperature coefficients for c-Si module with frame insulation experienced least variability • It is recommended to use average value from four temperature sensors for uninsulated crystalline silicon PV module • Backsheet with aluminum cover experiences higher operating temperature due to blocking of radiative losses. • Mapping of thermal uniformity of PV modules in a plant • Position (four corners or center) of the hottest modules depends on the wind speed, wind direction and height of array. 18
  19. 19. 19 Part 2 Climate-specific Thermal Model Coefficients for PVsyst (for Phoenix, Arizona)
  20. 20. 1. For free-standing arrays Uc = 25 W/m²·K, Uv = 1.2 W/m²·K /m/s 2. For free-standing arrays (when the wind velocity is not present in the data) Uc = 29 W/m²·K, Uv = 0 W/m²·K /m/s 3. For fully insulated arrays Uc = 15 W/m²·K, Uv = 0 W/m²·K /m/s Default values provided by PVsyst 20 Climate-specific Thermal Model Coefficients for PVsyst Goal : Develop thermal model coefficients for specific PV technologies and specific climate
  21. 21. 21 System description • 14 PV modules from 7 different manufacturers and of 6 different technologies • a-Si technology is from two different manufacturers (glass superstrate and Tefzel/Polymer superstrate) • South facing, latitude-tilt, open rack system • Near Pmax operation with power resistors • Data stored for every 5 minute interval • Hot desert climate conditions (Phoenix, Arizona) • Average wind speed= 1.84 m/s • Average ambient temperature= 23.6 oC • Average measured POA (annual) during the solar window time period 10am-2pm= 837 W/m2 Climate-specific Thermal Model Coefficients for PVsyst
  22. 22. Retrieve monthly data with main parameters together: Irradiance (W/m2), wind speed (m/s), module temperature (oC) and ambient temperature (oC) at five-minute interval Filter the data for solar window time from 10am to 2pm Calculate the following values: ΔT=Tmod-Tamb and ( 𝐈𝐫𝐫𝐚𝐝𝐢𝐚𝐧𝐜𝐞 𝚫𝐓 ) Remove prominent outliers (due to data logging issues) Plot ( 𝑰𝒓𝒓𝒂𝒅𝒊𝒂𝒏𝒄𝒆 𝚫𝑻 ) versus wind speed Intercept of the line = Uc and Slope of the line = Uv Performed model-adequacy checking of the residuals to statistically determine the values Average the values for two modules with same model number, cell technology and manufacturer Flow chart to determine Uc and Uv coefficients 22
  23. 23. 0 1 2 3 4 5 6 7 8 9 10 0 5 10 15 20 25 30 35 Uv(W/m3Ks) Uc(W/m2K) Uc and Uv values for all PV technologies based on one year data at one hour interval (10am-2pm) for desert climate (Phoenix, Arizona) Uc Uv 23
  24. 24. • Considering all the PV technologies, Uc and Uv value tend to follow the trend of: Polymer-Polymer > Glass-Polymer > Glass-Glass • For c-Si PV technology (when average wind speed= 1.84 m/s): Uc = 25.46 W/m2K Uv = 4.31 W/m3K.s CONCLUSION 24
  25. 25. THANK YOU Ashwini Pavgi ashwini.pavgi@asu.edu MS Thesis – Free Downloading: repository.asu.edu 25

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