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2014 PV Performance Modeling Workshop: Toward Reliable Module Temperature Measurements: Considerations for Indoor Performance Testing
 

2014 PV Performance Modeling Workshop: Toward Reliable Module Temperature Measurements: Considerations for Indoor Performance Testing

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2014 PV Performance Modeling Workshop: Toward Reliable Module Temperature Measurements: Considerations for Indoor Performance Testing

2014 PV Performance Modeling Workshop: Toward Reliable Module Temperature Measurements: Considerations for Indoor Performance Testing

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    2014 PV Performance Modeling Workshop: Toward Reliable Module Temperature Measurements: Considerations for Indoor Performance Testing 2014 PV Performance Modeling Workshop: Toward Reliable Module Temperature Measurements: Considerations for Indoor Performance Testing Presentation Transcript

    • May5,2014 MONALI JOSHI, BLACK & VEATCH RAJEEV SINGH, PV EVOLUTION LABS TOWARD RELIABLE MODULE TEMPERATURE MEASUREMENT: CONSIDERATIONS FOR INDOOR PERFORMANCE TESTING
    • • Black & Veatch is a leading global engineering and consulting company specializing in infrastructure development in energy, water, telecommunications, management consulting, federal and environmental markets • Founded in 1915 • $3.4 Billion in revenue in 2013 • Over 9000 employees worldwide • Over 100 offices worldwide • Completed projects in over 100 countries on six continents WHO IS BLACK & VEATCH? 2
    • • Involved in 45% of operating PV projects in North America and 20% of projects in advanced development (on a MW basis) • Engaged as Independent Engineer, Owner's Engineer, Power Purchaser rep. • Advisor to equity investors, lenders, venture capital firms, major utilities, and government agencies • Leader in PV third party technical due diligence and extended engineering services SOLAR PV QUALIFICATIONS & EXPERIENCE 3 • Feasibility Studies • Resource Assessment • Interconnection Planning and Design • Power Purchase Agreement Support • Energy Production Estimating • Technology Due Diligence • EPC Specification Development • Owner’s Engineer Support • Construction Monitoring • Performance Monitoring • Generation of PVsyst module characterization files (“PAN files”) from laboratory measurements of module performance
    • TEMPERATURE-DEPENDENCE OF MODULE POWER OUTPUT 4 Operating temperature is dependent upon many factors: • Solar irradiance • Ambient temperature • Wind speed • Wind direction • Panel material composition • Mounting structure PV module operating temperature impacts energy production
    • TEMPERATURE-DEPENDENCE OF MODULE POWER OUTPUT 5 Significant Heat Loss Mechanisms 1) Conduction through encapsulation 2) Convection from surfaces 3) Radiation to surroundings Significant Heat Sources 1) IR radiation from solar spectrum 2) PV conversion “inefficiency” Cell Operating Temperature (Tcell) is result of thermal balance
    • TEMPERATURE-DEPENDENCE OF MODULE POWER OUTPUT 6 Thermal gradients within the module should be considered when assessing Tcell Layer Thickness (mm) Thermal Conductivity (W*m-1*K-1) Glass 3.0 1-2 EVA 0.5 0.2-0.3 Si 0.250 148 Al back contact 0.01 237 EVA 0.5 0.2-0.3 Tedlar 0.1 0.2-0.3 PV module operating temperature impacts energy production
    • U · (Tcell-Tamb) = α· Ginc ·(1-η) (1) U = Uc + Uv · V (2) 7 PVsyst computes module efficiency based on irradiance and modeled Tcell PV system energy simulation relies on estimation of Tcell Within PVsyst : MODELING TCELL FOR ENERGY PREDICTION 1) Tcell calculated from incident irradiance (Ginc), ambient temperature (Tamb), and wind speed • Optical absorption • User-defined thermal loss factors 2) Estimate module IV curve characteristics at calculated Tcell • PAN file defines η surface, function of Ginc, Tcell
    • INDOOR MODULE PERFORMANCE CHARACTERIZATION CONSIDERATIONS 8 Goal of customized PAN files: High fidelity representation of measured module performance a function of incident irradiance and cell temperature IEC 61853-1: PV Module Performance Testing and Energy Rating • Describes “requirements for evaluating PV module performance” • Specifies measurement of back-of module temp (Tmod) • Not prescriptive on method of temperature control Because temperature control methodologies can vary, 1) Possible Tmod ≠Tcell 2) Tmod /Tcell relationship may not be fixed or predictable
    • INDOOR MODULE PERFORMANCE CHARACTERIZATION CONSIDERATIONS 9 Factors impacting accurate and repeatable temperature measurements: • Directionality of heat source vs.
    • INDOOR MODULE PERFORMANCE CHARACTERIZATION CONSIDERATIONS 10 Factors impacting accurate and repeatable temperature measurements: • Directionality of heat source • Uniformity of heat source vs.
    • INDOOR MODULE PERFORMANCE CHARACTERIZATION CONSIDERATIONS 11 Factors impacting accurate and repeatable temperature measurements: • Directionality of heat source • Uniformity of heat source • Hold time at temperature
    • INDOOR MODULE PERFORMANCE CHARACTERIZATION CONSIDERATIONS 12 Factors impacting accurate and repeatable temperature measurements: • Directionality of heat source • Uniformity of heat source • Hold time at temperature • Number, type, location of sensors x x x x x x x x vs.
    • INDOOR MODULE PERFORMANCE CHARACTERIZATION CONSIDERATIONS 13 Factors impacting accurate and repeatable temperature measurements: • Directionality of heat source • Uniformity of heat source • Hold time at temperature • Number, type, location of sensors • Calibration Lack of specificity in many of these factors in 61853-1 leaves room for lab-to-lab variation
    • 14 “Oven” • Module heated on all sides by laminar flow of hot gas • In-situ IV curve measurement • Uniform temperature profiles possible • Equilibrium possible “Hot Potato” • Module heated in thermal chamber; placed in ambient • IV curves assessed while cooling (no temp control) • Non-uniform temperature profiles possible • Non-steady state “Back-side Toaster” • Constant, adjustable heat source at back surface • Uniform x-y thermal profile possible • Non-uniform thermal profile in z • ~ Steady state possible MODULE PERFORMANCE CHARACTERIZATION FOR ENERGY PREDICTION Variety of indoor temperature control methodologies currently in use , all of which may be consistent with 61853 guidelines, but differences can lead to largely different results x y z
    • 15 Each temperature control methodology leads to a distinctive relationship between Tback/mod and Tcell thus measured power output and thermal coefficients may vary if measured as a function of Tmod Tfront Tback Tcell = = Toven/ambient = Tfront Tback Tcell ≠ < Tambient < Theat source < Tfront Tback Tcell ≠ ≠ Tambient ≠ MODULE PERFORMANCE CHARACTERIZATION FOR ENERGY PREDICTION “Oven” “Hot Potato” “Back-side Toaster”
    • CASE STUDY—IMPACT OF MEASUREMENT LOCATION USING “TOASTER” HEATING 16 In conjunction with PV Evolution Labs “Backside Toaster” heating methodology, two temperature measurement methodologies: Temperature controlled such that CP temperature is within ± 0.5° of 61853 temperature targets (15°C, 25°C, 50°C, 75°C) 1. Cell probes (CP): hypodermic thermocouple needles inserted underneath backsheet and contacting cell busbar 2. Backsheet (BP) probes : standard thermocouples adhered to backsheet using Kapton (polyimide) tape 1 2
    • 17 60 cell p-Si Module Type 1 No systematic correlation between Tmod and Tcell even among same footprint, same manufacturer For this test set-up, Tcell cannot be reliably predicted from Tmod 60 cell p-Si Module Type 2 CASE STUDY RESULTS—TCELL VS TMOD
    • 0 50 100 150 200 250 300 0.0 20.0 40.0 60.0 80.0 100.0 PowerOutput Temperature Cell Probe Backsheet Probe CASE STUDY RESULTS—IMPACT ON NORMALIZED POWER CURVES 18 Power output curves (normalized to nominal output at STC) developed for each dataset For this case, referring to back of module temp as proxy for operating temp leads to overestimation of module performance 1100 W/m2 1000 W/m2 800 W/m2 600 W/m2
    • CASE STUDY RESULTS – IMPACT ON PAN FILE OPTIMIZATION AND ENERGY PREDICTION 19 Optimized PAN File Parameters Using Tmod Optimized PAN File Parameters Using Tcell Parameter Value Isc (A) 9.20 Voc (V) 37.9 Imp (A) 8.61 Vmp (V) 30.2 T. Coeff. Isc (mA/°C) 3.57 Rshunt (Ω) 333 Rseries (Ω) 0.390 Rshunt at G = 0 (Ω) 830 Rshunt exp 5.5 T. Coeff. Pmp (%/°C) -0.37 Using B&V’s iterative optimization process to replicate the measured efficiencies within PVsyst, different optimized PAN file parameters result In this case, all thermal coefficients found to differ by 15% Parameter Value Isc (A) 9.20 Voc (V) 37.9 Imp (A) 8.61 Vmp (V) 30.2 T. Coeff. Isc (mA/°C) 4.18 Rshunt (Ω) 333 Rseries (Ω) 0.400 Rshunt at G = 0 (Ω) 830 Rshunt exp 5.5 T. Coeff. Pmp (%/°C) -0.44
    • CASE STUDY RESULTS – IMPACT ON PAN FILE OPTIMIZATION AND ENERGY PREDICTION 20 Optimized PAN File Parameters Using Tmod Location Difference in Predicted Energy* Arizona + 1.4% Central California + 1.1% Ontario +0.01% *with respect to PAN file based on Tcell Parameter Value Isc (A) 9.20 Voc (V) 37.9 Imp (A) 8.61 Vmp (V) 30.2 T. Coeff. Isc (mA/°C) 3.57 Rshunt (Ω) 333 Rseries (Ω) 0.390 Rshunt at G = 0 (Ω) 830 Rshunt exp 5.5 T. Coeff. Pmp (%/°C) -0.37 Parameter Value Isc (A) 9.20 Voc (V) 37.9 Imp (A) 8.61 Vmp (V) 30.2 T. Coeff. Isc (mA/°C) 4.18 Rshunt (Ω) 333 Rseries (Ω) 0.400 Rshunt at G = 0 (Ω) 830 Rshunt exp 5.5 T. Coeff. Pmp (%/°C) -0.44 Optimized PAN File Parameters Using Tcell
    • CASE STUDY RESULTS—HIGHER RELIABILITY, REPEATABILITY WITH CELL TEMP PROBES 21 For this configuration, temperature coefficients derived using cell probe method are more repeatable Sample 1 Sample 2 Sample 1 (repeat) Sample 2 (repeat) Datasheet Value
    • INDOOR MODULE CHARACTERIZATION FOR DEVELOPMENT MUST GO BEYOND 61853 22 • Direct measurement of Tcell or demonstration of front/backside equilibrium • Modify procedure for data quality and consistency  Demonstrated temperature control repeatability  Demonstrated irradiance control repeatability  Ideally, IV curves measured at steady state • Incorporate additional, more granular measurements for more assessment of temperature coefficients
    • BLACK &VEATCH PAN FILE DATA MEASUREMENT SPECIFICATION The B&V specification requires:  In addition to methods outlined in 61853  Measurement of Tcell or demonstration of frontside/backside equilibrium  IV curve assessment under 61853-1 defined conditions  Redundant measurements to demonstrate repeatability of irradiance and temperature control  Linearity of Isc to validate irradiance control  Temp. Coeff. Measurement • 61215 measurement range: 5° increments over 30° • Reference Tcell 15°C 25°C 50°C 75°C 1100 W/m2    1000 W/m2     800 W/m2     600 W/m2     400 W/m2    200 W/m2   100 W/m2   30°C 35°C 40°C 45°C 1000 W/m2    
    • CONCLUSIONS 24 • Module performance and simulation of module performance within PVsyst rely on Tcell • Lab methodologies may be consistent with 61853-1 requirements, however differences in temperature control process may lead to different results • For indoor characterization procedures, relationship between Tmod and Tcell may vary with temperature control methodology, leading to differences in measured performance • Unreliable characterization of performance leads to non-trival accuracy errors in energy forecasting • Modification of 61853-1 procedure necessary to produce reliable, repeatable indoor performance data for generating PAN files
    • FUTURE WORK 25 • B&V Thin Film Module Specification for Indoor Characterization • Considerations: light stabilization; response time/pulse length; • B&V Outdoor Characterization Specification • Considerations: Placement of temperature sensors, Backside insulation for temp. coeff measurements, Irradiance measurement/spectral correction • Characterization of Thermal Loss constants in PVsyst • Considerations: PV technology/BOM/mounting method
    • THANK YOU PRESENTER NAME OPTIONAL TITLE COMPANY DIVISION 26
    • www.bv.com © Black & Veatch Holding Company 2012. All Rights Reserved. The Black & Veatch name and logo are registered trademarks of Black & Veatch Holding Company.