New Tools for PV Array Commissioning and Troubleshooting

Transcription

1 New Tools for PV Array Commissioning and Troubleshooting June 30, 2011 Paul Hernday Applications Engineer cell Bryan Bass Sales Engineer

2 Solmetric Solutions

3 Free I-V Curve Poster

4 Introduction to the Solmetric PV Analyzer Training videos coming soon

5 Topics PV Array Performance Verification I-V Curves, and How They re Measured The Solmetric PVA-600 PV Analyzer Test Process (example: commissioning) Live Demo of the PV Analyzer User Interface I-V Signatures of Electrical Impairments I-V Signatures of Shading Effects

6 Array Performance Test Methods Inverter readout String DC measurements String I-V curve measurements Basic Comprehensive I V Verification methods are evolving in response to increasing emphasis on energy production (rather than up-front incentives).

7 Curve Tracing Adjustable Load Sweeping too fast can distort the I-V curves of high-efficiency PV modules. Measure voltage Current Measure current Voltage Load can be Resistive Capacitive Electronic

8 When To Test Array Performance? Install QA/Start-up Commissioning Periodic checkups Service alarms

9 Benefits of I-V Curve Performance Testing Commissioning New PV Systems A single electrical connection & a single measurement The most comprehensive PV measurement possible No need to bring the inverter on-line to fully test the array Close out projects earlier ($$$ flow earlier) Detailed baseline for comparison as arrays age & degrade Maintaining PV Systems (O&M, Asset Management) Troubleshoot more efficiently Sort out module versus inverter issues Provide convincing data for module warranty claims Assure nervous owners that arrays are working properly

10 Benefits of I-V Curve Performance Testing Enhancing Your Quality Assurance Capabilities Make visible ALL of the array performance parameters, to inform future designs Take advantage of string-level performance statistics to set appropriate system margins & set appropriate pass-fail criteria Develop a strong intuitive understanding of PV operation - as Bill Brooks calls it, Think like a PV system

11 Topics PV Array Performance Verification I-V Curves and How They re Measured The Solmetric PVA-600 PV Analyzer Test Process (example: commissioning) Live Demo of the PV Analyzer User Interface I-V Signatures of Electrical Impairments I-V Signatures of Shading Effects

12 Essential Functions of a Solar Cell Photon E 1. Photon generates charges (electron and hole ) 2. Built-in electric field (E) separates the charges 3. Metallization collects the charges

13 I-V Curve Represents all possible operating or load points Isc Imp I-V curve Max power point Current Voltage Vmp Voc

14 P-V Curve Calculated from the measured I-V curve Isc Imp I-V curve Pmax Current P-V curve Power Voltage Vmp Voc

15 Fill Factor A measure of the square-ness of the I-V curve Isc Imp Max Power Point (Imp, Vmp) Current Voltage Vmp Voc Fill Factor = Imp x Vmp (watts) Isc x Voc (watts) = asi: xsi: GaAs:

16 Array of Cells, Cell Strings or Modules I Current Parallel I-V building Series Total (net) I-V curve blocks V Voltage This building block graphic is useful in troubleshooting arrays

17 I-V Curve Signatures of PV Problems Isc Current (A) Reduced current Normal I-V curve Shunt losses* Mismatch losses (incl. shading) Any reduction of the knee of the curve means reduced output power. Series losses** Max power point Voltage (V) Reduced voltage Voc Conventions measurements miss many of these effects

18 Topics PV Array Performance Verification I-V Curves, and How They re Measured The Solmetric PVA-600 PV Analyzer Test Process (example: commissioning) Live Demo of the PV Analyzer User Interface I-V Signatures of Electrical Impairments I-V Signatures of Shading Effects

19 Example Measurement Setup Courtesy of Chevron Energy Solutions 2011

20 Example Measurement Setup Courtesy of Advanced Alternative Energy Systems

21 Example Measurement Setup Courtesy of: Integrated Energy Systems Pittsburg Unified School District Sage Renewables Stellar Energy Solutions

22 Solmetric PVA-600 PV Analyzer Single connection & measurement Detailed performance picture Comparison to built-in model (5 dots) Convenient wireless interface Rugged and easy to use String measurement showing I-V and P-V curves, and comparison of I-V curve with model (5 dots).

23 Touch Screen User Interface PC is user-supplied (Samsung Q1 Ultra shown here) Showing the Verify tab screen. Performance Factor (%) = Measured Pmax Predicted Pmax x100

24 Optional wireless sensor kit Irradiance & temperature sensors

25 PVA-600 Block Diagram (simplified) Battery charging connector CPU & wireless module C (1 of 3) V sense PV Source I sense Control button with LED indicator NEMA 4X FG Enclosure Capacitive load method Electrically isolated, no ground lead required Protected for over-voltage, -current, -temperature, & reverse polarity

26 PVA-600 Specifications Max DC input voltage: 600V Max DC input current: 20A* Maximum DC power: Min recommended Voc: Min recommended Isc: I-V measurement time: Points per I-V trace: Storage capacity: Safety: *Strings of high-efficiency modules should be measured singly, not in parallel 12 KW (instantaneous) 20V 1A mS typical 100 (typical) 1,000+ (PC running PVA SW) IEC Measuring Category CAT III, 600V

27 Static Load I-V Measurement Setup

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29 PV Models in the PV Analyzer Predict PV array performance for immediate comparison Sandia National Labs PV Array Model Most comprehensive (30 + parameters) ~500 PV modules 5-Parameter Model Developed at U. Wisconsin, used by CEC for NSHP program ~5000 PV modules Simple Datasheet Model (predicts Pmax) User enters data sheet parameters (Isc, Voc, Pmax & temp co s) Translates datasheet Pmax (STC) to actual irradiance & temperature These 3 methods are available in the Solar Advisor Model (SAM) from NREL and are embedded in the Solmetric PV Analyzer.

30 Topics PV Array Performance Verification I-V Curves, and How They re Measured The Solmetric PVA-600 PV Analyzer Test Process (example: commissioning) Live Demo of the PV Analyzer User Interface I-V Signatures of Electrical Impairments I-V Signatures of Shading Effects

31 Ideal Environmental Conditions For Array Performance Testing Cloudless sky 4 hours centered on solar noon No wind

32 Problem Conditions, Example 1 Small, discrete clouds

33 Problem Conditions, Example 2 Easy-to-overlook cirrus clouds

34 Problem Conditions, Example 3 Cloud effect

35 I-V Measurement Setup Example: measuring strings at a combiner box

36 Test Process Example: testing at a combiner box Hardware setup (do once): 1. Place the irradiance & temperature sensors 2. Isolate the combiner box (open the DC disconnect) 3. De-energize the buss bars (lift the string fuses) 4. Clip test leads to the buss bars Electrical measurement (repeat for each string): 1. Insert a string fuse 2. Press Measure 3. View and save results 4. Lift the fuse 15 seconds typically

37 Example Measurement Setup 860kW 7-inverter system Courtesy of Portland Habilitation Center and Dynalectric Oregon

38 Example Measurement Setup Combiner boxes for one inverter Courtesy of Portland Habilitation Center and Dynalectric Oregon

39 Example Measurement Setup Combiner boxes for one inverter Courtesy of Portland Habilitation Center and Dynalectric Oregon

40 Example Measurement Setup Combiner box wiring Courtesy of Portland Habilitation Center and Dynalectric Oregon

41 Example Measurement Setup Inserting single fuse to test corresponding string Courtesy of Portland Habilitation Center and Dynalectric Oregon

42 Performance analysis Using the optional Solmetric I-V Data Analysis Tool Distributions Pmax Fill factor Imp/Isc Vmp/Voc Isc, Voc, etc Array Tree Table of key performance parameters Overlay plots of I-V curves

43 Displays Generated by the I-V Data Analysis Tool Current (Amps) Voltage (Volts) Frequency Pmax (Watts)

44 Topics PV Array Performance Verification I-V Curves, and How They re Measured The Solmetric PVA-600 PV Analyzer Test Process (example: commissioning) Live Demo of the PV Analyzer User Interface I-V Signatures of Electrical Impairments I-V Signatures of Shading Effects

45 Topics PV Array Performance Verification I-V Curves, and How They re Measured The Solmetric PVA-600 PV Analyzer Test Process (example: commissioning) Live Demo of the PV Analyzer User Interface I-V Signatures of Electrical Impairments I-V Signatures of Shading Effects

46 PV module with 100 ohm shunt resistance Demonstration: Single PV module with external resistor

47 PV module with 2.5 ohm added series resistance

48 Troubleshooting example Anomalous slope in string I-V caused by single high-resistance module Current - A String 4B14 String 4B Voltage - V

49 String of Field-aged, Early TF Modules Array-as-sensor mode for viewing relative changes in curve shape

50 Topics PV Array Performance Verification I-V Curves, and How They re Measured The Solmetric PVA-600 PV Analyzer Test Process (example: commissioning) Live Demo of the PV Analyzer User Interface I-V Signatures of Electrical Impairments I-V Signatures of Shading Effects

51 Review of Bypass Diodes Purposes: Prevent damage and preserve performance under mismatch conditions, including non-uniform shading

52 What happens without bypass diodes? Thought experiment 360v + + Shading one cell reduces current in the entire string, and all cell voltages increase + Inverter dc input voltage 0.5v Shaded cell sees reverse voltage, breaks down, dissipates power as if it were a resistive load Cell and module are likely to be destroyed 0.52v 0v *Assume 10-module strings, 72 cell modules, no bypass diodes

53 PV Module with Bypass Diodes Typical 72-cell PV Module (bypass diodes shown) +

54 Bypass Diode Action Effect of shading one cell +

55 Which shading pattern is worse? +

56 Which soiling pattern is worse? +

57 I-V Curve of a Partially Shaded String Isc Multiple knees in the I-V curve mean multiple peaks in the P-V curve Inverter s job is track the highest peak Tricky when shading is changing rapidly Power Current Voltage Voc

58 Partially shaded residential array Measure the single string mounted along lower edge of roof

59 I-V Curve of the partially shaded string Single string mounted along lower edge of roof Approximately 40% reduction in string s output power

60 Effects of Particular Shading & Soiling Patterns

61 Shade 2 cells in the same cell-string Single module with 72 cells and 3 bypass diodes

62 Shade 2 cells in adjacent cell-strings Single module with 72 cells and 3 bypass diodes

63 Shadow of leafless tree branch Single module with 72 cells and 3 bypass diodes

64 Edge and Corner Soiling Common in low-tilt arrays Dirty Cleaning the top 90% of module area recovered 50% of the performance. Cleaning the bottom 10% recovered the rest. Clean

65 Conclusions Curve tracing is fast and automated Most complete performance description possible Independent measurement of each string s max power Instant comparison to predictions of built-in PV models Helps users Think like a PV array I V

66 Free I-V Curve Poster

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68 New Tools for PV Array Commissioning and Troubleshooting June 9, 2011 Paul Hernday Applications Engineer cell Bryan Bass Sales Engineer