New Tools for PV Array Commissioning and Troubleshooting

Transcription

1 New Tools for PV Array Commissioning and Troubleshooting Solmetric PVA-600 Megger MIT430 Paul Hernday Applications Engineer cell April 5, 2012 Audio is available by telephone or your computer

2 Solmetric Solutions

3 Solar PV Installation Life Cycle Sales Call Preliminary Site survey Preliminary design Proposal Contract Detailed Site Survey Final Design Installation Checkout Startup Performance Verification Performance Monitoring Service

4 Topics I-V curve tracing and PV performance verification Introduction to I-V curves The Solmetric PVA-600 PV Analyzer Demo of the PV Analyzer user interface Features of the new PV Analyzer software Commissioning & troubleshooting PV array performance Meg testing with the Megger MIT430

5 Array Performance Test Methods For Startup/Commissioning/Checkups/Service Alarms 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

6 I-V Curve Tracing is a PV Best Practice I-V curve tracing is the most informative measurement that can be performed on a PV module or array. David King DK Solar Works Developer of the Sandia PV Array Model at Sandia National Labs SolarPro, Aug/Sep 2011 I often tell students in my classes to learn to think like a PV array. Thinking like a PV array requires understanding the I-V curve and how it changes based on ambient conditions and array problems. An I-V curve tracer is the best way to gain an understanding of these changes, since it provides a graphical representation of the array operating characteristics. Bill Brooks Brooks Engineering SolarPro, Aug/Sep 2011

7 Benefits of I-V Curve Performance Testing Commissioning New PV Systems Fast a single electrical connection & a single measurement Most complete test method 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 Keep arrays producing maximum energy

8 Solmetric PV Analyzer Users EPC organizations System Integrators Electrical contractors Module Manufacturers I Consulting Engineers Inverter Manufacturers V O&M Companies Technical colleges IBEW Training Centers Training Organizations

9 Topics I-V curve tracing and PV performance verification Introduction to I-V curves The Solmetric PVA-600 PV Analyzer Demo of the PV Analyzer user interface Features of the new PV Analyzer software Commissioning & troubleshooting PV array performance Meg testing with the Megger MIT430

10 Incoming Photon Solar Cell 1 3 Top layer Fingers 1 Charge generation 2 2 Charge separation Bottom layer 3 Charge collection 3 Backside Ideally, the same current flows through series cells. In practice, any cell can be a bottleneck. A 12-module string may have 12 x 72 = 864 cells in series.

11 What is an I-V curve and how is it measured? Adjustable Load Measure voltage Measure current Built-in PV models mean user can instantly check performance against expectations for the existing irradiance and temperature. Current Voltage Load can be Resistive Capacitive Electronic

12 I-V and P-V* Curves Expect this shape for healthy cells, modules, strings, arrays Isc Imp I-V curve Pmax Current P-V curve Power Voltage Vmp Voc *P-V curve is calculated from the measured I-V curve

13 Stacking PV Modules into Arrays I Current Parallel I-V building Series Total (net) I-V curve blocks V Voltage This building block analogy is useful in troubleshooting arrays

14 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 Conventional measurements do not reveal many of these effects.

15 Topics I-V curve tracing and PV performance verification Introduction to I-V curves The Solmetric PVA-600 PV Analyzer Demo of the PV Analyzer user interface Features of the new PV Analyzer software Commissioning & troubleshooting PV array performance Meg testing with the Megger MIT430

16 Solmetric PVA-600 PV Analyzer Complete performance measurement up to 600V, 20A Comparison to built-in models Wireless interface to your PC String measurement showing I-V and P-V curves, and comparison of I-V curve with model (5 dots).

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

18 Example Measurement Setup Courtesy of Chevron Energy Solutions 2011

19 PVA-600 Block Diagram (simplified) Battery charging connector Controller & Wireless C (1 of 3) V sense PV Test Leads I sense Control button with LED indicator NEMA 4X FG Enclosure Capacitive load method (3 capacitor values, auto-selected) Electrically isolated. Ground lead is not required Protection for over-voltage, -current, -temperature, & reverse polarity

20 Wireless Sensor Kit Irradiance & temperature sensors Irradiance transmitter. K-type thermocouple Omega Part # 5SRTC-GG-K Receiver (USB) Temperature transmitter

21 Comparing PVA measurement with resistive load method Resistive load Resistive load Switch

22 Data points from the resistive load method Method: Clear sky, solar noon. Quickly alternate the two methods. New resistance at each load point.

23 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 Less reliable results for amorphous silicon technologies 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.

24 Topics I-V curve tracing and PV performance verification Introduction to I-V curves The Solmetric PVA-600 PV Analyzer Demo of the PV Analyzer user interface Features of the new PV Analyzer software Commissioning & troubleshooting PV array performance Meg testing with the Megger MIT430

25 Topics I-V curve tracing and PV performance verification Introduction to I-V curves The Solmetric PVA-600 PV Analyzer Demo of the PV Analyzer user interface Features of the new PV Analyzer software Commissioning & troubleshooting PV array performance Meg testing with the Megger MIT430

26 Features of the new PVA software Easy model setup -New Project Wizard -Site information from the web Easy data management -Database replaces existing folder tree -Array Navigator graphical interface (touch to save or recall data) -Outputs data in the traditional csv format (compatible with Data Analysis Tool) Translation to STC (built in) History tab -Shows tabular values for the last 20 measurements Archiving of Meg Test data -Saves manually entered meg test data to the new database (NEW - Solmetric now offers the Megger MIT-430 Insulation Tester)

27 Traces tab

28 System name & path screen

29 Performance model screen

30 Site info screen

31 Roof Measurement Tool

32 Latitude manual entry

33 Longitude manual entry

34 Array Navigator screen

35 Add inverter screen

36 Array Navigator screen

37 Saving a meg test result

38 Meg Test tab

39 Topics I-V curve tracing and PV performance verification Introduction to I-V curves The Solmetric PVA-600 PV Analyzer Demo of the PV Analyzer user interface Features of the new PV Analyzer software Commissioning & troubleshooting PV arrays Meg testing with the Megger MIT430

40 Example Measurement Setup

41 I-V Measurement Setup Example: Measuring strings at a combiner box Attach the thermocouple well away from module edges, using polyimide (Kapton) tape for best mechanical properties at high temperatures.

42 Test Process Example: Measuring strings at a combiner box Hardware setup (do once at each combiner box): 1. Move the sensors (if necessary to get wireless range) 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 seconds, typically

43 Example Measurement Setup 860kW 7-inverter system Open the DC disconnect for the sub-array you want to test. Courtesy of Portland Habilitation Center and Dynalectric Oregon

44 Example Measurement Setup Combiner boxes for one inverter Locate the combiner box Courtesy of Portland Habilitation Center and Dynalectric Oregon

45 Example Measurement Setup Combiner box wiring With a clamp-meter, verify that the load has been disconnected. Then lift all of the fuses. Courtesy of Portland Habilitation Center and Dynalectric Oregon

46 Example Measurement Setup Insert a single fuse to test the corresponding string Clip the PV Analyzer to the buss bars. Push down one fuse at a time and make I-V curve measurements. View and save results. Courtesy of Portland Habilitation Center and Dynalectric Oregon

47 How data is exported Created when you install the PVA PC software This format makes it easy to locate particular data. It also allows automating the analysis of large amounts of data. Identify non-conforming strings Generate convincing charts for your commissioning report

48 Demo of I-V Data Analysis Tool

49 Displays Generated by the I-V Data Analysis Tool* Current (Amps) Voltage (Volts) Frequency *Optional, MS Excel-based tool, $ Pmax (Watts)

50 Recommended Sky Conditions For Array Performance Testing 800 W/m 2 Clear sky (for high, stable irradiance) Height of I-V curve varies directly with irradiance Shape of I-V curve changes at low irradiance Translation to STC is much less accurate from low light conditions 4 hour window centered on solar noon* Avoids low-light, spectral, and angle of incidence issues Low/No wind (for more consistent module temperature) Width of I-V curve varies inversely with temperature Temperature is not uniform across an array under any conditions Inconsistent conditions (clouds, wind) cause more variation in PV measurement results for any test method or meter, making strings look less consistent and making it harder to spot performance issues. *Solar Noon Calculator:

51 Problem Sky Conditions

52 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 Conventional measurements do not reveal many of these effects.

53 Useful diagnostics Fill Factor, Current Ratio, Voltage Ratio Isc Imp Current ratio Imp/Isc Max Power Point Current Voltage ratio Vmp/Voc Voltage Vmp Voc Fill Factor = Imp x Vmp (watts) Isc x Voc (watts) = asi: xsi: GaAs:

54 String of Field-aged, Early TF Modules Degraded fill factor, lower output power Array-as-sensor mode for viewing relative changes in curve shape

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

56 Example of a series resistance failure inside a module J-box Probably failure mode: Heat cycling bond degradation resistive heating

57 Dropped Cell String Shorted bypass diode, or Mismatch causing diode to turn on when current starts flowing

58 I-V Curve of a Partially Shaded String Multiple knees multiple power peaks Peaks evolve as conditions change Inverter tries to find and track the highest peak Isc Power Current Voltage Voc

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

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

61 Shading one cell string drops 1/3 of PV module voltage and power Shade 2 cells in the same cell-string Single module with 72 cells and 3 bypass diodes

62 The same amount of shade, oriented differently, drops 2/3 of PV module voltage and power. Shade 2 cells in adjacent cell-strings Single module with 72 cells and 3 bypass diodes

63 IR signature of bypassed cell string Cardboard shading a cell Measured using the FLIR i7 infrared camera Image C 45 C

64 What is the PV Analyzer all about? Testing PV array performance faster and better Single measurement for each string Most complete performance measurement possible Independent max power measurement for each string Built-in PV models give instant performance check Don t need to bring inverter online Automated data analysis I Teaches us to think like a PV array V Next topic: Insulation resistance testing

65 Topics I-V curve tracing and PV performance verification Introduction to I-V curves The Solmetric PVA-600 PV Analyzer Demo of the PV Analyzer user interface Features of the new PV Analyzer software Commissioning & troubleshooting PV arraysrays Meg testing with the Megger MIT430

66 Insulation Resistance Testing of PV Arrays Where are we? Best practice is to test all systems during commissioning and maintenance Today, meg testing is not done on all commercial systems, and it is less common in residential systems. Source circuits are often tested in aggregate Individual strings are tested only if aggregate resistance is low Methods for subarray test are not standardized or widely understood Best reference is the re-wrenches blog (Home Power Magazine) Trend is toward specifying meg testing for commercial systems Insulation problems will be much more common as PV systems age

67 Meg Testing at the Subarray Level Preparation: Open the DC Disconnect Lift string fuses Lift negative feeder cable(s) Lift Lift Lift Example assumes a negative-grounded array Combiner box

68 Meg Testing at the String Level Preparation: Open the DC Disconnect Lift string fuses Lift negative source cable Lift Lift Lift Example assumes a negative-grounded array

69 5-Minute PV Analyzer Training Videos

70 Free I-V Curve Poster

71 SolarPro Magazine, Aug/Sep 2011

72 New Tools for PV Array Commissioning and Troubleshooting April 5, 2012 Paul Hernday Applications Engineer cell