Getting Started
1-4
I-V Measurement Unit cannot be turned on .................................................................................................... 5-96
Thermal fuse ................................................................................................................................................... 5-96
6 MEASURING IRRADIANCE, TEMPERATURE, AND TILT ................................................................... 6-97
INTRODUCTION .................................................................................................................................................... 6-97
MEASURING IRRADIANCE WITH SOLSENSOR ....................................................................................................... 6-99
SolSensor irradiance sensor ............................................................................................................................ 6-99
Preliminary vs Effective Irradiance ................................................................................................................ 6-99
SolSensor Precautions ..................................................................................................................................... 6-99
Protecting the Irradiance Sensor Element ................................................................................................... 6-99
Cleaning the Irradiance Sensor ................................................................................................................... 6-99
Orienting and mounting the irradiance sensor ................................................................................................ 6-99
Albedo effects ............................................................................................................................................... 6-100
Diffuse light .................................................................................................................................................. 6-100
DETERMINING IRRADIANCE FROM THE MEASURED I-V CURVE ......................................................................... 6-101
ENTERING IRRADIANCE MANUALLY .................................................................................................................. 6-102
MEASURING PV MODULE BACKSIDE TEMPERATURE WITH A THERMOCOUPLE ................................................. 6-102
Selecting a thermocouple wire gauge ........................................................................................................... 6-103
Selecting a thermocouple tip ......................................................................................................................... 6-103
Selecting a tape for thermocouple attachment .............................................................................................. 6-103
Attaching the thermocouple to the module backside .................................................................................... 6-104
Choosing a location to mount the thermocouple on the module or array...................................................... 6-104
MEASURING PV MODULE TEMPERATURE WITH AN INFRARED THERMOMETER ................................................... 6-104
DETERMINING CELL TEMPERATURE FROM THE MEASURED I-V CURVE ............................................................ 6-105
USING SMARTTEMP TO MEASURE CELL TEMPERATURE .................................................................................... 6-106
7 INTERPRETING MEASURED I-V CURVES ............................................................................................ 7-107
INTRODUCTION .................................................................................................................................................. 7-107
INPUTS TO THE PV MODEL ................................................................................................................................. 7-107
I-V CURVE TERMINOLOGY ................................................................................................................................ 7-108
Performance Factor ....................................................................................................................................... 7-108
Fill Factor ...................................................................................................................................................... 7-108
THE SHAPE OF A NORMAL I-V CURVE ............................................................................................................... 7-109
INTERPRETING I-V CURVES ............................................................................................................................... 7-110
1. NOTCHES OR STEPS ........................................................................................................................................ 7-112
Array Is Partially Shaded, or non-uniform soiling or debris is present ......................................................... 7-114
PV Cells Are Damaged ................................................................................................................................. 7-114
2. LOW CURRENT ............................................................................................................................................... 7-114
Uniform soiling ............................................................................................................................................. 7-115
Strip shade .................................................................................................................................................... 7-115
Dirt dam ........................................................................................................................................................ 7-115
Module Degradation ..................................................................................................................................... 7-115
Incorrect PV Module Is Selected for the PV Model ..................................................................................... 7-115
Number of PV Strings in Parallel Is Not Entered Correctly in the Model .................................................... 7-115
Irradiance Changed Between Irradiance and I-V Measurements .................................................................. 7-115
Irradiance Sensor Is Not Oriented in the Plane of Array .............................................................................. 7-116
Albedo Effects (reflection) ........................................................................................................................... 7-116
Manual Irradiance Sensor Is Not Accurate ................................................................................................... 7-116
3. LOW VOLTAGE ............................................................................................................................................... 7-117
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