Photovoltaic (PV) / Solar String Monitors Information
Photovoltaic (PV) / solar string monitors perform in-situ diagnostics of strings or sub-arrays in a PV or solar power system. PV string monitors collect current, voltage, or power levels from a string or small group of strings and transmit this information to a monitoring system. Software analysis of the data can identify errors that cause insufficient output from the string. Solar string monitors are instrumental in boosting efficiency and troubleshooting PV and solar power systems.
A common system configuration for PV string monitors is to have multiple current and voltage measuring modules, each capable of measuring the output from multiple strings. A communications module collects the measured values and sends them to a higher level controller via a communications interface, such as RS-485.
Some PV string monitors combine the functions of current measurement and error reporting in one instrument. In this arrangement, an analog current signal corresponding to the string current is converted by a microcontroller into a digital value. This current value is analyzed according to an algorithm to determine whether the string is operating normally. String status is output by communication signal or visual display.
PV string monitors indicate irregular operating condition in the solar string, such as:
Backfed (negative) current. This can be caused by ground or line faults, partial shadings, PV module degradation, or other conditions in which the electrical characteristics of one or more PV modules are significantly different from those of other PV modules in the string.
Zero current. This can be a result of blown fuse or other open circuit fault, or environmental conditions such as negligible irradiance during nighttime.
- Type of measurement - the technology used to measure current from the PV string, for example DC shunt or Hall effect
- DC shunts offer current measurements of higher accuracy that are not affected by variations in temperature.
- Hall effect sensors allow contact-free measurement with no interruption of the current-carrying cable.
- Number of inputs - the number of PV strings that can be monitored
- Rated current - the current from each PV string that can be handled
- Rated voltage - the voltage of the PV string that can be monitored
- Digital inputs - receive signals from other monitoring equipment such as surge protection modules
- Communications interface - the link over which data is sent, for example RS-485 Modbus or Ethernet
- Built-in LCD display or LED indicators to provide quick diagnostic visualization
- Temperature monitoring of PV panels
- Overvoltage monitoring of PV strings