PV monitoring

Whatever the size and use of a PV installation, the main purpose of a monitoring system is to follow the PV-produced energy, assess PV system performance, detect drifts or malfunctions, and notify about all faults immediately. Monitoring architectures and requirements are presented in this section.

PV installations for commercial and industrial buildings

PV system monitoring

In PV installations for grid export, the monitoring system provides:

• Measurement of the produced PV energy and calculation of its economic benefit on a daily and monthly basis
• Performance assessment of the PV system (detecting a decrease in the performance ratio and identifying potential causes, e.g., temperature, dirt or dust accumulation on the PV panel surface, mismatch and wiring losses, inverter status and operation)

The monitoring architecture is based on a data-logger, mostly equipped with a RS232/485serial port to communicate with the inverters, using Modbus or a proprietary protocol. Data acquisition is based on a low-speed polling rate,every 10 minutes on average. Data may be stored locally in the data-logger for a short period of time, or pushed to an external server which store can data for years. The data-logger can also be equipped with auxiliary inputs, such as analogue inputs to monitor temperature irradiance sensors, digital input to monitor the status of an equipment, and/or pulse input to connect with an energy meter.

Once the data are collected locally, the system sends output data and alerts as soon as they are generated to a remote monitoring system, where cloud-based applications, analytics, or services can be provided in addition.

Fig. P31 – Monitoring system for commercial PV installations

Requirements for self-consumption

In the case of self-consumption, the produced PV energy is consumed by the building loads. The PV production excess (if any) is generally injected into the grid. To understand how the energy is used and how it can be optimized, Key Performance Indicators should be followed, such as:

• % use of PV production (self-consumption vs grid export)
• Self-consumption ratio
• Self-production ratio
• Trend analysis of PV production versus building consumption

The monitoring system should consolidate data from both PV production and building consumption. The monitoring system can be a building management or dedicated power management system, integrating PV production monitoring.

Utility scale power plants

Systems for utility-scale power plant, from 500 kWp upwards, are able to monitor the complete installation, from the string input to the point of connection to the grid.

These systems are based on a SCADA (Supervision Control And Data Acquisition) system, which enables multi-site monitoring, DC and AC measurements, remote control of motorized equipment, smart alarming, report generation, performance indication, and other capabilities such as in-depth analysis.

These systems also include other equipment to run the site more efficiently, such as a weather station (temperature, wind and rain gauges), irradiance sensors,a plant controller communicating with the grid operator, to adapt the production of the site to the grid variation (voltage, power factor) – and specific meters such as revenue grade meters, close the point of connection

These SCADA systems can be local and/or remote, with redundancy capabilities and high performance data processing.

This type of installation is mostly served by a service contract for operations and maintenance and, in many cases, with performance objectives, which can include production, performance ratio, or availability.

Fig. P32 – Example of a system for remote monitoring used in utility-scale power plants