Photovoltaic system Monitoring

Monitoring and control of photovoltaic systems is essential for reliable functioning and maximum yield of any solar electric system. The simplest monitoring of an inverter can be performed by reading values on display - display (usually LCD) is part of almost each grid-connected inverter. Most important inverter and grid related parameters are available on LCD screen in such case. Values like PV array power, AC grid power, PV array current are usually available. For sophisticated monitoring and control purposes environmental data - like module temperature, ambient temperature, solar radiation, wind speed can also be data logged, stored and analysed later. Remote control and monitoring can be performed by various remote connections: analog modem, ISDN, GSM etc. The most common connection for local/remote control are USB (sometimes even RS232) for local monitoring, RS485 and powerline for inverter interconnection. For wireless connection Bluetooth and Wi-Fi are most common used.

Local monitoring

Most simple way to perform local monitoring is display available on inverter or on inverter control unit. Other possibilities of local monitoring includes monitoring by local PC via RS232 connection and/or remote display located in living room for example (connection between inverter and display is usually wireless). The following parameters can usually be monitored, datalogged and stored in inverter's memory or external data logger for particular time (up to 1 year usually). Sometimes additional sensor related units (external or internal) are also required:

Array voltage VDC V
Grid voltage VAC V
Array current IDC A
Grid current IAC A
Array power PDC W
Grid power PAC W

TABLE 1: Most common inverter/grid monitoring parameters

Module temperature Tmod °C
Ambient temperature Tamb °C
Global irradiance [1] G W/m2
Global irradiation [2] H J/m2
Wind speed v m/s

TABLE 2: Most common ambient monitoring parameters

Remote monitoring

Remote control and communication between inverters can be realized with wireless connection (bluetooth or Wi-Fi), trough RS485 interface or via grid (powerline connection) [3]. Distances up to 1200 m represents no problem, several tenth inverters can be connected in chain and monitored at the same time. For remote monitoring different ways of communication can be used: Ethernet, Internet, dial up access, GSM etc. System can send alerts and status messages to the control center or user. Alerts and system messages can be send by SMS service, GSM, fax machine etc.

Monitoring trough Internet, courtesy SMA

Remote control of SMA inverters trough Internet
(courtesy: SMA)

Data logging

Data can be stored in inverters memory or in external units (data loggers). Different solutions are available on the market. Some producers offer also additional memory increase or upgrade. Better data loggers offer monitoring functions (data logging) for various environmental and additional system related parameters what can give the user detailed overview about the whole system. Additional parameters that can be monitored are module- and ambient temperature, solar radiation, solar irradiation, wind speed (hybrid systems), in some cases also air pressure and air humidity (sophisticated electronic weather station) etc. Temperature sensors are usually PT100 or PT1000 sensors. Solar radiation is measured with reference solar cells (Si-mono), analog inputs of the control equipment are usually standard 4-20 mA or 0-10 V inputs. Digital inputs are also available and can be used for net-meter/control equipment interconnection.

Public displays

Public displays are widely used not only as public monitoring tool they are used as promotional or educational purposes as well. Communication between photovoltaic system and public display is usually realized via RS232 port, some producers offer also wireless connection. Most common display types are LCD displays, numbers can clearly be read from distances up to 40 m, depends on number sizes.

Public display, credit pvresources

Remote monitoring of PV array with public display
(credit: pvresources)


[1] Common term meaning solar irradiance is also solar power.
[2] The unit Wh/m2 (kWh/m2) is often used in technical practise in Europe. Sometimes also term insolation (incident solar radiation) is used. Please look for further information and additional symbols in suggested literature.
[2] Please note that different monitoring equipment and communication possibilities of different producers are not compatible. For system monitoring inverters and control equipment of the same producer must be used.

HW monitoring tools and data loggers

Public displays

Monitoring and telemetry tools

Remote monitoring portals

Sources ans Additional Information

IEEE 802.11, IEEE Standard for Information technology — Telecommunications and information exchange between systems — Local and metropolitan area networks — Specific requirements — Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications.
Wi-Fi Alliance, global non-profit organization with the goal of driving adoption of a single worldwide standard for high-speed wireless local area networking.
USB Implementers Forum, is a non-profit corporation founded by the group of companies that developed the Universal Serial Bus specification. The USB-IF was formed to provide a support organization and forum for the advancement and adoption of Universal Serial Bus technology.
Bluetooth, official Bluetooth® technology web site.
Lamert Bies's web site with detailed information about serial communication. Descriptions of RS485, RS422, RS232 ports included.