PV monitoring: Difference between revisions
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Since the profitability of photovoltaic installations depends mainly on operational uptime, it is essential to ensure that they are permanently up and running. The best way of ensuring this is to install a monitoring system covering key equipments of the installation. This system should notify all faults immediately, be capable of detecting drifts in output, and possibly control equipment remotely. | |||
== Types of monitoring systems == | |||
Several types of monitoring systems are available for installations, depending mainly of the size of the installation. | |||
'''Systems for Residential up to commercial, 1 to 1000 kWp''', are able to monitor the inverters – status, measurements and alarms - and key electrical values related to the output of the installation. | |||
These systems are based on a data -logger, mostly equipped with a RS232/485 serial port to communicate with the inverters, using Modbus or a proprietary protocol. Data acquisition is based on low speed polling rate, every 10 minutes in average. Data may be stored locally in the data-logger, for free, but for a short period of time, or pushed to an external server which store the data over the years and deliver a front end, providing an annual service fee. In that case, the communication with the distant server can be or via GPRS, or via Ethernet | |||
The data-logger can also be equipped with auxiliary inputs, such as analogue inputs to monitor temperature or irradiance sensors, digital input to monitor the status of an equipment and/or pulse input to connect with an energy meter equipped with digital output. | |||
'''Systems for large commercial up to 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 enable multi site monitoring, DC & AC measurements, remote control of motorized equipments, smart alarming, generation of reports, performance indication and other capabilities such as in-depth analysis. | ||
These systems also include other equipment to run the site more efficiently, such as weather station (temperatures, wind rain gauge ), irradiance sensors, a plant controller - device which communicate 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 popint of connection | |||
These scada systems can be local and/or remote, with redundancy capabilities and high performance for data processing. | |||
This type of installation is mostly served by a Service contract for Operations & Maintenance and in many cases, with performance objectives which can be production, performance ratio or availability. | |||
== Monitoring systems == | |||
== | These systems may be autonomous or include remote monitoring, accessible from the "cloud". | ||
[[Image:Fig P18 GB.jpg|none]] | |||
'''''Fig. P30:''''' ''Example of an autonomous monitoring system mostly used in residential to commercial PV installations'' | |||
Once the data is collected locally, the system sends output data and alerts as soon as they are generated to a remote monitoring system capable of managing stand-by periods for maintenance work. This enables the installation to be monitored closely, which is essential where operators of photovoltaic installations are not necessarily the site occupants. | |||
[[Image:Fig P19 GB.jpg|none|821x488px]] | |||
'''''Fig. P19:''''' ''Example of a system for remote monitoring mostly used in utility scale power plants'' | |||
== Sensors == | |||
Sensors provide data to the monitoring systems and include: | Sensors provide data to the monitoring systems and include: | ||
*A sensor for measuring instantaneous luminous flux such as a pyranometer (heat flow sensor used to measure the quantity of solar energy in natural light (W/m<sup>2</sup>), see '''Fig. | *A sensor for measuring instantaneous luminous flux such as a pyranometer (heat flow sensor used to measure the quantity of solar energy in natural light (W/m<sup>2</sup>), see '''Fig. P32'''). This is the standard reference for the installation. It may be used to identify shifts over time and is recommended to all suppliers wishing to conduct comparative analyses and compile statistics for their installations. At least one sensor is needed at the location however, it is not uncommon for at least two to be installed: one in the global horizontal (GHoz.) position and one in the plan of the array (POA) assuming the system is installed at some angle other than horizontal. | ||
- | [[Image:Fig P20.jpg|none]] | ||
'''''Fig. P20:''''' ''Pyranometer - Kipp & Zonen'' | |||
*A temperature sensor – this is an important factor for photovoltaic power supply. This sensor either serves as an external probe, is attached to the back of a module or both. | |||
*A kilowatt hour meter - more often that not this meter is of a "revenue grade" <+/-2% tolerance. This is especially important for companies that engaged in power purchase agreements (PPA) which rely on accurate data for billing purposes.<!-- | |||
*A kilowatt hour meter - more often that not this meter is of a "revenue grade" <+/-2% tolerance. This is especially important for companies that engaged in power purchase agreements (PPA) which rely on accurate data for billing purposes. | --><p>In the United States of America, the owner of the photovoltaic system may often install their own revenue grade meter to bill the purchaser. At times, the purchaser may also install a meter to verify the output or demand the seller's meter to be calibrated regularly. In other markets it may be the case when selling power, only the kilowatt hour meter operated by the energy distributor purchasing the electricity may be used as a reference.</p><!-- | ||
--><p>The other meters fitted within an installation (in the inverter or next to the official meter) are only indicators with their own specific levels of accuracy. Variations of more than 10% may occur between the values given by an installation’s devices and that given by the official meter. However, these variations are not only due to different levels of accuracy. They are also caused by energy lost in the cables and safety devices downstream from the inverter.</p><!-- | |||
--><p>It is therefore important to use cables of minimal length and clearly identify:</p> | |||
** The location where the installation will be connected to the network | |||
** The locations where the energy distributor’s meters will be connected | |||
== | == Security of the installation == | ||
Since modules are expensive and in some cases openly accessible, sites need to be monitored by security such as: | Since modules are expensive and in some cases openly accessible, sites need to be monitored by security such as: | ||
| Line 62: | Line 71: | ||
*Active Personnel | *Active Personnel | ||
*Other electronic means | *Other electronic means | ||
(1) NB – although this type of surveillance is authorised for private sites, filming of public highways may be prohibited in the installed location. | |||
[[zh:光伏监控]] | [[zh:光伏监控]] | ||
Revision as of 12:28, 18 October 2013
Since the profitability of photovoltaic installations depends mainly on operational uptime, it is essential to ensure that they are permanently up and running. The best way of ensuring this is to install a monitoring system covering key equipments of the installation. This system should notify all faults immediately, be capable of detecting drifts in output, and possibly control equipment remotely.
Types of monitoring systems
Several types of monitoring systems are available for installations, depending mainly of the size of the installation.
Systems for Residential up to commercial, 1 to 1000 kWp, are able to monitor the inverters – status, measurements and alarms - and key electrical values related to the output of the installation.
These systems are based on a data -logger, mostly equipped with a RS232/485 serial port to communicate with the inverters, using Modbus or a proprietary protocol. Data acquisition is based on low speed polling rate, every 10 minutes in average. Data may be stored locally in the data-logger, for free, but for a short period of time, or pushed to an external server which store the data over the years and deliver a front end, providing an annual service fee. In that case, the communication with the distant server can be or via GPRS, or via Ethernet
The data-logger can also be equipped with auxiliary inputs, such as analogue inputs to monitor temperature or irradiance sensors, digital input to monitor the status of an equipment and/or pulse input to connect with an energy meter equipped with digital output.
Systems for large commercial up to 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 enable multi site monitoring, DC & AC measurements, remote control of motorized equipments, smart alarming, generation of reports, performance indication and other capabilities such as in-depth analysis.
These systems also include other equipment to run the site more efficiently, such as weather station (temperatures, wind rain gauge ), irradiance sensors, a plant controller - device which communicate 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 popint of connection
These scada systems can be local and/or remote, with redundancy capabilities and high performance for data processing.
This type of installation is mostly served by a Service contract for Operations & Maintenance and in many cases, with performance objectives which can be production, performance ratio or availability.
Monitoring systems
These systems may be autonomous or include remote monitoring, accessible from the "cloud".
Fig. P30: Example of an autonomous monitoring system mostly used in residential to commercial PV installations
Once the data is collected locally, the system sends output data and alerts as soon as they are generated to a remote monitoring system capable of managing stand-by periods for maintenance work. This enables the installation to be monitored closely, which is essential where operators of photovoltaic installations are not necessarily the site occupants.
Fig. P19: Example of a system for remote monitoring mostly used in utility scale power plants
Sensors
Sensors provide data to the monitoring systems and include:
- A sensor for measuring instantaneous luminous flux such as a pyranometer (heat flow sensor used to measure the quantity of solar energy in natural light (W/m2), see Fig. P32). This is the standard reference for the installation. It may be used to identify shifts over time and is recommended to all suppliers wishing to conduct comparative analyses and compile statistics for their installations. At least one sensor is needed at the location however, it is not uncommon for at least two to be installed: one in the global horizontal (GHoz.) position and one in the plan of the array (POA) assuming the system is installed at some angle other than horizontal.
Fig. P20: Pyranometer - Kipp & Zonen
- A temperature sensor – this is an important factor for photovoltaic power supply. This sensor either serves as an external probe, is attached to the back of a module or both.
- A kilowatt hour meter - more often that not this meter is of a "revenue grade" <+/-2% tolerance. This is especially important for companies that engaged in power purchase agreements (PPA) which rely on accurate data for billing purposes.
In the United States of America, the owner of the photovoltaic system may often install their own revenue grade meter to bill the purchaser. At times, the purchaser may also install a meter to verify the output or demand the seller's meter to be calibrated regularly. In other markets it may be the case when selling power, only the kilowatt hour meter operated by the energy distributor purchasing the electricity may be used as a reference.
The other meters fitted within an installation (in the inverter or next to the official meter) are only indicators with their own specific levels of accuracy. Variations of more than 10% may occur between the values given by an installation’s devices and that given by the official meter. However, these variations are not only due to different levels of accuracy. They are also caused by energy lost in the cables and safety devices downstream from the inverter.
It is therefore important to use cables of minimal length and clearly identify:
- The location where the installation will be connected to the network
- The locations where the energy distributor’s meters will be connected
Security of the installation
Since modules are expensive and in some cases openly accessible, sites need to be monitored by security such as:
- Cameras (1)
- Microwave
- Motion Sensors
- Active Personnel
- Other electronic means
(1) NB – although this type of surveillance is authorised for private sites, filming of public highways may be prohibited in the installed location.
