The test process of the photovoltaic system to confirm that the photovoltaic system outputs power and interacts with the grid correctly is called system trial operation. Before the installer delivers the photovoltaic system to the user, he should test and inspect the photovoltaic system to ensure that the system complies with national and local standards and specifications, and that all components can be installed safely and that all components work normally as expected. Many power grid companies have established rules or procedures that must be followed during system trial operation. In some cases, power grid companies may wish to conduct trial operation inspections. These requirements should have been discussed with the grid company when obtaining the grid connection permit.
The inspection, testing, and commissioning processes and the training requirements for personnel performing these processes shall comply with local codes and regulations. These processes are outlined below.
1. Final inspection of system installation
Before the PV system is commissioned, a final inspection of the system should be carried out to ensure that the system test is ready. If any problems are found, they should be notified before any part of the system is connected and/or tested. The equipment and installation engineering should be inspected to ensure:
·The equipment and components are not damaged.
·The system complies with the design documents, and all devices are correctly connected in accordance with the wiring diagram.
·The equipment and components comply with local safety standards and are suitable for grid interactive photovoltaic systems.
·The site is clean and tidy, and there is no danger to the general public.
· Set up signals and warning signs in accordance with local regulations.
The array and array frame should be checked to ensure correct installation and suitability for the site conditions. This includes checking whether the frame is solid, whether the rating is reasonably calibrated according to local wind and snow conditions, and whether all roof perforations are properly sealed and weatherproof.
The inspection of the inverter should be preceded by the trial operation to ensure that the inverter is installed safely, and all electrical access and outgoing connections of the inverter are well and fastened. The installation location of the inverter should also be considered during the inspection to ensure that the location is easy to approach during maintenance and emergency disconnection, is appropriately weatherproof, and has adequate ventilation conditions. Weather resistance can be verified by checking the IP or NEMA ratings of the inverter. The ventilation conditions should also be checked according to the manufacturer’s recommendations.
The wiring and electrical components should also be checked to ensure that all wiring and components have been safely installed and adequate protection is provided to prevent mechanical and environmental damage. It should also be ensured that it is fully operational, the capacity is correctly set, and that it is installed in accordance with standard specifications. All disconnecting devices/isolating devices must be easily accessible in emergency situations.
The inspection process should be put on record, and a copy of the document should be left to the user as a record.
After visual inspection of the system, it should be tested in accordance with current national standards. National standards may require installers to ensure that the following requirements have been met before system testing:
· There is no voltage at the output terminal of the photovoltaic array (and the output terminal of each photovoltaic module string in the case of multi-module strings). This can be achieved by disconnecting or unplugging one of the photovoltaic module interconnection devices.
· All fuses have been removed, and all circuit breakers are in the “off” position.
• The AC and DC main circuit breakers/isolating devices are in the “off” position; local codes may also require these devices to be labeled or locked during testing.
· All components (such as inverters) are off.
After the safety requirements of local regulations have been implemented, testing can be performed. Each element and each isolation device are closed separately, starting from the array and ending with the load (such as household appliances). Perform tests in this order to ensure safety; this reduces the risk of danger and equipment damage. In each step, the system parameters are measured by using meters and displays on different components (such as the display screen of the inverter will display important data about the system) to complete the system test. If the system starts to work outside the expected parameters at any stage, the electrical engineer must identify the problem and solve it before continuing the test. Usually test parameters include:
· Continuity between adjacent components of the system.
·The resistance of the cable insulation.
·The measured value of the open circuit voltage of the photovoltaic array and the module string (the open circuit voltage of the same module string is very different or the open circuit voltage is very different from the expected value, which indicates that there is a problem).
·The measured value of the short-circuit current of the photovoltaic array and module string (dangerous, see the column below).
·The measured value of the voltage drop across the fuse of the component string.
· Polarity inspection of installed components.
·System grounding test, usually including loop impedance test or ground electrode test, the latter requires a grounding tester.
3. Trial run
The trial operation is the first time that a complete system is closed and power is sent to the grid. As mentioned many times, this process generally involves a large number of detailed requirements of national standards and specifications, and the electrical engineer who implements the trial operation of the photovoltaic system should be very familiar with this. The column below highlights the necessary post-commissioning tests to ensure that the system interacts with the grid and operates as expected. In accordance with local standards, disconnect and reconnect the photovoltaic system and the grid, this test is particularly important. This requires ensuring that islanding does not occur.
4. System documentation
Upon completion of the installation, a system manual containing system information should be provided to the owner. Local regulations usually specify the documents that should be submitted; general guidelines are given below:
·List of equipment provided: The system manual should include a complete list of all installed components, including photovoltaic modules, inverters, photovoltaic array frames, photovoltaic combiner boxes, string isolation devices, fuses or circuit breakers, and DC And AC main circuit breaker/isolation device. The list should include the number of equipment used.
·System diagram: Basic circuit diagram and wiring diagram should be included in the manual. Building structure drawings or site plans showing the main components are also useful.
·System performance estimation: The manual should include the expected value of system output calculated by the designer. It can also include information on local financial incentives and what it means to the system from the perspective of revenue and/or electricity savings. There is another important point that needs to be emphasized. This is only an estimate, and it is normal to change slightly every year.
·Operation instructions for the system and its components: The manual should include an overview of the system, the functions of the main components, and how the system operates. Any information important to a given system should be included in the manual. It is important to explain to the owner that the system will shut down when the grid is out of power (that is, when there is no available power from the grid).
· Shutdown and isolation procedures for emergency and maintenance situations: The manual should include procedures for maintenance and emergency situations. Depending on the size of the system, the maintenance process may not need to shut down the system as a whole.
·Maintenance process and schedule: The maintenance requirements information of the grid-connected photovoltaic system should be used in conjunction with the system manual.
·Installation and trial operation records: These records should be signed and included in the system manual.
·System monitoring: The manual should have a section to provide system owners with suggestions on how to monitor the system to ensure that the system operates correctly. Many inverters already have monitoring capabilities. If the inverter includes these features, instructions on how to use them should be provided. If a separate monitoring unit is provided along with the system, the manual should include the operation information of the monitoring unit.
·Quality Assurance Information: Grid-connected photovoltaic system is connected by system installers to separate products into a system. There are 4 quality assurance methods for this type of system:
1) Product warranty covering defects in the production process.
2) Product warranty related to long-term output performance.
3) System warranty related to the long-term reasonable work of the installed system.
4) The power performance quality assurance related to the grid-connected photovoltaic system for a period of time (typically 1 year) guarantees the output power.
The first two warranty methods are the responsibility of the equipment manufacturer, but if the system owner requests a warranty claim, you can contact the installer for help. The latter two warranty methods are provided by the system installation company. All quality assurance details should be included in the system manual.
·Documents and manuals of equipment manufacturers: All product manuals provided by different manufacturers should be included in the system manual. Examples include inverter manuals, photovoltaic module data sheets and technical information on balance of systems (BOS) equipment.