On-site inverter tests check that the installed unit is the certified one, that it starts with the grid parameters approved for the project and that it delivers the power its array allows. Before startup, the DC side and the AC connection are tested; at startup, the grid profile, the firmware version, the reactive power modes and the limits are verified; and with the plant exporting, the power per MPPT is compared with the expected one. Islanding detection is demonstrated by the manufacturer's IEC 62116 type test, not by a field test.
What is tested and why
A photovoltaic inverter arrives from the factory with routine tests and with type certificates for its model. What the factory cannot test is what depends on the project: the module array connected to each input, the grid parameters approved for that point of connection, the communications with the plant controller and the real power under the site’s sun. On-site tests cover that, and they are the basis for the plant tests that come later in front of the utility. The context of the inverter in the plant is in central vs. string inverters in solar plants.
Before startup: the DC side and the AC connection
The inverter is not started until its array has been tested: polarity of each string, open-circuit voltage within the inverter’s input range at the site’s minimum temperature, current per string and insulation resistance of the generator. A reversed string or an open-circuit voltage above the maximum input can damage the unit at the first startup. The DC-side string tests (polarity, Voc and Isc) are part of the plant’s commissioning sequence.
On the AC side, the connection to the panel or to the transformer station is verified, together with the phase sequence, the grounding and the tightness of terminals, and that the upstream protection has been tested.
At startup: the equipment and its parameters
| Check | What is verified | Why it matters |
|---|---|---|
| Model and firmware | That they match those on the product certificate | Type certificates are valid for one model and one version; the grid code usually asks for this for anti-islanding |
| Grid profile | Nominal voltage and frequency, disconnection windows, reconnection times | A profile from another country or the factory default makes the inverter trip for no reason or prevents it from tripping when it should |
| Reactive power | Control mode (power factor, fixed reactive power, voltage-dependent curves) and its setpoints | It must match what the utility requires and the plant controller’s strategy |
| Active power limits | Export limit, ramps, remote setpoints | Avoids exceeding the approved capacity and lets the plant controller command |
| Anti-islanding | That the function is enabled with the approved settings | The function’s test is a type test, but its enabling is verified on each unit |
| Insulation monitoring | That the function is active and its alarm reaches the monitoring system | It is the first alarm of an earth fault in the array |
Anti-islanding: type test vs. on-site verification. IEC 62116 is the test procedure for the islanding prevention measures of grid-connected photovoltaic inverters: it is done in a laboratory, with tuned resonant loads, and is recorded in the manufacturer’s certificate. It is not a field test. When the anti-islanding is in the protection at the point of connection, that protection is tested by injection, against the local grid code and the utility’s requirements.
Grid functions. For plants connected to the transmission and sub-transmission grid, the local grid code sets requirements for reactive power capability, voltage and frequency control, ramps and operation through voltage dips. Those requirements are demonstrated at plant level, with the plant controller, in the tests in front of the utility. What is verified on each inverter is that it has enabled the modes and the settings that the controller is going to use. The design and the settings are adapted to the local code and to the requirements the utility gives us.
Communications
Each inverter is integrated into the monitoring system and the plant controller, almost always over Modbus TCP or RTU, directly or through a data logger; the test of that link is in integration of inverters into SCADA. The register map (address, data type, scale and units) is verified, along with whether the measurements read match those of the inverter. It is also verified that the active and reactive power setpoints are executed, and that a loss of communication leaves the inverter in the state defined in the design. See solar plant communications, which also explains the role of the plant controller.
With the plant exporting: power per inverter and per MPPT
With stable sun, the power of each inverter is compared with the expected one for the irradiance and temperature of the moment, and that of each MPPT with identical inputs. Plane-of-array irradiance and temperature come from the weather station, per IEC 61724-1:2021. An input that delivers less than its peers points to an open string, a blown fuse, a damaged module or a wiring error; it is confirmed with the I-V curve (PV string I-V curve tracing) and the thermographic survey of the array.
At this stage the thermography of the AC connections under load is also done, and the events and alarms of the first operating period are logged; they often reveal settings that need correcting.
What the test leaves behind
- Record of the model, serial number and firmware version of each inverter.
- Export or capture of the loaded grid parameters, compared with the approved ones.
- Verified communication map.
- Power per inverter and per MPPT at startup, with the irradiance and temperature conditions.
- List of alarms and their closure.
We help you plan and run your inverter tests
Our team performs the commissioning of solar plants, in Colombia, or elsewhere on request, or supports your local crew online. It includes the DC array tests before startup (I-V curve, insulation resistance, polarity, Voc and Isc), thermography of modules from the ground and with a drone, and of the connections under load. It also includes the protection at the point of connection and the integration with control and communications. For inverter startup and grid functions, we help you plan the verifications together with the manufacturer. Depending on your plant, we recommend which tests to run and with what equipment, and we include it in the quote: that way you run the tests you really need, without paying for extra ones. Write to us through contact.
Related guides
- Solar plant commissioning tests before energization
- Solar plant testing by stage: from FAT to O&M
- Solar plant communications
- PV string I-V curve tracing
References
- IEC 62116, Utility-interconnected photovoltaic inverters – Test procedure of islanding prevention measures.
- IEC 61724-1:2021, Photovoltaic system performance – Part 1: Monitoring.
- IEC 62446-1:2016+AMD1:2018, commissioning tests of grid-connected photovoltaic systems.
Frequently asked questions
Is the inverter's anti-islanding tested on site?
Inverter islanding detection is demonstrated by the IEC 62116 type test, which a laboratory performs and which is recorded in the manufacturer's certificate. On site, you verify that the model and firmware match those on the certificate and that the function is enabled with the approved settings. If the project's anti-islanding sits in the protection at the point of connection, that protection is tested by injection according to the local grid code and the utility's test requirements.
Why does one inverter deliver less power than its neighbors under the same sun?
The most frequent causes are in its array: an open string or a blown fuse, an MPPT with fewer modules, soiling or localized shading, or a power limit set wrongly. The power and current of each MPPT are compared with those of identical inverters, and confirmed with the I-V curve of the suspect strings and a thermographic survey of the array.
Who sets the inverter's grid parameters?
The parameters are fixed by the interconnection study and by what the utility approves, and they are loaded by the manufacturer or the integrator with their software. At commissioning, you verify that the loaded ones match the approved ones and keep a record for each inverter, because a firmware update or a later change can alter them.