When a solar inverter reduces output or displays messages such as LimByVar, Grid Overvoltage, or Power Derating, the message itself does not explain the cause. It indicates that the inverter has detected conditions that require it to limit export in order to stay within operating limits. Those conditions are shaped by how grid voltage behaves on the street, how voltage rises as solar export increases through the day, how the system is connected through its wiring, and how mandatory voltage-control and export control settings respond to those changes. Network export limits, phase imbalance, and inverter control modes such as Volt-Watt all influence how much power the system is allowed to deliver at any given moment. Inverter-related issues, including sensing accuracy, internal measurement behaviour, or firmware operation, can also contribute to output being reduced under certain conditions. Understanding why output is being limited requires looking at how the inverter, meter, and grid interact as a system, rather than treating the service message as a standalone fault.
High Street Voltage:
High grid voltage on the street is one of the most common reasons an inverter reduces output or limits export. The inverter continuously measures voltage at the point of connection to the utility grid, and when background voltage is already elevated, exporting additional power would push the system into Overvoltage or Grid Overvoltage conditions. To remain compliant, the inverter applies export control through its internal logic, resulting in reduced production, power curtailment, or service messages such as LimByVar. In these cases, the behaviour is driven by measured grid conditions at the meter, enforced through inverter firmware and voltage-control settings, rather than a simple inverter fault.
Midday Solar Congestion
Midday solar congestion develops when a large number of PV systems on the same street export power simultaneously, typically during clear conditions when solar production is highest. As export increases across multiple properties, cumulative current flowing back toward the utility grid causes progressive voltage rise along shared poles, transformers, and service lines. Each inverter measures voltage locally, not at the substation, so limiting can begin even when the broader network appears stable. When measured grid voltage approaches allowable thresholds, the inverter responds through Volt-Watt behaviour or other export control logic defined in its firmware, reducing output to prevent Grid Overvoltage. This is why power curtailment often appears consistently around the same time of day, clears in the afternoon, and repeats under similar conditions. The pattern reflects network congestion rather than an isolated inverter fault, and cannot be resolved without addressing how the system interacts with surrounding export and local grid capacity.
Service Cable Voltage Rise
Long or undersized service cables can significantly increase voltage rise between the meter, inverter, and the utility grid, even when street grid voltage appears acceptable. As solar production increases and current flows back toward the grid, resistance in the wiring, communication cables, MC4 heads, and connection points causes voltage to climb at the inverter terminals. The longer the cable run, or the smaller the conductor size, the more pronounced this effect becomes. In these cases, the inverter may detect Overvoltage or Grid Overvoltage conditions and apply export control or power curtailment, despite no obvious external fault. This behaviour is governed by inverter firmware, Standard Mode Settings, and grid industry standards, not by a failure of the solar panels themselves. Identifying this issue requires electricians to assess cable length, conductor sizing, terminations, and voltage behaviour under load, rather than relying on alarm messages or error codes alone.
Mandatory Inverter Voltage-Control Modes
In some systems, output is reduced because voltage-control modes have been configured into the inverter, not because voltage conditions strictly require them at all times. These controls are applied through inverter firmware and Standard Mode Settings, often during commissioning, network approval, upgrades, or later adjustments. Once set, they shape how the inverter responds to grid voltage, regardless of whether the underlying conditions still justify the limitation.
Controls such as Volt-Watt or export limits configured through the meter, Export Power Manager, or EPM setup can remain active long after network conditions have changed. When this happens, the inverter may begin power curtailment, reduced production, or display messages such as LimByVar or Power Derating even when street voltage appears stable. From the user’s perspective, this looks like unexplained loss of output, because the inverter is operating within imposed constraints rather than reacting to a live fault.
The key issue is that these settings are not visible from monitoring apps or error messages alone. Determining whether voltage-control modes are appropriately applied, overly conservative, or no longer aligned with current grid conditions requires reviewing how the inverter has been configured and how it behaves under real operating conditions, not just what it reports on screen.
Network Export Limits and Phase Imbalance
Network export limits can restrict solar production even when grid voltage appears normal and no obvious fault is present. These limits are applied by the network to manage capacity on the utility grid and are often enforced through the meter, export control settings, or devices such as Export Power Manager and EPM setup. When export limits are reached, the inverter reduces output through power curtailment, sometimes showing messages such as LimByVar, Grid Overvoltage, or Power Derating, even though the system itself is capable of generating more power.
Phase imbalance can create similar behaviour. On streets with mixed single-phase and three-phase PV systems, voltage can rise unevenly across phases. An inverter connected to the higher-voltage phase may begin throttling while others continue exporting normally. From the user’s perspective, this looks inconsistent or unexplained, because the limitation is driven by phase conditions rather than overall system performance. These constraints are enforced through inverter firmware, network rules, and industry standards, not by a failure of panels or internal parts.
Because export limits and phase imbalance are applied upstream of the inverter, they are not always visible through monitoring apps or alarm messages alone. Identifying whether throttling is being caused by network limits, phase behaviour, or configuration requires looking at how the inverter, meter, and grid interact under load.
Inverter Sensing, Firmware, or Internal Hardware Degradation
In some cases, reduced output is driven by how the inverter is measuring and interpreting conditions rather than by actual grid voltage on the utility grid. The inverter relies on internal sensing circuits, voltage references, current transformers, and control boards, all governed by firmware, to assess grid voltage, grid frequency, DC input, and OV-DC thresholds. If any part of that measurement chain degrades or fails, the inverter can misreport voltage and trigger power curtailment, export control, or limiting states such as LimByVar even when true Grid Overvoltage is not present.
Age, heat cycling, and electrical stress can affect internal parts such as voltage sensing components, DC bus measurement circuits, relay assemblies, or power stage electronics. As these components drift or deteriorate, the inverter may behave increasingly conservatively, logging alarm messages, alarm codes, or error codes related to voltage even under stable conditions. This can be compounded by firmware behaviour that responds aggressively to uncertain measurements, as well as issues in communication cables, RS485, CT cables, or other communication connections that influence how data is processed internally.
In these situations, the inverter is not simply reacting to the grid, it is reacting to its own degraded or unreliable measurements. Distinguishing between grid-driven behaviour and internal inverter degradation requires comparing inverter-reported values with independent measurements at the meter, rather than assuming the service message alone identifies the true cause.
