SolaX Grid Disconnection Fault — G99 Overvoltage Fix UK
Your SolaX inverter has disconnected from the grid. It may be showing an E012 voltage fault, a PLL Lost error, or simply dropping offline every sunny afternoon. In most cases this is not an inverter defect — the grid voltage at your property is exceeding the 253V safe limit, and the inverter is disconnecting because UK grid code requires it.
Grid overvoltage is the most common cause of repeated SolaX disconnections in the UK. We review your SolaX Cloud voltage data, identify the pattern, and recommend the right fix — export limitation, DNO report, or reactive power adjustment.
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6-step grid disconnection diagnosis
Work through these steps to understand why your SolaX inverter is disconnecting from the grid, whether it is a network issue or a configuration problem, and what to do about it.
Check SolaX Cloud for the fault code and voltage reading
Log into SolaX Cloud and check the fault history. The specific code tells you what the inverter detected:
If the voltage reading at disconnection was above 253V, the inverter disconnected because UK grid code requires it — the system is working correctly.
Identify the disconnection pattern from the event log
The pattern tells you the root cause. Check the SolaX Cloud event log covering at least the last 30 days:
Export the event log with timestamps — this data is exactly what a diagnostic engineer or your DNO needs to identify the root cause.
Understand the cause — this is usually a grid issue, not an inverter fault
SolaX X-Hybrid inverters comply with G98 and G99 UK grid codes. They are required to disconnect when grid voltage exceeds 253V or when frequency moves outside the safe range. This is a safety mechanism protecting the equipment and the network.
On UK distribution networks where multiple solar systems are connected to the same transformer, simultaneous export during peak generation pushes the local voltage upward. The houses furthest from the transformer see the highest voltage and are the first to trip. This is a network capacity issue — the solution is either export limitation on the inverter side or infrastructure reinforcement by the DNO.
Check if your system needs export limitation configured
If your SolaX system is rated above 3.68kW, it was installed under G99 regulations and may require export limitation. Export limitation restricts how much power the inverter sends to the grid, reducing your contribution to local overvoltage.
On the inverter, navigate to Settings → Advanced Settings → Export Control. If export control is not enabled and your DNO approval letter specifies an export limit, this must be configured. The inverter also needs a CT clamp or meter installed to measure export accurately.
Without correct export control, a G99 system may be non-compliant — the DNO can require disconnection, and you may lose Smart Export Guarantee payments.
Report to your DNO if voltage is persistently above 250V
If SolaX Cloud shows grid voltage regularly exceeding 250V during generation hours, contact your Distribution Network Operator. The DNO is responsible for maintaining voltage within the statutory range. They can adjust the transformer tap setting to lower voltage across the local network, or reinforce the infrastructure if needed.
Find your DNO by entering your postcode on the Energy Networks Association website. When reporting, provide the voltage readings and timestamps from SolaX Cloud. If your neighbours also have solar systems that are tripping, a joint complaint carries more weight with the DNO.
Book a diagnostic for configuration or reactive power adjustments
If grid disconnections continue despite correct export limitation, the inverter's reactive power settings or grid protection parameters may need adjusting within the G99-permitted range. These are installer-level settings that require technical knowledge to configure correctly.
STS can review your SolaX Cloud voltage data remotely, identify whether the issue is a network problem requiring DNO involvement or a configuration issue that can be resolved at the inverter, and recommend the appropriate fix. Remote diagnostic sessions start from £75.
Why grid disconnection faults are increasing on UK SolaX systems
Grid disconnection faults are becoming more frequent across the UK as solar installation density increases. The distribution networks in most residential areas were designed for one-way power delivery — from the transformer to the house. When multiple solar systems on the same network begin exporting simultaneously, power flows in the opposite direction and the voltage at the far end of the network rises. Once it exceeds 253V, every inverter on that section is required to disconnect.
Rural and suburban networks are the most affected. These networks tend to have higher impedance — longer cable runs from the transformer — which means voltage rises more for the same amount of export. A street with five or six solar systems can push the local voltage above the trip threshold on a clear summer afternoon, even if each system is relatively small. The houses furthest from the transformer will trip first and most frequently.
SolaX systems installed under G99 (above 3.68kW) should have export limitation configured to reduce their contribution to voltage rise. But many G99 systems were installed without export control enabled, or the CT clamp was never fitted, or the limit was set incorrectly. Correcting the export control configuration often reduces or eliminates the disconnection events without any network reinforcement needed. For systems where export limitation alone is not enough, the DNO needs to adjust the transformer tap or reinforce the local network.
SolaX grid disconnection fault codes
Grid voltage outside the 216V–253V safe range. Most commonly overvoltage above 253V during peak solar export. Inverter reconnects automatically when voltage drops.
Inverter lost synchronisation with grid frequency. Often occurs during grid instability after storms, outages, or rapid voltage fluctuations. Usually clears within minutes.
Inverter cannot measure grid voltage at all. Check AC isolators, consumer unit breakers, and wiring connections. If the mains supply is present, the AC cable or a relay inside the inverter may be faulty.
Internal relay switch malfunction. Can be caused by a poorly connected neutral line or three-phase imbalance on X3-Hybrid systems. May require inverter inspection or replacement.
Grid disconnection faults — common questions
A SolaX grid disconnection fault occurs when the inverter detects grid voltage above 253V, below 216V, or frequency outside the safe range. The inverter disconnects as required by UK grid codes G98 and G99. The most common cause is grid overvoltage — multiple solar systems on the same local network exporting simultaneously during sunny afternoons push the voltage above the threshold. This is a grid capacity issue, not an inverter defect. Other causes include power cuts, storm damage, loose AC connections, and missing export limitation on G99 systems.
If your SolaX inverter trips repeatedly on sunny afternoons, the most likely cause is grid overvoltage. When solar systems across your local network export at full power simultaneously, the distribution voltage rises. The houses furthest from the transformer experience the highest voltage and trip first. The inverter is doing exactly what it should — disconnecting when voltage exceeds 253V. Check SolaX Cloud for the voltage reading at disconnection. If it was above 253V, report this to your DNO and consider export limitation configuration to reduce your contribution to the voltage rise.
The voltage and frequency trip settings are governed by UK grid codes G98 and G99. They can only be adjusted within the ranges permitted by the grid code, and only by a qualified installer with advanced settings access. Raising the overvoltage threshold beyond the permitted range would make the system non-compliant and could result in the DNO requiring disconnection. The correct approach is to configure export limitation to reduce your system's contribution to local voltage rise, and to report the issue to your DNO so they can address the underlying network capacity.
G98 applies to SolaX systems rated at 3.68kW or below per phase. These are installed under a fit-and-inform process — the installer notifies the DNO within 28 days but no pre-approval is needed. G99 applies to systems above 3.68kW per phase and requires DNO approval before installation. G99 systems often have export limitation conditions attached. If a G99 system is installed without proper approval or without the required export limit configured, the DNO can require disconnection. Both standards define the same voltage and frequency protection thresholds.
The amount of lost generation depends on how frequently the inverter trips and how long it stays offline each time. A single trip during a brief voltage spike costs very little. An inverter that trips repeatedly throughout every sunny afternoon can lose 20 to 40 percent of its potential generation during those hours. SolaX Cloud records production data alongside fault events, so you can calculate the exact loss by comparing actual versus expected production. If the loss is significant, configuring export limitation or reporting to the DNO is the priority.
Grid tripping? We identify the cause remotely.
We review your SolaX Cloud voltage data and fault history to determine whether the issue is a network problem requiring DNO action, a missing export limit, or a configuration fix we can resolve remotely.