Solar inverter grid overvoltage
Your solar system is disconnecting on sunny days — especially in summer — and the event log shows a grid overvoltage or frequency fault. This is one of the most common UK solar problems. It is caused by the grid voltage running too high when everyone is generating simultaneously, and your inverter correctly tripping for safety.
The good news: this is not a problem with your system. It is a network operator problem. There are steps you can take to reduce nuisance disconnects, and you can push your DNO to fix the underlying infrastructure.
A remote diagnostic session reviews your voltage history, confirms overvoltage as the cause, and recommends specific settings adjustments (Volt-Watt response, export limiting) that can reduce nuisance disconnects in your specific situation.
Book a Remote Diagnostic — from £75 → What's includedUnderstanding UK grid voltage
Grid voltage varies throughout the day and year. Your inverter disconnects if it detects dangerously high voltage.
The UK electrical system is designed to operate at 230V AC. This is the standard three-phase voltage used in UK homes.
This is ±10% tolerance. Utilities are required to keep voltage within these statutory limits. Outside this range, equipment can be damaged.
In most UK areas, grid voltage sits in the 235–245V range during normal daytime hours. In summer with high solar generation, it often rises to 240–250V.
When many neighbours are generating simultaneously and the grid is weak (rural areas, long cable runs), voltage can peak at 245–253V or even higher. This is when disconnects happen.
Most inverters are programmed to disconnect if grid voltage exceeds approximately 253V for more than a few seconds. This is a safety mechanism to protect the grid and connected equipment.
In rural and semi-rural areas, the grid connection is typically a long cable run. When many solar systems are exporting simultaneously (afternoon sun), they feed power into a thin cable, raising the voltage at that location. This is Ohm's law: V = I × R.
Key insight: Grid overvoltage is not your system's fault. It is a network operator problem. When too many generators (solar systems) export power into a weak grid connection, the voltage rises. The inverter disconnect is correct and protective. The solution is for the DNO to upgrade the network — but you can reduce nuisance disconnects with settings adjustments.
What causes grid overvoltage in your area
Rural or semi-rural areas often have long cable runs from the substation. The cable resistance is significant. When many solar systems export power simultaneously, the voltage rise is pronounced (Ohm's law: V=IR).
Urban areas with shorter, thicker cables rarely have this problem.
If your street has many solar systems, they all export power simultaneously at peak generation (midday). On a weak connection, this collective export causes voltage to spike.
This is especially pronounced in affluent suburbs and rural communities where solar adoption is high.
Most UK DNOs are not yet actively managing voltage to accommodate high solar penetration. They rely on reactive measures (customer complaints) rather than proactive upgrades. This is changing, but slowly.
Occasionally, a faulty transformer on your local substation can cause chronic overvoltage. If all neighbours report high voltage consistently, escalate to your DNO.
On an afternoon with strong sun, many households have air conditioning or heating off (good weather). Demand is low. Solar export is high. Result: significant voltage rise.
The problem is seasonal and time-dependent.
Step-by-step diagnostic
Follow these steps to confirm grid overvoltage is the cause of your disconnects.
Open your inverter portal and find the event log or alarm log. Search for entries containing 'overvoltage', 'over voltage', 'OVP', 'grid fault', 'frequency', or 'disconnect'. If you see many overvoltage or grid fault entries during sunny afternoons, this confirms the problem.
Most inverter portals show a voltage graph in the monitoring section. Look for a sunny day from the past week and examine the voltage trace over 24 hours.
Check for peaks above 250V, especially between 11:00–15:00. If you consistently see 250–253V peaks followed by a disconnect, this is overvoltage. Note the peak voltage — you will need this information.
Hover over the voltage graph at the time of disconnect (if your portal allows). Most disconnects occur at approximately 253V, though this varies by inverter model.
If disconnects happen at lower voltage (e.g., 248V), the inverter's Over Voltage Trip Point (OVTP) may be set too conservatively. If they happen at 253V or above, the inverter is behaving normally for UK grid standards.
Open your inverter configuration/settings. Look for 'Volt-Watt response', 'Volt-Watt control', 'automatic voltage regulation', 'reactive power control', or 'voltage management'.
If this feature exists and is currently disabled, enabling it can help prevent disconnects by automatically reducing output as voltage rises. Consult your inverter manual or contact the manufacturer to enable this safely.
High voltage is often caused by high solar export. Open your inverter settings and check the export limit. If it is set to a high value (e.g., 4 kW on a 5 kW system), reducing it can lower the voltage rise and reduce disconnects.
This is a temporary workaround — the real fix is for your DNO to upgrade the network. But it can reduce nuisance disconnects while you work with the DNO.
If your neighbours with solar systems also have regular overvoltage disconnects, this confirms it is a network-wide issue. If only you have the problem, it might be a local issue at your connection point.
If multiple customers report overvoltage, this is stronger justification for escalating to the DNO and requesting network upgrades.
What is Volt-Watt response and how does it help?
Volt-Watt response is an automatic mechanism that reduces inverter output as grid voltage rises, keeping the system online and preventing disconnects.
How it works
Without Volt-Watt: When grid voltage reaches the disconnect threshold (e.g., 253V), the inverter trips immediately. The system stops exporting. Customers see lost generation and frequent disconnects.
With Volt-Watt enabled: As voltage rises toward the threshold, the inverter automatically starts reducing its output power. At 250V it might export 80% of available power. At 252V it might export 50%. This gradual reduction prevents voltage from spiking above the disconnect threshold, so the system stays online.
The benefit: The inverter loses some energy output, but stays connected continuously instead of disconnecting repeatedly. Net result: more total energy exported over the day.
Important: Volt-Watt response is not enabled by default on many UK inverters. It requires manual configuration in the inverter settings. If your inverter supports it (check your manual), enabling it can significantly reduce overvoltage disconnects. However, you will lose some generation when voltage is high. This is a trade-off between continuous operation and maximum output.
How to reduce overvoltage disconnects
This is the most effective and recommended approach. Check your inverter manual to see if Volt-Watt response, automatic voltage regulation, or similar is supported. If yes, enable it following the manual's instructions. This keeps your system online while automatically managing output to prevent overvoltage.
Lower export limits reduce the power injected into the grid, which lowers the voltage rise. This is not a permanent solution but can reduce nuisance disconnects while you work with the DNO.
Example: Reduce export limit from 4 kW to 2 kW. This reduces the voltage spike by approximately half, potentially preventing disconnects. The trade-off is lost export earnings.
Grid overvoltage is a network operator problem. Contact your DNO (your approval letter has their contact details) and report:
Multiple customer complaints drive infrastructure investment. Document everything and follow up formally.
If overvoltage disconnects are severe, a battery system with smart charging can help. During high-voltage periods, excess solar can be stored in the battery instead of exported, reducing the voltage spike. This is a significant investment but addresses the root problem locally.
Working with your DNO to fix the problem
Grid overvoltage is your network operator's responsibility, not yours. Here is how to escalate effectively:
Export voltage logs from your portal for at least 1–2 weeks of sunny days. Show peaks above 250V. This is evidence of the problem.
Your G98/G99 approval letter lists the network operator and their contact details. Common UK DNOs: UK Power Networks (DNO for Greater London, SE, and E Anglia), Wiltshire Networks, Scottish Power, Niagara Hudson, etc.
Call or email your DNO. Explain that your inverter is regularly disconnecting due to high grid voltage (attach voltage logs). Request an investigation and ask what steps they will take to manage voltage in your area.
Send a formal complaint letter (email is acceptable) to the DNO, copying their complaints department. Reference your complaint, the dates, and the voltage data. Keep copies of all correspondence.
If the DNO does not respond or dismisses your complaint, you can escalate to Ofgem (the energy regulator). Keep documentation of all contact attempts and responses.
Frequently asked questions
No. Grid overvoltage is a problem with the network operator's infrastructure, not your inverter. Your inverter is behaving correctly by disconnecting when voltage exceeds safety limits. The problem is that the grid is not being managed properly. Multiple customers in the same area will typically experience the same issue.
Some inverters allow adjustment of the Over Voltage Trip Point (OVTP). However, raising it above UK grid standards (253V) can violate your G98/G99 approval and may cause grid safety issues. Do not attempt this without confirming with your DNO. Volt-Watt response is the recommended approach — it keeps the system online while preventing overvoltage.
Yes, slightly. During high-voltage periods, Volt-Watt response reduces inverter output to prevent voltage rise. You will lose some generation when voltage is high. However, the alternative is a complete disconnect, which loses all generation. In most cases, Volt-Watt results in more total daily energy exported because you stay connected continuously rather than disconnecting repeatedly.
Yes, very common, especially in rural and semi-rural areas. Urban areas with strong grid connections rarely have overvoltage issues. As solar penetration increases, more areas are experiencing chronic overvoltage. This is a network-wide problem that requires DNO intervention. Reporting it formally to your network operator helps drive infrastructure investment.
You can attempt to claim compensation from your DNO, though success is variable. Document all disconnects with timestamps and estimated lost generation. Submit the claim in writing to the network operator. If they refuse, you can escalate to Ofgem. Legal costs often exceed the compensation value, so evaluate carefully. Multiple customer claims strengthen the case for network investment.
Yes. A battery with smart charge scheduling can store excess solar during high-voltage periods instead of exporting it to the grid. This reduces the voltage spike and prevents disconnects. You will lose export earnings but gain stored energy for evening use. This is an effective long-term solution if overvoltage is severe, though it requires significant capital investment.
Need expert advice on reducing your overvoltage disconnects?
A remote diagnostic reviews your voltage history and identifies the best mitigation — whether that's enabling Volt-Watt response, adjusting export limits, or escalating to your DNO.