Power Cut Over but Solar Still Off? What G99 Reconnection Actually Does

Grid rules & fault-finding · Updated 2026

Solar Panels Not Working After a Power Cut? What G99 Reconnection Actually Does

The 20-second rule: what G99 reconnection actually does

Here’s the bit almost nobody explains properly, and it’s the reason most “my solar’s broken after the power cut” panic calls are wasted. When the mains fails, your inverter’s loss-of-mains protection drops the connection in well under a second — the standard G98/G99 setting is a rate-of-change-of-frequency trigger of 1.0 Hz/s with a definite delay of about half a second. You never see that part, because the lights were out anyway.

The part you do see is the way back. Under the Energy Networks Association’s Engineering Recommendations G98 and G99, an inverter may only reconnect once voltage and frequency have stayed inside its protection limits for a minimum of 20 seconds. Twenty seconds is the floor, not the promise. On top of it, your inverter runs its own routine: confirming the grid is stable, checking its DC side, proving its internal relays have released cleanly. In practice that’s why most UK systems take one to five minutes from “lights back on” to “generation ramping up”, and why I tell people to give it a full five minutes, in daylight, before assuming anything has died.

Two footnotes people mix up. First, G98 versus G99: G98 is the connect-and-notify route for small, fully type-tested systems up to 16 A per phase (roughly 3.68 kW single-phase, 11.04 kW three-phase), while G99 covers anything bigger and normally needs the network operator’s approval before you install. Different paperwork, same reconnection discipline — your inverter behaves the same after a cut either way. Second, a genuinely 2026 one: EREC G99 Issue 2, published on 10 March 2025, made new requirements for generating modules that include electricity storage mandatory from 1 March 2026. If you’re commissioning or re-commissioning a battery or hybrid system this year, the inverter and any interface protection need to be declared against Issue 2 — worth knowing if an installer is quoting you after a cut.

Normal or not: the after-cut timeline

Fault-finding for a living teaches you that the most useful first question after a power cut isn’t “is it broken?” but “where am I on the clock?” The second is “is there any light?” An inverter can’t generate after dark or under heavy gloom, so a cut that ended at 9pm tells you nothing about your system. Use this table before you touch anything.

Why your solar shuts off the moment the grid dies

Worth restating, because it surprises everyone once: your panels keep generating in daylight during a cut, at up to several hundred volts DC, with nowhere to put it. The inverter disconnects because it must — anti-islanding is mandatory under G98 and G99 so that nobody back-feeds a “dead” street cable that a line engineer believes is safe. It’s the same rule that stops plug-in solar kits mid-cut, and the same reason your Smart Export Guarantee income simply pauses for the duration. Our fuller walkthrough of what happens to solar panels during a power cut covers the during-cut side, including what backup wiring will and won’t run.

What G99 reconnection doesn’t do

Half the confusion after a cut comes from believing the reconnection process involves somebody else. It doesn’t.

• Nobody switches your solar back on. Not the DNO, not your supplier, not your installer. Reconnection is automatic and lives inside the inverter (or the interface protection on larger systems). If a forum tells you to “get the DNO to reset your export”, they’re thinking of a different problem.
• It isn’t a metering event. Your SEG arrangement doesn’t lapse because the grid went down. Export resumes when the inverter reconnects; no re-application, no paperwork.
• You can’t hurry it. Cycling the isolators during the wait doesn’t speed anything up — it restarts the self-check routine and puts needless wear on the relays. The wait is the system doing its job.
• Backup mode is not a loophole. Anti-islanding still applies: a backup circuit can power your wired loads during a cut, but nothing may export into the dead network. Any device claiming otherwise isn’t compliant for UK connection.
• The settings aren’t yours to tweak. Voltage windows, loss-of-mains settings and export limits form part of your connection agreement with the DNO, and the standards require them to be protected by a password or seal for a reason. Cowboy edits in the installer menu can void your warranty and MCS paperwork in one tap — a line I hold firmly.

The six usual culprits when it stays off

If you’re past the fifteen-minute mark in daylight with nothing happening, or there’s a code on the screen, work down this list in order. It’s arranged by how often I meet each one in the field.

A word on the voltage one, because it gets blamed on the cut. UK supply voltage is allowed to reach 253 V (230 V plus 10%). The default G98/G99 protection hard-trips the inverter at 262.2 V for one second, and inverters also throttle back or drop out when readings sit near 253 V for a sustained period. On a lightly loaded street on a sunny day, that’s enough to knock an otherwise healthy system offline. The signature is a system that reconnects, exports happily for an hour, then drops out around midday, again and again. It’s usually not new: the cut just made you watch the inverter closely for the first time. Occasionally, repairs leave the network on a temporary running arrangement that shifts voltage for a while, and your network operator can tell you if that’s the case. Either way it’s not broken; it’s compliant. Our fault code explainer covers the over-voltage family and the evidence your installer will want before approaching the DNO.

Battery and hybrid systems: the extra things that catch people out

A battery adds a second brain to the system, and after a cut the two don’t always agree about who’s in charge. If you have one, add these to the list:

• Stuck in backup, off-grid or EPS mode. A changeover contactor that chattered during the cut, or software that didn’t swap back, leaves the inverter waiting for a grid it’s already connected to. Check the mode in the app or menu, then restart in the maker’s sequence.
• Battery flat or in protection. After a long cut the battery can sit in standby or protection until it sees enough charge. Some need a manual restart. Follow the manual; never bypass or jump anything.
• Inverter-to-battery comms dropped. BMS or communication warnings usually clear after a restart done in the right order. Battery systems are the most order-sensitive, so check the manual before you improvise.
• No backup circuit was ever wired. A standard grid-tied hybrid goes dark with the grid, exactly like a solar-only system. Backup only exists if your system was designed for it: a wired emergency socket (EPS), protected circuits or whole-home backup. Our solar tech guide explains the inverter and battery options.

The safe reset sequence, step by step

Everything here is ground-level and safe. Nothing involves the roof, the DC connectors or the inside of any box.

1. Check the light and the clock, then read before you touch. Is it daylight, and has it been five minutes? If so, photograph the inverter screen or LED state, any code exactly as shown, and the generation graph in your app. Engineers diagnose patterns, and patterns need timestamps.
2. Consumer unit. Find the breaker labelled solar PV or inverter. A tripped RCBO often rests mid-position, so push it fully to off, then firmly to on. Once. If it trips again instantly, stop — that’s an earth fault talking.
3. Isolators, in your manual’s order. Makers differ on whether AC or DC goes on first, so check the label or manual rather than guessing. Then wait three to five minutes for the grid sync. Screens don’t wake instantly, and the wait feels longer than it is.
4. Battery systems: check the mode. If it’s sitting in backup, off-grid or EPS mode with the grid healthy, follow the manual’s restart sequence. A changeover contactor that chattered during the cut sometimes needs exactly this.
5. Respect the window. Twenty seconds minimum plus self-checks. Don’t churn the isolators inside it — you’re restarting the clock, not beating it.
6. Check the boring stuff. Router on? Monitoring dongle seated? An offline app with a green inverter LED is a comms sulk, not a dead array. Our solar monitoring guide covers the apps and hardware.
7. One controlled reset, then judge. AC isolator off, five minutes, back on (battery systems: follow the manual). If a transient alarm clears, fine. If a lockout-family code returns — earth fault, arc fault, RCD, relay fault — stop resetting and book the fault in.

If the sequence fails, build the two-minute evidence pack — photos of the screen, serial label, isolator positions, consumer unit and the array from the ground — and email your installer with the warranty reference. Half the time they’ll diagnose from the photos and arrive with the right part. Our ten-minute diagnostic in solar panels producing nothing uses the same order for a reason: cheapest and safest first.

Grid or kit: who to call

The fastest way to a long hold is ringing the wrong organisation. Aim the first call properly and the whole thing resolves faster.

For anything supply-side, Ofgem’s guidance on reporting a power cut and claiming compensation is the plain-English starting point: 105 connects you free to your local network operator in England, Scotland and Wales. Voltage-rise investigations are their job, not yours — but your installer starts that conversation, because they hold the connection documents.

Export, SEG and the money side

Three money points people get wrong after a cut. One: during the outage you export nothing, so SEG income simply pauses for those hours — there’s no claim to make and no penalty. Two: once the inverter reconnects, export and payments resume automatically; nothing needs re-registering. Three: if your smart meter’s export readings stall after the outage — a comms drop between meter and data network is a classic post-cut gremlin — that’s a metering fault quietly eating income, not a generation fault. A typical 4 kWp system exports around 2,000 kWh a year, roughly 170 kWh a month, so a month of missing readings is worth about £25 at a 15p tariff (about £5 at 3p, over £40 at 25p). Our fix guide for a smart meter not sending export readings covers what to check and what to ask your supplier.

And if the cut has you reviewing your setup anyway, check what your exports actually earn. On 2,000 kWh exported, the gap between the worst and best 2026 SEG tariffs is roughly £60 versus £500 a year. The catch: the top rates are tied to having your system installed by that supplier, while open-to-all fixed rates sit nearer 13p (about £260). Rates move often, so use our SEG rate comparison, which flags which tariffs need a battery or an import switch.

FAQs

Technical figures in this guide come from the Energy Networks Association’s Engineering Recommendations G98 and G99 (Issue 2, 10 March 2025). Always follow your inverter manufacturer’s manual and your installer’s advice for your own system.