Why On-Grid Solar Stops in a Power Cut (and the Fixes)

Quick answer: An on-grid (grid-tied) solar inverter shuts down within about two seconds of a grid outage. This is anti-islanding protection, a mandatory safety feature, not a fault. If the inverter kept pushing power into a "dead" line, it could electrocute a TANGEDCO lineman repairing that line. It restarts on its own once the grid has been back and stable for a short period, typically one to five minutes. To use your solar during power cuts you need a hybrid inverter with a battery, or a battery retrofit. Both remain eligible for subsidy when grid-connected.

What Anti-Islanding Means

An "island" is a small section of the grid that stays energised by local generators (your rooftop solar, your neighbour's) after the main supply has been cut. Islands are dangerous for three reasons:

Lineman safety. Crews isolate a line before working on it. Solar back-feeding through your service connection can make an "isolated" line live again, often at full 230 V on the low-tension side and much higher through the transformer.
Equipment damage. An island runs at uncontrolled voltage and frequency, which damages appliances when the grid reconnects out of phase.
Grid restoration. Uncontrolled islands make it harder for TANGEDCO to bring a feeder back safely.

So every grid-tied inverter sold in India must detect loss of grid and disconnect. The relevant standards are IEC 62116 / IS 16169 (the islanding test) and the CEA Technical Standards for Connectivity of Distributed Generation Resources, which require it for any system connected to the distribution network. An inverter without anti-islanding certification won't pass TANGEDCO inspection for net metering.

What Actually Happens During a Cut

Time	What your system does
Grid trips	Inverter detects voltage/frequency out of range
Within ~2 seconds	Inverter stops exporting and disconnects its AC relay
During the outage	Panels still receive sunlight, but no power is converted. Your house is dark unless you have backup
Grid returns	Inverter checks voltage and frequency stay within limits
After ~1–5 minutes stable	Inverter reconnects and resumes generation

That reconnection delay is also deliberate. It stops many inverters slamming back onto a feeder at the same instant.

In areas with frequent short cuts (rural feeders, some parts of Coimbatore and Salem districts during load-shedding), you'll see generation dips on your inverter app that match the outages. Those are lost units. A 3 kW system loses about 2.5 units for every midday hour without grid.

The Four Fixes

1. Hybrid inverter with battery (new install)

A hybrid inverter stays grid-connected for net metering but has a battery port and a separate backup output. During a cut it isolates your house from the grid (so anti-islanding is still satisfied), then powers your backup loads from solar and battery.

Typical cost: roughly 50–70% more than an equivalent on-grid system, depending on battery size
Subsidy: grid-connected hybrids remain eligible for PM Surya Ghar and G.O. 102
Switchover: near-instant with good models (under 20 ms), so fans, Wi-Fi and lights won't flicker

Detail: on-grid vs hybrid ROI in power-cut areas and battery storage in Tamil Nadu.

2. AC-coupled battery retrofit (existing on-grid system)

Keep your existing on-grid inverter and add a separate battery inverter on the AC side. During a cut, the battery inverter forms a local "micro-grid" for your house, isolated from TANGEDCO. In many setups your on-grid inverter then sees a valid grid and resumes generation, recharging the battery.

Good for: owners who don't want to replace a working on-grid inverter
Check: compatibility between the two inverters and correct isolation. This is not a DIY job.

3. Keep your existing home UPS

Most Tamil Nadu homes already have a 1–2 kVA UPS with lead-acid batteries for lights and fans. It keeps working exactly as before. Solar charges it indirectly through daytime grid power, but it won't run on solar during a cut. This is the zero-cost option if your cuts are short and your backup needs are small. See power cut solutions for Tamil Nadu.

4. Accept it

In most urban Chennai and Coimbatore areas, daytime outages add up to a handful of hours a month. Losing 10–20 units a month on a 3 kW system is under 5% of generation and doesn't justify a battery on economics alone. Pure on-grid is still the fastest payback.

Things That Look Like Anti-Islanding but Aren't

If your inverter is off and the grid is on, it's something else:

Grid over-voltage trip. Common at the end of long rural lines on sunny afternoons, when many rooftops export at once. The inverter app usually shows "Grid over-voltage" or "Vac high". Your installer can sometimes adjust settings within TANGEDCO-permitted limits, or the section office may need to adjust transformer tapping.
Earth fault or insulation error. Often after rain. See inverter faults.
Tripped AC MCB or SPD in the ACDB.

FAQ

Why does my solar not work when there is a power cut?

On-grid solar inverters are required to shut down when grid supply fails, a safety feature called anti-islanding. It prevents your system from back-feeding power into lines that TANGEDCO crews may be repairing. The inverter restarts automatically after the grid returns and stays stable.

Can I use solar power during a power cut without a battery?

Not with a standard on-grid system. Some hybrid inverters offer a limited daytime-only backup socket without a battery, but output depends on sunlight and is unstable under cloud. For dependable backup you need a battery.

Is anti-islanding mandatory in India?

Yes. Grid-connected inverters must pass anti-islanding tests (IEC 62116 / IS 16169) and meet CEA technical standards for distributed generation connectivity. TANGEDCO won't approve net metering for an inverter without this certification.

How long does an on-grid inverter take to restart after a power cut?

Typically one to five minutes after the grid returns and holds stable voltage and frequency. The delay is intentional and set within grid-code limits.

Does a hybrid solar system get subsidy in Tamil Nadu?

Yes, if it is grid-connected with net metering. Hybrid inverters are permitted under PM Surya Ghar, and grid-connected hybrids also qualify for the Tamil Nadu G.O. 102 top-up. Off-grid systems are not eligible.

Sources & Updates

IEC 62116:2014: test procedure for islanding prevention in utility-interconnected PV inverters. India's equivalent is IS 16169, published by the Bureau of Indian Standards.
Central Electricity Authority (CEA): Technical Standards for Connectivity of the Distributed Generation Resources Regulations, 2013 (as amended), which require anti-islanding protection for generators connected to the distribution network.
PM Surya Ghar national portal and G.O. (Ms) No. 102, Energy Department, Government of Tamil Nadu, dated 19 September 2026: the state top-up of ₹5,000 / ₹10,000 / ₹22,000, disbursed by TEDA. Summary and eligibility in our G.O. 102 guide: grid-connected hybrid systems remain subsidy-eligible; off-grid systems don't.
Reconnection delays (about 1–5 minutes) and hybrid switchover times (under 20 ms) are typical inverter datasheet values and vary by model and grid-code settings. Check your inverter's manual.
Tristar estimates: lost-generation figures (about 2.5 units per midday hour for 3 kW) and cost ranges are our calculations.

Last verified: 5 November 2026.

Why Does On-Grid Solar Stop Working During a Power Cut?