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Solar panels in a blackout: why they switch off and how to keep your power on

By Solariña · Updated November 4, 2026

On 28 April 2025, during the blackout, most homes in Spain with solar panels lost power just like their neighbours. It wasn't a fault: the rules require the inverter to disconnect when the grid goes down. For your solar panels to keep the lights on in a blackout, you need three more pieces: a battery, an inverter with a backup output and a switch that separates your home from the grid.

What happened on 28 April 2025

The cause? According to the Spanish Government, an overvoltage with several origins (analysis committee, 17/06/2025). According to ENTSO-E's final report, a combination of many interacting factors (ENTSO-E, 20/03/2026).

Why do solar panels switch off in a blackout?

It happened at midday, when panels produce the most, and yet homes that only had panels lost power: when the grid goes down, the inverter has to disconnect.

Spanish law requires it. Royal Decree 1699/2011 says that when the distribution line is disconnected, «las instalaciones no deberán mantener tensión en la línea de distribución»: installations must not keep the line live (article 11.2, BOE, checked on 03/11/2026). It protects whoever is working on the line: if your system kept feeding it, the technician repairing the fault could get a shock.

That is why grid-connected inverters have "anti-islanding" protection, which shuts them down as soon as the grid fails. The Low Voltage Regulation requires these systems to prevent the distribution network from working "in island" (ITC-BT-40, section 4.3).

And a battery isn't enough on its own. Bloomberg reported it a few days later, talking to solar owners who were left in the dark like their neighbours: most solar systems in Europe, including those with batteries, are not equipped to work "in island", separated from the grid (Bloomberg, via Energy Connects, 03/05/2025).

What does your home need to keep the lights on in a blackout?

Three pieces that work together: an inverter with a backup output, a battery and a system that separates your home from the grid when it goes down (Energías Renovables, 03/07/2025).

1. An inverter with a backup output

It keeps powering your home from the battery and the panels when the grid fails. That output has a power limit, stated on its datasheet: on some models it is the inverter's full power; on others, a few kilowatts on a single phase. You choose it by what you want to keep running.

2. A fast switchover

Some systems take a few seconds to switch to backup; others do it in under 20 milliseconds, like a UPS, according to each manufacturer's datasheet. With a few seconds, the house flickers and the router, the computer or the TV restart. With milliseconds, you won't even notice.

3. A battery with a reserve for blackouts

The same battery you use every evening powers your home during an outage. On models that allow it, it's worth keeping a reserve that daily use doesn't touch, kept for a blackout.

4. A circuit for the essentials

The usual approach isn't to back up the whole house, but a backup panel or line with what matters (Energías Renovables):

• the fridge and the freezer;
• the lights and the main sockets;
• the router and phone chargers;
• an oil, gas or pellet boiler, which won't start without power;
• the alarm, the garage door or any medical device you use at home.

The big consumers, like a heat pump, an electric water heater or the oven, are best left out: they would drain the battery quickly. The hob can be included if the backup output and the battery can handle it.

5. Panels that keep charging during the blackout

In a long outage, this is the difference between one night with power and several days. Some systems recharge the battery from the panels while the blackout lasts, and even restart on their own if the battery ran flat; others don't. It has to be checked model by model.

6. If your home has three-phase power

Some models, in a three-phase home, only power one phase during a blackout, and with less power. Others keep all three. If you have three-phase power, it's one of the first things to check.

7. A generator, if you can't be without power

Some inverters accept a generator to charge the battery when there's no sun. In Galicia, in winter, there can be several cloudy days in a row.

Is it legal for your home to run separated from the grid?

Yes, as long as what you produce during the blackout is only for your home and a switch separates it from the grid while the outage lasts. Royal Decree 1699/2011 allows «el trabajo en isla, sobre sus propios consumos, nunca alimentando a otros usuarios de la red»: island operation for your own consumption, never feeding other users (article 12.1).

And the Low Voltage Regulation requires a switching system that prevents your home from being connected to the grid and to your own equipment at the same time (ITC-BT-40). It is still a grid-connected self-consumption system, with the usual paperwork, and batteries are allowed (Royal Decree 244/2019).

What if you already have panels without a battery?

It depends on your inverter. If it's a hybrid that accepts a battery and a backup output, they can be added; if not, it has to be replaced, or a battery unit with its own backup has to be added. Send us a photo of your inverter's label on WhatsApp and we'll tell you which way to go.

What about the income tax deduction?

The battery counts. If it's installed with new panels, it is part of the energy-efficiency deduction: in a house, up to 60 % of what you pay, if the energy certificate after the work shows the improvement.

If the installation is finished and paid for in 2026, there's another one: 10 % of what you pay, battery included, on a base of up to €5,000 (in a flat it can be 20 %), with its electrical installation certificate and not paid in cash (Spanish Tax Agency, checked on 03/11/2026). The two can't be combined for the same installation: you choose one.

Should you prepare for another blackout?

The European Commission recommends keeping essential supplies to last at least 72 hours in an emergency (Preparedness Union Strategy, 26/03/2025). The April blackout showed that the grid can go down completely in seconds.

And 2026 has shown how quickly energy can get more expensive: since 28 February, the war in the Middle East blocked oil tankers in the Strait of Hormuz, through which around 20 % of the world's gas and oil passes. Brent went above $119 a barrel and gas rose 55 % in two weeks (BOE, Royal Decree-law 7/2026).

We don't know when the next blackout will come, or whether it will. A home with panels, a battery and backup depends less on all of that: the sun covers the day-to-day and, if the grid goes down, the essentials stay on. A battery isn't an expense you hope never to use: it works every day to lower your bill, and on the day of the blackout it's your insurance.

How we do it at Solariña

1. We ask what you want to keep running in a blackout, and size the backup output and the battery around it.
2. We choose an inverter that switches to backup in milliseconds, recharges the battery from the panels during the outage and, if your home is three-phase, keeps the phases you need.
3. We install a backup circuit with the essentials and the switch that separates your home from the grid.
4. We legalise it like any self-consumption system: the work is done by an authorised installer, who signs the electrical certificate.
5. On handover day, we test it with you: we cut the mains and check that the essentials keep working.

Frequently asked questions

Solariña

We design and install solar self-consumption systems for homes all over Galicia, mainly in the province of A Coruña. Every study starts from your bill and your measured roof; the work is done by an authorised installer, who signs the electrical certificate, and the energy certificates are signed by a qualified technician. If something doesn't pay off for you, we'll tell you.