Do solar panels work in a blackout in Spain? What the 28 April outage showed

Short answer: a grid-tied solar system without a battery does not work during a blackout in Spain: the inverter disconnects as soon as the grid voltage disappears, even in full sun. To keep the lights on you need a hybrid inverter with a backup output, a battery and a backup circuit for the essentials. Below: why, what it costs and how many hours a battery lasts. Facts checked as of October 2026.

What happened in the 28 April 2025 blackout?

According to the report of the analysis committee presented by the Spanish government in June 2025, on 28 April 2025 between 12:33:18 and 12:33:30 the Iberian peninsula's grid went to zero voltage, and the Spanish and Portuguese power systems separated from the rest of Europe.

The report calls the cause multifactorial: not enough voltage-control capacity, oscillations that constrained how the system was run, and generators disconnecting — in some cases apparently improperly — ending in a cascading overvoltage. ENTSO-E, the association of European grid operators, published its final report in March 2026 with 22 recommendations and likewise found no single cause.

Power came back gradually. According to Spain's Ministry for the Ecological Transition, about 50% of demand had been restored by around 22:00, and 99.95% by 07:00 on 29 April. Many homes were without power for anything from a few hours to most of a day.

Most homes with rooftop solar went dark too. That was not a fault — it is how grid-tied systems are designed.

Why do solar panels switch off when the grid goes down?

A grid-tied self-consumption inverter runs in step with the grid. When the grid fails, it must disconnect and stop pushing current out. This is called anti-islanding protection.

The reason is safety: if your system kept energising a line the distribution company believes is dead, it could endanger the people repairing it. So Spain's Low Voltage Electrotechnical Regulation (REBT), in its instruction ITC-BT-40 as amended by Royal Decree 244/2019, requires every generating installation connected to the low-voltage grid to have devices that prevent island operation of that grid. The same instruction says the interconnection switch must open on a grid fault and must not reclose until the grid voltage is stable again.

In practice: panels on your roof do not give you power in a blackout on their own. You need equipment that can separate the house from the grid and keep running it from a battery and the sun. This is what installers call "island mode" or "backup mode": the house (or part of it) runs on its own, while the public grid never receives voltage.

Grid-tied, battery or off-grid: what works in a blackout?

Note the second column: a battery alone does not guarantee power in a blackout. Many systems with batteries are designed only to save money. If the inverter has no backup output, or that output is not wired to a circuit in the house, the system switches off like any other.

What do you need to keep the lights on in a blackout?

1. A hybrid inverter with a backup output (often labelled backup, EPS or load), sized for what will run at the same time and for the start-up surge of motors (fridge, water pump).
2. A battery, usually lithium iron phosphate (LiFePO4). Its capacity in kWh decides how many hours you last.
3. A backup circuit in the consumer unit carrying the essentials: fridge, router, lights, sockets for laptops and phones and, if you have one, the gas boiler. The oven, hob, electric water heater and air conditioning usually stay on the normal circuit so they do not empty the battery in an hour.
4. Switching and protection: the device that separates the house from the grid (built into the inverter or an external changeover switch), breakers, an RCD and, if useful, a bypass to keep grid power while the inverter is serviced. For installations that can supply loads from either a generator or the grid, ITC-BT-40 requires switching systems that prevent both sources being connected at the same time.
5. An authorised installation company. The REBT (art. 22) reserves low-voltage installation work to authorised installation companies, which issue the electrical installation certificate (CIE). Since Royal Decree 244/2019, self-consumption generators with surplus export (and those without export above 800 VA) must connect through a dedicated circuit with a type A RCD, 30 mA in homes. Royal Decree 244/2019 (art. 5.7) allows storage in self-consumption systems as long as it has the protections required by safety rules.

Before you buy, check the datasheet for the switchover time to backup mode and whether the system can reserve part of the battery for outages. If the battery is empty at 7 pm because it was used to cut the bill, the backup will not help much.

How long does a battery last? A worked example

We use typical loads from SolarPlan's model (average draw during an outage, allowing for the fridge not running all the time):

Together that averages about 350 W; the model rounds it to 0.4 kW as the "essentials" scenario. Hours from a full battery with no help from the sun (the model allows for the unused part of the battery and conversion losses):

Applied to 28 April: from 12:33 to 07:00 the next day is about 18.5 hours. A full 10 kWh battery running only the essentials would have carried the house through to morning — and that afternoon the panels would have kept recharging it. At a steady 1 kW (say, adding a well pump or a washing machine) it would have lasted about 8.5 hours, and at 2 kW about 4. What matters is not only battery size but what you put on the backup circuit.

How much does blackout-ready solar cost in Spain?

Using SolarPlan's price index (October 2026, VAT included, no subsidies), a 5 kWp system for a single-family house:

So a 10 kWh battery with its hybrid inverter adds roughly €5,700–6,800 to a new installation. If you already have panels and add the battery later, SolarPlan's storage index puts an installed home battery at about €3,500–5,500 (5 kWh), €7,000–11,000 (10 kWh) and €8,000–12,800 (15 kWh).

These ranges are SolarPlan model estimates and do not itemise the backup circuit or changeover switch: ask for them as separate lines in the quote, as they depend heavily on your consumer unit. Real prices vary with the brand, the roof and the installer. More on the solar with battery backup page, the 10 kWh battery page and the storage price index.

Tax relief in 2026. Royal Decree-law 7/2026 created an IRPF deduction of 10% (20% in predominantly residential buildings) for self-consumption installations, storage included, on up to €5,000 a year, provided the installation is done, finished and paid for in 2026, has a CIE and is not paid in cash. It cannot be combined with the energy-efficiency deductions on the same installation. See the IRPF deduction page and confirm your case with the tax agency or an adviser.

I already have panels: can I make them blackout-ready?

Usually yes. There are two routes:

• Replace the grid-tied inverter with a hybrid one that has a backup output, and add the battery. The cleanest option when the current inverter is old or small.
• Keep the current inverter and add an AC-coupled battery inverter with a backup function. Useful when the grid-tied inverter is recent. In island mode the battery inverter forms a small internal grid and the solar inverter may keep producing inside it, depending on how compatible the two are.

Either way, the backup circuit has to be wired, protections checked and the installation paperwork updated. If the system gains storage or changes power, your installer should tell you whether it must be notified to your region's self-consumption register and to the distribution company. Check your inverter's compatibility with the installer before buying anything.

Which setup is right for you?

• You mainly want lower bills and outages are rare: grid-tied panels; pick an inverter that can take a battery later.
• You want to ride out a blackout like 28 April: a hybrid inverter with backup output and a 10 kWh battery for the essentials.
• You have a well pump, medical equipment at home or critical remote work: 15 kWh or more and a backup circuit sized for those peaks.
• You live in a flat without your own roof: backup depends on your consumer unit and your building's community; a portable power station may be enough for the router, lights and phones.

Rather than guess, start a free plan: SolarPlan lays out panels on your roof in 2D and 3D, sizes the battery for your loads and outage hours, shows the price and payback, and lets you get offers from verified installers in one format. It costs you nothing. Technical and tax rules change, so agree the final wiring with your installer and confirm any incentive with the relevant agency. More context on the solar in Spain page and the solar price index.