What Happens to Solar Panels During a Blackout in Spain?

The morning after the apagón on 28 April 2025, our phones did not stop. 

• Half the callers were clients with backup boxes. They rang to tell us their lights had stayed on. 
• The other half wanted to know why their system had shut down.

Solar panels keep generating during a blackout in Spain, but the inverter shuts itself down when the grid fails, so that power never reaches your home. Anti-islanding protection is the reason. Only a system built to isolate itself from the grid keeps supplying the house.

That surprises most people. It surprised one of our own clients, who had a battery fitted and assumed a blackout could not touch him.

I’m Adam Millington, co-owner of Marblanc Solar and a qualified electrician. Below I’ll explain what your system is doing during a cut – not how to fix it, but what is physically happening on your roof, inside your inverter and in your battery while the house sits dark.

You can read more about our backup box installation services in Spain. 

What Happens to Your Solar System When the Grid Goes Down?

When the grid goes down, a grid-tied solar system stops supplying your home. The panels carry on producing DC electricity on the roof. The inverter stops converting it into usable AC power, so your lights, sockets and appliances go dead like every other house on the street.

The word that matters there is supply.

Generation and supply are separate jobs, handled by separate equipment. People treat them as one thing because in normal use they are invisible to each other.

Your panels make direct current, while your house runs on alternating current. The inverter sits between them and does the conversion, every second of every day, without you thinking about it.

Take the grid away and the inverter stops. The conversion stops with it.

What each part of your system is doing, before and during a cut:

Component	What it does	Normal operation	During an outage
Solar panels	Convert sunlight into DC electricity	Generate whenever light falls on them	Still generating DC on the roof
Inverter	Converts DC into AC your home can use	Converts and feeds the house, exports the surplus	Shuts down and raises a Grid Loss alarm
Solar battery	Stores surplus energy for later	Charges by day, discharges in the evening	Shuts down too, unless the system can isolate itself
Household supply	Delivers power to your sockets and circuits	Drawn from solar, battery and grid together	Dead, the same as any home without solar

Do your solar panels stop generating electricity?

No part of the array switches off. Sunlight hits the cells and the cells produce voltage – that is physics, and a power cut does not reach it.

What changes is where that electricity can go. With the inverter down, the answer is nowhere.

So the panels spend the whole blackout working – but that power has no route into your home. That is the part people find hardest to understand. But it is a safety feature that genuinely is built in to save lives (see further down).

Why does the inverter switch itself off?

Your inverter watches the grid constantly. It’s checking voltage and frequency, confirming that what it’s connected to is a live, stable network.

When that signal disappears, it stops. It will not start again until the grid is back – Huawei states this plainly in the SUN2000 user manual for example.

This is a protection, not a fault.

Why is your house dark when the panels are still working?

Your house goes dark because generation and supply are two separate things. Sunlight on the roof still produces DC voltage in the array. Nothing can reach your sockets without the inverter, and the inverter shuts down the moment grid voltage disappears.

There is a safety point here I want to make as an electrician rather than as an installer.

During the apagón, people improvised. I heard from some homeowners they were planning to fiddle with the DC side of an array directly when the house was dark.

Do not go near it. The DC side of a solar array stays live in daylight whether the grid is up or down, at voltages far above anything in your domestic wiring. There is no safe way for a homeowner to interact with it. Leave it alone and call your installer.

Why Are Solar Systems Built to Shut Down in a Power Cut?

Solar systems shut down in a power cut because of anti-islanding protection, a safety function inside the inverter. Without it, your panels could push electricity into local lines that engineers believe are dead and lead to electrocution. The protection ships as standard on every inverter we fit.

Picture the engineer working on the line outside your urbanisation. He has confirmed the section is dead and is holding a cable in his hands.

If the solar system on your roof were still feeding the network, that cable would be live – and he would have no way of knowing.

Four terms worth knowing before we go further:

• Islanding: a generator such as a solar system continuing to energise part of the network after the main grid has failed, creating a live “island” inside a network that should be dead.
• Anti-islanding protection: a function inside the inverter that detects the loss of the grid’s voltage and frequency reference and stops the inverter feeding power out. It is built into the hardware rather than added as an option.
• Backfeeding: electricity flowing from a property back into the local distribution network. Normal when the grid is live and exporting surplus solar; dangerous when the grid is down and crews are working on it.
• Grid frequency synchronisation: the inverter matching its output to the voltage and frequency of the grid it is connected to. Losing that reference is how the inverter knows the grid has failed.

What is anti-islanding?

It is the reason your system shuts down, and it is not optional.

Huawei lists it among the standard protections on the SUN2000 inverters we fit, alongside surge, overvoltage and overcurrent protection, in the published specification.

It sits in the same list as the protections that stop your inverter destroying itself in a thunderstorm. That tells you how the manufacturer views it.

Do all solar systems in Spain shut down automatically?

Every grid-tied system does. The protection lives inside the inverter rather than in something bolted on afterwards, so there is no version of a grid-tied install where it’s absent. It isn’t a setting your installer chooses at the end of the job. It arrives in the box.

A system that keeps running through a cut is not one with the protection switched off. It is one with extra hardware that isolates your house first, so that nothing can flow back to the street.

That piece of hardware is called a “backup box” – you can read more about how backup boxes work.

Will Your Solar Battery Keep Working During a Blackout?

A solar battery keeps working in a blackout only if the system can isolate your home from the grid. With isolation hardware fitted, the battery powers the house as normal. Without it, the battery shuts down with everything else, however much charge it holds.

This is the misconception I’d like to address here.

I had a client sit through a cut with a full battery on the wall and no power in the house. He was not being careless. He had simply assumed, as most people do, that a battery is a backup.

A solar battery does not provide power during a blackout – unless you have a backup box.

Those are two different pieces of equipment doing two different jobs.

Does having a battery mean you have backup power?

Having a battery and having backup power depend on different equipment. A battery stores energy for later use. Backup power needs hardware that disconnects your home from the grid and reroutes that stored energy, which most standard battery installations do not include.

A solar battery storage system exists to shift your own energy from midday to the evening. That is its purpose and it does it well.

But in a cut, the battery faces the same problem as the panels. There is no safe route from the battery into your house while your house is still wired to a dead grid.

One narrow exception is worth knowing about. Some inverters carry a small dedicated outlet that works in daylight without any battery at all – enough for a phone or a laptop, not enough to run a home. It is a socket, not a backup system.

Why does a battery shut down with the rest of the system?

The battery talks to the house through the inverter, exactly as the panels do. When the inverter stops, the battery has no more route into your circuits than the roof does. Stored charge and available charge are not the same thing.

Can your panels still charge the battery while the grid is down?

They can, on a system built to isolate itself.

Huawei sets the order of priority for off-grid running in the SmartGuard manual: solar generation first, then battery discharge, then a generator. The manual even gives the procedure for bringing a flat system back to life by charging the battery from the strings.

So on a backup-capable system in daylight, the sun runs your house and tops up the battery at the same time.

On a standard system, none of that happens. The inverter is down, so nothing charges and nothing discharges until the grid comes back.

How Long Could Solar Power Keep Your Home Running in a Blackout?

How long solar power lasts in a blackout depends on your usable battery capacity divided by the load you are running. A fridge, router and lights draw little and stretch the charge. Air conditioning, an oven or a pool pump empty it fast.

I won’t give you a number of hours, because anyone who does is guessing about your house.

What I can give you is the maths.

What actually determines how long your battery lasts?

Three things set the runtime: the usable capacity of the battery, the size of the load and how much sun reaches the panels during the outage. Capacity sets the ceiling. Daylight generation can extend it, and at night nothing refills the battery.

The load matters more than people expect – a fridge, a router, a few lights and some phone chargers is a small, steady draw that a battery can carry for a long stretch.

Switch on the aircon and you are in a different conversation.

What happens when the battery runs out?

When the battery reaches its end-of-discharge limit, it stops supplying the house and backup power ends. The system goes quiet until something recharges it. Sunlight on the panels the next morning will do it, and so will the grid returning.

Huawei describes the battery entering hibernation at that point in its residential storage documentation, returning to normal once charging becomes possible.

Which leads to the fact I think matters most in this whole post:

In a blackout that runs overnight, backup power ends when the battery empties and returns when the sun comes up. If the apagón had lasted into a second day, that is the rhythm most backed-up homes would have lived by.

What Happens When the Power Comes Back On?

When power returns, the restart runs in five stages, from the grid voltage coming back to your monitoring catching up last. The inverter watches the grid long enough to confirm it is stable before reconnecting – you do nothing – the wait is set by the inverter’s configured grid profile.

This is the part nobody writes about, and it’s the part we get the most calls about.

1. Grid voltage returns: your neighbours’ lights come on. Your house comes back on grid power, the same as any other home.
2. The inverter observes the grid: it checks that voltage and frequency are steady rather than reconnecting into an unstable network.
3. The Grid Loss alarm clears: the inverter detects that the condition has passed.
4. The inverter reconnects and begins converting: solar generation resumes and the battery starts charging again.
5. Monitoring catches up: your app reconnects once the router and internet are back, and there may be a gap in the recorded history.

Does your inverter restart automatically?

It does, and you do not need to be at home for it.

Huawei’s manual describes the inverter monitoring its own status and returning to operating mode once the conditions are met. It can only start once the grid has recovered – which is why nothing you do during the cut will speed it up.

How long does your system take to come back?

The delay before your inverter reconnects is set by the grid profile it was commissioned with, not by a universal figure. It waits for voltage and frequency to hold steady, then reconnects on its own. Neighbouring homes can come back at different moments for this reason.

Huawei doesn’t publish a universal figure here; I’d be wary of anyone who quotes you one. The reconnection conditions sit inside the grid-code profile loaded at commissioning.

Do you need to reset anything after a power cut?

No, leave the system alone.

Huawei’s manual treats the DC switch as a deliberate step in its power-on and power-off procedures, and gives no instruction to touch it after a grid-loss alarm. Nothing about a routine cut asks anything of you.

The exception is worth knowing. If your neighbours have power and your system is still showing an alarm, that is no longer the blackout. Do not keep flipping breakers – Huawei’s own guidance is to have the AC supply and cabling checked, and that is a call to your installer.

Why does your production stop and start during a long outage?

Production drops back during a long outage because an isolated system has nowhere to send surplus power. Solar serves the house first, then charges the battery. Once the battery is full and the load is small, output is held down to match what the home can take.

On a normal day your surplus goes to the grid. During a cut that route is closed, because closing it is the entire point of the hardware.

So the system generates what the house can absorb, and no more. Watching that on your app can look like a fault. It isn’t.

How Can You Keep Your Solar Running Through a Blackout in Spain?

Keeping solar running through a blackout takes a backup box: a unit that disconnects your home from the grid and switches it onto your own supply. Fitted alongside a battery, it keeps the house powered at night as well as in daylight.

That is the category of hardware, and it is the only route to a house that stays lit.

I’ve written the full explanation separately – our article on how a backup box keeps your home powered covers what’s inside one and how it behaves when the grid drops.

Frequently Asked Questions

Can a blackout damage your solar panels or inverter?

A normal blackout is not, by itself, a sign of damage. Huawei records loss of grid supply as alarm 2032, with external causes listed – the grid has failed, or the AC supply is disconnected. The inverter starts again once the grid recovers. A cut that comes with lightning or a surge is a different event, which is why surge and overvoltage protection are built into the inverter as standard.

Should you switch your solar system off during a power cut?

There is no need, the inverter has already stopped feeding your home on its own, and Huawei’s documentation asks nothing of the owner during a routine outage. Switching things off by hand adds risk and achieves nothing.

Will your monitoring app still work in a blackout?

Often not, even on a system that is still running. Most installations send their data through your home router, and the router loses power with everything else. That said, a powered 4G dongle can stay online. If the inverter is still running, the FusionSolar app can also connect to it directly over its own local WLAN with no internet involved. Missing data may sync afterwards, though not every setup backfills the gap.

Does blackout backup work at night?

It works at night only if there is charge in the battery. Panels contribute nothing after dark, so an overnight cut runs on stored energy alone – and ends when that runs out, until the sun returns.

What about a planned outage (corte programado)?

Your system behaves the same way in a scheduled cut as in an unexpected one: the inverter shuts down either way. The difference is that you get notice, so it’s the one occasion you can prepare – go into it with the battery full, and you know roughly when supply will return.

Not sure what your system would do in a blackout?

Most homeowners only find out the hard way. If you’d rather know in advance, book a free solar survey with us at Marblanc Solar.

An engineer visits your property, inspects your roof by drone and assesses how you actually use electricity. We come back with two costed proposals, a 3D performance model and a break-even estimate for each – plus a straight answer on what your setup would and wouldn’t keep running.

You can also call us directly, details on our Contact page.