Power cut: what really works to keep electricity at home

The unpleasant surprise: having panels doesn't mean having power

It is the question we are asked most often after a blackout: “I have panels on the roof, so why did I lose power?”

The answer is a safety requirement. When the grid goes down, the inverter must shut off. This is called anti-islanding protection, and it exists so that your installation doesn't keep feeding electricity into a line where engineers are working. Without that protection, a home system could electrocute the people repairing the fault.

In other words: a normal photovoltaic system, without additional equipment, gives you no autonomy at all during a power cut. If that matters to you, you need to tell the installer before the system is sized.

Option 1: a portable power station

It is a battery with a built-in inverter and sockets, about the size of a suitcase. It needs no building work and no electrician, and it works in any home — even one without panels.

A unit of around 1 kWh powers a fridge, a router, LED lighting and phone charging for several hours. That is enough to get through the vast majority of power cuts, which rarely last more than two or three hours.

What it can't do: power an electric water heater, an induction hob, a tumble dryer or air conditioning. Those loads call for equipment on a different scale.

Choose LiFePO4 cells — they last many more cycles than conventional lithium-ion cells and are more stable. If you have panels, check the solar input voltage it accepts before buying a foldable panel to recharge it.

Option 2: a hybrid inverter with a backup output

This is the right solution for anyone who wants autonomy built into the house. A hybrid inverter with a battery and a dedicated emergency output switches over automatically when the grid goes down, usually in less than a second.

The detail many people overlook: that output doesn't power the whole house. It powers a specific circuit, which has to be defined and wired during installation — typically the fridge, lighting, essential sockets and internet.

If you want cooking or air conditioning on that circuit, it has to be sized accordingly, and that changes the inverter and the battery. Say so before the work starts, because adding it later costs much more.

Option 3: a complete off-grid system

It makes sense in places with no grid or with frequent, prolonged power cuts — isolated rural properties, wineries, farms.

It requires a battery bank with enough autonomy for several days without sun, an inverter sized for motor start-up loads and, almost always, a backup generator for the winter.

It is the most expensive option and the one least justified in an urban home with a stable grid.

What to decide before spending money

Ask yourself three questions. How long do power cuts typically last in your area? What do you really need to keep running? And is there anyone at home who depends on medical equipment or on refrigeration for medication?

If the answer to the last one is yes, backup stops being a comfort and becomes a necessity — and then the solution has to be properly sized, not improvised.

For most Portuguese homes, where power cuts are short and infrequent, a portable power station does the job for a fraction of the cost of a fixed battery. For anyone already installing solar with a battery, the logical step is to ask for the backup output from the start: at that point it costs little; later on, it means building work.