Residential Backup Box Installations in Spain

Yes – adding a backup box to an existing solar installation is something we do regularly, including for systems we didn’t originally install. If you already have solar panels and want to add backup protection, get in touch and we’ll assess your current setup. In some cases, particularly where the original installation wasn’t carried out to a high standard, additional work may be required before a backup box can be added safely. We’ll always advise you on exactly what’s involved before any work begins. At Marblanc Solar, every backup box installation is backed by a 25-year workmanship warranty – so whether it’s a new installation or an upgrade to an existing system, you have complete peace of mind on performance and long-term reliability.

No – you can install a backup box without a solar battery, and it will work during a power cut. If the outage happens during daylight hours and your panels are generating, your home will stay powered. However, if the grid goes down in the evening or at night, a backup box without a battery won’t provide power, as there’s nothing stored to draw from. For most homeowners, pairing a backup box with a battery is the setup that provides genuine peace of mind – covering outages at any time of day or night. That said, if budget is a consideration, starting with a backup box and adding a battery later is a valid approach, provided the system is designed from the outset to accommodate the upgrade.

A backup box on its own – paired only with solar panels and no battery – will keep your home powered for as long as your panels are generating electricity. That means daylight hours only. If the power cuts out in the evening or overnight, a standalone backup box without a battery won’t help. The best setup is a backup box paired with a solar battery. That way, whether the outage happens at midday or midnight, your stored energy kicks in and your home keeps running. How long that lasts depends on the size of your battery and what you’re running. During our Free Solar Survey, we’ll calculate exactly how long your system would last based on your actual usage – so you know precisely what to expect before you invest.

A standard 3kW backup box can comfortably run the essentials: a fridge and freezer, internal and external lighting, a Wi-Fi router, a home security or alarm system, and plug sockets in key rooms for charging phones, laptops, or running smaller kitchen appliances. The key is selecting your priority circuits sensibly. Where a standard backup box falls short is if you try to run high-draw appliances at the same time – an electric boiler, oven, and car charger on priority circuits simultaneously would trip the system. During our Free Solar Survey, we’ll walk you through exactly which circuits to prioritise based on your home and your lifestyle, so the system performs exactly as expected when you need it most.

There are two types of backup system available. A standard backup box supplies up to around 3kW of power to essential circuits during a blackout. During our Free Solar Survey, we’ll sit down with you and map out exactly which parts of your home should stay powered – typically things like plug sockets in key rooms, the fridge and freezer, lighting, your Wi-Fi router, and a home security system. Non-essential loads like a pool pump, electric oven, or car charger go on a separate circuit and won’t run during an outage. A UPS (Uninterrupted Power Supply) backup box is the whole-home solution – it powers every circuit in the house seamlessly, with no interruption, for as long as there’s energy available in your battery. If you don’t want to think about priority circuits and simply want everything to keep running as normal, a UPS is the way to go. A standard backup box can be three to four times cheaper than a UPS – so understanding which one you actually need can make a significant difference to the cost of your installation.

When the grid goes down, your solar inverter shuts off automatically – even on a bright sunny day, and even if you have a solar battery installed. This is a mandatory safety feature, not a fault. Your inverter relies on a signal from the grid to function, and when that signal disappears, it cuts off power flow from your panels to your home. The reason this is required by law is to protect utility workers – if solar systems continued feeding electricity back into the grid during a repair, engineers working on the lines could be electrocuted. As a solar installer operating in Spain, this is non-negotiable for us. It applies to every solar system in the country, regardless of who installed it or what equipment is fitted.

A backup box is the piece of equipment that keeps your home powered when the grid goes down. It works by constantly monitoring the connection between your home and the grid using smart relays inside the unit. The moment grid power cuts out – even for a fraction of a second – those relays isolate your fuse board and switch your home’s power source to your solar system or battery. The whole process happens in 0.1 to 0.2 milliseconds. That’s fast enough that sensitive electronics like Wi-Fi routers, fridges, and lights keep running without interruption. The lights don’t flicker. The fridge stays cold. Your desktop computer or TV shouldn’t even turn off. It’s a seamless switch that makes a significant difference for anyone living in an area with unreliable power.