Backup power for critical infrastructure: what it must do

A critical site needs a back-up that takes over without a gap and runs for the hours you have defined. It also needs a second line when the first one fails, and it must report its own state. Our guide to emergency power supply for your business compares UPS, generator and battery for the everyday cases. For masts, radio links and control rooms, business battery systems give the instant, silent first line. A generator or a second battery covers the long hours.

You run a site that other people depend on. A radio link on a mast, a pumping station alarm, a dispatch desk, a tower at an airfield. "The UPS will cover it" is what everyone says. Then one morning the grid goes, and nobody knows for how long.

The risk is not the cut itself, but the gap between what the back-up was sized for and what the cut demands. A UPS built for a clean shutdown of ten minutes. A generator that has not started since the last test. An alarm that should have reached the technician, sent over the very mobile network that just went dark. In September 2024, during a power cut in the Rotterdam port area, the masts began to fail and mobile phones lost signal, Rijnmond reported. During the Iberian blackout of April 2025, communication systems largely failed, the Dutch institute NIPV reports.

Public infrastructure is not new to us. On the cycle bridge between Waregem and Wielsbeke, the nearest grid connection was very far away. The navigation lights for shipping and the street lighting run on our off-grid system with solar panels. In Maasmechelen, a generator kept for emergencies stood idle until our semi off-grid system of 24 kVA with 30.8 kWh of battery made it useful. In our media section you will also find a video about a back-up system for an airport control tower.

Which sites count as critical infrastructure in Belgium?

Two laws decide it: the Belgian NIS2 law on network and information security, and the CER law on critical entities. The CER law dates from 19 December 2025. Both cover energy, transport, digital infrastructure and water, among other sectors. The National Crisis Centre lists electronic communications networks, airports and air traffic control among the covered activities.

Critical entities under the CER law must have a resilience plan with resilience measures. Article 18 of that law asks for measures to recover from incidents, taking business continuity into account. The EU NIS2 directive names power failures explicitly as a hazard that security measures must cover.

Not covered by either law? The same logic still works as a template. Our article on what a company should do about a blackout in Belgium explains who falls under NIS2 and how the load-shedding plan works.

How long does a telecom mast keep working during a power cut?

Often only minutes. Orange (France) states that its mobile antennas keep working up to 20 minutes after the start of a load-shedding cut. Mast batteries are sized to bridge a short cut, not a long one.

For an operator with thousands of sites, longer autonomy per mast is a large investment. For you as a user it means one thing. Do not build your own alarm or back-up communication on the assumption that the public mobile network will outlast your battery. It may go dark first.

This matters for every critical site, not only for telecom operators. A pumping station that texts its alarm, a camera that streams over 4G, a technician who must be called. Plan a second path for the message: a fixed line, a private radio link or satellite. The American agency CISA advises communication diversity along exactly those lines.

How many hours of autonomy does a critical site need?

As many hours as it takes before the grid is back or a second source has taken over, plus a margin. There is no single legal number in Belgium. You set it in your risk analysis and your resilience plan.

CISA, the American agency for infrastructure security, gives a useful scale. Its resilience levels keep fuel and other supplies for about three days, seven days or around 30 days. The highest level aims at no unplanned downtime at all.

A battery alone rarely carries days. The usual answer is layered: a battery for the first hours, a generator or a second grid feed for the days after. The battery covers the gap while the generator starts, and it lets the generator run less and more evenly.

How do you calculate the battery size for a control room or radio site?

Multiply the power of the critical loads by the hours they must run, then add a margin. The critical load list is the hard part, not the arithmetic.

A simple example with round figures. A control room that draws 3 kW for radios, screens, servers and network needs 24 kWh for eight hours. Add the cooling that keeps that equipment within its temperature range: it is the load people forget. Then add a margin, because a battery loses capacity as it ages and works less well in the cold.

If you have no measurements yet, we can measure your consumption first with our monitoring software. That way the battery is sized on real data, not on a guess.

Why do telecom sites run on 48 volt DC, and what does it mean for your back-up?

Telecom equipment is often powered at -48 volt DC, with rectifiers and a battery string on the same bus. The European standard ETSI EN 300 132-2 sets the normal service range at that interface from -40.5 to -57 volt.

That design has one advantage: the battery sits directly on the equipment bus, so there is no switchover at all. The weak point is autonomy. The battery string in a shelter is usually sized for a short cut.

A larger battery system can extend it in two ways. It can feed the rectifiers on the AC side, as if the grid never left. Or a dedicated DC system can be enlarged on the 48 V bus itself. Which one fits depends on the equipment owner, the warranty on the telecom gear and the space in the shelter. Ask that question before anyone draws a system.

What does redundancy mean for critical backup power: N, N+1 or 2N?

Redundancy means one failure does not take the site down. N is exactly enough capacity, N+1 has one spare unit, and 2N doubles the whole chain.

CISA advises at least two back-up generation sources for its higher resilience levels. For the most critical sites it asks for two independent grid feeds plus two separated back-up sources. Two different technologies protect you better than two identical ones, because one fault or one fuel problem does not hit both.

Our project in Saint-Georges-sur-Meuse shows the layered idea on a farm without a grid connection. The farm used to run entirely on a generator. With solar panels and a 30 kVA system with 46.2 kWh of battery, the generator now serves only as back-up.

How do you monitor a back-up system on an unmanned site?

With remote monitoring that sends alarms before the battery is empty, over a path that still works during the cut. A site nobody visits must report on itself.

Our systems are followed in the app and the VRM portal. They show consumption, yield and the state of the battery in real time, and you can set an alert for a low battery level. For a critical site, add three things.

1. Step 1: Alarm on the events that matter: grid lost, battery below a set level, generator failed to start, temperature too high.
2. Step 2: Send those alarms over two paths, for example the fixed network and a separate mobile or radio path.
3. Step 3: Test under load on a schedule. CISA advises regularly scheduled maintenance and load testing, documented. A self-test with no load proves little.

What maintenance and service a business battery should come with is covered in our article on warranty and maintenance for a business battery.

What does a control room or control tower demand from its back-up?

Zero switchover time, clean power and no single point of failure. Radios, screens and servers must not notice that the grid has gone.

A generator always leaves a gap of a few seconds while it starts. A UPS or a battery inverter closes that gap. According to Victron, a MultiPlus-II takes over in less than 20 milliseconds, fast enough to keep computers running.

The difference between a small UPS and a central battery is the duration. A UPS usually gives minutes for a clean shutdown; a control room must keep working. Our article on dozens of small UPS units or one central battery weighs the two. The article on a manual or automatic transfer switch for your generator explains the handover to the second line.

Care institutions face the same questions with other loads. Read what a care home or medical practice needs during a power cut.

Battery, generator or both for critical infrastructure?

For most critical sites: both. The battery for the first seconds and hours, the generator for the days.

For remote sites far from any cable, solar panels with a battery can be the main supply, as on the Waregem bridge. Our article on lighting, signage and cameras without a grid connection goes deeper into those sites. Planning a generator? Check first which permit and inspection a back-up generator needs. Placing a large battery in a shelter or technical room? Read how safe a business battery is.

When is a battery back-up not the right answer for a critical site?

When the site must run for weeks without the grid and has no room for solar panels. Then fuel logistics decide, and a generator with a fuel contract is the backbone.

Two other cases. A single small device, such as one radio or one router, is often better served by the DC back-up its supplier offers. And a data centre at megawatt scale has its own design standards and specialist engineers. There, a battery is one part of a much larger chain.

What happens when you ask us to design back-up power for a critical site?

We start with what must keep running, for how long, and what happens when the first line fails.

1. Step 1: Analysis and sizing. We list the critical loads and measure them where data is missing.
2. Step 2: Technical design. We choose the autonomy, the inverter power, the redundancy and the handover to a generator or second feed.
3. Step 3: Installation and commissioning.
4. Step 4: Monitoring and ongoing support, with alerts such as a low battery level.

Our battery systems for businesses range from small installations to modular systems up to 1 MW, with monitoring and control included.