Which backup power system suits your business?

Good backup power for a business does not start with a device. It starts with the question of which loads must keep running, for how long and how fast they must be back. Servers and controls that cannot handle any interruption need a UPS or a battery system with island mode. For hours of autonomy, a standby generator or a larger battery is the classic choice. A battery system for businesses has an extra advantage: it can shave your quarter-hour peak every day and still hold a reserve for a power cut. So the investment also works on all the days the grid is simply there.

The lights flicker, the PLC drops out and a production batch is lost. Or the power is gone for three hours and nobody knows whether the cold stores will hold. Most businesses only find out what their backup really covers during the outage itself.

What you do not see before that day: a generator that stands idle for years is the most expensive insurance you own, and it still leaves a gap of a few seconds that servers and controls do not survive. A home in the woods near Gedinne shows another set-up. The public grid there delivered only 180 V instead of 230 V. A semi-off-grid battery system now supplies 3 x 400 V and uses the weak grid only to charge, and a generator is connected for power cuts.

Which loads must keep running during a power cut?

The AREI makes a clear distinction, and it is a good starting point for any backup power study. According to book 1 of the AREI:

• Safety installations keep loads in service for the safety of people. They are fed by a safety source.
• Critical installations must keep working for other reasons, such as a production line, a server room, a control room or an intensive livestock building. They can be fed by a replacement source.

In both cases the operator defines the installations based on a risk analysis. The operator makes a list with the required operating time per load, and plans that are checked at the inspection.

Make that list concrete: which circuits, what power, which starting currents, how long. A cold room that can go an hour without power needs something different from a PLC that loses a production batch at the smallest dip. Security of supply is an engineering question, not a product purchase. A good business battery project with a backup function therefore starts from that list and from measured consumption. Working in care? Read what must keep running in a care home, medical practice or pharmacy during a power cut.

What is the difference between a UPS, a standby generator and a battery system?

For safety sources, the AREI allows among others rechargeable batteries, generators independent of the normal supply, and UPS units. In practice they differ a lot.

UPS system. According to Vertiv, an online double-conversion UPS feeds the load permanently through its inverter, so there is no switchover. An offline UPS interrupts the supply for about 6 to 8 milliseconds, a line-interactive UPS for 4 to 6 milliseconds. A UPS is made to bridge a short outage or shut a system down cleanly, not to run a business for hours.

Standby generator. A diesel or gas generator supplies power as long as there is fuel. After a grid failure the engine has to start and come up to speed, so there is always a break of a few seconds. That is why many businesses combine a generator with a UPS for the most sensitive loads.

Battery system. A battery system with an inverter that can run in island mode takes over as soon as the grid fails. According to Victron, a Quattro and a MultiPlus-II do this in less than 20 milliseconds, fast enough to keep computers running without interruption.

What is a no break system?

A no break system is a supply that keeps running through a grid failure without a noticeable interruption. That can be an online UPS, or a battery system that takes over fast enough. A generator on its own is not a no break: it needs something to bridge the start.

Combinations exist too. In a Victron system a GX device can, according to the Victron manual, start and stop a generator automatically. It does so based on, among other things, the battery state of charge, the load or an inverter overload. The battery then covers the first minutes or hours, and the generator takes over in a long outage. In our media section you will find a video on a backup system for an airport control tower.

How long must your backup power last?

That depends on the risk you want to cover. A short grid fault often lasts seconds to minutes. In load shedding under the federal load-shedding plan, part of the grid is cut on purpose to avoid a blackout. According to the FPS Economy, Belgium is divided into 8 sheddable tranches. According to its FAQ for businesses, the interruptions should normally last only a few hours.

So size on measured consumption, not on rated power. The quarter-hour profile of your critical circuits shows what those loads really need.

Worked example (illustrative figures)

A food business wants to keep its server room, cold rooms and controls running through a 4-hour outage.

With a margin for ageing and discharge limits, the usable reserve comes to about 55 kWh. The inverter must handle more than 11 kW, because the cold room compressors briefly draw much more when they start: the measurement shows how much. If the same system is also used for peak shaving, that capacity comes on top of the 55 kWh reserve.

An outage of a full day needs 11 kW x 24 hours = 264 kWh. Then a generator as a second line, started automatically by the battery system, often makes more sense than a much larger battery.

Which rules apply to backup power in a business?

AREI (federal, the Belgian electrical code). According to the AREI, a safety source must switch on automatically when the normal supply fails and must be installed at a fixed location. It stands in a suitable room used only for that purpose and accessible only to instructed (BA4) or skilled (BA5) persons. The room must be properly ventilated. A second connection to the distribution grid does not count as a safety source. The operator must run a switchover test under load at least once a year and document the maintenance. For critical installations the risk analysis sets the measures, and sources not designed for parallel operation must be protected against it.

Grid operator. The technical rule Synergrid C10/11, which applies across Belgium, calls a generating unit that only feeds an island an emergency supply system. It may run in parallel with the grid only occasionally and briefly, for example at most 5 minutes per switchover after a grid fault. Every parallel connection must be logged. A battery that also shaves peaks every day is not an emergency supply system but an energy storage system, and it must be declared to your grid operator: to Fluvius in Flanders, and to ORES in its Walloon area, where a battery above 10 kVA needs a more detailed study.

Environment. The rules are regional. In Flanders, according to the Department of Environment, standby generators under 400 kVA that run less than 100 hours per calendar year are not classified under VLAREM heading 12.1, but you must record the running hours. In Wallonia a fixed generator is a combustion installation, classified on its nominal thermal power; check whether it needs a declaration or a permit with the SPW heading tool or your municipality. Our article on a generator with a battery goes deeper into those rules. For the full picture, read whether you need a permit or inspection for a back-up generator at your company.

How do you make backup power pay off every day?

A generator or UPS stands idle most of the time. A battery system can work every day, as long as the control protects the emergency reserve. In a Victron system you set a minimum state of charge in ESS on the GX device. According to the ESS manual, the system only uses that reserve when the grid fails. Above it, the battery can shave peaks and store solar surplus. The AREI also allows a safety source to feed other loads, as long as the availability for the safety loads is not affected.

How such a system is built is explained in our article on BESS and battery storage for businesses. After installation you follow state of charge and consumption through the monitoring in the VRM portal. Looking for backup power at home? Our article on a home battery with backup power explains what really works there.