Does your business need a solar, battery or UPS inverter?

Most businesses with solar panels do not need a new solar inverter. They need a battery inverter-charger that sits between the grid and the site. It keeps the existing panels working, stores their surplus, trims the peaks and takes over in milliseconds when the grid fails. That is how our commercial battery systems are built, from SME installations to modular systems up to 1 MW. A plain UPS is only the right answer when you just want to protect servers for a few minutes.

You asked for a quote and got three different words back. One installer offers a hybrid inverter. Another wants to keep your string inverter and add a "battery inverter". Your IT supplier talks about replacing the UPS in the server room. On a three-phase site someone then asks whether you want one unit or three. Nobody tells you which question to answer first.

That is the hidden cost. The inverter decides what your site can do for the next ten years. Does it keep running in a power cut? Is your solar limit already used up? Can a big motor start on battery power? Picking it from a solar quote alone often means buying twice. On farm forums, owners report that no supplier would guarantee their three-phase motors start on a hybrid inverter. Others believe they may not touch their old solar inverters at all.

A flax processing company in Wielsbeke shows the other route. Running it on the street grid would have needed a large medium-voltage cabin. A generator starts the heavy machine and keeps running while it works, and charges the batteries on the side. A battery system of 3 x 8 kVA and 30.8 kWh then supplies the rest of the day.

What is the difference between a solar inverter, a hybrid inverter and a battery inverter?

A solar inverter only converts panel power. A hybrid inverter also charges a battery. A battery inverter-charger manages the battery and the site. A UPS is a fourth device: it protects a few loads against short cuts. The difference shows when the grid fails.

Look at the third column first. A standard solar inverter follows the grid, so it switches off when the grid is gone. Victron explains that in an island system the inverter-charger forms the grid and the solar inverter on its output follows it. That is why a battery inverter can keep the panels producing during a cut, and a stand-alone solar inverter cannot.

Does your solar inverter already switch off on sunny days? Then the cause is often the grid voltage, not the inverter. Our article on a solar inverter that trips on high grid voltage explains what to do about it.

Is a UPS the same as an inverter for a business?

No. A UPS contains an inverter, but it is built to protect a few loads for a short time. It keeps servers, network gear or a control system running through a cut and gives them time to shut down cleanly.

There are three UPS types. An off-line UPS switches to its battery when the mains leaves set limits. A line-interactive UPS corrects the voltage all the time and switches within a few milliseconds. An on-line double-conversion UPS runs the load through its inverter all the time, so there is no switchover at all. Five to fifteen minutes of autonomy is enough in most cases, according to one UPS supplier guide. That covers a shutdown or the start of a generator.

A battery inverter-charger does the same trick for a whole circuit, and for much longer. The Victron Quattro we use has a no-break main output: it takes over in less than 20 milliseconds, so the connected equipment keeps working. Behind it sits a battery of tens of kWh instead of a few minutes of UPS battery. Our guide to the right emergency power supply for your business compares UPS, generator and battery in detail.

Hybrid inverter or separate battery inverter: which is better for a business?

For a business with solar panels already on the roof, a separate battery inverter is usually the better choice. You keep the existing solar inverters, you do not touch a working installation, and in Flanders you do not use up your solar limit.

Fluvius counts every inverter that can deliver solar power toward the limit of your connection. That is at most 5 kVA on single-phase, and 25 kVA on three-phase before a grid study is needed. A hybrid inverter counts, because it serves both the panels and the battery. An inverter that only serves a battery, listed by Synergrid as "energy storage", does not. In Wallonia, Energie Wallonie takes the AC nameplate power of the inverters as the reference for a small installation of up to 10 kVA.

There is one technical rule to know with a separate battery inverter. Say the solar inverter sits on the backup output of a Victron inverter-charger (AC coupling). Then its power may not exceed the continuous output power of that inverter-charger. Victron calls it the Factor 1.0 rule. Solar panels connected on the DC side through an MPPT charger have no such limit.

A hybrid inverter still makes sense on a small site that installs panels and a battery at once, with kVA to spare. Check two things before you sign: how much power the backup output delivers, and whether it backs up all three phases or only one.

Want more panels than your connection allows? Then read what you can do when you want more solar than your connection allows.

Three-phase inverter for a business: one unit or one per phase?

On a 3 x 400 V business connection you need a three-phase inverter set-up: either one three-phase unit or three single-phase units, one per phase. Above 5 kVA of solar, Fluvius already requires a three-phase connection.

With modular battery inverters, three units are linked as one three-phase system. In the off-grid case we worked out for a 3 x 400 V supply, we installed three inverters, one for each phase. In Wielsbeke the battery system has 3 x 8 kVA. Victron allows up to six Quattro units in parallel, and three-phase set-ups, so the power can grow with the site. Our modular battery systems go up to 1 MW for large industrial sites.

Why this matters in a business:

• Loads are rarely balanced. Farms and workshops often have one busy phase with lighting, sockets and single-phase machines, next to three-phase motors. The inverter on that phase must carry it on its own.
• One phase can fail alone. Make sure the backup reacts when one phase drops, not only when all three are gone.
• The battery is not three-phase, the inverter is. One battery bank can feed three inverters; what you size per phase is the inverter power.

How big should an inverter for a business be?

Size the inverter on the highest power you need at one moment (kVA). Size the battery on the energy you need over time (kWh). For a business the highest power is almost always a motor start.

A motor that starts straight on the supply draws 6 to 8 times its rated current for a moment. The inverter, the battery current and the cables must all handle that peak. Soft starters or frequency drives (controllers that let a motor start gently) lower it. Our article on more power without a heavier grid connection goes deeper into pumps and machines.

Work through these questions with your installer:

What does a business inverter do when the grid fails?

It depends on which inverter sits where. With only a solar inverter, the site goes dark and the panels stop. With a battery inverter-charger in front of the critical circuits, the site keeps running and the panels keep producing.

The same logic works with a generator. In Wielsbeke the generator carries the heavy machine. Loading it a little more to charge the batteries turned out to be the right choice to supply the rest of the day. For the full picture of a site that runs without a grid, see our guide to the parts of an off-grid system.

Which inverter set-up fits which business?

Start from your problem, not from the device. These are the set-ups we see most often on business sites.

Is the connection the problem rather than the inverter? Then a semi off-grid system lets the battery supply the site and uses the grid as a charger.

When is a battery inverter not for you? Say you have a small roof, no heavy loads and no costly power-cut risk. There is no capacity-tariff peak worth cutting either. Then a good string inverter is enough. And if only your servers matter, a UPS does the job for less.

What happens when you ask us to design your inverter set-up?

We start with measuring, not with a brand.

1. Step 1: Analysis and sizing. We measure your actual consumption and your peaks over a period, and size everything from generator and battery to inverters and cables.
2. Step 2: Technical design. We choose the inverter set-up per phase, the battery and, where useful, the link with your existing solar inverters and a generator.
3. Step 3: Installation and commissioning.
4. Step 4: Monitoring and ongoing support. You follow consumption, production and the battery in real time in our monitoring software.