Can a workshop or garage run off-grid with heavy tools?

A workshop or garage can run on an off-grid system with compressors, welders and three-phase machines. Solar panels and a battery supply the daily work. Three inverters form your own 3 x 400 V grid, and a generator covers the dark weeks. What makes it work is sizing: the inverter on the start of your largest motor, the battery on a working day, the panels on January.

Maybe your workshop sits at the back of the yard, or in a shared garage where a new cable means breaking open the driveway. Maybe the grid operator quoted a connection you do not want to pay for a building you use a few days a week. On forums, workshop owners who took the step describe the same surprise. "Running the compressor is fine, it's starting it," one blacksmith wrote. Another measured his compressor at 56 A to start and 10 A once it runs.

That is what most kits and power stations do not tell you. An inverter chosen on the average load trips at the first compressor start, and then the whole workshop goes dark. The usual fix is to buy a second, bigger inverter on top of the first one. One workshop owner sold his first three inverters for bigger ones, and the advice he got from the forum was simple: "do it once, and do it right".

Take a look at the garage in Turnhout. It is used as a hobby room, and it had no electricity. Because the garage is shared property, one connection would have meant opening up the driveway. An off-grid system with 3 kVA of inverter power and 15.4 kWh of battery made that unnecessary. A professional workshop needs more, and that is what this article is about.

What does an off-grid workshop need: running power, start peaks or energy?

An off-grid workshop needs three numbers. The power of everything that runs at the same time, the start peak of the biggest motor, and the energy of a full working day. Each number sizes a different part: the inverter, the inverter's peak capacity with the battery and cables, and the battery with the solar panels.

Write down every machine with the numbers on its rating plate. The list matters more than the brand of the inverter. A general description of "a few tools and a welder" cannot be sized; a list with kW, amps and phases can.

Can an off-grid system start a compressor?

Yes, if the inverter, the battery and the cables can deliver the start peak of the compressor motor. A motor started straight on the supply draws 6 to 8 times its rated current for a moment. The running load is rarely the problem off-grid. The start is.

An inverter-charger has a continuous rating and a peak rating. The peak lasts only a few seconds, but that is exactly the moment a compressor needs. The datasheet of the Victron Quattro, the inverter in our worked off-grid case, shows the gap.

Heat matters too. The same Quattro 48/8000 delivers 5,500 W continuously at 40 °C instead of 6,400 W at 25 °C. A workshop that gets hot in summer needs a margin on the inverter.

There are three ways to make a compressor start easier:

Starting motors on a grid connection that is too small is a related problem. Our article on more power for a new pump or machine explains inrush current and frequency drives in detail.

Can you weld off-grid, and which welder works best?

Yes, you can weld off-grid, and a modern inverter welder is the easiest machine in the workshop to power. Its power comes in bursts, it starts softly, and it tells you on its rating plate exactly how much power it needs.

Welders are rated with a duty cycle: the share of a ten-minute period the machine can weld at a given current. Fronius gives its TransSteel 3500 Compact, a three-phase 3 x 400 V welder, 350 A at 40% and 250 A at 100% at 40 °C. At full current it welds four minutes out of ten, so the energy use is lower than the peak power suggests. The inverter still has to deliver that peak for as long as the arc burns.

Welding manufacturers also set rules for generators, and they show how picky a welder is about its source. For its TransSteel machines, Fronius asks for a generator apparent power of at least 1.35 times the maximum apparent power (S1max) of the welder. The generator must never be smaller than S1max. Read S1max on the rating plate: that is the number your off-grid designer needs.

Forum owners confirm the difference between welder types. A modern inverter MIG welder ran at full output on two 6 kW inverters without problems. An old transformer TIG welder needed about 36,000 W of input power at full output, far more than the rest of the workshop.

Does one machine need far more power than everything else? Then it can make sense to start it with a generator that keeps running during the work. A flax-processing company in Wielsbeke does exactly that: loading the generator a little extra charges the battery for the rest of the day. The system has 3 x 8 kVA of inverter power and 30.8 kWh of battery.

How do three-phase machines run on an off-grid system?

Three-phase machines run on three inverters, one per phase, which together form a 3 x 400 V grid. In our worked off-grid case we installed three Victron Quattro inverters for a 3 x 400 V supply, one for each phase.

According to the Quattro datasheet, three units can be set up for three-phase output. Up to four sets of three 15 kVA units can run in parallel, for 180 kVA of inverter power. So the ceiling is not the technology; it is the budget and how big your starts are.

Each phase keeps its own limit. A three-phase motor loads all three phases evenly, but single-phase loads do not. Put the welder, the kettle and the chargers on the same phase, and that one inverter runs out long before the others. Spread single-phase loads over the three phases when the wiring is designed.

Which inverter a business needs in general, on or off the grid, is explained in our guide on solar inverters, battery inverters and UPS systems for businesses.

How big must the battery and solar panels be for an off-grid workshop?

Size the battery on a full working day plus a reserve, and the solar panels on January, not on a sunny day in June. The inverter decides whether a machine starts; the battery and panels decide how many days you can keep working.

One forum member estimated a full working day with a compressor, tools, lights and a welder at about 20 kWh. That is a rough American figure, but it shows the order of size. Our own projects show the range:

Take a look at the projects: Turnhout, Maasmechelen, Wielsbeke and St-Georges-sur-Meuse.

Winter is the hard part. Special Renting Van Zele in Zele runs a warehouse, offices and electric lifting gear off-grid. There, the design counted on the generator for about 5% of the yearly demand. The generator steps in for a few days from December, and January is the worst month. Our article on off-grid solar panels with a battery walks you through the sizing step by step.

Do you need a generator for an off-grid workshop?

In Belgium, almost always: a generator covers the dark weeks and the heavy days that the battery cannot. The point is that it starts only when needed, not that it runs all day.

A Quattro has two AC inputs, for example a generator and the grid, and connects automatically to the active one. With PowerAssist, the battery adds power when the generator alone is not enough, so a smaller generator can serve a bigger peak. When the load drops, the spare power charges the battery again.

Already have a generator? At Maasmechelen the customer had one for emergencies. The semi off-grid system made it useful: the customer chooses the street or the generator as the charger. At the farm in St-Georges-sur-Meuse, the generator ran day and night before the solar panels and battery arrived. Now it is only a back-up. Our article on a generator with a battery off-grid explains auto start and generator sizing.

Off-grid, semi-off-grid or a grid connection for your workshop?

Full off-grid pays off when the connection is the expensive or slow option and your heavy use is limited in time. When the workshop welds and machines all day, every day, a small connection or a generator for the heavy work usually costs less.

Semi-off-grid is often the middle road. At the plant nursery in Jabbeke, a new pump would have needed medium voltage at a high price. With a semi off-grid system, the nursery kept its 3 x 400 V 32 A street connection and uses it only as a charger. How a connection cost compares with a battery is worked out in our article on grid extension costs versus a battery.

Does your business want to go off-grid more broadly, with warehouses or farm buildings? Our guide on when off-grid pays off for a business compares Belgian projects and costs.

Which rules apply to an off-grid workshop in Belgium?

The Belgian electrical safety code (AREI) applies with or without a grid connection, and a new installation is inspected by an approved body before use. In Flanders, an island installation (running on its own, without the grid) of 800 VA or more is also notified to the Vlaamse Nutsregulator.

Protection needs extra care off-grid. On the grid, a short circuit draws a huge current that trips a normal breaker at once. An inverter cannot deliver that: the Quattro 48/8000, for example, gives a maximum fault current of 100 A for one second. The breakers and earthing of an off-grid workshop have to be designed for that lower current.

The battery room has its own conditions: waterproof, a stable floor, ventilation, no flammable materials nearby and a temperature within the range the battery accepts. A dusty, unheated workshop is not automatically a good place. Our guide on whether a business battery is safe covers fire safety, permits and insurance.

How do we design an off-grid workshop?

We start from your machines and your measured use, not from a standard kit. The steps are the same for a garage, a metal workshop or a farm workshop.

1. Step 1: You send us the list of machines with their rating plates, how often they run, and what the grid operator said if you asked for a connection.
2. Step 2: We measure your actual and peak use over a period where possible. That lets us size everything, from the generator and the battery to the inverters and the cables.
3. Step 3: We design the system: inverters per phase sized on your starts, the battery on your working day, the panels on January, and a generator with automatic start.
4. Step 4: We install and commission the system, and have it inspected before it is put into use.
5. Step 5: You follow production, storage and use in real time with our monitoring software. The system stays expandable: more panels, more battery or another source later.

Want to see how the parts of a professional system fit together first? Then read our overview of the components of an off-grid system, or everything about our off-grid systems for workshops and businesses.