Treat the battery or off-grid system as a building service, like heating, and design it with the building from the first sketch. Decide early which grid route the site takes, what must run and when, and where the battery, the inverters and a possible generator go. Then the roof, the technical room and the cable routes follow from it. For an on-grid site that mainly needs to cut its peak, see our business battery systems.
Maybe you know the pattern. The client mentions a battery at the end of the design, or asks "can we go off-grid?" after the permit drawings are in. The technical room is already drawn as a narrow corner next to the boiler. There is no duct from the roof, and the roof itself is full of skylights and HVAC units. The grid operator's offer arrives late, and it is higher than anyone expected.
What the design team rarely sees is that the expensive part is not the battery. It is the late change: a bigger room, new ducts, a roof redrawn, a connection request made again. A battery or off-grid system is easy to fit when it is in the brief. It is hard to fit when it arrives after the shell.
The new warehouse of Special Renting Van Zele in Zele was designed around its own power from the start. It has no grid connection at all. Solar panels of 30 kWp, a battery and a generator supply the warehouse, the offices and the electric lifting gear. The place of the generator was a design choice too. It stands in the basement, so its heat can warm the floor, as the press article on the project explains.
When should the battery installer join the design team?
At the sketch or preliminary design stage, before the grid connection is requested and before the permit drawings are final. Those are the moments when the roof, the technical room and the connection are still open.
The EU Energy Performance of Buildings Directive (2024/1275) points the same way. It asks member states to make sure all new buildings are designed to optimise their solar potential. By 31 December 2026, all new public and non-residential buildings above 250 m² useful floor area need solar installations. The condition: it must be technically and economically feasible. Member states had to transpose these rules by 29 May 2026, so check how your region applies them.
When each energy decision falls in the design
Does the site risk a long wait or a refusal from the grid operator? Then read our article on your options when a heavier connection is refused, because grid congestion now blocks new connections in several places.
On-grid, semi off-grid or off-grid: which choice shapes the building design?
The grid route decides the roof area, the size of the technical room and whether you need a meter cabinet at all. Choose it before the design is fixed, not after.
| Route | What it means | What it changes in the design |
|---|---|---|
| On-grid with a battery | Grid connection stays; the battery stores solar power and cuts the peak | Normal connection and meter; battery room; roof sized on self-use |
| Semi off-grid | The site runs on its own system; the grid acts as a back-up and never charges the battery | Connection stays; transfer switch between grid and own system; less roof and battery than full off-grid |
| Fully off-grid | No grid connection; solar, battery and a generator carry the site | No meter cabinet; roof sized for winter; larger battery; place, fuel and exhaust for the generator |
Our semi off-grid system works for powers up to 75.6 kVA (3 x 400 V + N, 63 A). When the public grid is interrupted, the site keeps working on its own installation.
Going fully off-grid with an off-grid system for your business removes the connection cost. For a new warehouse, the connection, the extra meters and a decoupling board easily cost 20,000 euro before a single solar panel is in place. The house in Lokeren was built without a connection from the start: no connection costs, and never a meter in the house. Is the grid study already saying no to your building? Our guide on what to do when a new building gets no grid connection covers that situation in depth.
What does an engineering firm need to size a battery for a new building?
A load list with power and timing, not a yearly kWh figure. A new building has no meter history, so the design team's load list becomes the basis for the battery design. Every installation is calculated on its use, its production and its future plans.
What runs, and when?
Office hours, shifts, weekends and seasons. A building that uses power mainly by day needs a different battery than one that runs at night.
Which big loads start at the same moment?
Motors, compressors, a heat pump and lifts. Their start-up decides the inverter power (kVA), not the average use.
How much vehicle charging comes?
Forklifts, cars, vans or trucks. In Van Zele, surplus solar power charges the electric lifting gear.
What must keep running in a power cut?
Put those circuits on a separate board, so the back-up only carries what matters.
What will be added in the next five to ten years?
An extra hall, more chargers, a second heat pump. Size cables and the room for it now.
Where an existing site moves into a new building, the old use is a good start. Before an off-grid system is built, we can monitor the consumption for a short period. That confirms the sizing of the panels and the battery. Our monitoring software keeps doing that after commissioning.
How do you design the technical room for a battery and inverters?
Give the battery a dry, ventilated room with a stable temperature, and put the inverters right next to it. The battery is not a cabinet you hide in a leftover corner.
The battery location must meet these conditions:
- Dry and clean: a watertight room with minimal dust.
- Stable floor: level and strong enough for the battery racks.
- Temperature: between 0 and 50 °C, as constant as possible, with constant humidity. Outside that range the battery switches itself off.
- Distance: at least 2 m from a heat source and at least 0.5 m from the ventilation of the inverter.
- Ventilation: mandatory for the room. Never cover the battery.
- Safety: no flammable materials or explosives nearby; no access for unauthorised people.
The inverters have their own rules. We use Victron inverters. Victron asks for a dry, well-ventilated place as close as possible to the batteries. Each unit needs at least 10 cm of free space around it for cooling. They must never hang directly above the batteries. Too much heat shortens their life and lowers their power, so the room needs to get rid of the heat they produce.
Watch out
The AREI is the Belgian electrical safety code. Above 20 kWh (20,000 VAh) of grouped fixed batteries in a non-household building, it asks for a battery cabinet or a dedicated electrical room. Fire zones can add their own conditions, especially for an outdoor container. Our article on business battery safety, permits and insurance covers those rules in detail.
Tip
Draw a short, direct route between battery and inverters, and a duct from the technical room to the roof. Short DC cables and a free duct save time on site and make an extension easy.
How do you design the roof when the building runs on its own solar power?
Size the roof on winter, not on summer. In summer almost any solar roof covers the day. The dark weeks decide how much the battery and the generator must do.
In Van Zele, 30 kWp of solar panels covers the demand easily for most of the year. Only in winter is the battery capacity not enough, and the generator has to help. That starts in December with a few days, and January is the worst month. The generator is expected to cover about 5% of the yearly demand.
Where an off-grid warehouse gets its power over a year
So keep the roof free where it counts. Plan skylights, HVAC units and smoke vents so they do not shade the panels, and check the roof structure for the extra load. A flat roof gives freedom: in Lokeren, the flat roof was given exactly the panel layout the system needed. The house needed solar panels anyway to reach its E-level (the Flemish energy performance score). Those same panels now feed the off-grid system.
Want to know which parts make up such a system, from panels to inverter and battery? Our overview of off-grid system components explains each part.
Heat pump, EV charging and the distribution board: what should you plan now?
Plan the big electric loads and the distribution board together with the battery, because they decide its power. A heat pump and chargers can double the peak of a building that looked modest on paper.
- Heat pump: it uses the most power in winter, exactly when solar gives the least. On an off-grid site that means more battery, more generator hours or a semi off-grid route. In Van Zele the floor heating runs on a heat pump, and the generator in the basement adds its heat to the floor.
- Vehicle charging: the EU directive covers new non-residential buildings with more than five parking spaces. It asks for at least one charging point per five spaces, pre-cabling for at least 50% of the spaces, and ducts for the rest. In Flanders, every non-residential building with more than twenty parking spaces had to have at least two charging points by 1 January 2025.
- Distribution board: separate the circuits that must keep running in a power cut, and leave room for extra groups and a bigger main switch later.
- Future growth: we take a possible extension into account from the start, and size inverters, cables and loads for the future.
Chargers on a connection that cannot grow? Our article on charging points without a heavier grid connection shows how a battery fills that gap.
Designing a building with a battery or its own power? Talk to our engineers before the drawings are final.
What should the specification for a battery or off-grid system include?
A good specification describes the result and the constraints, and leaves the exact sizing to the installer's study. These are the items an engineering firm should write down.
| Item | What to write down | Why it matters |
|---|---|---|
| Energy profile | Load list with kW, start-up loads, hours, charging needs | Sets inverter power and battery capacity |
| Grid route | On-grid, semi off-grid or off-grid; connection size | Fixes meter cabinet, cabin and roof size |
| Technical room | Place, size, ventilation, 0 to 50 °C, access | Battery and inverter conditions |
| Roof | Free area, orientation, structural load, shading | Winter yield |
| Cable routes | Short battery to inverter route; ducts to roof and chargers | Losses, cost and later extension |
| Critical circuits | Which circuits stay on in a power cut | Back-up size and board layout |
| Generator (off-grid) | Place, fuel, exhaust, sound, heat use | Winter supply and permit |
| Monitoring | Internet in the technical room; remote access | Follow-up via app and VRM portal |
| Inspection | AREI inspection before use; grid operator notification where connected | Legal commissioning |
Watch out
Avoid fixing a battery brand, capacity or inverter type in the specification before the study is done. A capacity chosen from floor area rarely matches how the building will really use power.
Which inspections and rules should the design team plan for?
Plan an AREI inspection before the installation is used, and a periodic one after that. For non-household installations, the periodic inspection comes every five years.
Where the building stays connected in Flanders, the storage system must be notified to Fluvius. Up to 25 kVA that goes through Mijn Fluvius with a valid AREI inspection; larger systems go through a grid study. Rules for permits, fire safety and distances differ by fire zone and by region, including Wallonia and Brussels. Our article on battery safety and permits lists them, so they are not repeated here.
When is a battery or off-grid design not the right choice?
When the building has a strong connection, uses little power by day and has no peak problem, a battery often adds cost without much return. Then a solar roof and a well-chosen tariff may be enough.
Fully off-grid is also not for every building. A site with a large heat pump, heavy winter use and little roof will run its generator a lot in the dark months. There, semi off-grid, or a grid connection with a battery, is usually the wiser route.
Our verdict
A battery or off-grid system belongs in the design in three cases. The connection is expensive, late or refused; the peak is high; or the client wants to keep working during a power cut. Then deciding it in the sketch phase is far cheaper than adding it after the shell.
How do we work with architects and engineering firms?
We take the energy part of the project from analysis to monitoring, and we work alongside your design team.
- Step 1: Analysis and sizing. We go through the load list, the grid situation and the future plans. Then we calculate the ideal mix of solar panels, inverters, battery and, where needed, a generator.
- Step 2: Technical design. We define the system and what it needs from the building: room, roof, cable routes and critical circuits.
- Step 3: Installation and commissioning.
- Step 4: Monitoring and support. The owner follows the system in the app and the VRM portal, and the system can be extended later.
A school in Incourt, in Walloon Brabant, shows the range. A fully off-grid system with new solar panels, a battery and a generator was worked out for the site.
Frequently asked questions
Can we reserve space now and add the battery later?
Yes. Reserve the room, the ducts and the cable capacity now. Our systems can be extended later, both in battery capacity and in solar power, as in Lokeren. What is hard to add later is the room itself and the route to the roof.
Does a building without a grid connection still need a meter cabinet?
No. Without a connection there is no grid meter. You still need a place for the inverters, the battery and the distribution board, and on most off-grid sites a generator.
Who designs the battery system: the engineering firm or the installer?
Usually the engineering firm sets the requirements and the building constraints, and the installer sizes the system in its own study. Agree early who draws what, so the room and the routes match the system.
Should the battery stand inside or outside the building?
Both are possible. Inside needs a suitable room; outside usually means a container with distances set by the fire zone. Our article on business battery safety compares the two.
Does a battery have to be notified to the grid operator?
In Flanders, yes, when the building is connected: notify Fluvius, through Mijn Fluvius up to 25 kVA. A fully off-grid building has no grid operator to notify, but it still needs its AREI inspection.
Is a battery or off-grid system on the table for your next building?
Send us the sketch, the load list you have and the grid situation. We will tell you which route fits, what the system needs from the building, and what to put in the specification. The sooner we see the drawings, the less has to change.
Sources
- EUR-Lex: Directive (EU) 2024/1275 on the energy performance of buildings (articles 10 and 14)
- Departement Omgeving: charging points mandatory at certain buildings in Flanders
- Victron Energy: Quattro manual, installation location
- FOD Economie: AREI Book 1, low-voltage installations (2026)
- FOD Economie: inspection of electrical installations
- Fluvius: notify a storage system