A professional off-grid system has six components designed together. Solar panels make the energy, charge controllers feed the battery, and a battery management system (BMS) protects it. An inverter-charger forms your own 230 or 400 V grid, a generator starts itself, and control ties it together. Each part is sized on measured use, peak power and January.
Maybe your site has no connection, or one that would cost a fortune. Or your system runs fine all summer, then in December the battery is empty every morning and the generator runs far more than planned.
A meditation centre in Hechtel-Eksel shows the other side: no extra panels were needed, because the design followed how the site is actually used.
What does each component of an off-grid system do?
Every off-grid system, from a cabin to a warehouse, has the same blocks. Online kits put a few panels, a battery and an inverter in one box. A professional system chooses and sizes each block for your site.
| Part | What it does | What to check |
|---|---|---|
| Solar panels (sometimes wind) | Make the energy. Their number, type and position are chosen for the location. | Winter yield, not the yearly total. Space to add panels later. |
| Charge controllers (MPPT) or AC-coupled solar inverter | Bring the solar power to the battery or to the loads. | How the panels connect, and whether the inverter-charger can limit them when the battery is full. |
| Battery with BMS | Stores energy for the night and for grey days. The BMS watches voltage, current and temperature. | Usable capacity, cycle life, charging temperature, and a BMS that talks to the inverter. |
| Inverter-charger | Forms the grid for your site, charges the battery from the generator, and switches between sources. | Power in kVA for your biggest start, one or three phases, number of AC inputs. |
| Generator with auto start | Covers the dark weeks and long peaks. Starts and stops by itself. | Size, fuel, and a stable output the inverter accepts. |
| Control and monitoring | Decides when the generator runs and shows production, storage and use in real time. | Remote access, alarms, and data you can use to adjust the system. |
Our engineering office calculates each part for your site. That covers the type, number and position of the panels, the type and power of the inverters, the generator if needed and the batteries.
The panels connect in two ways. DC-coupled, an MPPT charge controller charges the battery directly: the usual choice for new panels off-grid. AC-coupled, existing panels keep their solar inverter, which throttles down when the inverter-charger raises its frequency with a full battery.
Victron advises keeping the solar inverter power within the continuous power of the inverter-charger, and sets a minimum battery size per kWp. Both ways can be combined, for example existing panels AC-coupled and new panels via an MPPT. More on this choice in our article on off-grid solar panels with a battery.
What does an off-grid inverter do?
An off-grid inverter, or inverter-charger, forms the grid itself from the battery: 230 V on one phase or 400 V on three. A grid-tied solar inverter cannot, as it needs a grid to follow.
It turns battery power (DC) into the alternating current (AC) your site uses. When a generator runs, it charges the battery and feeds the site. A Victron Quattro takes two AC sources, such as a generator and a grid connection, and connects automatically to the active one.
- Power in kVA for your running load and your largest motor start. For a house at 3 x 400 V we installed three Quattros, one per phase; up to six run in parallel, also three-phase.
- Switchover in less than 20 milliseconds on the main output, so computers and control systems keep running.
- PowerAssist first cuts battery charging when a generator would be overloaded, then adds battery power on top if needed.
Tip
A second Quattro output feeds loads that only run when AC power is available, such as water heating while the generator runs. They then stay off the battery.
Running a business on the grid instead? Read which inverter a business needs: solar, battery or UPS.
Which off-grid battery and battery management system do you need?
Lithium iron phosphate batteries (LiFePO4, or LFP) are a common choice for off-grid storage today. They handle many deep cycles, and lithium is much more energy efficient than lead-acid.
Cycle life depends on how deep you discharge. Victron rates its LFP batteries at 2,500 cycles at 80% depth of discharge and 5,000 at 50%, down to 80% of capacity. They only charge between +5 °C and +50 °C, so a battery room that freezes in winter is a design error.
The BMS is not optional: Victron's Lithium Smart batteries only work with a separate BMS. In our systems it manages voltage, current and temperature and steps in when they go too far. It also balances charge and discharge, so the battery lasts longer.
In Hechtel-Eksel a connection was far too expensive and use is low, mostly at weekends. Six existing panels feed a hybrid Victron system (solar inverter and charger in one) that charges during the week for the weekend. The winter battery calculation is worked out in our article on off-grid solar panels with a battery.
Why does an off-grid system still need a generator with auto start?
Because in Belgium the winter gap is too big for panels and a battery alone. The generator is not a failure of the design: it is part of it. The goal is that it runs as little as possible, and never for nothing.
At Special Renting Van Zele in Zele, 30 kWp of solar panels supply a warehouse, offices and electric lifting gear, without any grid connection. The generator only starts when solar power is not enough, in dark months or at peaks with a low battery.
The design assumed it would cover about 5% of the annual demand. In the monitoring data it only ran in winter, from December for a few days, with January as the hardest month.
How the generator starts and stops by itself
A Victron GX device starts it on battery state of charge, voltage, AC load or battery current. Stricter night settings stop it waking the site for a small load.
Watch out
Wind & Sun advises running a generator at no less than about 40% of its capacity under the expected loads. A good design charges the battery at that healthy load and then stops. Read whether an off-grid generator really has to run 24/7.
How do you size an off-grid system?
Each part has its own number. Using one number for everything, usually the yearly consumption, is the most common design error.
Solar panels: size on January, not on the year
In December, 1 kWp in East Flanders gives about a quarter of its June yield. A system that is fine in June falls short.
What 1 kWp of solar panels yields per month in East Flanders
Battery: size on your nights and a few grey days
The generator covers the long gaps. Count usable capacity, not the label.
Inverter-charger: size on your biggest 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 all have to handle that peak.
Generator: size to charge, not to follow every load
It charges the battery and carries the site at once. Too big, it runs lightly loaded; too small, it falls behind in January.
To measure is to know. We measure actual and peak consumption over a period and size generator, battery, inverters and cables on it. Starting pumps and compressors are covered in our article on more power for a new pump or machine.
Not sure your off-grid design adds up?
Send us your consumption and your largest machines. One of our engineers checks each part against your winter and your motor starts.
What goes wrong with off-grid systems?
Most failures show up in winter or at a motor start, not on a sunny day in June. No grid hides a design mistake: the lights go out or the fuel bill climbs. Fixing it later means a second battery or a bigger inverter.
A motor start trips the inverter
The pump runs fine once going, but its start overloads the inverter. Running is not the problem; starting is.
The inverter keeps dropping the generator
A common cause is a generator whose voltage or frequency is not stable enough for the inverter-charger. Choose and set up generator and inverter as a pair.
A home battery used off-grid
Many are built to work next to the grid, not to form one through a long grey spell.
An oversized generator
It runs at low load and burns fuel for very little energy.
No monitoring
Nobody sees the battery ageing, dirty panels or a generator running more every month, until something stops.
No room to grow
A new machine, building or electric vehicle, and the inverter, cables or battery cannot follow. We size every part for a future extension.
Want someone to look at your off-grid plan, or at a system that keeps failing? Call us or send a message.
When is a professional off-grid system not the right choice?
Our verdict
Full off-grid makes sense when the grid is the expensive option: no connection, a long cable, or a cabin needed only for extra power. It is usually wrong with a good connection at a normal price, most use on winter nights, or one large machine running nonstop. Then semi-off-grid, where the grid only charges the battery, or a business battery behind your connection works better.
A hybrid sits between the two. In Wingene, a farm gets 3 x 400 V at 63 A from its battery, with solar and wind on top. The grid is only a back-up charger, a full battery heats a water boiler, and no medium voltage was needed.
Frequently asked questions
How do you go off grid with electricity?
Measure your use and peak power, then size the six components together, with a generator on auto start for the winter.
Which safety rules apply to an off-grid solar system with batteries in Belgium?
The AREI applies in full: a new installation is inspected before use. In Flanders an island installation from 800 VA is also notified to the Vlaamse Nutsregulator. Your permit and municipality decide on a site without connection (off-grid for businesses).
Can a home battery work off-grid?
Only if the system is designed for it. It needs an inverter-charger that forms a grid, a battery for the night and usually a winter generator.
Can you extend an off-grid system or connect it to the grid later?
Yes, if designed for it: add panels, storage or a wind turbine, or connect the grid as a semi-off-grid charger. Read whether a small wind turbine pays off on a farm or business.
Which company can install an off-grid system in Belgium?
One with its own engineering office, references and experience with generators and motor loads. YouPower in Zele, a Victron Energy Certified Partner, works in Flanders and Wallonia. It designs, installs and monitors off-grid and semi-off-grid systems for businesses, farms and homes.
Want an off-grid system that holds up in January?
Send your consumption or planned loads, your largest motors and any grid operator answer. We measure, then calculate panels, inverters, battery, generator and cables.
We install and have it inspected before use. The app then shows production, storage, consumption and how much solar power is used directly or stored.
One of our engineers tells you honestly if off-grid, semi-off-grid or a battery behind your connection fits best.
Sources
- Victron Energy, Quattro inverter/charger product page (two AC inputs, switchover below 20 ms, PowerAssist, parallel and three-phase operation).
- Victron Energy, Lithium Battery Smart technical data (cycle life, charge temperature, BMS required).
- Victron Energy, GX device manual, generator auto start/stop.
- Victron Energy, AC coupling manual (frequency shifting, factor 1.0 rule, minimum battery capacity).
- European Commission JRC, PVGIS 5.3, monthly PV yield for Hamme (south, 35 degrees).
- Wind & Sun, generator sizing advice (at least 40% load).
- Vlaamse Nutsregulator, notification of island installations; FOD Economie, AREI inspection.
- YouPower project references: Hechtel-Eksel, Special Renting Van Zele, Wingene.