Off-grid capability
Water, power, and the payload left to carry both.
Fresh water is usually the first thing to run out, and every litre you carry weighs a kilogram.
The battery, the solar array and the inverter work as one system, and the smallest of the three limits what the van can do.
Updated . 11 min read • Technical Guide
How much water the van carries, how much power it stores and replaces, and how much payload remains to carry both.
A van with big tanks and a big battery bank can still lack the payload allowance to carry them.
- Typical fresh water - around 190L (across vans on our site that give a fresh water figure)
- Typical battery bank - around 300Ah (across vans on our site that give a battery figure)
How long the water lasts
Fresh water is usually the first thing to run out on an off-grid trip. Tank size, against how many people use it and how carefully, decides how long it lasts. Across the vans on our site that give a figure, a typical fresh water tank holds about 190L. Use that as a sense of scale only, and size for your own trips.
Grey water, the water that has already been used, has to go somewhere too. Grey tanks tend to run smaller, typically around 80L on the vans that publish a figure, which means grey water often fills up before fresh water runs out.
Every litre of water weighs one kilogram, so tank size is not a free number. A full fresh tank alone can account for a meaningful share of a van's entire payload allowance before a single bag or battery goes in, so read water and payload together.
For typical tank, solar and battery sizes, what Australian caravans come with lays the figures out side by side.
Battery, solar and inverter, as one system
Power off-grid comes down to three linked figures: how much the battery stores, how much the solar array can put back in a day, and how much the inverter can turn into usable 240V. Across the vans on our site that give these figures, a typical battery bank is about 300Ah and a typical roof array about 600W.
None of the three numbers works alone. A big battery with a small inverter cannot run much, and a big battery with a small solar array takes days to refill once it is drawn down. The smallest of the three usually sets how long the van can stay out.
The full breakdown lives on its own pages
How to size the setup and what each part does is covered in how much solar does a caravan need, and the AGM-versus-lithium choice inside the battery figure is covered in caravan battery types compared.
Payload margin: off-grid gear uses it up first
Payload is the gap between a van's tare (its empty weight) and its ATM (aggregate trailer mass, the most it may legally weigh loaded). That gap has to cover everything you add: water, gas, batteries, gear, food and people. Across the vans on our site that give both weights, the typical payload allowance is about 630kg.
Off-grid gear is heavy. A full fresh water tank and a lithium battery bank can take a large share of a tight allowance. A van with big tanks and batteries can have little left for the packing list.
Work out your own spare payload before you shop.Caravan weights explained walks through ATM, tare, payload and ball weight with real numbers.
Water, power and payload work as a set
None of the three numbers on its own tells you how a van performs off-grid. A quick way to sense-check any van you are looking at:
- Add the weight of a full fresh water tank (one litre equals one kilogram) to the published or likely battery weight.
- Compare that total against the van's published payload.
- Check whether the inverter rating, if published, actually covers what you plan to run.
- If any one of the three looks tight, treat the whole setup as tight.
More on off-grid power and water
The solar setup, the battery choice and free-camp habits each have their own guide.
Off-grid capability questions, answered
What makes a caravan genuinely off-grid capable?
It needs enough water, power and payload margin, and all three have to work together. Big tanks are only useful if the van also has the payload allowance to actually fill them, and a big battery and solar array only matter if the van's inverter can turn that stored power into something you can plug in. Checking one figure on its own can make a van look more capable than it is.
How much fresh water does a caravan need for off-grid travel?
That depends entirely on how many people, how many days between refills, and how carefully you use it. Every litre of water weighs one kilogram, so a 100L fresh tank is 100kg of payload the moment it is full, before anything else goes in. Work backwards from your own trip length and household size rather than assuming a bigger tank is automatically better.
Does a bigger battery always mean better off-grid capability?
Not on its own. A big battery bank with a small or absent inverter still cannot run a 240V appliance, and a big battery with a small solar array cannot refill itself quickly once it is drawn down. The battery, the solar and the inverter are one system, and the smallest of the three usually sets what the van can actually do.
What is payload margin and why does it matter for off-grid trips?
Payload is the gap between a van's Tare (empty) weight and its ATM, and it is everything you are allowed to add: water, gas, batteries, gear, food and people. Off-grid travel adds weight, mostly in full water tanks and extra battery capacity. A van with a tight payload can have big tanks and a big battery bank and still lack the legal allowance to carry them full. Our caravan weights guide explains how to work out your own figure.