A solar setup that keeps the fridge cold for two days but leaves the battery flat before breakfast on day three is not a good off-grid system. For caravan travellers, campers and 4WD owners, learning how to plan off grid solar starts with a realistic look at how you use power, not with choosing the biggest panel that will fit on the roof.
The right system is a balance of panel capacity, battery storage, charging equipment, cable sizing and the way you travel. A van that moves most days can rely heavily on roof solar and vehicle charging. A rig parked under trees for a week needs more battery capacity, portable panels or another charging option. Planning those details before buying components prevents expensive mismatches later.
Start with the power you actually use
Every off-grid solar plan begins with a daily energy budget. List the 12V appliances you expect to run, how many watts they draw and how long they operate each day. Fridges, lights, water pumps, fans, phone charging, TV systems, satellite receivers and CPAP machines are common loads in caravans and motorhomes.
The basic calculation is straightforward:
Watts x hours used per day = watt-hours per day
For example, a 50W television used for four hours consumes about 200Wh. A 12V compressor fridge is harder to calculate because it cycles on and off, but its manufacturer’s specification or real-world monitoring figures will provide a useful daily estimate. In warm Queensland conditions, a fridge working in a sun-exposed caravan can use considerably more power than it does in mild weather.
Add every item together, then include a sensible margin. Ten to 20 per cent is usually worthwhile for charging losses, unexpected use and appliances that draw more than their label suggests. If you plan to use a 240V inverter for a coffee machine, air fryer, hair dryer or microwave, treat those loads carefully. They may only run briefly, but they can demand a large amount of current from the battery and a suitably sized inverter.
Do not confuse watts, watt-hours and amp-hours
Watts describe the rate at which an appliance uses power. Watt-hours describe total energy used over time. Amp-hours are commonly used to describe battery capacity, but only make sense when you also know the system voltage.
A 200Ah lithium battery at 12.8V stores roughly 2,560Wh of energy. Not all of that should necessarily be considered available, depending on the battery’s recommended discharge limit and the battery management system. Lithium batteries generally offer more usable capacity and faster charging than lead-acid batteries, but they cost more upfront and need compatible charging settings.
Size the battery before choosing solar panels
Your battery bank determines how long you can operate when solar production is poor. This is particularly relevant during wet weather, winter travel, or campsites shaded by gums and awnings.
For a basic weekend setup, one day of usable battery capacity may be enough. For free camping or extended stays, planning for two or three days gives far better flexibility. If your estimated daily use is 1,000Wh, a battery bank with around 2,000 to 3,000Wh of usable capacity is a practical starting point for two to three days of autonomy.
It depends on your travel style. Grey nomads moving every day may prioritise battery charging from the vehicle while driving. A family staying at a remote bush camp may need more storage for lights, fans, devices and entertainment. A larger battery is not automatically the answer if the charging system cannot refill it in reasonable conditions.
Also check the battery’s continuous discharge rating. A battery may have ample capacity for a fridge and lights but be unable to supply the current required by a large inverter. The battery management system, cables, fuses and isolators must all be rated for the expected load.
How to plan off grid solar panel capacity
Once you know your daily consumption, select enough solar to replace that energy during average usable sunshine. In much of Australia, a fixed roof panel will not produce its nameplate output all day. Panel angle, heat, cloud, dirt, shading and the position of the caravan all reduce production.
A practical planning rule is to allow for around four to five useful sun-hours per day in favourable conditions, then account for system losses. A 400W solar array might theoretically produce 1,600 to 2,000Wh on a good day. In reality, its output can be far lower in winter, in overcast weather or when one small shadow falls across part of the panel.
For that reason, avoid sizing a system so tightly that it only works under perfect skies. If your daily budget is 1,000Wh, 400W of quality solar can be suitable for many touring setups, particularly when combined with a lithium battery and DC-DC charging. If you routinely run a compressor fridge, TV, satellite equipment, fans and charging devices while staying put, 600W or more may be justified where roof space permits.
Fixed panels, portable panels or both?
Roof-mounted panels are convenient because they charge whenever the sun is available. They are ideal for travellers who move regularly and do not want to set up equipment at every stop. Their limitation is that the caravan or motorhome must be parked in the sun.
Portable solar panels let you park in shade while placing the panel in clear sunlight. They can also be aimed towards the sun for better output. The trade-off is setup time, storage space, security and the need to avoid damage from wind, vehicles or foot traffic.
For many caravans, the most practical arrangement is fixed roof solar for daily charging plus a portable panel for longer stays or shaded sites. This gives you a useful backup without relying on portable solar every day.
Choose the right charge controller and charging sources
Solar panels need a regulator between the array and battery. An MPPT solar controller is generally the better choice for caravan and off-grid systems because it can convert excess panel voltage into useful charging current more efficiently than a basic PWM regulator. This becomes especially valuable with higher-voltage panel configurations and in cooler conditions.
The controller must suit the solar array’s voltage and current, as well as the battery chemistry. Check its maximum PV input voltage, output current rating and charging profiles. A controller that is too small can limit output or be damaged; one with incorrect lithium settings may not charge the battery properly.
Solar should not be the only charging path where reliability matters. A DC-DC charger connected to the tow vehicle or motorhome alternator can replenish the battery while driving, and it is particularly useful after cloudy weather. If you use powered sites from time to time, a quality 240V mains charger provides another recovery option. These sources work together, but they must be installed and configured correctly to suit the battery.
Plan for safe wiring, protection and monitoring
Good components can still perform poorly with undersized cable or poor connections. Long cable runs create voltage drop, which reduces charging performance and can cause sensitive equipment to shut down. Keep cable runs as short as practical and select cable size based on current, length and allowable voltage drop.
Every circuit needs suitable protection. Solar inputs, battery connections, DC-DC chargers, inverters and distribution circuits require correctly rated fuses or circuit breakers placed close to the energy source where appropriate. Battery isolation, secure cable routing and protected terminals are equally important in caravans and 4WDs that endure vibration, dust and corrugated roads.
A battery monitor is one of the most useful additions to an off-grid system. Voltage alone is a poor guide to lithium battery state of charge. A proper shunt-based monitor shows current flowing in and out, energy consumed and remaining capacity. It turns guesswork into information you can use before the battery reaches a low-voltage cut-out.
Allow for the conditions you will travel in
Australian conditions are hard on electrical systems. Heat reduces solar efficiency and can affect battery performance. Dust, salt air and rain demand weather-resistant equipment and sensible mounting. A roof panel installation needs solid brackets, sealed cable entries and enough clearance for airflow beneath the panels.
Think about where equipment will live. Batteries should be mounted securely in a suitable location, away from direct heat and protected from physical damage. Inverters need ventilation. Portable panels need connectors that are compatible with the regulator arrangement, not simply a plug that happens to fit.
Before heading away, test the whole system at home. Run the fridge, TV, satellite receiver or VAST setup, lights and charging devices as you would at camp. Watch the battery monitor through an evening and the next morning. This is the easiest time to find a weak connection, unexpected load or charging issue.
A well-planned off-grid system should suit the way you travel rather than force you to ration power constantly. If you are unsure whether a panel, lithium battery, MPPT controller, DC-DC charger and inverter will work together, getting practical advice before installation is cheaper than replacing the wrong component after the first trip. Access 2 QLD Antennas and Satellites can help match caravan-ready power equipment to your expected loads, available space and travel plans.