How to Size a Solar Array for Your RV or Campervan

A well-sized solar array can keep an RV or campervan’s fridge, lights, fans, communications equipment and small appliances running without relying heavily on powered campsites. The right capacity depends on daily energy use, battery storage, available roof space and the amount of sunlight your route receives.

Australian travel conditions make the calculation especially important. A van touring from Melbourne to the Victorian High Country experiences different solar conditions from one spending winter around Brisbane or Darwin. Dust, shade, heat, rooftop accessories and several days of cloudy weather can all reduce the energy collected by photovoltaic panels.

Start with your daily energy budget

List every appliance you expect to use and record its wattage and hours of operation per day. Energy consumption is calculated in watt-hours: a 60-watt compressor fridge running for an estimated eight hours uses about 480 watt-hours, although its compressor normally cycles rather than operating continuously.

Include LED lighting, a water pump, roof fan, television, laptops, camera batteries, induction cooking and inverter losses. USB devices may use little individually, but several phones, tablets and navigation units can create a meaningful load during a long trip. For a practical estimate, add 15–25% to the total to cover wiring losses, standby consumption and imperfect assumptions.

Convert consumption into solar capacity

Once daily energy use is known, divide it by the expected usable peak-sun hours for your travel area. A campervan using 1,000 watt-hours per day and receiving four effective sun hours would appear to need a 250-watt array. In practice, that figure should be increased because panels rarely deliver their rated output for the entire solar window.

A useful planning formula is: solar array watts = daily watt-hours ÷ peak-sun hours ÷ system efficiency. Using 75–85% overall efficiency, the same 1,000-watt-hour load may require roughly 300–335 watts. This margin accommodates hot panels, dust, cable losses, imperfect orientation and brief shading from trees or roof equipment.

Account for Australian travel conditions

Australia has excellent solar potential, but the resource changes significantly by region and season. Adelaide, Perth and much of inland Australia can provide strong summer production, while Melbourne’s winter cloud and shorter days may require more panel capacity or greater battery reserves. Coastal humidity, red dust on an outback route and salt air near the coast can also affect maintenance and performance.

Free camping often means several days away from mains power, so sizing for the average sunny day alone can be risky. A traveller who spends weekends in a powered caravan park may manage with a smaller array, whereas a grey nomad travelling through remote Queensland may value extra capacity and a portable folding panel. Allow room for seasonal variation rather than designing around the best January conditions.

Match the array to your battery bank

Solar panels produce energy, while the battery stores it for use after sunset. A common Australian touring setup uses a 12-volt LiFePO4 battery, although larger vans may use 24-volt systems to reduce current and cable size. Battery capacity should cover overnight demand and provide a buffer for cloudy weather.

A 100Ah, 12.8-volt LiFePO4 battery stores approximately 1,280 watt-hours in theory. Its usable capacity is usually much greater than an equivalent lead-acid battery because it can safely use a larger proportion of its rated energy. Even so, a 200Ah bank may be more suitable for a van operating a compressor fridge, inverter, laptops and a fan over multiple days.

The panel array and battery must work together. A very large battery paired with a small array may never recharge fully, while oversized panels with limited storage can waste potential energy during low-load periods. Follow the battery manufacturer’s recommended charging current and confirm that the solar controller supports the battery chemistry.

Choose panels for the available roof

Measure the usable roof area before choosing a target wattage. Air conditioners, roof vents, skylights, satellite dishes and storage boxes create shade and may leave only narrow spaces for panels. Two or three smaller modules can sometimes use the roof more effectively than one large panel, particularly on a compact campervan.

Fixed rigid panels generally provide good durability and ventilation, while semi-flexible panels suit curved roofs and low-profile installations. Flexible products can be easier to install but may run hotter and have shorter service lives if bonded directly to a surface with little airflow. A portable panel can supplement a modest rooftop array when the van is parked under trees.

Parallel and series wiring each have advantages. Parallel connections can keep production going when one panel is partly shaded, while series connections can deliver higher voltage and reduce cable losses over longer runs. The final design should suit the MPPT controller’s voltage range, cable length and the conditions expected on Australian roads.

Use an MPPT controller and efficient wiring

An MPPT solar charge controller extracts more usable power than a basic PWM controller, especially when panel voltage is higher than battery voltage or temperatures are cool. Choose a controller with enough current capacity for the array and leave a reasonable allowance for future expansion. For example, a 400-watt array on a 12-volt battery can produce more than 25 amps under favourable conditions, so a 30-amp controller may be marginal depending on the manufacturer’s specifications.

Cable sizing matters in a mobile installation. Excessive voltage drop between the panels, controller and battery reduces charging performance and creates unnecessary heat. Use appropriately rated solar cable, fuses or circuit breakers, weather-resistant connectors and secure cable routing. Australian electrical and recreational-vehicle requirements should be checked, particularly when an inverter, mains charger or 240-volt wiring is included.

A battery monitor with a shunt gives a clearer view of state of charge than a simple voltage reading. It helps reveal whether the array is replacing the energy used each day and shows when a generator, alternator charger or powered campsite is needed. If an inverter is part of the system, understanding solar generator options can also help compare integrated and component-based power solutions.

Build in reserve for shade and bad weather

Solar sizing should reflect the least convenient days you expect to encounter, not just the ideal conditions. A van parked beneath eucalyptus trees may collect very little energy even under a bright sky. Partial shade can reduce output sharply, especially when panels are wired in series and one shaded module limits the string.

For regular short trips, a reserve of 20–30% above calculated demand is often practical. Remote travellers may choose 40–60% extra capacity, combine rooftop and portable panels, or carry an alternator-to-battery charger. A DC-DC charger can replenish the house battery while driving, which is useful after several cloudy days or during winter travel in Tasmania and Victoria.

Reduce consumption as well as increasing generation. A compressor fridge is generally more efficient than an absorption fridge running from an inverter, and laptops can often be charged directly through USB-C rather than through a large inverter. Shade the vehicle strategically, clean panels after dusty roads and avoid leaving the battery at a very low state of charge for extended periods.

Compare practical system sizes

The following examples assume a 12-volt LiFePO4 system, approximately 80% usable solar-system efficiency and average daily consumption rather than extreme weather. They are starting points rather than substitutes for a detailed load calculation.

Travel style	Approximate daily use	Suggested solar array	Suitable battery range
Basic weekend campervan	500–700 Wh	150–250 W	100 Ah
Fridge, lights and devices	800–1,200 Wh	300–400 W	100–200 Ah
Full-time touring with inverter	1,400–2,000 Wh	500–700 W	200–300 Ah
Remote or shaded-site travel	2,000 Wh or more	700 W plus portable support	300 Ah or more

These ranges assume sensible energy management and reasonable sunlight. Someone touring around sunny South Australia may obtain strong results from the lower end, while a vehicle spending winter among tall trees near the Great Ocean Road may need additional charging support. Roof limitations can also make a portable panel, second charging source or larger battery more useful than continually adding fixed modules.

The best design leaves enough headroom for future equipment without exceeding the controller, battery or roof limits. Check every component as a system: panel voltage, controller rating, battery charging profile, fuse protection, cable gauge and inverter demand all affect real-world reliability. A correctly sized array will keep the battery healthy, reduce generator use and make longer Australian journeys more comfortable.