“How long can we stay?” sounds like a camping question, but for an off-grid caravan it is really an energy-balance question. Your answer changes with the battery’s usable energy, the appliances you run, the solar energy recovered and the reserve you keep for poor conditions.
The practical answer: estimate daily demand in watt-hours, subtract realistic daily solar recovery, then compare any remaining daily shortfall with usable battery energy. The free Off-Grid Days Calculator organises those figures into a planning estimate. It cannot promise a number of days because weather, shade, temperature, equipment condition and changing behaviour all affect the result.
Why off-grid endurance is not one fixed number
A caravan might last several days during cool, clear weather and far less during hot, cloudy weather. A compressor fridge may work harder in heat. Fans, communications and water pumps may run longer. Rooftop solar can be shaded just when demand rises.
It is more useful to create at least two scenarios: a reasonable good-weather case and a conservative poor-weather case. Treat the poorer result as the basis for reserves, not as a prediction that conditions will behave exactly that way.
The energy terms in plain English
Amp-hours, volts and watt-hours
Amp-hours (Ah) describe electrical charge. Voltage (V) describes electrical potential. Multiplying amp-hours by nominal voltage gives an approximate nominal energy figure in watt-hours (Wh):
Nominal energy (Wh) = battery capacity (Ah) × nominal voltage (V)
Watt-hours are useful because appliance demand and solar recovery can be compared in the same unit. Amp-hours alone are not directly comparable when system voltages differ.
Usable energy and reserve
The nameplate figure is not automatically the amount you should plan to consume. Battery chemistry, battery-management settings, manufacturer limits, age, temperature and condition affect usable energy. Enter the usable percentage supported by your battery manufacturer and system settings, while retaining an appropriate reserve.
Daily consumption
Daily consumption is the energy used by all loads over 24 hours. A 40-watt appliance running for five hours uses about 200 Wh. Cycling appliances need a measured or manufacturer-supported daily estimate rather than rated watts multiplied by 24.
Solar recovery
A planning estimate is:
Solar recovery (Wh/day) = array watts × effective peak-sun hours × overall efficiency
Effective peak-sun hours are an energy-equivalent planning input, not simply daylight hours. Overall efficiency represents real losses and operating conditions. The Bureau of Meteorology shows that Australian solar exposure varies with location, season, cloud and the sun’s position.
Figures to collect before calculating
- Battery-bank capacity in Ah and its nominal system voltage.
- Manufacturer-supported usable capacity or reserve settings.
- Battery age, chemistry, condition and any monitoring data.
- Daily Wh for the fridge, lights, pumps, fans and television.
- Daily Wh for phones, laptops, cameras, satellite communications and other charging.
- Inverter appliance demand including conversion and standby losses.
- Solar-array rated watts and controller specifications.
- Conservative effective sun-hours and system-efficiency assumptions for the place and season.
- Any non-solar charging you can genuinely rely on.
Use monitoring data from a normal trip where possible. A product label gives rated power, while a shunt or energy meter can show what your particular setup actually consumes.
Build a realistic daily appliance budget
Begin with equipment that must run, then add comfort and communication loads. Separate “always planned” loads from discretionary ones. This makes it easier to respond calmly if recovery falls behind.
- Refrigeration: record measured daily use in representative weather if possible.
- Lighting: multiply each light’s watts by expected hours, then total them.
- Water pump: use measured daily energy or realistic minutes of operation.
- Fans: include overnight operation during warm weather.
- Communications: include routers, satellite equipment and device charging.
- Inverter loads: include appliance energy plus conversion and standby losses.
Do not count only the obvious high-power appliance. Many moderate loads running for hours can dominate a daily total.
A worked good-weather and poor-weather example
Consider a fictional 12 V, 300 Ah battery bank with 80% entered as usable before the chosen reserve:
- Nominal energy: 300 Ah × 12 V = 3,600 Wh.
- Usable stored energy: 3,600 Wh × 0.80 = 2,880 Wh.
- Daily appliance demand: 1,200 Wh.
- Solar array: 400 W.
Good-weather planning case
With 4.5 effective sun-hours and 75% entered efficiency:
400 W × 4.5 × 0.75 = 1,350 Wh/day estimated recovery.
Recovery exceeds the 1,200 Wh daily estimate by 150 Wh. That does not mean unlimited power: the battery must begin in a suitable state, the controller must accept the energy, and individual days will vary.
Poor-weather planning case
With 1.5 effective sun-hours and the same efficiency:
400 W × 1.5 × 0.75 = 450 Wh/day.
Daily shortfall becomes 1,200 − 450 = 750 Wh/day. The simplified endurance to the chosen reserve is 2,880 ÷ 750 = 3.84 days. In practice, round down and preserve contingency rather than planning to arrive exactly at the reserve.
Why real endurance differs from the calculation
Solar panels rarely deliver their rated output for every effective hour. Shade from a tree, aerial or roof equipment can materially reduce recovery. Heat can reduce panel output. Dust, orientation, cloud and controller behaviour also matter.
Battery capacity can be lower than the original nameplate figure as a system ages or operates outside ideal temperatures. Cables, chargers and inverters introduce losses. Appliance use changes with weather and people. A calculator can make assumptions visible, but it cannot remove those uncertainties.
Plan reserves and decision points
Choose a battery state at which you will reduce discretionary loads, relocate, use an approved alternative charging method or seek powered accommodation. Do not wait for equipment to shut down unexpectedly.
A simple priority list might protect refrigeration, water pumping, lighting and essential communications first. Entertainment, heating appliances through an inverter and non-essential charging can be reduced. Never bypass battery-management protections or improvise unsafe charging.
Write the decision point into the trip plan and share it with everyone travelling. A reserve is only useful when the group understands which loads will be reduced and when a campsite or route must change.
Common off-grid planning mistakes
- Using battery Ah without considering voltage or usable percentage.
- Entering appliance watts as though they were daily watt-hours.
- Assuming rated solar watts are produced all day.
- Planning from the best summer day for a winter or shaded campsite.
- Omitting inverter standby and conversion losses.
- Treating an energy-positive average as a guarantee for every day.
- Changing battery or charging equipment without qualified advice.
A calm pre-trip routine
- Record the system specifications and manufacturer limits.
- Measure a normal day’s appliance use.
- Create good- and poor-weather solar scenarios.
- Choose a reserve and clear action point.
- Test the system close to home before depending on it remotely.
- Monitor daily use, solar input and battery state during the trip.
- Update the estimates when people, weather or equipment change.
The published off-grid power, water and communications guide provides a broader remote-camping framework. For the units behind this calculation, read caravan battery capacity explained and how much solar a caravan may need.
Electrical safety and professional help
This article does not provide installation instructions. Follow battery, inverter, controller and appliance manufacturer requirements. Lithium-ion batteries can present serious fire risks if damaged, overheated, incorrectly charged or modified. Stop using equipment showing swelling, leakage, unusual heat, damage or venting and follow manufacturer and emergency guidance.
Caravan electrical work is regulated. Use appropriately qualified or licensed people for design, installation, alteration and inspection where required. WA Building and Energy notes that caravan wiring must comply with AS/NZS 3001; requirements and enforcement arrangements can differ by jurisdiction.
Ready to estimate your own off-grid days?
Gather the battery, daily-use and solar figures above, then use the free Australian Off-Grid Days Calculator. Run more than one weather scenario and keep a practical reserve.
The result is a planning estimate, not an electrical design or guarantee of endurance. You can also explore all free Australian caravan calculators and tools.
Frequently asked questions
Does energy-positive mean I can stay indefinitely?
No. It means the entered average solar recovery meets or exceeds entered average use. Weather, shade, equipment limits and battery state still vary.
Should I enter appliance watts or Wh per day?
Enter daily watt-hours. For cycling appliances, monitoring data is usually more useful than rated watts alone.
Can I compare Ah between 12 V and 24 V systems?
Not directly. Convert both to watt-hours using their nominal voltage and then consider usable capacity.
What if the calculator shows less than one day?
Recheck inputs, identify essential loads and seek qualified advice before depending on the system. Do not simply reduce a manufacturer-required reserve.
Does the estimate include alternator or generator charging?
No, unless that energy is explicitly and realistically included. Use only approved equipment and manufacturer-supported methods.
Sources and safety note
Last checked: 12 August 2026.
- Australian Government — Solar PV and batteries
- ACCC Product Safety — Lithium-ion batteries guide
- Bureau of Meteorology — Average daily solar exposure maps
- WA Building and Energy — Camping safely with gas and electricity
This article provides general educational information. Verify manufacturer limits and current jurisdictional requirements, and use appropriately qualified electrical professionals.