How much solar do I need for a caravan off-grid?

Start with your daily watt-hour budget

Add the daily energy use of your fridge, lighting, fans, charging, water pump and any other loads. For each steady load, watts multiplied by operating hours gives watt-hours; use measured daily consumption for cycling appliances.

For example, a 12V fridge consuming 450Wh per day plus 150Wh of other loads gives a 600Wh daily energy target. These figures are illustrative, not a claim about any particular fridge.

Estimate solar harvest conservatively

An indicative planning equation is daily solar Wh ≈ panel watts × effective peak-sun-hours × overall system factor. Effective sun hours depend on location, season, orientation and shading; the system factor accounts for real-world losses.

For illustration only, a 200W panel × 4 effective sun hours × 0.7 system factor yields around 560Wh in a day. Actual output may be much lower in winter, cloud or partial shade.

Work backwards to panel watts

If you need 600Wh per day and assume four effective sun hours with a 0.7 factor, the indicative minimum is about 215W of panels (600 ÷ 4 ÷ 0.7). A practical system needs additional margin and may require substantially more panel capacity for poor weather.

Use location- and season-appropriate solar data rather than treating four hours as a universal Australian figure. Check the available roof area, portable panel positioning and how much battery reserve you need.

Match panels to the whole system

Confirm the solar controller's permitted input voltage and current, the battery's charging profile, cable ratings, connector polarity and the manufacturer's instructions. Panel wattage alone does not establish compatibility.

Portable panels can be moved out of shade; roof panels may charge without deployment but are limited by roof orientation and obstructions. Consider combining solar with appropriately designed alternator or mains charging.

Before you buy: checklist

• List daily energy use in Wh
• Choose seasonal and regional effective sun hours
• Allow for heat, angle, shade and controller losses
• Calculate indicative panel wattage with margin
• Check battery and regulator compatibility
• Plan for cloudy-day battery reserve

Frequently asked questions

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