How much solar do I need for a campervan?
Solar is the difference between watching your battery monitor and forgetting it exists. The trick is matching the panels to what you use, not the roof space you happen to have. Work out your daily power use, know what a panel realistically makes in the UK, and the wattage you need is straightforward. Here is how it works.
The method in three steps
Solar sizing comes down to covering your daily use with a sensible margin for cloudy days.
Total the amp hours you get through in a day. A fridge, lights and charging is around 40 to 60Ah. Add heating, water and a TV and you are nearer 75 to 90Ah.
In the UK, a flat-mounted 100W panel with a good MPPT puts back around 25Ah a day on average between April and October. High summer is more, the shoulder months less.
Divide your daily use by what 100W gives you, then add a panel for cloudy days. Aim to replace most of what you use, and let the battery carry you through the dull spells.
How much panel for your use
A practical starting point for the UK in the touring season. Figures assume flat roof mounting and a Victron-style MPPT.
| Your daily use | Solar gives back | Panel to aim for |
|---|---|---|
| Light weekenderFridge, lights, charging, around 40Ah a day | ~25Ah from 100W | 150 to 200W |
| Typical touringHeater, water, TV, around 75Ah a day | ~50Ah from 200W | 300 to 400W |
| Heavy or full-timeInverter cooking, around 120Ah a day | ~75Ah from 300W | 500W+ or hook-up |
| Winter useShort days, low sun, any setup | A fraction of summer | Plan to drive or hook up |
Solar in a British winter does very little, so size your battery for the dark months and treat solar as a strong April-to-October bonus. Run your exact panels and month in the solar calculator.
What changes your real yield
Two identical vans with the same panel can get very different results. The things that matter most:
- Time of year. A panel in June can make four or five times what it makes in December. Most of your solar happens between April and October.
- Shading. Even a small shadow from a roof vent, aerial or overhanging branch can knock a panel right down. Keep them clear.
- Mounting. Flat on the roof is convenient and what most vans use. A panel tilted towards the sun makes noticeably more, especially in the shoulder months.
- Controller. An MPPT controller harvests more than an older PWM type, particularly in cooler, brighter conditions. It is worth the extra.
The calculator accounts for the season and conditions so you get a realistic figure rather than the optimistic number on the panel box.
Solar and battery work together
Solar and battery size are two halves of the same question. Solar replaces what you use during the day. The battery carries you through the night and the dull spells when the panels are not keeping up. Undersize either one and the system disappoints.
The sensible approach is to size the battery for the worst conditions you expect, then add enough solar to keep it topped up in normal use. Start with the battery size calculator, then the solar calculator, and the two numbers will tell you whether you are balanced.
