Size a caravan or camping solar system correctly using daily consumption, the panel, charge controller, battery, inverter and safety steps.
Short answer: A solar system for a caravan is not chosen by looking at panel wattage. First you work out the daily energy consumption; then the solar generation, battery capacity, charge controller, inverter and the cabling and protection devices are sized so that they work together. Portability, shading and limited roof area are the fundamental differences in this kind of design.
This guide is for general information. Changes made to a vehicle's electrical installation can create a risk of fire and electric shock; the manufacturer's instructions and a check by a competent installer should be taken as the basis.
First step: work out your daily energy budget
For each appliance, write down the power in watts and the daily running time in hours. Approximate daily consumption is calculated in Wh by multiplying watts by hours. For example, a high-power appliance that runs briefly and a low-power refrigerator that runs all day create very different load profiles. The duty cycle of the refrigerator compressor, lighting hours, phone and laptop charging, the water pump and ventilation should each be considered separately.
Resistive, high-power 230 V appliances such as a coffee machine, hairdryer, kettle or air conditioner quickly increase the size of the system. Whether these appliances are genuinely necessary, and whether gas or lower-power alternatives exist, directly affects the design decision. A safe margin for cable, inverter and charging losses should be added to the calculation.
How is panel capacity determined?
A panel's rated power is the peak value under laboratory conditions. On a caravan, the panel lying flat, shading during the day, high temperatures, soiling and seasonal variation can all reduce actual generation. Fixed assumptions of the form "an X watt panel generates Y Wh every day" are therefore not reliable. The route, the season and the style of camping all need to be taken into account.
A roof-mounted fixed panel offers ease of use and the advantage of generating while driving. However, generation drops when the caravan is parked in tree shade. A folding or portable panel can be aimed at the sun; in return, setting it up, cable safety and the risk of theft have to be managed each time. For most users, considering fixed and portable panels together provides flexibility.
What does an MPPT charge controller do?
The charge controller manages the flow of energy between the panel and the battery. An MPPT controller tracks the panel's optimum operating point and converts the energy to battery voltage under changing solar conditions. When selecting one, it is not only the amp rating that matters; the permitted panel open-circuit voltage, the system voltage, temperature limits and compatibility with the battery chemistry must all be checked.
The panel array's open-circuit voltage in cold weather must not exceed the device's limit. Cable cross-section, run length and connection quality affect voltage drop and heating. Each circuit — between panel and controller, and between controller and battery — must be protected by a suitable fuse or circuit breaker.
Battery capacity and usable energy
A battery's amp-hour rating alone is not enough; it should be converted into energy in Wh together with the system voltage. In addition, the full nominal capacity is not used. The usable proportion depends on the battery chemistry, the manufacturer's discharge limit, temperature and the expected cycle life. Lead-acid and LFP batteries do not have the same charging profiles or the same usable capacity.
The number of sunless days you are designing for is the main input that determines battery size. A caravan used only in summer and driven regularly does not need the same capacity as a vehicle that stays parked at a campsite for long periods in winter. The battery should be positioned with ventilation, mechanical fixing, short-circuit protection and suitable temperature conditions in mind.
When is an inverter needed?
An inverter converts the DC energy in the battery into 230 V AC. It is needed only if AC appliances are going to be used. Running whatever appliances you can directly at a suitable DC voltage can reduce conversion losses. The inverter's short-term surge power matters as much as its continuous power; compressors and motor-driven appliances can draw much more power on start-up.
A pure sine wave inverter is in most cases the more suitable choice for sensitive electronics and motor-driven appliances. The inverter should be located close to the battery in a ventilated, dry position, and the DC cables should be short and of the correct cross-section. If the inverter output is to be connected to the vehicle's fixed wiring, the residual current and earthing arrangement should be designed by a specialist.
How are alternator and mains charging added to the system?
Solar does not have to be the only energy source. A suitable DC-DC charger can be used to charge from the alternator while driving. On newer vehicles with smart alternators, a direct connection may not give the expected result and may damage the vehicle's electrical system. The vehicle manufacturer's limits and the cable and fuse ratings must be verified.
Charging from the campsite mains requires an AC charger suited to the battery chemistry. In a system where more than one source charges the same battery, the voltage settings and temperature sensors must be compatible. A system monitor makes it easier to track not only voltage but also current and the calculated state of charge.
Installation safety checklist
- Verify the panel's mechanical fixing against road vibration, wind and water ingress.
- Use a fuse or circuit breaker of the correct type and rating close to every power source.
- Select cable cross-section according to current, length, ambient temperature and the accepted voltage drop.
- Protect cables from sharp edges, hot surfaces, moving parts and crushing.
- Fix the battery mechanically and comply with the manufacturer's ventilation and temperature requirements.
- Separate the AC and DC circuits, label them, and leave them accessible for maintenance.
If a portable panel's cable crosses a walkway it creates a trip and crush hazard. Connectors should not be left open in the rain, and the circuit should be safely isolated before the panel is packed away.
Frequently asked questions
There is no single correct figure. Daily appliance consumption, the travel season, shading, panel orientation and the reserve time you want from the battery all have to be calculated together.
A fixed panel offers ease of use; a portable panel lets you park the caravan in the shade and aim the panel at the sun. The two solutions can also be used together.
No. It is needed only if 230 V AC appliances are going to be used; suitable DC appliances can reduce inverter losses.
It can be integrated using a suitable DC-DC charger and taking the vehicle manufacturer's limits into account; an unprotected direct connection should not be made.
Conclusion: the use case comes before the panel
A successful caravan solar system is built not by buying the biggest panel but by reducing the energy requirement and selecting compatible components. Once the daily Wh table, the expected solar conditions and the reserve time are established, the choice of panel, battery and inverter becomes traceable. For more comprehensive systems for permanent living, you can review our off-grid solutions , or use the contact page for a preliminary technical assessment.
Cover photograph: Philip Halling, "Romany caravan with solar panels", Geograph/Wikimedia Commons, CC BY-SA 2.0 . The image has been converted to WebP. Source image .
