How does the solar panel calculator work?
The solar panel calculator determines how many solar panels you need and which charge controller is recommended. Based on your daily consumption, the number of peak sun hours and system efficiency, you get a concrete recommendation.
Calculating required wattage
The required panel wattage is calculated as: daily consumption (Wh) / (peak sun hours × efficiency). The efficiency accounts for losses in the charge controller, wiring, panel temperature and non-optimal angle. Typically this is between 70% and 80%. The number of panels is the required wattage divided by the wattage per panel, rounded up.
Sizing the charge controller
The recommended charge controller is calculated as: total installed panel wattage / battery voltage × 1.25 safety margin. The 25% margin protects against peak moments during optimal sunlight and low temperatures, when panels deliver more current than their rated value.
Peak sun hours by region
Peak sun hours indicate how many hours per day the sun shines at full power. In the Netherlands this averages 3–4 hours per day (annual basis). In Southern Europe (Spain, Italy, Greece) it is 5–6 hours. In winter, this can drop to 1 hour per day in the Netherlands. Design your system around the season you will use the van the most.
Sources and standards
Peak sun hours (PSH) are based on data from KNMI (Netherlands), PVGIS (EU Joint Research Centre) and NASA Surface Meteorology. STC specifications of solar panels (25°C, 1000 W/m²) are defined in IEC 61215. The system efficiency of 75-80% is a common rule of thumb combining losses from temperature (-0.4%/°C for silicon), wiring (1-3%), controller efficiency (95-98% MPPT) and non-optimal tilt angle. The 25% safety margin for the charge controller follows the recommendation of Victron Energy and other manufacturers.
Frequently asked questions
How many sun hours should I use?
For the Netherlands and Belgium, use an average of 3–3.5 peak sun hours per day on an annual basis. In summer it is 5–6 hours, in winter only 1–2 hours. If you mainly travel in Southern Europe, you can use 5–6 hours. Choose a conservative value if you want enough power even during overcast periods.
What is the difference between PWM and MPPT?
A PWM controller (Pulse Width Modulation) is simple and cheap but does not use the full power of your panels. An MPPT controller (Maximum Power Point Tracking) optimises the panel voltage and extracts up to 30% more energy from the same panels. For camper vans, MPPT is almost always recommended.
What efficiency should I set?
An efficiency of 75–80% is realistic for a well-installed system with an MPPT controller. With shading, dirty panels, very high temperatures or a PWM controller, efficiency can drop to 60–70%. Flat mounting on the roof costs about 10% compared to the optimal angle.
What is the difference between Wp and actual output?
Wp (Watt-peak) is power under ideal test conditions (25°C, full sun). In practice you produce 60-80% of this, depending on temperature, shade and panel mounting.
How many solar panels fit on a camper van?
A standard van (Sprinter/Ducato) fits 400-800Wp. On a long wheelbase up to 1200Wp. Flexible panels use roof area better but produce slightly less per Wp.
What is better: MPPT or PWM charge controller?
MPPT is 20-30% more efficient than PWM and works better in cloudy conditions and higher panel voltages. PWM is cheaper but only suitable for small systems (<200Wp).