Campervan Solar Power Calculator
Designing an off-grid campervan electrical system starts with understanding how much solar energy is realistically available where you plan to travel. This tool estimates the average daily solar power generation by month for any location in the world based on your solar panel size and system efficiency.
The solar data used in this calculator comes from the NASA POWER (Prediction Of Worldwide Energy Resources) dataset, which provides long-term global averages of solar irradiance. The calculator converts this data into peak sun hours and then estimates how much electrical energy your solar panels could generate each day.
Estimated daily generation is calculated using:
Solar panel watts × peak sun hours × system efficiency
Peak sun hours represent the equivalent number of hours per day that sunlight averages 1000 W/m², which is the standard condition used to rate solar panels.
The NASA dataset used here measures global horizontal irradiance, which represents solar energy falling on a flat horizontal surface. Because campervan solar panels are normally mounted flat on the roof, this provides a realistic estimate of solar production for van and RV installations.
Solar systems with tilted panels (such as residential rooftop arrays) may produce somewhat more energy, particularly during winter when the sun is lower in the sky. However, for campervans and other mobile installations with flat-mounted panels, these estimates are generally a good approximation of real-world performance.
Because this tool uses long-term climatological averages, the results should be used for system planning rather than predicting exact daily output.
How to Use This Tool for Campervan Solar Planning
A good solar system design starts with planning for the worst realistic conditions, not the best ones. This calculator helps you understand how solar energy changes throughout the year so you can size your system accordingly.
A practical approach is:
1. Decide where and when you will travel
Think about the locations and seasons where your campervan will spend time off-grid. Solar energy varies significantly with latitude and time of year.
For example:
- Winter in southern New Zealand
- Northern Europe in autumn
- Canadian mountain regions in spring
These conditions often represent the lowest solar production your system will experience.
2. Estimate your daily power consumption
Before sizing solar panels, estimate how much energy your campervan uses each day.
Typical off-grid loads might include:
- 12V fridge
- lighting
- water pump
- diesel heater fan
- device charging
- laptop use
- ventilation fans
This gives you a daily energy demand in watt-hours (Wh).
3. Enter your solar panel size
Enter the total wattage of the solar panels installed on your campervan roof.
For example:
- 200W – small van builds
- 400W – common campervan systems
- 600–800W – larger off-grid setups
4. Set a realistic system efficiency
Solar systems never operate at 100% efficiency. Losses occur from:
- temperature
- wiring
- charge controllers
- dust or dirt on panels
- shading
- flat mounting angle
A good planning value is typically 65–85% system efficiency.
5. Compare generation across months
The chart shows the estimated average daily energy generation for each month.
Pay particular attention to:
- worst month generation
- average generation
- best month generation
Sizing your system for the worst month you expect to rely on solar ensures your setup works year-round.
Section: Sharing results
Sharing Solar System Estimates
This tool allows you to easily share your results when asking for advice or discussing system designs.
You can:
Copy a shareable link
The share link includes:
- location
- solar panel wattage
- system efficiency
Anyone opening the link will see the same solar generation estimate.
Download the chart as an image
The chart download includes:
- location
- solar panel size
- efficiency
- estimated daily generation by month
This makes it easy to share your setup in:
- campervan forums
- Facebook groups
- solar design discussions
- build blogs
Copy a system summary
The summary includes:
- location
- panel wattage
- efficiency
- worst / average / best month generation
- solar hours reference
This is useful when asking questions like:
“Will this solar setup be enough for winter?”
Important real-world considerations
While solar averages are useful for planning, real-world output depends on several factors including:
- shading from trees or buildings
- weather conditions
- panel tilt and orientation
- seasonal sun angle
- snow, dust, or dirt on panels
For campervans with flat roof-mounted panels, actual production can sometimes be 10–30% lower than theoretical values.
For this reason many off-grid builds combine solar with:
- alternator charging
- shore power charging
- larger battery storage