Daily Solar Energy Calculator

This page is designed to answer the question:

"How much power will a solar panel generate".

Use this tool to calculate the average daily insolation anywhere in the world, by month. Useful for vanlife builders looking to estimate real solar panel output.

Daily Solar Insolation Calculator

This calculator is based on NASA CERES project data. The last seven years of data has been processed and incorporated into this tool.

The amount of solar energy available in a given location depends on a number of factors:​

  • Weather

  • Season

  • Location (latitude and longitude)

  • Altitude

  • Solar panel orientation

This tool account for all of the above assuming panels are horizontal.

What does insolation mean?

Insolation refers to the amount of energy (in Joules or more commonly kilowatt hours) per unit area for a given time. For solar array sizing the most useful units are in kWh per m² per day. 

Irradiance is another term thrown around. Solar irradiance is the amount of power (in Joules per second or Watts) arriving at any moment. It's a measure of the energy arriving per unit area, per second. Common units are W per m².


This tool provides insolation data which is useful for sizing solar systems.

What about panel orientation?

This calculator assumes solar panels are mounted horizontally (e.g. on the roof of a truck or van) and do not track the sun throughout the day. This is the most common setup for vehicle-based systems and therefore most relevant to val life, expedition trucks, and overlanders.

For this purpose it is necessary to use horizontal insolation data. As pictured above direct normal insolation data assumes the square meter of interest is exactly facing the sun which is rarely the case in camper builds. This tool outputs the horizontal insolation.

Daily Solar Insolation Calculator

Start typing address then select from dropdown


Manually enter latitude and longitude

Latitude (decimal)

Longitude (decimal)


What next?

Calculate how much power a panel or array will produce per day

Multiply the value for a given month by the wattage of your solar array.


This might seem like a strange calculation but it works because of how the manufacturer tests the wattage (under Standard Test Condition STC)

Or to get the result in kWh:

The result is the expected power generated for an average day in January at the location you input at the top.


Calculate how much power can be produced per m²

This calculation requires an addition piece of information, the module efficiency of the solar panels.

Module efficiency ranges from about 15% to 23% with the higher values achieved by the latest and most expensive solar panels.

For a safe estimate assume 15%.

Technical References and Resources

Links to other calculators 

Other tools are available from unaffiliated websites. These can be used to cross-validate any results, or use them if you prefer.

[1] Calculator from the Solar Electricity Handbook website

[2] Tool from Cableizer

[3] Map based tool from Global Solar Atlas

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