How to obtain solar radiation data?

May 18, 2026

How to Obtain Solar Radiation Data

Visual Crossing provides historical, current, and forecast solar radiation data through the Weather Data tools and the Timeline Weather API.

Solar data can be useful for:

Solar-energy analysis
Photovoltaic system planning
Agriculture
Crop modeling
Building-energy analysis
Environmental research
Irrigation and evapotranspiration studies
Weather and climate analysis

The standard Weather API includes core solar fields such as:

solarradiation
solarenergy

Additional energy-focused solar elements are also available on supported subscription levels, including:

dniradiation
difradiation
ghiradiation
gtiradiation
sunelevation
sunazimuth

You can explore and download solar data using Visual Crossing Weather Data or retrieve it programmatically using the Visual Crossing Weather API.

If you do not already have an account, you can sign up for Visual Crossing Weather.

What is solar radiation?

Solar radiation is electromagnetic energy from the sun reaching the Earth’s surface.

The amount of solar radiation available at a location depends on factors including:

Time of day
Season
Latitude
Cloud cover
Atmospheric conditions
Terrain and surface orientation

Solar radiation is commonly expressed as power per unit area:

W/m²

or watts per square meter.

This represents the rate at which solar energy is reaching a surface.

Solar radiation versus solar energy

The two core Visual Crossing solar elements represent different quantities.

`solarradiation`

solarradiation represents solar radiation power.

Units:

W/m²

For hourly data, it describes the solar radiation associated with the hourly period.

For example:

solarradiation = 650

means solar radiation of approximately:

650 W/m²

for that record.

`solarenergy`

solarenergy represents the amount of solar energy accumulated during the period.

Units:

MJ/m²

For example:

solarenergy = 2.34

means approximately:

2.34 megajoules per square meter

of solar energy accumulated during that record’s period.

The distinction is similar to the difference between:

power

and:

energy

Power describes the rate at which energy is being received, while energy describes the amount accumulated over time.

Converting solar energy to kWh/m²

Solar-energy applications often use:

kWh/m²

instead of MJ/m².

The conversion is:

1 kWh = 3.6 MJ

Therefore:

kWh/m² = MJ/m² ÷ 3.6

For example:

solarenergy = 18 MJ/m²

is:

18 ÷ 3.6 = 5 kWh/m²

Core solar fields

The standard solar fields available in Visual Crossing Weather Data include:

Element	Description	Units
`solarradiation`	Solar radiation power	W/m²
`solarenergy`	Accumulated solar energy	MJ/m²

These values use the same units across the standard Visual Crossing unit groups.

For the complete field definitions, see the Weather Data Documentation.

Advanced solar radiation fields

Visual Crossing also provides more detailed solar-energy elements for supported subscription levels.

These include:

Element	Description
`dniradiation`	Direct normal irradiance
`difradiation`	Diffuse horizontal radiation
`ghiradiation`	Global horizontal radiation
`gtiradiation`	Global tilted radiation
`sunelevation`	Solar elevation angle
`sunazimuth`	Solar azimuth angle

These advanced fields are particularly useful for photovoltaic and solar-energy applications.

See Energy Elements in the Timeline Weather API for current availability and subscription requirements.

Direct normal irradiance

The:

dniradiation

field represents direct normal irradiance.

This is the direct solar radiation arriving from the direction of the sun, measured on a surface perpendicular to the incoming solar rays.

It is commonly abbreviated:

DNI

DNI is especially important for:

Concentrated solar power
Solar tracking systems
Solar-resource analysis

Units:

W/m²

Diffuse horizontal radiation

The:

difradiation

field represents diffuse solar radiation reaching a horizontal surface from the sky.

This energy has been scattered by:

Clouds
Aerosols
Molecules in the atmosphere

It is commonly associated with diffuse horizontal irradiance.

Units:

W/m²

Global horizontal radiation

The:

ghiradiation

field represents global horizontal radiation.

This combines direct and diffuse solar radiation on a horizontal surface.

It is commonly abbreviated:

GHI

GHI is one of the most widely used measurements in solar-energy analysis because it describes the total solar radiation available to a horizontal surface.

Units:

W/m²

The core:

solarradiation

and advanced:

ghiradiation

elements both represent global horizontal solar radiation, but they can be derived from different source diagnostics and may differ slightly under changing cloud or atmospheric conditions.

Global tilted radiation

Solar panels are often installed at an angle rather than horizontally.

The:

gtiradiation

field estimates solar radiation on a tilted surface.

Use the:

solarTiltAngle

parameter to specify the panel tilt.

For example:

solarTiltAngle=30

represents a surface tilted 30 degrees.

A request can include:

elements=datetime,gtiradiation,sunelevation,sunazimuth

together with:

solarTiltAngle=30

Global tilted radiation is particularly useful when estimating solar energy available to a fixed-angle photovoltaic array.

Solar elevation

The:

sunelevation

field represents the angle of the sun above the horizon.

A value near:

0°

means the sun is close to the horizon.

A larger value means the sun is higher in the sky.

Solar elevation affects the amount of direct solar energy received by horizontal and tilted surfaces.

Solar azimuth

The:

sunazimuth

field represents the horizontal direction of the sun.

Solar azimuth is useful when determining the angle between incoming sunlight and a solar panel or other oriented surface.

Together:

sunazimuth
sunelevation

describe the sun’s position in the sky.

Historical solar radiation data

Historical solar radiation is available through the Timeline Weather API.

For example:

https://weather.visualcrossing.com/VisualCrossingWebServices/rest/services/timeline/Denver,CO/2026-07-01/2026-07-07?unitGroup=metric&include=days&elements=datetime,solarradiation,solarenergy&key=YOUR_API_KEY

This returns daily solar-radiation and solar-energy values for the requested period.

For hourly data:

https://weather.visualcrossing.com/VisualCrossingWebServices/rest/services/timeline/Denver,CO/2026-07-01?unitGroup=metric&include=hours&elements=datetime,solarradiation,solarenergy&key=YOUR_API_KEY

Hourly data is usually preferable when you need to understand the solar profile through the day.

Forecast solar radiation data

Forecast solar data is available through the same Timeline endpoint.

For example:

https://weather.visualcrossing.com/VisualCrossingWebServices/rest/services/timeline/Denver,CO?unitGroup=metric&include=days,hours&elements=datetime,solarradiation,solarenergy&key=YOUR_API_KEY

This can be useful for:

Solar generation forecasts
Energy scheduling
Agriculture
Building-energy management
Irrigation planning

The Timeline API returns the available forecast period when dates are omitted.

Current solar radiation

Current conditions may also include solar fields where available.

Request:

include=current

and inspect:

currentConditions

Possible fields include:

solarradiation
solarenergy

Current solar values can be useful for:

Live energy dashboards
Solar-production monitoring
Building automation
Operational applications

Request advanced solar fields

A Timeline API request for advanced solar data can include:

elements=datetime,ghiradiation,dniradiation,difradiation,sunelevation,sunazimuth

For example:

https://weather.visualcrossing.com/VisualCrossingWebServices/rest/services/timeline/Denver,CO/2026-07-01?unitGroup=metric&include=hours&elements=datetime,ghiradiation,dniradiation,difradiation,sunelevation,sunazimuth&key=YOUR_API_KEY

For tilted radiation:

elements=datetime,gtiradiation,sunelevation,sunazimuth

and:

solarTiltAngle=30

Advanced energy elements are available only on supported subscription levels.

See Energy Elements in the Timeline Weather API for current access information.

Historical availability

Solar availability depends on the specific element, location, date, and underlying source.

Core:

solarradiation
solarenergy

availability can differ from advanced solar-energy elements.

Current Visual Crossing documentation lists historical and forecast hourly advanced solar elements from:

2015-01-01

onward.

Do not assume that every solar element has identical historical coverage.

For current availability, see the Weather Data Documentation and the Weather Data Availability Guide.

Historical solar-data sources

Historical solar radiation can be derived from multiple available observation and modeled sources.

Depending on the location and time period, these can include:

Surface observations
Satellite-derived solar data
Other gridded or modeled solar products

The available source may differ from the sources used for other weather elements such as temperature or precipitation.

This is important because the absence of a nearby weather station measuring solar radiation does not necessarily mean that solar data is unavailable for the location.

Hourly versus daily solar data

The correct resolution depends on the application.

Use hourly solar data when you need:

Solar generation profiles
Peak radiation timing
Panel-performance analysis
Daylight-hour analysis
Intraday energy modeling

Use daily data when you need:

Daily solar-energy totals
Long historical datasets
Monthly or seasonal analysis
Climate summaries

Daily solar radiation versus daily solar energy

These two daily values should be interpreted differently.

Daily:

solarradiation

is a summary of the day’s radiation level.

Daily:

solarenergy

represents accumulated solar energy for the day.

Therefore, if you are calculating total available solar energy over a week or month, solarenergy is generally the more appropriate field to aggregate.

For example:

monthly solar energy =
sum(daily solarenergy)

Do not sum `solarradiation`

Because solarradiation is a power or intensity measurement, simply summing daily or hourly W/m² values without accounting for the time interval does not produce a physically meaningful energy total.

If you need accumulated energy, use:

solarenergy

or perform a proper time integration.

Example: solar-energy analysis

Suppose an hourly record contains:

datetime = 13:00
solarradiation = 720 W/m²
solarenergy = 2.59 MJ/m²

The first value describes the radiation intensity associated with the period.

The second represents the accumulated solar energy for that hourly interval.

For photovoltaic analysis, you may also request:

dniradiation
difradiation
ghiradiation
gtiradiation
sunelevation
sunazimuth

to understand direct, diffuse, horizontal, and tilted solar radiation.

Example: monthly solar-energy total

If daily records contain:

solarenergy

you can calculate a monthly total using:

monthly solar energy =
sum(daily solarenergy)

For example:

July 1: 22.4 MJ/m²
July 2: 21.8 MJ/m²
July 3: 18.5 MJ/m²
...

Summing these values gives total solar energy over the month.

You can convert the final result into:

kWh/m²

by dividing by:

3.6

Solar radiation and cloud cover

Cloud cover is one of the major influences on surface solar radiation.

Useful fields to analyze together include:

cloudcover
solarradiation
solarenergy

For example, a clear day may have much higher midday solar radiation than an overcast day at the same location and time of year.

However, cloud cover alone should not be used as a substitute for solar-radiation data.

The relationship depends on:

Cloud type
Cloud thickness
Sun angle
Atmospheric conditions
Local geography

Use the actual solar fields when solar energy is the quantity of interest.

Solar radiation and sun angle

Sun angle strongly affects available solar radiation.

At low solar elevation:

sunelevation

is small and sunlight passes through more atmosphere.

Near solar noon, the sun is typically higher in the sky and direct solar radiation can be stronger.

For energy applications, combining:

dniradiation
difradiation
ghiradiation
sunelevation
sunazimuth

provides a more complete description of solar conditions.

Solar radiation for photovoltaic systems

For a simple solar-resource estimate, the most useful fields may be:

solarenergy
ghiradiation

For more detailed photovoltaic modeling, consider:

dniradiation
difradiation
ghiradiation
gtiradiation
sunelevation
sunazimuth

The:

gtiradiation

field is especially useful when the panel tilt is known.

Actual photovoltaic output will also depend on factors outside weather data, including:

Panel efficiency
Panel orientation
Inverter losses
Shading
Dirt and snow
Temperature effects
System design

Solar weather data describes the available solar resource, not the final electrical output of a particular installation.

Solar data for agriculture

Solar radiation and solar energy can also be important for:

Crop growth
Evapotranspiration
Greenhouse management
Irrigation
Plant-development models

Useful fields may include:

solarenergy
solarradiation
temp
humidity
windspeed

along with advanced agricultural elements where available.

Viewing solar data without programming

You do not need to write code to retrieve solar radiation data.

Use the Visual Crossing Weather Query Builder to:

Enter a location.
Choose historical or forecast dates.
Select the desired weather elements.
Run the query.
Preview the data.
Download the results.

You can download the resulting dataset for use in:

Excel
Power BI
Tableau
Databases
Python
R
Other analytical tools

See Visual Crossing Weather Data to get started.

Request only the solar fields you need

Use the:

elements

parameter to reduce the response.

For basic solar data:

elements=datetime,solarradiation,solarenergy

For advanced energy analysis:

elements=datetime,solarradiation,solarenergy,ghiradiation,dniradiation,difradiation,sunelevation,sunazimuth

This makes the resulting dataset easier to process.

CSV and JSON

The Timeline Weather API can return solar data in JSON or CSV.

JSON is useful for application development and structured Timeline responses.

CSV is convenient for:

Excel
BI tools
Databases
Analytical workflows

You do not need to request every Weather API field just to retrieve solar data.

Use elements to select the specific solar fields you want.

Solar-data quality

Solar-radiation accuracy depends on factors including:

Available source data
Satellite or model resolution
Local cloud conditions
Terrain
Observation density
Forecast-model performance

Solar radiation can also vary over very short time periods as clouds move through a location.

For applications that depend on precise intraday solar variability, use the highest appropriate temporal resolution available for the required dataset.

Summary

The core Visual Crossing solar fields are:

solarradiation

Solar radiation power in:

W/m²

and:

solarenergy

Accumulated solar energy in:

MJ/m²

Advanced solar-energy elements include:

dniradiation
difradiation
ghiradiation
gtiradiation
sunelevation
sunazimuth

Use:

solarradiation when you need solar-radiation intensity.
solarenergy when you need accumulated solar energy.
ghiradiation for global horizontal radiation.
dniradiation for direct normal radiation.
difradiation for diffuse radiation.
gtiradiation for radiation on a tilted surface.
sunelevation and sunazimuth for solar position.

You can retrieve these values through the Visual Crossing Weather Query Builder or the Timeline Weather API.

For basic field definitions, see the Weather Data Documentation.

For advanced energy fields, see Energy Elements in the Timeline Weather API.

For complete API request documentation, see the Timeline Weather API.

How to obtain solar radiation data?

How to Obtain Solar Radiation Data

What is solar radiation?

Solar radiation versus solar energy

solarradiation

solarenergy

Converting solar energy to kWh/m²

Core solar fields

Advanced solar radiation fields

Direct normal irradiance

Diffuse horizontal radiation

Global horizontal radiation

Global tilted radiation

Solar elevation

Solar azimuth

Historical solar radiation data

Forecast solar radiation data

Current solar radiation

Request advanced solar fields

Historical availability

Historical solar-data sources

Hourly versus daily solar data

Daily solar radiation versus daily solar energy

Do not sum solarradiation

Example: solar-energy analysis

Example: monthly solar-energy total

Solar radiation and cloud cover

Solar radiation and sun angle

Solar radiation for photovoltaic systems

Solar data for agriculture

Viewing solar data without programming

Request only the solar fields you need

CSV and JSON

Solar-data quality

Summary

`solarradiation`

`solarenergy`

Do not sum `solarradiation`