Sol - Sun Energy Calculator

Download Sol here: Version 1.07

Sol calculates the solar energy a 1m2 panel would receive on a clear day.


Diffuse spectrum Green  Sky Radiation - from clouds or unclear atmosphere. (Panel)
Direct spectrum Red   Radiation from the direction of the sun. (Ground normal)
Extraterrestrial spectrum Black Radiation with no atmosphere or clouds. (Ground normal)
Global spectrum Yellow Sum of Direct and Diffuse radiation. (Panel)

The "Day Report..." button generates a fake log file for viewing with the Display utility  in c:\hotbox\gen.log.

Time Zone

This is the time difference ahead of GMT.

Example 5.5 for India, -5.0 for US Eastern Time, -8.0 for US Pacific Time. This is filled from the computer's time zone configuration in the Control Panel Date Time applet.


The generated file uses the flow and Specific Heat set in Display, requests an efficiency figure and simulates the temperature drop across the heat exchanger.

Default settings set a flow of 50mL with Specific Heat of water 4184. (Change these settings using Display.)

Display showing a simulated summer trace and winter trace:

The clipped sine on the winter trace is due to the simulated sensor seeing the sunrise. Also the sensor is not directed to the south, so gradually looses insolation before sunset.

Sol uses NREL's SOLPOS 1.1 published C source code. (Converted to C++, globals removed...)

A good site to find Latitude and Longitude here.

Download Sol here: Version 1.07

(Time zones and daylight saving now supported. Here's some Test code !)


NASA will provide you with Solar Energy data. You have to register, but that's painless.

Here's the email I received from them:

The Atmospheric Sciences Data Center at NASA Langley Research Center announces the availability of Release 4 Surface meteorology and Solar Energy (SSE) data.

Release 4 includes three new applications to view the SSE data in different ways:

1. Global data of selected parameters can be easily downloaded for each quadrant of the globe. The data table, containing all months and all locations in one quadrant of the globe, will fit on one 1.44 MB floppy disk. The data are easy to import into spreadsheet software.

2. The user may now define a region to subset and download tables containing spatial or temporal coverage of data by region.

3. The user may download daily data for each 1x 1 region and any time period from one day to ten years.

Release 4 total data content is more than twice as large as Release 3.

New monthly solar, wind, and temperature parameters included in Release 4 are:

Diffuse and direct normal radiation using two different methods.

Equator-facing, tilted-surface radiations estimated using three different methods each for 10-yr average, minimum, and maximum horizontal surface insolation. Values are given at six different equator-facing tilt angles (latitude, latitude + 25, latitude - 25, 0, 90, and optimum angle for maximum radiation).

Wind speed estimates are improved from values in Release 3, but are still based on height above the ground, snow, water, or ice instead of the effective surface. Fifty-meter height speeds are now provided, and 10-m averages are also available for 17 surface/vegetation types for each 1-deg cell over the globe. Both direction and diurnal information are also improved.

Additional heating degree-day values. Values relative to 0 and 10 C are now provided in addition to values relative to 18 C.

SSE Web Site:

For information regarding our data holdings or for assistance, please contact:
NASA Langley Atmospheric Sciences Data Center
Science, User and Data Services
Mail Stop 157D, 2 S. Wright Street
Hampton, VA 23681-2199
Phone: 757-864-8656
Fax: 757-864-8807
E-mail: [email protected]

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Page last updated March 20th 2009