Software tools

Solar radiation data are used to predict the performance of many different systems from heating loads on buildings to electricity produced by concentrating collectors. It's not feasible to measure the solar resource for all these potential uses; rather, we must use models to calculate the incident solar radiation.

We have developed tools based on models to facilitate the use of solar radiation data and present results in a useful format. Comments, suggestions, and questions about our software are always appreciated and will help us provide a better product.

Below are links to our various software tools.

Sun path charts

The sun path chart program plots the path of the sun across the sky. These charts are used in site evaluation forms to identify trees, buildings, or other obstructions that would block direct access of solar radiation collecter to the sun. To create a sun path chart, you need to know the latitude and longitude of the site within about one degree or, for US locations, the local zip code. For more information, see our page about sun path charts.

Online data plotting

Our data plotting program graphically depicts selected data, allowing you to see at a glance how irradiance values, solar cell performance, or meteorological readings varied on particular days at specified monitoring stations. In addition to this general program interface, we've included links to it from all of our Web pages devoted to currently active monitoring stations (such as: Eugene ). These links cause the program to display charts of the most recent data we have from our active stations.

Microsoft Excel data plotting

To download a zip file containing an Excel macro used to plot data from 5-, 10-, and 15-minute data click here for the plot macro. To run the program, load the macro in Excel and click on the 'spade' button. The program will ask for the name of the file to be plotted. The file has to be in the UO SRML format.

Sundial program

Our sun dial program shows how the shadow of a vertical rod, or 'gnomon' moves across a horizontal surface at specific times at various locations on the earth. This application is useful for anticipating the shading effects of objects near a PV array, and, of course, it can be used to design an actual sun dial.

Solar position calculator

The solar position calculator was developed to more accurately obtain astromonical parameters such as solar declination, solar zenith angle, equation of time, and hour angle used in calculating the position of the sun. It's based on the work of Joe Michalsky and the algorithm is used by SolPos, whose source code is available on NREL's Web site.

This program generates all the information needed to determine the position of the sun, based on date, time, and location. Also calculated are sunrise and sun set times, the instantaneousextraterrestrial radiation and the daily extraterrestrial radiation. These values are used when modeling solar radiation.


The photovoltaic performance calculator, PVWatt, is located on NREL's Web site. It calculates typical performance of solar electric arrays for more than 200 locations in the National Solar Radiation Database, given the system peak output and orientation. Since actual performance will vary from year to year, we created a modified version of PVWatt that works with data from the UO SRML database. This downloadable program is available as shareware on this Website.

For more information

Information about instruments used to collect solar radiation data, and about our monitoring stations, is found in the solar data section of this site.

The basics of solar resource assessment and solar radiation modeling will be incorporated in our section devoted to educational material.

Further information on solar radiation modeling is available in our Solar Radiation Data book and other publications on our Web site.

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