An Innovative Software for Analysis of Sun Position Algorithms

Abstract

A fundamental aspect of concentrating solar power is the ability to compute the position of the sun within a desired accuracy and speed. There are many algorithms from which to choose, and these algorithms range from quite simple to fairly complex. The tradeoff is one of code size, complexity and speed vs. accuracy. The solar plant designer must evaluate the available models and choose the best fit. Tietronix Software has developed a software called TieSOL::SolTime to assist the designer in this process. TieSOL::SolTime is an innovative tool that provides instantaneous sun (and moon) position data, to varying precisions, between the years 1753 and 6000. More importantly, TieSOL::SolTime also allows the designer to graphically compare sun position algorithms. Built in to TieSOL::SolTime are ten baseline models, ranging in accuracy from 36 to 0.01 arc seconds. The user can select two algorithms and graphically compare the evolution and behavior of the sun position vector components, range, right ascension, declination, ecliptic latitude and longitude, and azimuth and elevation angles over a user-defined time span, at a user- specified step size. Furthermore, the user can evaluate their own algorithm by importing an ephemeris file. Errors, abnormalities and numerical instabilities in a proposed algorithm can be easily identified. TieSOL::SolTime utilizes the GPU as well as all CPU cores, generating sun ephemerides as fast as 95 million vectors per second at the 36 arc second level of accuracy. Comparing two algorithms at 1 arc second precision, over a 30 year period with a time step size of 5 minutes, takes less than 20 seconds.