Table of Contents
ISRN Renewable Energy
Volume 2011, Article ID 217484, 5 pages
Research Article

Spline-Based Formulas for the Determination of Equation of Time and Declination Angle

1Department of Computer Engineering, College of Engineering, Nahrain University, P.O. Box 64040, Jadriya, Baghdad, Iraq
2Computer Center, Al-Iraqiya University, P.O. Box 70710, Aadamiya, Baghdad, Iraq

Received 22 August 2011; Accepted 22 September 2011

Academic Editor: A. Romeo

Copyright © 2011 Fawzi Al-Naima and Bilal Abdul Majeed. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


This paper presents new approximation formulas for the determination of the equation of time and declination angle. The proposed approach is based on the cubic spline interpolation techniques defined for sixteen or twenty chosen knots over the whole year. The results obtained by the proposed formulas for both equation of time and declination angle show marked improvements in terms of speed and sum of squared errors and maximum absolute error over the whole year in comparison with other five existing methods for analytical evaluation of equation of time and two existing methods for analytical evaluation of declination angle.