Computing the solar vector

High-concentration solar thermal systems require the Sun to be tracked with great accuracy. The higher the system concentration, the greater this accu racy must be. The current trend in solar concentrator tracking systems is t o use open-loop controllers that compute the direction of the solar Vector based on location and time. To keep down the price of the tracking system, the controller is based on a low-cost microprocessor. These two facts impos e important restrictions on the Sun position algorithm to be used in the co ntroller, as it must be highly accurate and efficiently computable at the s ame time. In this paper, various algorithms currently available in the sola r literature are reviewed and a new algorithm, developed at the Plataforma Solar de Almeria, which combines these two characteristics of accuracy and simplicity, is presented. The algorithm allows of the true solar vector to be determined with an accuracy of 0.5 minutes of are for the period 1999-20 15. (C) 2001 Elsevier Science Ltd. All rights reserved.