THE AUTHOR STATES THAT HIS ESSAY IS NOT AN HISTORICAL STUDY. ANY HISTORICAL FACTS ARE NOT INTENDED TO PROVE HIS POINTS BUT MERELY TO ILLUSTRATE THEM, TO MAKE THEM MORE COMPREHENSIBLE TO READERS UNFAMILIAR WITH THE CONDITIONS UNDER WHICH WE LIVE. THE ESSAY HE MAINTAINS, IS REALLY A REACTION TO A CHALLENGE IMPLIED IN NUMEROUS DISCUSSIONS WITH CZECH AND OCCASIONALLY SLOVAK AND POLISH FRIENDS DISCUSSIONS THAT WERE, FOR THE MOST PART, RUDIMENTARY AND RATHER GROPING. HIS PURPOSE IS TO PROVOKE DISCUSSION, NOT TO SUMMARIZE AND DRAW CONCLUSIONS.
Field testing is costly, time-consuming and depends heavily on prevailing weather conditions. Adequate security and weather protection must also be provided at the test site. Delays can be caused due to bad weather and system failures. To overcome these problems, a photovoltaic array simulation may be used. In any simulation scheme involving photovoltaic systems, one important choice is the selection of a mathematical model.In the literature several approaches to the problem have been made. Most procedures designed for this purpose are based on analytical descriptions of the physical mechanisms inside the solar cell that can be represented by a circuit diagram with discrete components, like a two-exponential model. Such simulators have some merits. However, their limited flexibility in readily simulating the influence of solar radiation, temperature and various array parameters is a serious drawback that has been noted. To get more accurate results in predicting the actual performance of photovoltaic modules, the parameters influencing incoming (optical parameters) and outgoing power flow (electrical and thermal parameters) were investigated by simulation and by some verifying experiments, to get a closer insight into the response behavior of this element, and to estimate the overall performance as well as optimization of the parameters.
Knowledge of the solar radiation available on the earth's surface is essential for the development of solar energy devices and for estimating of their performance efficiencies. For this purpose it is helpful to study the attenuation of direct normal irradiance by the atmosphere, in terms of fundamental quantities, including optical thickness, relative optical air mass, water vapor content, and aerosol amount. In the present article, we will not deal with cloudy atmospheres because of their great variability in space and time, but will focus our attention on atmospheres characterized by the complete absence of condensed water. The objectives of this article are to report data on aerosol optical depth and atmospheric turbidity coefficients for a desert climate, and to compare them with those of a temperate climate. Aerosol optical depth, the Linke turbidity factor, TL, and ngström turbidity coefficients, _, are calculated from measurements of broadband filters at Helwan, Egypt, which has a desert climate. A linear regression model is to be determined between the Linke factor and the ngström turbidity coefficient. This relation is compared with similar relations reported for a temperate climate [Prague, Czech Republic]. This comparison is made to determine whether a universal relation exists between these two important coefficients, or whether the relation is location dependent.
