It is common knowledge that solar radiationis unevenly distributed, and that it varies in intenasity from one geographic location to another deapending upon the latitude, season, and time of day.Until recently, valid records for solar radiation havebeen very scanty in the vast majority of the developing countries
. In the absence of such useful information as a guide for the proper exploitation ofsolar energy, only general hints can be offered regarding the geographic areas with favourable conditions for solar energy applications.For convenience and simplicity
the geographic distribution of total solar radiation on aglobal scale is divided in terms of intensity intofour broad belts around the earth. These are illustrated in Figure 2, and also described brieflyhereunder with respect to the northern hemisphere, with the understanding that the sameconditions apply to the corresponding belts inthe southern hemisphere:
.(I) Most Favourable belt This belt, lying between latitudes 15 N, and35 N, embraces the regions that are naturallyendowed with the most favourable conditionsfor solar energy applications. These semi-aridregions are characterized by having the greatestamount of solar radiation, more than 90% of which comes as direct radiation because of the limited cloud coverage and rainfall (less than 250mm per year).
(IIl) Less Favourable belt This belt lies between latitude 35 N and45 N. Although the average solar intensity isroughly about the same as for the other two belts,there are marked seasonal variations in both radiation intensity and daylight hours. During the winter months solar radiation is relatively lower than in the rest of the year.
(IV)Least Favourable beltThe regions in this belt tie beyond latitude45 N. They include the USSR, and the greaterparts of northern Europe and North America .Here, about half of the total radiation is diffuse radiation, with a higher proportion inwinter than in summer primarily because ofthe rather frequent and extensive cloud coverage.
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