PROCEDURES FOR SEPARATING DIRECT AND DIFFUSE INSOLATION ON A HORIZONTAL SURFACE AND PREDICTION OF INSOLATION ON TILTED SURFACES

WATANABE TOSHIYUKI, URANO YOSHIMI, HAYASHI TETSUO

doi:10.3130/aijsaxx.330.0_96

For the real evaluation of solar energy utilizing systems, we have to know both direct and diffuse solar radiation as well as global solar radiation on an hourly (or shorter) data basis. Then, it is necessary to divide global solar radiation into the direct and diffuse components when global solar radiation is only available. In this paper, by analizing the data of global solar radiation TH, direct solar radiation DN, and diffuse solar radiation SH, observed at Hakozaki (33°37′N, 130°26′E) in Fukuoka for the period January through December in 1980, correlations between these solar radiation, the atmospheric transmittance P, and the total cloud amount C have been examined. Based these correlations, two types of empirical equations for dividing TH into SH and DH (direct solar radiation incident on a horizontal surface) are derived as follows; [numerical formula]…(1) where I_0 is the extraterrestrial exposure and h is the solar altitude, or [numerical formula]…(2) [numerical formula] The standard errors on DN and SH estimated by Eqs. (1) and (2) are compared with ones by earlier presented equations. Eqs. (1) and (2) have been developed to predict the hourly (or shorter) values of insolation on tilted surface of different orientations. Solar radiation values measured on the tilted south-and east-facing surfaces are compared with values calculated for the same surfaces using observed global solar radiation. The use of DN and SH by Eq. (1) or (2) resulted in smaller errors in almost all cases.

PROCEDURES FOR SEPARATING DIRECT AND DIFFUSE INSOLATION ON A HORIZONTAL SURFACE AND PREDICTION OF INSOLATION ON TILTED SURFACES

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