Diffuse fraction correlations

Journal Article · Mon Jan 01 04:00:00 EST 1990 · Solar Energy (Journal of Solar Energy Science and Engineering); (USA)

DOI:https://doi.org/10.1016/0038-092X(90)90060-P· OSTI ID:6301352

Reindl, D T; Beckman, W A; Duffie, J A ^[1]

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1. Univ. of Wisconsin, Madison (USA)

The influence of climatic and geometric variables on the hourly diffuse fraction has been studied, based on a data set with 22,000 hourly measurements from five European and North America locations. The goal is to determine if other predictor variables, in addition to the clearness index, will significantly reduce the standard error of Liu- and Jordan-type correlations (I{sub d}/I = f(k{sub t})). Stepwise regression is used to reduce a set of 28 potential predictor variables down to four significant predictors: the clearness index, solar altitude, ambient temperature, and relative humidity. A piecewise correlation over three ranges of clearness indices is developed to predict the diffuse fraction as a function of these four variables. A second piecewise correlation is developed for predicting the diffuse fraction as a function of the clearness index and solar altitude, for use when temperature and relative humidity are not available. A third piecewise correlation of the Liu- and Jordan-type is developed from the same data set. Comparing this correlation with the new correlations provides a direct measure of the value of added predictor variables. The full diffuse fraction correlation reduced the residual sum squares by 14% when compared to the correlation that is a function of the clearness index only. The correlation including the clearness index and solar altitude diminished the residual sum squares by 9%. The correlations exhibited some degree of location dependence. This is expected, as the climates are quite different. The correlations also showed some seasonal dependence; the errors are higher in the fall and winter than on an annual basis.

• OSTI ID: 6301352
• Journal Information: Solar Energy (Journal of Solar Energy Science and Engineering); (USA), Journal Name: Solar Energy (Journal of Solar Energy Science and Engineering); (USA) Vol. 45:1; ISSN SRENA; ISSN 0038-092X
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
140100* -- Solar Energy-- Resources & Availability
ALTITUDE
AMBIENT TEMPERATURE
CLIMATES
CORRELATIONS
DIFFUSE SOLAR RADIATION
EQUATIONS
EUROPE
HOURLY VARIATIONS
HUMIDITY
MATHEMATICAL MODELS
MATHEMATICS
NORTH AMERICA
OPACITY
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
PREDICTION EQUATIONS
RADIATIONS
REGRESSION ANALYSIS
SEASONAL VARIATIONS
SITE SURVEYS
SOLAR FLUX
SOLAR RADIATION
STATISTICS
STELLAR RADIATION
VARIATIONS