Modeling Solar Radiation at the Earth’s Surface

Quality Assessment Based Upon Physical Limits

As the name implies, the physical limits approach to solar data quality assessment compares measured data with estimated or defined limits. For instance, is the radia­tion component within the range of zero to the maximum possible expected value? Is the direct normal irradiance greater than zero and less than the extraterrestrial value? Is the global horizontal no greater than the vertical component of the extraterrestrial beam? Is the diffuse irradiance more than the expected Rayleigh diffuse sky? Note that while somewhat crude, and allowing the possibility of one or more components to pass such tests even when bad (such as direct beam of zero on a clear day, be­cause the tracker was not pointing correctly, or an attenuated DNI due to a dirty pyrheliometer window), the last example above did lead to the identification of the thermal offset problem described in Sect. 5.

However, for the most part, the physical limits tests cannot provide the level of accuracy needed to assure that measurement instrumentation is indeed functioning properly, unless used with intensive human interaction. This interaction includes regular cleaning of windows, checking of tracker and shading disk alignment, etc. Other intensive human operations involve daily inspection of diurnal irradiance pro­files, combined with knowledge of meteorological conditions on the day being in­spected. Clearly, these are difficult procedures to automate and implement. They also involve a good deal of qualitative, rather than quantitative evaluation. Thus, the quality assessment may be more subjective than objective.

Modeling Solar Radiation at the Earth’s Surface

Quality Assessment Based Upon Comparison with Models

Many models based on the physics of radiation transfer through the clear atmo­sphere have been developed (Lacis and Hansen 1974; Atwater and Ball 1978; Hoyt 1978; Bird and Hulstrom 1981a, …

Solar Horizontal Diffuse and Beam Irradiation on Clear Days

There exist a number of models to determine the solar horizontal diffuse irradia­tion on a clear day (Kondratyev 1969) but they are complex and have very stringent conditions. Similarly, there …

Foreword

Reading the twenty chapters of this book caused me mixed reactions, though all were positive. My responses were shaped by several factors. Although I have main­tained a “watching brief’ on …

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