Resumen de Calculating solar radiation for horizontal surfaces—II. Empirically based approaches

J. E. Hay

• This paper reviews the evolution of empirically based methods for estimating the global irradiation at the earth's surface and its direct and diffuse components. The models studied here have little theoretical basis, but their forms can be linked to more fundamental approaches. Both sunshine and cloud based models are described. The accuracy of irradiation estimates using these approaches is discussed, in both absolute terms and in comparison to the cloud layer models described in Part I of this paper. Studies suggest that the empirical models offer little advantage over the more theoretically based models if various factors are taken into account.