Modelling the time correlation in hourly observations of direct radiation in clear skies

✍ Scribed by Henrik Madsen; Poul Thyregod

• Publisher: Elsevier Science
• Year: 1988
• Tongue: English
• Weight: 846 KB
• Volume: 11
• Category: Article
• ISSN: 0378-7788
• DOI: 10.1016/0378-7788(88)90036-9

✦ Synopsis

In the paper we discuss the formulation and estimation of a stochastic model for the direct radiation in clear skies. The only external variable in the model is the solar elevation. An important feature of the method is that the strong hourly correlation that is not explicable by the solar elevation is taken into account by the model.

The application of the method is illustrated on a series of hourly values of direct radia. tion in periods of clear skies during eight years at a location near Copenhagen, Denmark. The periods of clear skies have been selected by means of hourly observations of cloud cover. The direct radiation has not been recorded, but calculated from observations of global and diffuse radiation. Maximum likelihood estimates of the parameters in the model are found by numerical methods, and an indication of the estimation error under the model is given. Moreover, the consequences of neglecting the correlation structure at the estimation is demonstrated.

Finally, two examples show the importance of modelling the correlation structure in applications of the model for simulation and forecasting purposes.