DNI Estimation Procedures for the Assessment of Solar Radiation Availability in Concentrating Systems

DNI (Direct Normal Irradiance) is the resource utilized by solar concentrators. Besides, the determination of DNI is needed in the models for the estimation of global irradiance on tilted planes, which is the input to flat-plate systems. This paper describes a study of different estimation procedures for the assessment of the DNI , using experimental data with a time scale of 1 min, taken at two different latitudes. The analyzed approaches include measuring techniques and models. The results show that the different estimation methods can lead to quite different conclusions when comparing the solar radiation availability in concentrating and flat-plate systems and this can affect the energy and economic evaluations. Based on the experimental analysis, indications for reducing the uncertainty in the estimation of DNI are discussed.