Long Term Estimation of DNI From Solar Global Irradiation. a Model to Estimate DNI From Monthly Clearness Index

Sara Moreno (1) , Lourdes Ramírez (2) , Carlos M. Fernández-Peruchena (2) , Perez Elena (1) , Ana Bernardos (2) , Silva Manuel (1)

1 AICIA
2 Department of Solar Thermal Energy [Sevilla]

In this work, the measurements of five meteorological stations sited throughout Spain are used to develop a model between monthly average beam irradiance and monthly clearness index.Then this expression is used to calculate monthly direct normal radiation from measured monthly horizontal global radiation data. This method can be applied to the extensive databases of horizontal global radiation values in order to study the long-time behavior of the direct normal radiation.After that, the accuracy of the model is evaluated with the recorded data of 16 different meteorological stations, also located throughout Spain. The Mean Bias Error and the Root Mean Squared Error obtained as function of the seasons and the different latitudes are evaluated. In addition, the results of all stations are compared with the monthly direct normal radiation obtained with a similar expression proposed by Ari Rabl[1] in 1981. The results show how it could be possible to estimate monthly normal direct radiation values from monthly horizontal global irradiation measures assuming mean errors similar to the uncertainty of the measurement equipments.

Mots clés: direct normal radiation; clearness index; global-to-beam models; monthly radiation data

Domaines: Ingénierie de l'environnement

Sara Moreno, Lourdes Ramírez, Carlos M. Fernández-Peruchena, Perez Elena, Ana Bernardos, et al.. Long Term Estimation of DNI From Solar Global Irradiation. a Model to Estimate DNI From Monthly Clearness Index. 16th SolarPACES Conference, Sep 2010, Perpignan, France. pp.277. ⟨hal-00919078⟩