TITLE:
Effects of Sky Conditions Measured by the Clearness Index on the Estimation of Solar Radiation Using a Digital Elevation Model
AUTHORS:
Marcelo de Carvalho Alves, Luciana Sanches, José de Souza Nogueira, Vanessa Augusto Mattos Silva
KEYWORDS:
Sky Cover; Spatial; Radiation; Mapping Solar; Geographic Information Systems
JOURNAL NAME:
Atmospheric and Climate Sciences,
Vol.3 No.4,
October
31,
2013
ABSTRACT: This study evaluated the effects of
sky conditions (measured by the clearness index, KT) on the estimation of solar radiation and its
components. Solar radiation was calculated by a digital elevation model derived
from the Shuttle Radar Topography Mission (SRTM). The calculated radiation was
parameterized and validated with measured solar radiation from two stations
inside the urban perimeter of the city of Cuiabá, Brazil,
during 2006 to 2008. The measured solar radiation varied seasonally, with the
highest values in December-March and the lowest in June-September. Comparisons
between calculated and measured values for two sites in Cuiabá demonstrate that
the model is accurate for daily Rg estimates
under clear sky conditions based on Root Mean Square Error, Mean Bias Error and
Willmott’s index. However, under partially cloudy and cloudy sky conditions the
model was not able to provide robust estimates. Spatially, the highest values
of incident Rg occurred on strands
with North, Northeast and Northwest orientations and were lowest on those
oriented to the South, Southeast and Southwest.