Abstract
It was evaluated the annual evolution of global, direct and diffuse components of incident solar radiation on tilted surfaces to 12.85, 22.85 and 32.85º, facing north, in Botucatu, state of São Paulo, Brazil. The radiometric fractions were obtained for each component of the radiation in the aforementioned surfaces, through the ratio with the global and top of the atmosphere radiations. Seasonality was evaluated based on monthly averages of daily values. The measures occurred between 04/1998 and 07/2001 at 22.85º; 08/2001 and 02/2003 at 12.85º; and from 03/2003 to 12/2007 at 32.85º, with concomitant measures in the horizontal surface (reference). The levels of global and direct radiation on tilted surfaces were lower in summer and higher in the equinoxes when compared with the horizontal. The diffuse radiation on tilted surfaces was lower in most months, with losses of up to 65%. A trend of increasing differences occurred between horizontal and tilted surfaces with the increase of the angle in all the components and fractions of incident radiation. The annual evolution of rainfall and cloud cover ratio directly affected the atmospheric transmissivity of direct and diffuse components in the region.
Highlights
The knowledge of the incidence levels of solar radiation on surfaces with different topographies may be used in a wide variety of applications, including engineering designs for solar collectors, architectural projects, urban planning, agronomic studies of heatstroke on vegetation, models to estimate plant development, and meteorological studies on local circulation (LI et al, 2008; NOORIAN et al, 2008; SILVA et al, 2010; SOUZA et al, 2010; EL-SEBAII et al, 2010)
The direct and reflected components may be obtained with good accuracy using simple algorithms, but the diffuse component requires isotropic and anisotropic corrections (IQBAL, 1983; VERTIAINEN, 2000; DIEZ-MEDIAVILLA et al, 2005; NOORIAN et al, 2008; PANDEY & KATYIAR, 2009; EL-SEBAII et al, 2010), dependent on atmospheric change
The global radiation received by the tilted plane at 12.85° (Figure 1a) was below the horizontal plane between November and February, and in December it was found lower levels, of around 0.77 MJ m-2 d-1
Summary
Any factor that modifies the amount of incident energy at a site affects directly or indirectly the levels of solar energy available. In this context, there is influence of topography according to the variability of altitude, inclination (slope), orientation (azimuth) and shading (DUBAYAH & RICH, 1995; WENXIAN et al, 1995; KAMALI et al, 2006). The direct and reflected components may be obtained with good accuracy using simple algorithms, but the diffuse component requires isotropic and anisotropic corrections (IQBAL, 1983; VERTIAINEN, 2000; DIEZ-MEDIAVILLA et al, 2005; NOORIAN et al, 2008; PANDEY & KATYIAR, 2009; EL-SEBAII et al, 2010), dependent on atmospheric change
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