Simple Solar Spectral Model for Direct and Diffuse Irradiance on Horizontal and Tilted Planes at the Earth's Surface for Cloudless Atmospheres

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4.0 Comparisons of the New Simple Model with Rigorous Models and Measurements



The primary goal of this work on simple spectral models is to give researchers the capability to calculate spectral irradiance using microcomputers. The spectra can then be used in models to evaluate solar device performance. For example, scientists can produce spectra by varying input parameters such as air mass, atmospheric turbidity and water vapor, and day of year, and use the spectra to examine the performance of spectrally selective photovoltaic devices under different conditions.

Examples of spectra generated using the simple model for clear days at the equinoxes and solstices and three different turbidity and water vapor combinations are shown in Figure 5-1. Spectra were calculated at 60-min intervals that are symmetrical about solar noon from sunrise to sunset. Only the morning spectra are plotted since the afternoon spectra are theoretically identical. These spectra were produced for a south-facing surface tilted 37° from the horizontal at sea level for latitude 37° and longitude 100°. The spectra may not be representative of a particular site, but serve as examples of differences in spectral irradiance under different conditions. Of note in these spectra are the effects of high turbidity and air mass on the visible portion of the spectrum and the difference in spectral content at different times of the year due to differences in air mass values.

These spectra can easily be converted to photon flux per wavelength or to photon flux per electron-volt if this format is more useful for particular applications. Examples of conversion results are shown in Figures 5-2 and 5-3.

6.0 References

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