Geographic Dependence of the Solar Radiation Spectrum at Intermediate to High Frequencies

TL;DR

This study investigates how geographic location influences the spectral power-law behavior of solar radiation across different frequencies, with implications for renewable energy and climate systems.

Contribution

It introduces a model quantifying the geographic variability of the solar radiation spectrum's power-law decay, highlighting latitudinal effects on spectral characteristics.

Findings

Significant spatial variability in spectral power-law exponents across locations.

Different spectral behaviors observed between intermediate and high frequencies.

Geographic factors, especially latitude, influence solar radiation spectral properties.

Abstract

The solar radiation spectrum is important for renewable energy harvesting, as well as climate and ecological systems analysis. In addition to seasonal/annual and diurnal oscillations, the signal is composed of different frequencies ($f$) that modulate each other. This results in a continuous spectrum with a power-law dependence over the entire frequency range from 1/year up to at least 1/min. Geographical location plays an important role in determining the temporal variability of solar radiation and naturally affects its spectral power-law decay, primarily due to the latitudinal dependence of daylight duration and its seasonal variation,. Employing a model to calculate the clear sky solar radiation intensity at various global locations, we show that significant spatial variability exists, particularly versus the latitude, which we quantify via the exponent of the spectral power-law. At most locations, the spectral power-law dependence of the intermediate (1/day $< f <$ 1/hour) frequencies is different from that of the high ($f > 1/$hour) frequencies. We demonstrate the origin of this power-law dependence from simple arguments, explain its geographic dependence and discuss the implications for photovoltaic power generation and solar-driven systems, and hence the impact on grid stability.