Solar constant

About: Solar constant is a research topic. Over the lifetime, 967 publications have been published within this topic receiving 29647 citations.

Solar radiative fluxes in the clear-sky atmosphere of Western Siberia: A comparison of simulations with field measurements

Abstract: We compare the calculations and measurements of downward solar radiative fluxes on the Earth’s surface, performed in the clear-sky atmosphere during summers of 2010–2012 in the background area of the boreal zone of Siberia (Tomsk). The comparison is performed taking into account the instrumental errors and uncertainties of determining the atmospheric characteristics. The aerosol optical characteristics were specified using data of ground-based photometric measurements, obtained at the Tomsk station of the AERONET network. It is shown that the relative differences between the model-based and experimental values of the fluxes of direct and total radiation, on average, do not exceed 1% and 3%, respectively.

Variations of the solar activity and irradiance, and their influence on the flooding of the river Nile

Abstract: Autocorrelation and power spectra analysis are carried out for different lengths of time series Of the following data:(l) Solar activity (sunspot, faculae and radio flux on 2800 MHz);(2) Irradiance (solar Constant measured at earth's surface and by the artificial satellite (Nimbus- 7); (3) River Nile flood (old water level, maximum flood level, and the difference between the both levels) measured at Cairo. The results showing remarkable similarity between the power spectra of solar activity, irradiance (solar constant) and river Nile flood. We conclude that any short or long-term variations in the solar activity lead to similar variations in the solar constant. Also, annual and secular variations of solar activity yield information’s on the suspected annual and secular variations of the river Nile flood.

Solar irradiance at the earth's surface: long-term behavior observed at the South Pole

Abstract: . This research examines a 17-year database of UV-A (320–400 nm) and visible (400–600 nm) solar irradiance obtained by a scanning spectroradiometer located at the South Pole. The goal is to define the variability in solar irradiance reaching the polar surface, with emphasis on the influence of cloudiness and on identifying systematic trends and possible links to the solar cycle. To eliminate changes associated with the varying solar elevation, the analysis focuses on data averaged over 30–35 day periods centered on each year's austral summer solstice. The long-term average effect of South Polar clouds is a small attenuation, with the mean measured irradiances being about 5–6% less than the clear-sky values, although at any specific time clouds may reduce or enhance the signal that reaches the sensor. The instantaneous fractional attenuation or enhancement is wavelength dependent, where the percent deviation from the clear-sky irradiance at 400–600 nm is typically 2.5 times that at 320–340 nm. When averaged over the period near each year's summer solstice, significant correlations appear between irradiances at all wavelengths and the solar cycle as measured by the 10.7 cm solar radio flux. An approximate 1.8 ± 1.0% decrease in ground-level irradiance occurs from solar maximum to solar minimum for the wavelength band 320–400 nm. The corresponding decrease for 400–600 nm is 2.4 ± 1.9%. The best-estimate declines appear too large to originate in the sun. If the correlations have a geophysical origin, they suggest a small variation in atmospheric attenuation with the solar cycle over the period of observation, with the greatest attenuation occurring at solar minimum.

Modeling the variation of optimum tilt angles for flat-plate solar collectors in Ifrane, Morocco

Abstract: The conventional flat-plate solar collectors that are used in domestic solar water heating systems are often mounted at a fixed position from the horizontal, which makes them less efficient as they do not always face the sun. Adjusting the tilt angle seasonally ensures high energy collection efficiency through different seasons, especially winter, when the sun radiation is limited. The purpose of this study is to determine the variations in tilt angles for domestic solar collectors in order to maximize the amount of solar radiation captured. As an example of this for the Moroccan environment, the monthly optimum tilt angles in Ifrane were determined from the monthly average direct and diffuse radiations on horizontal surfaces, which were estimated based on the Liu and Jordan model [1, 2]. The results showed high tilt angles during winter (71° average tilt) and autumn (47° average tilt) and very low tilt angles during summer season (5° average tilt). Moreover, a significant increase was noticed in the estimated solar radiation on tilted surfaces as we change the tilt angle monthly, seasonally and bi-annually instead of leaving it mounted at a fixed position throughout the entire year. The study indicates that changing the tilt angle monthly would result in an increase of total radiation on the inclined surface by 14.5% during winter season and a yearly average increase of 10% compared to a fixed position. On the other hand, adjusting the tilt angle bi-annually would result in an increase of 12.5% during winter season and a yearly average increase of 7% in total radiation.