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Solar Radiation and Earth's Climate
Published in Robert Ehrlich, Harold A. Geller, John R. Cressman, Renewable Energy, 2023
Robert Ehrlich, Harold A. Geller, John R. Cressman
On an annual basis, given that the Earth travels in an elliptical orbit rather than a perfect circle, the solar constant varies by around ±0.3% due to the varying distance to the sun. Interestingly, the Earth is closest to the sun in January rather than a summer month. On a bit longer timescale, there is also a variation of ±0.04% as a consequence of the 11-year sunspot cycle. Finally, the sun has dramatically evolved during the course of its life that began an estimated 4.5 billion years ago. Its brightness has drastically changed over that time and will do so again as it nears the end of its life when it approaches the red giant stage in perhaps another 4.5 billion years. It is believed, however, that the solar output has been relatively constant throughout the last 2,000 years, with variations of no more than 0.1%–0.2%.
Atmospheric Effects
Published in Wayne T. Davis, Joshua S. Fu, Thad Godish, Air Quality, 2021
Wayne T. Davis, Joshua S. Fu, Thad Godish
Average global surface temperatures are determined in part by the amount of solar radiation reaching the Earth’s atmosphere and surface. Astronomers have theorized that at least for long periods, solar output, and hence the quantity of solar radiation received by the Earth, is essentially constant. The solar constant (1.370 W/m2/s) is the total solar radiation received on a flat surface oriented perpendicular to the sun external to the Earth’s atmosphere. Its value is 1.94 cal/cm2/s. Satellite measurements have recently shown that solar radiation does vary and that the solar constant is not constant when viewed in the short term. Short-term changes in solar output are directly related to sunspot cycles. The peak value of solar irradiances occurs near the maximum of solar activity. The peak-to-peak variation in the sun’s total irradiance during the sunspot cycle is approximately 0.08%.
Solar energy and evapotranspiration: A control of the unsaturation state in soils
Published in H. Rahardjo, D.G. Toll, E.C. Leong, Unsaturated Soils for Asia, 2020
The solar constant is the quantity of solar energy at normal incident angles to the atmosphere at the mean sun-earth distance. Some of this incident radiation is reflected or absorbed by the atmosphere and does not reach the earth’s surface. Most of the radiation reaching the earth’s surface is confined to short wavelengths, in the band 0.3 - 3 μm. On reaching the ground some of the short-wave radiation is also reflected by the surface.
Effect of feedstock, impurities, and rancidity on likelihood of spontaneous combustion of oil and biodiesel
Published in Biofuels, 2022
Brian Hanson, Dev S. Shrestha, Chad Dunkel
From the preliminary results, we observed that the ambient temperature must be at or higher than a specific temperature for the spontaneous reaction to occur within a few days. Since the combustion process needs air, we used heated air to a specific temperature to warm up the environment. Stephan Boltzmann’s equation was used to estimate the temperature of a container placed under the sun that may likely occur at a biodiesel plant. Solar constant, which is the rate at which energy reaches the earth's surface from the sun, usually taken to be 1388 watts per square meter [14]. The value on the earth's surface is about 1050 W/m2 due to atmospheric absorption. In a theoretical scenario, if a container with a black body surface is kept on direct sunlight on a hot day, with an outside temperature of 40 °C, the surface temperature will reach up to 97.5 °C neglecting heat loss through conduction and convection. However, due to convective and conductive heat loss, the actual temperature is going to be less than the theoretical maximum. In this experiment, 80 °C was considered a conservative representative temperature likely to occur inside a trash can under the sun. Therefore, the inlet air temperature was set to 80 °C to be near real-world conditions.