The solar constant is a measure of the solar electromagnetic radiation available per square meter at the Earth’s distance from the sun. It quantifies the rate at which energy is received on a unit surface, such as a solar panel. In this context, the constant represents the total radiant energy from the sun that is absorbed at a specific location. It also finds applications in various atmospheric and geological sciences.
Despite being referred to as a constant, the solar constant is relatively constant, with a variation of about 0.2% in a cycle that peaks approximately every eleven years. The first estimation of this constant was made by Claude Pouillet in 1838 at 1.228 kW/m². Currently, the constant is rated at approximately 1.361 kW/m² during a solar minimum and around 1.362 kW/m² during a solar maximum.
Calculating Solar Constant
This constant represents the total spectrum of electromagnetic radiation, not limited to visible light alone, and is measured using direct satellite observations. Its calculation involves the utilization of the Stefan-Boltzmann constant, which is related to the power per unit area emitted by a black body based on its thermodynamic temperature.
The dimensional formula for this constant is as follows:
Solar constant = Energy / (Unit area x Unit time)
= ML²T⻲ / (L²T)
= MT⻳
The formula indicates that this constant has dimensions of mass (M) divided by time (T) cubed, which represents the incident solar energy per unit area per second on the Earth’s surface.
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