EML4450L6

EML4450L6 - Sustainable Energy Science and Engineering...

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S ustainable E nergy S cience and E ngineering C enter Solar Radiation The objectives of this section are: 1. to review the properties of solar radiation; 2. to determine theoretical upper limit of solar radiation available at the earth’s surface; 3. to determine the position of the sun in the sky and the beam radiation direction that is incident on surfaces of various orientations and shading. http://powerfromthesun.net/chapter3/Chapter3 Reference: Principles of Solar Engineering, Goswami, Kreith and Kreider, Taylor & Francis, 2000
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S ustainable E nergy S cience and E ngineering C enter Energy and Radiation* Radiation: The transfer of energy via electromagnetic waves that travel at the speed of light. The velocity of light in a vacuum is approximately 3 x 10 8 m/s. The time it takes light from the sun to reach the Earth is 8 minutes and 20 seconds. Heat transfer by electromagnetic radiation can travel through empty space. Any body above the temperature of absolute zero (-273.15 o C) radiate energy to their surrounding environment. The many different types of radiation is defined by its wavelength. The electromagnetic radiation can vary widely. *Source: http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/energy/nature_of_electromagnetic_radiation.html http://www.physicalgeography.net
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S ustainable E nergy S cience and E ngineering C enter Sun Radiation Spectrum Visible light has a wavelength of between 0.40 to 0.71 micrometers (μm). The sun emits only a portion (44%) of its radiation in this range. Solar radiation spans a spectrum from approximately 0.1 to 4.0 micrometers. About 7% of the sun's emission is in 0.1 to 0.4 micrometers wavelength band (UV). About 48% of the sun's radiation falls in the region between 0.71 to 4.0 micrometers (near infrared : 0.71 to 1.5 micrometers; far infrared: 1.5 to 4.0 micrometers). Solar radiation incident outside the earth's atmosphere is called extraterrestrial radiation. On average the extraterrestrial irradiance is 1367 W/m 2 . This value varies by ±3% as the earth orbits the sun.
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ustainable E nergy S cience and E ngineering C enter The amount of electromagnetic radiation emitted by a body is directly related to its temperature. If the body is a perfect emitter (black body), the amount of radiation given off is proportional to the 4th power of its temperature as measured in degrees Kelvin. This natural phenomenon is described by the Stephan-Boltzmann law: Where σ = 5.67 x 10 -8 Wm -2 k -4 and T is in K In general, good emitters of radiation are also good absorbers of radiation at specific wavelength bands. This is especially true of greenhouse gases. Some objects in nature have almost completely perfect abilities to absorb and emit radiation. We call these objects black bodies. The radiation characteristics of the sun and the Earth are very close to being black bodies. Stephan-Boltzmann Law
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EML4450L6 - Sustainable Energy Science and Engineering...

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