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ECE 333 Green Electric Energy

ECE 333 Green Electric Energy. Lecture 10 The Solar Resource Professor Tim O’Connell Department of Electrical and Computer Engineering. The Solar Resource. Before we can talk about solar power, we need to talk about the sun We can predict where the sun is at any time

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ECE 333 Green Electric Energy

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  1. ECE 333 Green Electric Energy Lecture 10 The Solar Resource Professor Tim O’Connell Department of Electrical andComputer Engineering

  2. The Solar Resource Before we can talk about solar power, we need to talk about the sun We can predict where the sun is at any time Need to know how much sunlight is available Insolation : incident solar radiation Want to determine the average daily insolation at a site Want to be able to chose effective locations and panel tilts of solar panels

  3. The Sun and Blackbody Radiation The Sun 1.4 million km in diameter 3.8 x 1020 MW of radiated electromagnetic energy Blackbodies Both a perfect emitter and a perfect absorber Perfect emitter – radiates more energy per unit of surface area than a real object of the same temperature Perfect absorber – absorbs all radiation, none is reflected

  4. Planck’s Law Planck’s Law – wavelengths emitted by a blackbody depend on temperature (4.1) • λ= wavelength [μm] • Eλ = emissive power per unit area of black body [W/(m2-μm)] • T = absolute temperature (K)

  5. Wien’s Displacement Rule The wavelength at which the emissive power per unit area reaches its maximum point (4.3) • T = absolute temperature [K] • λ= wavelength [μm] • λmax =0.5 μm for the sun , T = 5800 K • λmax = 10.1 μm for the earth (as a blackbody), T = 288 K

  6. Stefan-Boltzmann Law Total radiant power (W) emitted is given by the Stefan –Boltzman law of radiation: (4.2) • E = total blackbody emission rate [W] • σ= Stefan-Boltzmann constant = 5.67x10-8[W/(m2-K4)] • T = absolute temperature [K] • A = surface area of blackbody [m2]

  7. Electromagnetic Spectrum Visible light has a wavelength of between 0.4 and 0.7 μm, with ultraviolet values immediately shorter, and infrared immediately longer Source: en.wikipedia.org/wiki/Electromagnetic_radiation

  8. 288 K Blackbody Spectrum Earth as a blackbody; note 0.7 m is red light. Most all is infrared range, which is why the earth doesn’t glow! Book figure is slightly wrong! Figure 4.1 Area under curve is the total radiant power emitted

  9. Extraterrestrial Solar Spectrum Note: The y-axis of the blackbody curve (dotted line) has been scaled to match the observed solar insolation just outside of Earth.

  10. Air Mass Ratio Air mass ratio of 1 (“AM1”) means sun is directly overhead AM0 means no atmosphere AM1.5 is assumed average at the earth’s surface (4.4) As sunlight passes through the atmosphere, less energy arrives at the earth’s surface

  11. Solar Spectrum on Earth’s Surface As the sun appears lower in the sky, m increases. Notice there is a large losstowards the blue end for higher m, which is why the sun appears reddish at sun rise and sun set. Figure 4.4

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