Review - ELEG620: Solar Electric Systems University of...

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Unformatted text preview: ELEG620: Solar Electric Systems University of Delaware, ECE Spring 2009 S. Bremner Review ELEG620: Solar Electric Systems University of Delaware, ECE Spring 2009 S. Bremner Properties of Radiation Summary of equations & concepts: Wave/energy relationship: Common units of energy: electron-V (eV) 1 eV = 1.602x10-19 J Power density (H, W/m) and monochromatic photon flux ( , photons/secm): Power density (in W/m) is photon flux (# photons/msec) multiplied by energy per photon. ( ) m q J hc m W H 24 . 1 ) ( 2 = = Burn into brain! m m W 1 ELEG620: Solar Electric Systems University of Delaware, ECE Spring 2009 S. Bremner Black Body Radiation Blackbody: emits based on its temperature; absorbs all light incident on it. Power density for blackbody: Spectral Irradiance for black body: Depends on temperature of blackbody source 4 T H = T m p 2900 ) ( = ELEG620: Solar Electric Systems University of Delaware, ECE Spring 2009 S. Bremner Solar Radiation Sun approximates a black body at ~6000K, radiating with a power density of H sun 63 MW/m. Total power emitted is 4 R 2 sun , where the radius of the sun, R sun = 6.96 10 5 km. Power density at a distance D from sun is given by: sun sun H D R m W H = 2 2 ELEG620: Solar Electric Systems University of Delaware, ECE Spring 2009 S. Bremner Atmospheric Effects Earths atmosphere has several impacts on radiation: Scattering Scatters light so that some hits the earths surface at a wide range of angles and from a large area of the sky. So two components to light hitting the earths surface: Direct light is the light from the sun which reaches the earth without scattering. Diffuse light is scattered by the atmosphere. This light CANNOT be concentrated. Most effective for higher energy (blue) photons. 4 I ELEG620: Solar Electric Systems University of Delaware, ECE Spring 2009 S. Bremner Terrestrial Radiation The standard AM1.5 spectra consists of a standard spectral irradiance for terrestrial solar radiation. Direct radiative power can be approximated from AM value. Note the order! (I got it wrong!) Rule of thumb: 678 . 7 . 353 . 1 AM D I = I D is direct irradiance, I G is global irradiance (direct + indirect (diffuse))....
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Review - ELEG620: Solar Electric Systems University of...

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