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EE580 – Solar Cells Todd J. Kaiser

Learn about the wave-particle duality of light, properties of sunlight, electromagnetic spectrum, photon energy, radiant power density, blackbody radiation, and the effects of solar radiation on Earth's atmosphere.

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EE580 – Solar Cells Todd J. Kaiser

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  1. EE580 – Solar CellsTodd J. Kaiser • Lecture 03 • Nature of Sunlight Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  2. Wave-Particle Duality • Light acts as • Waves: electromagnetic radiation • Refraction - bending of light through a prism • Diffraction - bending of light around an edge • Interference – adding of light waves • Particles: photons – individual packets of energy • Photoelectric Effect • Blackbody Radiation Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  3. Properties of Light • Sunlight contains photons of many different frequencies ( we see as different colors) • Visible Light • 0.38 microns – 0.77 microns (10-6 meters) • Blue - Red • Frequency (f) and Wavelength ( l) are inversely related: f = 1/ l • High Energy High Frequency  Short Wavelength • Low Energy Low Frequency  Long Wavelength Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  4. Electromagnetic Spectrum 107 108 109 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 Radio Waves 10 1 10-1 10-2 10-3 10-4 10-5 10-6 10-7 10-8 10-9 10-10 10-11 10-12 Color, wavelength and frequency are interrelated Wavelength (meters) Frequency (Hz) Microwaves Roy G. BIV 0.77 microns Red Orange Yellow Green Blue Indigo Violet Infrared 0.6 microns Visible 0.5 microns Ultraviolet X Rays 0.4 microns 0.38 microns Gamma Rays Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  5. Photon Energy High energy photon for blue light Low energy photon for red light Very low energy photon for infrared (invisible) Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  6. Photon Flux & Energy Density For the same intensity of light shorter wavelengths require fewer photons, since the energy content of each individual photon is greater Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  7. Radiant Power Density • The total power density emitted from a light source • The spectral irradiance is multiplied by the wavelength range for which is was measured and summed over the measurement range F(B) F(O) F(G) F(R) F(Y) F(V) F(I) Dl1 Dl2 Dl3 Dl4 Dl5 Dl6 Dl7 Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  8. Spectral Irradiance Visible Xenon – (left axis) Sun - (right axis) Halogen – (left axis) Mercury – (left axis) Power Density at a particular wavelength Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  9. Solar Radiation Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  10. Blackbody Radiation • A body in thermal equilibrium emits and absorbs radiation at the same rate • A body that absorbs all the radiation incident on it is an ideal blackbody • The power per area radiated is given by the Stefan-Boltzmann Law • This function has a maximum given by Wien’s Displacement Law • The spectral irradiance of a blackbody radiator is given by Planck’s Law Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  11. Plot of Planck’s Law Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  12. Sun’s maximum at visible spectrum Visible Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  13. Sun Fusion reaction at 20,000,000 degrees Converts H to He Fusion reaction at 20,000,000 degrees Converts H to He Convection heat transfer Photosphere (sun’s surface) at 5760±50 K Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  14. Sunlight in Space The energy is emitted from the surface of the sun as a sphere of light The size of the sphere grows as the light moves farther from the sun causing the power density to reduce Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  15. Sunlight at Earth’s Orbit Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  16. Sunlight at Earth’s Surface • Atmospheric Effects • Absorption • Scattering • Local Variations • Clouds • Pollution • Weather • Latitude • Season of Year • Time of Day Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  17. 100 % input Clear Sky Absorption & Scattering 3% Scattered To Space Ozone 20-40 km 2% Absorbed Upper Dust Layer 15-35 km 0.5% Scattered to Space 1% Absorbed 1% Scattered to Earth 18% Absorbed Air Molecules 0-30 km 1% Scattered to Space 8% Absorbed 4% Scattered to Earth Water Vapor 0-3 km 0.5% Scattered to Space 6% Absorbed 1% Scattered to Earth Lower Dust 0-3 km 0.5% Scattered to Space 1% Absorbed 1% Scattered to Earth 70% Direct to Earth 7% Scattered To Earth BOR0606C Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  18. Air Mass • The path length that light takes through the atmosphere normalized to the shortest possible path length q x h Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  19. Measuring the Air Mass q h q Object of height (L) Neglects the curvature of the earth’s atmosphere Shadow from object (S) Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  20. EAST SOUTH NORTH WEST March 22: Spring Equinox Sept 23: Fall Equinox What time of year is this image true? Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  21. Declination Angle Mar 23 Declination (d) = 0º Dec 23 Declination (d) = -23.45º Jun 23 Declination (d) = 23.45º Sep 23 Declination (d) = 0º Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  22. Declination Angle of Sun Summer Solstice d = 23.45º North Pole d Fall Equinox d = 0º d Winter Solstice d = -23.45º Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  23. Elevation Angle The elevation angle is the angular height the sun makes with the horizontal Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  24. Polar Plot of Sun Position for Bozeman Summer Spring/Fall Winter Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  25. Passive Solar Heating Summer Sun Winter Sun Overhang designed to remove direct sunlight from window during the heat of summer and allow the sunlight in during cooler winters Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  26. Insolation Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  27. Solar Cell Land Area Requirements for the USA’s Energy with Solar PV • 100 miles by 100 miles in Nevada would provide the equivalent of the entire US electrical demand • Distributed (to sites with less sun) it would take less than 25% of the area covered by US roads. Montana State University: Solar Cells Lecture 3: Nature of Sunlight

  28. Solar Cell Land Area Requirements for the World’s Energy with Solar PV 6 Boxes at 3.3 TW Each Montana State University: Solar Cells Lecture 3: Nature of Sunlight

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