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Lecture notes for CHM115 filled in and complete. Lecture 27.

Lecture notes for CHM115 filled in and complete. Lecture...

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CHM 115-M01 CHM 115-M01 and M02 and M02 Lecture 27 Lecture 27
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Reading Interchapter: The Chemistry of Modern Materials, Pages 643-655 From WebCT: Energy, Chemistry, and Society - Omit discussion of MTBE Final Exam: Tuesday, December 11, 10:20 am
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Solar Energy Solar energy available in U.S. in 1 year is about 10 times total energy available in ALL known oil reserves on the planet. Earth U.S. avg. solar radiation ~125 W/m 2 ~250 W/m 2 surface area 5.10 x 10 8 km 2 (land: 1.49 x 10 8 km 2 ) 9.63 x 10 6 km 2 solar power available 6.38 x 10 16 W (land: 1.86 x 10 16 W) 2.41 x 10 15 W solar energy available (1 yr) land: 1.63 x 10 17 kWh 2.11 x 10 16 kWh total energy consumption per year (2003) 1.23 x 10 14 kWh 2.65 x 10 13 kWh (22% of world) solar energy available/year ~1300 times consumption ~800 times consumption solar radiation hitting Earth’s surface (for overhead midday sun) = 925 W/m 2 (power = energy per time, 1 W = 1 J/s) About 125 W/m^2 Abour 250 5.10E8 km^2^ Land: 1.49E8 km^2^ 9,63E6 km^2^ 6.38E16 W Land: 1.86E16 W Land: 1.63E17 1.23E14
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7 Solar Energy Solar Energy Obviously can’t use it all How much could we use? How is solar energy captured and used? How does the cost per Watt compare (today) to oil-based energy?
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8 Using Solar Energy “Passive” Allowing solar radiation to be captured as heat – such as heating water or bricks or other “heat stinks”. Heat is then released as needed. “Active” Allowing solar radiation to strike a solar cell which converts it to an electric current. Store the electricity in batteries to use later or use it do work (example, powering a motor)
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9 Passive Solar Panels “Solar Thermal” panels – the original solar panels Generally used to heat water
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Passive Solar Home Design Heat absorbing material which will radiate heat back out at night. Example: brick or certain tiles.
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11 Solar Cells (Photovoltaics) Overview of how they work…. To understand how solar cells work, we must understand “n” and “p” type semiconductors at the “band” level.
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12 Extrinsic and Intrinsic Semiconductors Intrinsic semiconductors – the pure, crystalline material has semiconducting properties (such as pure Si or Ge) Extrinsic semiconductors – The material is “doped” with a small amount of impurity of a similar material (about 1 in 10 6 to 1 in 10 8 atoms)
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13 Doped Semiconductors Decreased E g (band gap) relative to intrinsic material p-type : Doped with an element with fewer electrons.
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