Energy and Environment, Class 7

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Energy and Environment, Class 7

• Solar Energy Basics

http//nssdc.gsfc.nasa.gov/photo_gallery/photogall
ery-solar.html
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Solar Energy

• The sun is responsible (directly or indirectly)
  for most of the energy we use, including
• fossil fuels, wind power, solar power, tidal
  power and biomass energy.
• Non-solar energy includes nuclear power and
  geothermal energy.

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Solar Radiation

• At Earths distance from the sun, the density of
  solar power on a flat surface pointed at the sun
  is 1354 W/m2
• 429 Btu/(ft2 x hr)
• Incoming solar radiation (insolation) can be
  reflected back to space, absorbed in the
  atmosphere or scattered in the atmosphere before
  it reaches the ground.

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Global Energy Balance
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Incoming Solar Radiation
SPACE
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Reflected Solar Radiation
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20
4
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ATMOSPHERE
Back-Scattered by Air
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Absorbed by H2O, Dust, O3
Reflected by Clouds
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Absorbed in Clouds
Reflected by Surface
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OCEAN and LAND
Based on Wallace and Hobbs, p. 321
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Variation of Solar Radiation Intensity with
Latitude
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Why Do We Have Seasons?

• Demonstrate with lamp and globe.
• Common misconceptions
• Concept questions
• When is the sun directly overhead in Prescott?
• Where on Earth does the sun get directly
  overhead?
• What happens at the North Pole?

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Earth-Sun Geometry
Position of the equinoxes, solstices, aphelion,
and perihelion on the Earth's orbit.
http//www.geog.ouc.bc.ca/physgeog/contents/6h.htm
l
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http//solardat.uoregon.edu/SunChartProgram.html
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http//solardat.uoregon.edu/SunChartProgram.html
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Daily Cycle of Solar Power
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Solar Power Data

• National Renewable Energy Laboratory
  http//rredc.nrel.gov/
• Solar Radiation Data Manual for Buildings
  http//rredc.nrel.gov/solar/old_data/nsrdb/blueboo
  k/

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Climatic Considerations

• When do we want solar heating?
• Western Region Climate Center, historical
  summaries
• http//www.wrcc.dri.edu/climsum.html

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PRESCOTT, ARIZONA 1971 - 2000 Temperature and
Precipitation                                 
                                            
Data is smoothed using a 29 day running average.
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Solar Design

• DOE list of design tools
• http//www.eere.energy.gov/consumerinfo/tools_ssh.
  html
• Cute online calculators
• http//www.susdesign.com/design-tools.html

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Overhang Design
window in full shade
window in full sun
Elevation Angle a
Elevation Angle x
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Overhang Design, cont.
window in full shade
window in full sun
sohcahtoa sin opposite/hypotenuse cos
adjacent/hypotenuse tan opposite/adjacent
d2
a
d3
x
d1
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Overhang Design, cont.
sohcahtoa sin opposite/hypotenuse cos
adjacent/hypotenuse tan opposite/adjacent
d2
a
d3
x
d3, x and a are known. Want to calculate d1 and
d2
d1
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Overhang Design, cont.
Solve eq. 1 for d2
d2
a
Substitute into eq. 2
d3
x
d1
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Overhang Design, cont.
Substitute back into eq. 1
d2
a
d3
x
d1
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Practice

• Develop a window design for Prescott Arizona
• Assume the window is 4 ft. high
• Determine angles for full sun and full shade
• Calculate the height and depth of the optimal
  overhang

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Solar Heating Brainstorm

• How can we use the sun for heating our buildings?
• Passive solar
• Thermosiphon system
• Thermal Mass
• Biomass
• Solar cooling