ENGR 101 HUM 200: Technology

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ENGR 101/ HUM 200 Technology Society

• November 2, 2005

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Agenda

• Mid-quarter feedback
• Exam Rescheduled for Tuesday 11/8
• Project comments (Thursday class Define
  better, clearly define target users, if
  interviewing or testing them, how identify or
  recruit them, multiple ways to prototype)
• International perspectives on energy consumption
• Renewable energy

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International Issues

• Developing world energy sources
• About one-third of worlds population lacks
  access to modern energy sources
• Infrastructure is a significant expense
• Centralized technologies require enormous
  investments and maintanance
• Bioenergy (wood and other plant matter
  derivatives) is a cornerstone of sustainable
  energy strategy

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Biomass

• Can contribute to deforestation
• Labor intensive work of collecting firewood
• Indoor smoke pollution
• Examples
• Residues and waste
• Purpose-grown energy crops
• Natural vegetation
• Agriculturally, balance out food and energy crops

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Biomass Case Studies

• Ethanol from sugarcane in Brazil
• Sugarcane residue used for electricity generation
• Corn stalk processing for cooking fuel in China
• What infrastructure is required?

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Solar Power

• First explored by engineers over 100 years ago
  (not a byproduct of the US environmental movement
  in the 1970s!)
• Appealed to people for use in Algeria and India
• Early initiatives bypassed in favor of ease and
  cheap cost of coal and wood
• Early parabaolic reflectors kept getting felled
  by weather
• Decentralized technology. What infrastructure is
  required?

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Three Technologies for Solar Power

• Photovoltaic cells
• Concentrating solar power technologies
• Low-temperature solar collectors

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Photovoltaic Cells

• Convert sunlight directly into electricity
  (photovolt)
• Made of semiconductors such as crystalline
  silicon or various thin-film materials
• Also known as solar cells (put together into
  modules and arrays)
• Can provide anything from tiny amounts of power
  for watches to large amounts for the electric
  grid
• A PV System includes electrical connections,
  mounting hardware, power-conditioning equipment,
  and batteries that store solar energy for use
  when the sun isn't shining
• Current uses of PVs include communications
  satellites, water pumps, road and traffic signs

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Photovoltaics one cell produces 1 to 2 watts of
power
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Uses of Stand-alone PVs

• Replacement energy when other utilities are
• Unavailable, undesirable (no tolerance for
  interruption), too costly to extend power lines
• Can produce energy where and when it's needed, so
  complex wiring, storage, and control systems
  aren't needed
• Small systems produce less than 500 watts and
  weigh less than 68 kilograms (150 pounds) easy
  to transport and install
• Most installations take only a few hours and PV
  modules need only an occasional inspection and
  cleaning

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Concentrating Solar Power Technologies (CSPs)

• Use mirrors to concentrate the sun's heat energy
• Drive a steam generator to produce electricity
• Include dish/engine systems, parabolic troughs,
  and central power towers

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CSPs

• Relatively low cost and can deliver power when
  and where it is needed
• Excellent for satisfying need for distributed
  source of energy
• Can range from small-scale (village power, 10
  kilowatts) to large-scale (grid-connected
  applications, 100 megawatts).
• Can use thermal storage during cloudy periods or
  at night.
• Can also be combined with natural gas
• Amount of power generated depends on amount of
  direct sunlight. Good for sunbelt locations.
• Enough electric power for the entire country
  could be generated by covering about 9 percent of
  Nevadaa plot of land 100 miles on a sidewith
  parabolic trough systems.

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Two Designs of CSPs

• Troughs
• Parabolic shaped reflectors concentrate the suns
  energy pipe with oil runs down the middle and
  gets heated up by solar energy, which then
  generates electricity in a conventional steam
  generator
• Power towers
• Lots of large, suntracking mirrors that focus
  sunlight onto a receiver at the top of a tower
  heat transfer fluid (steam, molten nitrate salt)
  in the receiver generates steam

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Low-temperature Solar Collectors

• Absorb the sun's heat energy
• Heat is used directly for hot water or space
  heating for residential, commercial, and
  industrial facilities
• Different kinds of collectors used based on need

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Solar Case Studies

• Boosting a telephone signal in Nevada
• Providing water for cattle in South Dakota
• Powering a modern home in Florida

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Next class

• Make It Better activity
• Review of Amory Lovins video lecture
• Exam scheduled for Tuesday the 8th. Review
  session will be Monday 530pm-630 pm