Solar Energy: Fuel for the Future Chapter 9

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Announcements and Assignments

• Read Chapter 8
• Homework 1, 3, 9, 11, 13, 15, 20, 30
• Web Assignment Monday April 4th 600pm
• In Class Assignment Tuesday April 5th
• Quiz for Chapter 8 Thursday April 7th

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CH 8 Busy Electrons

• What is an electron?
• How do we use them as energy?

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Solar Energy Fuel for the Future

• Recent years have seen a rebirth of interest in
  solar energy - Why?
• 1. will someday be exhausted or become more
  expensive

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Solar Energy Fuel for the Future

• 2. fossil fuels are causing monumental
  environmental pollution and producing toxic
  substances to name a few

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Solar Energy Fuel for the Future

• 3. the promise of cheap energy
  has not been realized.

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Solar Energy Fuel for the Future

• Therefore, energy is available everyday on
  earth, and is virtually inexhaustible.
• Every year, kJ of solar energy fall on the
  planets surface - this is 15,000 times the
  worlds present energy supply.

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Solar Energy Fuel for the Future

• Then why cannot we go solar?
• - energy is not concentrated
• - need storage systems
• How do we store it for a rainy day?
• - need transforming systems
• How do we switch from fossil fuels?

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Heat from Sunlight

• Technology for long term storage of the heat from
  the sun does not yet exist. But many innovations
  do exist
• solar heating trapping the heat during
  the day and using it during the night in solar
  heated homes.
• - needs no like active solar heating.
• - Tin oxide is used as a coating on the panes to
  inhibit the transfer of heat

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Heat from the Sun

• - performance of these windows is give a code
  R-number. Thus, R-2 means the window has twice
  the to heat flow as that of a single pane
  window. Today, some windows have R-15 or greater
• - walls and ceiling are also insulated
• - humidity is kept at an appropriate level
  because moist air feels warmer than dry air.

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Heat from Sunlight

• - energy-saving strategies employed in model
  solar homes have been used in commercial
  buildings. Indeed, heating requirements have
  decreased by or more since 1960s.

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Water and Wind

• Note Energy used in transportation must be
• 1. portable
• 2.
• 3. convenient
• Waterfalls and windmills have long been used to
  drive electric generators. Huge dams associated
  with hydroelectric plants produce about 8 of the
  electric energy used in the US. Proposals to use
  tide energy are being explored.

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Water and Wind

• Currently, wind power supplies a tiny fraction of
  our electricity. More recently, array of
  windmills are being built in California covering
  12 square miles to produce electricity sufficient
  to meet the electricity needs of residents and
  businesses surrounding Palm Springs valley.
• More research is being devoted to developing
  direct means of using sunlight as an energy
  source such as

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Fuel from Sunlight

• Sun is the ultimate source of energy through
• .
• Surprisingly, only of the solar
  radiation reaching the surface of the earth is
  used for photosynthesis.
• Photosynthesis is being used to generate
  energy such as biomass.
• Attention has been given to plants that contain
  fuels such as corn and sugar cane in the
  fermentation of ethanol (ethyl alcohol)
• Biomass cannot meet all of our energy needs.

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Water Source of Fuel

• When two moles of hydrogen gas react with one
  mole of oxygen gas, two moles of water form and
  kJ of energy is given off.
• This suggests that hydrogen is an excellent fuel.
  Burning one gram of hydrogen produces kJ of
  energy.
• Burning one gram of coal produces only kJ of
  energy, and burning one gram of octane (gasoline)
  produces kJ.
• Clearly, hydrogen is potentially a powerful
  energy source.

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Water Source of Heat and Light

• Nearly all the hydrogen in the world is tied up
  in chemical compounds. Therefore, to obtain
  hydrogen as a fuel, we need energy to break
  compounds down.
• (Takes energy to make energy_)

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Water Source of Heat and Light

• 1. in other words, splitting water to
  hydrogen and oxygen using electricity. recall, we
  need 572 kJ of energy to produce two moles of
  hydrogen.
• 2. Decomposition of water in other words, hot
  steam is passed over at 8000 C. Hydrogen and
  carbon monoxide gases are produced.

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Electrolysis of water - Fig 8.16
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Hydrogen from Sunlight

• Sunlight appears to be the only energetically and
  economically feasible way of obtaining hydrogen
  from water. The major difficulty is the need for
  459 kJ/mole of energy to break the O---H bond in
  water
• This is done with the aid of a catalyst, mainly
  red light, in the photosynthetic process.
• The source of red light is a molecule called
  rubippy, ruthenium tris(bipyridine)chloride.

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Hydrogen from Sunlight

• When rubippy encounters a water molecule, an
  electron is released which breaks down water into
  1/2 mole of hydrogen gas.
• Therefore, rubippy is capable of splitting
  water into hydrogen and oxygen.
• Regrettably, the efficiency is only 1 and is
  costly. But water research is still a very hot
  research topic today.

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The Hydrogen Economy

• Although hydrogen fuel has a high efficiency, its
  storage and transportation are still a
  significant problem it occupies a volume (12
  liters (3 gallons) per gram)
• when liquefied, hydrogen must be cooled to
  - 0C, this is very costly
• A more convenient method of storing hydrogen
  involves it on activated carbon. When
  carbon is heated, hydrogen is released

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The Hydrogen Economy

• Another method is to react hydrogen with a metal
  forming a stable , which
  have high storage capacity. For instance if 10
  liters of hydrogen gas react with Li to form LiH,
  it would occupy only 4.3 ml. When the hydrides
  react with water, hydrogen gas is released.
  Prototype vehicles that use this principle have
  been built
• The best method of extracting energy from
  hydrogen is to burn it directly in power plants,
  vehicles, and homes

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The Hydrogen Economy

• Hydrogen burns smoothly, quietly, and safely in
  (21 Oxygen)
• But when hydrogen mixes with pure , a
  small spark is enough to detonate a devastating
  explosion
• Burning one gram of hydrogen releases 143kJ of
  energy, forming only non-polluting as
  end product.

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Fuel Cells A Slow Burn

• A is a controlled chemical reaction between
  hydrogen and oxygen to form electricity (a fancy
  battery)
• The principle is similar to a flashlight battery
• This is done when hydrogen gas is , where
  electrons form on the anode () and move to the
  (-) where oxygen is reduced (Leo goes Ger)
• Hot KOH is used as an electrolyte

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Fuel Cells A Slow Burn

• Anode and cathode are made up of carbon
  electrodes containing Ni and NiO respectively
• A is created between the two electrodes
  causing a voltage (volts) to form
• The at which electrons flow is measured in
  amperes (amps)
• The end product is 286 kJ per mole water,
  released in the form of as electricity and
  the rest is heat

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Fuel Cells A Slow Burn

• A new generation of hydrogen fuel cells are being
  developed using a polymer electrolyte at 6.00
  per gram. The cell uses Platinum electrodes
• Automakers have several commercial models for
  sale as hybrid cars or fuel cell vehicles. (see
  Web assignment)

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A Proton Exchange Membrane (PEM) fuel cell - Fig.
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Fig 8.10 Hydrogen fuel used in PEM
(proton-exchange membrane) cells for vehicles.
Fig. 8.10
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Fig. 8.12 NECAR 5 (New electric car) using
methanol fuel cells by Daimler-Chrysler.
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Fig. 8.14 a) Toyota Prius hybrid, b) Engine of
Prius
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Fig. 8.9 Portable fuel cell (behind the person).