date: November 6, 2001

Ch 8-- Alternative Sources of Energy

• some recommended problems at the end of the chapter
• 1,3,6,7,8, 9, 10
• 14,17,20, 26
• 29, 36, 40, 47

Let's look at the section headings in the book

• 8.1 Water as a fuel source
  • 8.2 splitting water
  • 8.3 hydrogen economy
• 8.4 Fuel Cells (slow burning)
• 8.5 Cells and batteries
  • 8.6 Batteries and Automobiles
• 8.7 Photovoltaic
• 8.8 Nuclear Fusion

Self help Assignment--

• look over each of these 8 sections, one by one
  • (Do one, see below. Then come back and try #2, etc.)
• Write down (need not be full of details)
  • one to four main points of that section
    • chemical, scientific, technical concept (if appropriate)
    • social, economic, environmental concept (if appropriate)
  • 2-5 specific words (vocabulary) from that section
    • write down the definition, if it seems appropriate
  • is this historical, current technology, developing technology, far in the future?
  • The list is repeated below
  • click on each heading and see how your list compares with mine
  • try to create 1-2 questions that have high probability of appearing on an exam
    • there are 6-7 topics and we'll usually have 5-8 questions across a chapter so there's likely to be one or two questions drawn from each section.
    • If you identify 3 questions, the odds are good you'll anticipate most of what I finally ask.
      • (don't try to anticipate the choices, but know the basics.)
• 8.1 Water as a fuel source
• 8.2 splitting water
• 8.3 hydrogen economy
• 8.4 Fuel Cells (slow burning)
• 8.5 Cells and batteries
• 8.6 Batteries and Automobiles
• 8.7 Photovoltaic
• 8.8 Nuclear Fusion

8.1 Water as a fuel source

• this is mostly a general introduction, few details
• key idea(s)
  • hydrogen is a good fuel, burns cleanly (no CO₂), lots of energy
  • we can produce hydrogen from water, but it costs energy
  • there are no natural sources of H₂ gas (in that form)
• vocabulary
  • exothermic, heat of combustion (terms used earlier in the book)
• technology
  • (treated in sections 2 and 3)
• presented as promising technology, not current technology

8.2 Splitting Water as a Way of Producing H₂ gas

• How Could we get a supply of Hydrogen?
  • Electrolysis of water forms H₂ and O₂
    • need to supply electrical energy
    • net energy loss, but may be worth it if H₂ is more convenient to use or can avoid problems like SO₂, CO, CO₂ or NOx production
    • would make economic sense only if electricity is cheap
    • would be environmentally better only if we could avoid fossil fuel consumption
      • use electricity from nuclear, geothermal or solar, for example
  • C + steam as an H₂ source
  • CH₄ and water as an H₂ source
    • both, of course, produce CO₂ (or CO) and rely on fossil fuel (C-from coal or methane)
• specific words (vocabulary) from that section
  • electrolysis
• is this historical, current technology, developing technology, far in the future?
  • We can do this now (current technology)
  • We don't, because the technology is not now economical; fossil fuels are cheaper to use directly

8.3 Hydrogen Economy

• To use H₂ as an energy source one needs
  • a source of hydrogen gas
  • storage and distribution of hydrogen
    • as compressed gas (BIG HEAVY TANKS)
    • as hydrides (higher density, no major pressure)
• main advantages
  • plentiful starting materials
  • clean burning fuel
    • need not be used like coal or gasoline (fires, internal combustion engines)-- see fuel cells below
• state of the technology
  • we CAN use H₂ easily now, but don't; it's rarely economical
  • no cheap available H₂
  • passenger cars, etc. won't use compressed H₂ (weight of tanks mainly)
  • hydride storage isn't a practical technology yet.
  • we might get forced to this or other technology (in spite of cost) just to avoid problems of gasoline powered internal combustion engines.

8.4 Fuel Cells (slow burning)

• Fuel Cell can make electricity directly from a fuel (no fires, engines, generators)
• need to separate oxidation and reduction, channel electrons in useful ways
  • fuels (material to be oxidized): H₂ (clean), CH₄, methanol (still produce CO₂)
  • oxidizer: O₂ in air usually, could be others (hydrogen peroxide, for example)
• words: oxidation, reduction
• status of technology: well established (used in spacecraft for example)
  • still too expensive for routine use
  • relatively maintenance free
  • promising-- can create car sized and house sized units, power on demand
  • will probably need improved design and better materials

8.5 Cells and batteries

• (Fairly large section, important chemical concepts, current applications)
• Devices that convert energy of chemical reaction directly into electrical power
• Several Types
  • primary, galvanic or voltaic cells (like flashlight batteries)
  • secondary or storage batteries (like auto battery, NiCad, Lithium Hydride)
    • supply power much like a primary battery
    • applying electrical power can reverse the reaction, regenerate reactants
    • can be use 100-1000 times
  • (fuel cell is another case, but discussed separately)
  • batteries are portable, convenient, but are an expensive source of electricity.
• As above, must separate oxidation from reduction
  • keep reactants separate
  • electrons go from anode (oxidation) to cathode (reduction)
  • electrons travel outside the battery, do useful work
  • cell components don't react unless in use (storage life)
    • important parameters: voltage, current, power/size, shelf life, cost, safe disposal
    • most are 1.0-1.5 volt; Lithium is 3 V. (Li is very reactive)
• Key examples:
  • know flashlight battery (Zinc, Carbon)
  • know lead acid storage cell (automobile)
  • know Nickel Cadmium battery
  • new: Lithium, lithium hydride (computers)
• status of technology
  • primary and secondary batteries are current technology, being improved
    • primary-- used more for convenience, portability
    • storage battery development needed to make alternative energy/car-design more competitive

8.6 Batteries and Automobiles

• Three important uses of batteries in cars
  • cars that are propelled by electrical motors and get all or some power from batteries (or fuel cells)
    • old electrical cars and some newer models-- lead acid or NiCad batteries recharged from power lines (some hybrid designs might use a small gasoline generator to keep recharging the battery.)
    • analog of diesel locomotive-- motor runs a generator, wheels are driven by the electrical motors
    • often use motors as generators when braking and thus recharge batteries.
  • cars that use electrical motors to help out a modest gasoline engine
  • even today's cars need electrical power for starter motor, ignition systems, lights and of course the radio
    • just about 100% use of Lead Acid storage battery
• What must such batteries do?
• technology status
  • simple electrical cars (low speed, short range, light weight) are around and were around in 1905.
  • only test vehicles or limited production with capacity of "normal" cars and trucks
  • batteries (cost, weight, lifetime) stand in the way of adoption -- battery life is a major problem now.
  • possibly is a future technology, but economics are poor now.
  • today's examples driven more by pollution concerns than by simple economics

8.7 Photovoltaic Cells

• Silicon is an insulator
  • doping makes it conductive
  • combining doped regions creates electrical devices
  • solar panels are typical of those devices
• visible light has enough energy to free an electron and give it a "push" of 1-2 volts
  • if we can direct those electrons through a wire we have electrical power source
• vocabulary: doping, P-doping, N-doping, junction, solar cell vs. solar panel, volt, ampere, electrical current
• status of the technology
  • in routine production
  • expensive source of electricity, but practical for many niche markets
  • prices keep coming down

8.8 Nuclear Fusion

• Concept is nuclear fusion as an energy source
• reaction type that powers sun and other starts
• fusion-- two smaller nuclei get together and make a larger nucleus
• if product weigh less than the starting materials, result is energy
• most common example is ₁2H + ₁2H ---> ₂4He + lots of energy
  • ₁2H is also known as deuterium or heavy hydrogen
  • there's enough on earth to be a practical source
  • difficulty in getting it to occur
• need to get nuclei very close together
  • but nuclei are + charged and normally repel (stay apart)
  • in H-bomb, we use the forces of an A-bomb to drive atoms together
  • in lab designs, we use magnetic fields to try to squeeze a "gas" or plasma of D-nuclei
• vocabulary: fusion (vs fission), magnetic confinement, Coulomb repulsion, deuterium and deuteron, A-bomb = fission, all operating reactors = fission, H bomb = fusion
• state of the technology
  • promising in the long range; very unlikely to be important in the next 20-30 years
  • some sample question areas?