energy production (Physics - Unit 8)

• the production of electrical power is achieved primarily with the release of thermal energy from a fuel.
• thermal energy can be completely converted into work, but the continuous conversion of this energy implies the use of machines that are continuously repeating their actions in a fixed cycle
• any cyclical process (of energy conversion) must involve the trasnfer of some energy from the system to the surroundings that is no longer available to perform useful work. This is known as degraded energy.
• in electrical power stations the fuel is used to release thermal energy. the thermal energy is then used to boil water to make steam. the steam is then used to turn turbines and the motion of the turbines is used to generate electrical energy.
• transformers alter the potential energy.
• power is defined as the rate at which energy is converted. the units of power are J S^-1 or W.
• the law of energy conservation states that energy is neither created nor detroyed, it just changes form.
• examples of renewable energy are: solar, wind, hydroelectric, photovoltaic cells, active solar heaters, biofuels
• examples of non-renewable energy sources are: coal, oil, natural gas, nuclear.
• possible sources of energy are: the sun's radiated energy, gravitational energy of sun and moon, nuclear energy stored in atoms. earth's internal heat energy.
• specific energy is defined as the energy liberated per unit mass of fuel consumed. It is measured in J KG^-1.
• specific energy is defined as the energy liberated per unit mass of fuel consumed. It is measured in J KG^-1.

  • it provides useful comparison between fuels. specific energy = energy released from fuel/mass of fuel consumed.
• specific energy influences fuel choice as: the greater the mass of fuel needed to be transported, the greater the cost.
• energy density is the energy liberated per unit volume of fuel consumed. Unit is J m^-3

  energy density = energy release from fuel/volume of fuel consumed.
• fossil fuels are: coal, oil, and natural gas.
• coal is formed from dead plant matter growing in swamps. layers of matter decomposed. as it was buried by more plant matter, the material became more compressed. and thus into coal.
• oil is formed from the remains of microscopic marine life. compression took place under the sea.
• natural gas also occurs in undergound pockets. it can be obtained as a by-product during the production of oil. Can also be manufactured from coal.
• process of energy storage in fossil fuels is:

  solar energy -> chemical energy in plants (by photosynthesis) -> chemical energy in fossil fuels (by compression).
• advantages of fossil fuel production:

  • high 'specific energy' and 'energy density' meaning alot of energy is released froma small mass.
  • relatively easy to transport
  • cheap compared to other sources
• disadvantages of fossil fuels:

  • combustion products produce pollution, acid rain.
  • contain 'greenhouse' gases (trapping heat in earth's atmosphere)
  • non-renewable
  • extracting them can damage environment.
  • coal-fired power stations need large amounts of fuel.