1 / 116

Electricity production

Electricity production. Generally (except for solar cells) a turbine is turned, which turns a generator, which makes electricity. Fossil fuels. Fossil fuels. In electricity production they are burned, the heat is used to heat water to make steam, the moving steam turns a turbine etc.

kaiser
Download Presentation

Electricity production

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Electricity production Generally (except for solar cells) a turbine is turned, which turns a generator, which makes electricity.

  2. Fossil fuels

  3. Fossil fuels In electricity production they are burned, the heat is used to heat water to make steam, the moving steam turns a turbine etc.

  4. Fossil fuels - Advantages • Relatively cheap • High energy density • Variety of engines and devices use them directly and easily • Extensive distribution network in place

  5. Fossil fuels - Disadvantages • Will run out • Pollute the environment (during mining sulphur and heavy metal content can be washed by rain into the environment) • Oil spillages etc. • Contribute to the greenhouse effect by releasing greenhouse gases

  6. Example question • A coal powered power plant has a power output of 400 MW and operates with an overall efficiency of 35%

  7. A coal powered power plant has a power output of 400 MW and operates with an overall efficiency of 35% • Calculate the rate at which thermal energy is provided by the coal

  8. A coal powered power plant has a power output of 400 MW and operates with an overall efficiency of 35% • Calculate the rate at which thermal energy is provided by the coal Efficiency = useful power output/power input Power input = output/efficiency Power input = 400/0.35 = 1.1 x 103 MW

  9. A coal powered power plant has a power output of 400 MW and operates with an overall efficiency of 35% • Calculate the rate at which coal is burned (Coal energy density = 30 MJ.kg-1)

  10. A coal powered power plant has a power output of 400 MW and operates with an overall efficiency of 35% • Calculate the rate at which coal is burned (Coal energy density = 30 MJ.kg-1) 1 kg of coal burned per second would produce 30 MJ. The power station needs 1.1 x 103 MJ per second. So Mass burned per second = 1.1 x 103/30 = 37 kg.s-1 Mass per year = 37x60x60x24x365 = 1.2 x 109 kg.yr-1

  11. A coal powered power plant has a power output of 400 MW and operates with an overall efficiency of 35% • The thermal energy produced by the power plant is removed by water. The temperature of the water must not increase by more than 5 °C. Calculate the rate of flow of water.

  12. A coal powered power plant has a power output of 400 MW and operates with an overall efficiency of 35% • The thermal energy produced by the power plant is removed by water. The temperature of the water must not increase by moe than 5 °C. Calculate the rate of flow of water. Rate of heat loss = 1.1 x 103 – 0.400 x 103 = 740 MW In one second, Q = mcΔT 740 x 106 = m x 4200 x 5 m = 35 x 103 kg So flow needs to be 35 x 103 kg.s-1

  13. Nuclear Fission

  14. Uranium Uranium 235 has a large unstable nucleus.

  15. Capture A lone neutron hitting the nucleus can be captured by the nucleus, forming Uranium 236.

  16. Capture A lone neutron hitting the nucleus can be captured by the nucleus, forming Uranium 236.

  17. Fission The Uranium 236 is very unstable and splits into two smaller nuclei (this is called nuclear fission)

  18. Fission The Uranium 236 is very unstable and splits into two smaller nuclei (this is called nuclear fission)

  19. Free neutrons As well as the two smaller nuclei (called daughternuclei), three neutrons are released (with lots of kinetic energy)

  20. Fission These free neutrons can strike more uranium nuclei, causing them to split.

  21. Chain Reaction If there is enough uranium (critical mass) a chain reaction occurs. Huge amounts of energy are released very quickly.

  22. Bang! This can result in a nuclear explosion!YouTube - nuclear bomb 4

  23. Controlled fission The chain reaction can be controlled using control rods and a moderator. The energy can then be used (normally to generate electricity).

  24. Fuel rods • In a Uranium reactor these contain Enriched Uranium (the percentage of U-235 has been increased – usually by centrifuging)

  25. Moderator This slows the free neutrons down, making them easier to absorb by the uranium 235 nuclei. Graphite or water is normally used. 1 eV neutrons are ideal)

  26. Control rods These absorb excess neutrons,making sure that the reaction does not get out of control. Boron is normally used.

  27. Heat The moderator gets hot from the energy it absorbs from the neutrons.

  28. Heat This heat is used to heat water (via a heat exchanger), to make steam, which turns a turbine, which turns a generator, which makes electricity.

  29. Useful by-products Uranium 238 in the fuel rods can also absorb neutrons to produce plutonium 239 which is itself is highly useful as a nuclear fuel (hence breeder reactors) It makes more fuel!!!

  30. Nuclear Power That’s how a nuclear power station works!

  31. Nuclear power - Advantages • High power output • Large reserves of nuclear fuels • No greenhouse gases

  32. Nuclear power - disadvantages • Waste products dangerous and difficult to dispose of • Major health hazard if there is an accident • Problems associated with uranium mining • Nuclear weapons

  33. Solar power

  34. The solar constant

  35. The solar constant The sun’s total power output is 3.9 x 1026 W!

  36. The solar constant The sun’s total power output is 3.9 x 1026 W! Only a fraction of this power actually reaches the earth, given by the formula I (Power per unit area) = P/4πr2 For the earth this is 1400 W.m-2 and is called the solar constant

  37. The solar constant For the earth this is 1400 W.m-2 and is called the solar constant This varies according to the power output of the sun (± 1.5%), distance from sun (± 4%), and angle of earth’s surface (tilt)

  38. Solar power - advantages • “Free” • Renewable • Clean

  39. Solar power - disadvantages • Only works during the day • Affected by cloudy weather • Low power output • Requires large areas • Initial costs are high

  40. Hydroelectric power

  41. Water storage in lakes “High” water has GPE. AS it falls this urns to KE, turns a turbine etc.

  42. Pumped storage • Excess electricity can be used to pump water up into a reservoir. It acts like a giant battery.

  43. Tidal water storage • Tide trapped behind a tidal barrage. Water turns turbine etc. • YouTube - TheUniversityofMaine's Channel

  44. Hydroelectric - Advantages • “Free” • Renewable • Clean

  45. Hydroelectric - disadvantages • Very dependent on location • Drastic changes to environment (flooding) • Initial costs very high

  46. Wind power

  47. Wind power Calculating power

  48. Wind moving at speed v, cross sectional area of turbines = A V A

  49. Wind moving at speed v, cross sectional area of turbines = A V Volume of air going through per second = Av Mass of air per second = Density x volume Mass of air per second = ρAv A

  50. Wind moving at speed v, cross sectional area of turbines = A V Mass of air per second = ρAv If all kinetic energy of air is transformed by the turbine, the amount of energy produced per second = ½mv2 = ½ρAv3 A

More Related