Options for energy_sustainability

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Options for energy_sustainability

  1. 1. Options for energy sustainability
  2. 2. The outline of the problem • Human activities often require energy – Power for equipment – Power for lighting – Heating for thermal comfort – Hot water for hygiene – Cooling in hot weather • All require external supplies of energy • Majority of external energy comes from non-renewable sources - fossil fuels
  3. 3. What are fossil fuels? • All “fossil” fuels are a product of ancient biological activity • Living plants capture and fix carbon dioxide (CO2) and water (H2O) as hydrocarbons through photosynthesis – Solar energy is converted to chemical energy, stored in the hydrocarbons • All life depends on this process and it also releases oxygen (O2) • Ancient plant and animal remains have been preserved, in some cases, as fossilised hydrocarbons – fossil fuels
  4. 4. Oil and gas: fluid fossil fuels
  5. 5. Coal and peat: solid fossil fuels
  6. 6. What are the problems with using fossil fuels? • They are finite resources which will eventually run out - sustainability? – There are vast reserves of coal but other fossil fuels are beginning to run out already • Burning fossil fuels (combining a hydrocarbon with oxygen) to release the stored chemical energy as heat reverses the photosynthetic process: CH4 + 2O2 >> CO2 + 2H2O Heat energy released Input: methane and oxygen Output: carbon dioxide, water and heat
  7. 7. Why is carbon dioxide (CO2) a problem? • Carbon dioxide (CO2) is essential for life and maintenance of life supporting temperatures, but… • An increase in atmospheric carbon dioxide could lead to significant global temperature rises through the “greenhouse effect” which will disrupt human societies – Rising sea levels - flooding – Changes in agricultural systems – Changes in water supply
  8. 8. What is the greenhouse effect? CO2
  9. 9. What is the greenhouse effect? CO2 in atmosphere does not let long wave infrared (IR) radiation through LWIR CO2
  10. 10. What is the greenhouse effect? CO2 in atmosphere does not let long wave infrared (IR) radiation through LWIR SWIR CO2
  11. 11. What is the greenhouse effect? CO2 in atmosphere does not let long wave infrared (IR) radiation through The Earth, warmed by short wave IR, emits long wave IR which cannot escape through the CO2 in the atmosphere. There is a one way traffic in energy input  temperatures rise LWIR SWIR CO2
  12. 12. Reducing CO2 emissions aka low carbon technologies • Use renewable, non-finite energy sources: – Direct solar radiation – Geothermal energy – Hydro electric power – Tidal power – Wind – Biogas – Nuclear energy • Design buildings to make best use of environmental energy
  13. 13. Reducing CO2 emissions aka low carbon technologies • Use renewable, non-finite energy sources: – Direct solar radiation – Geothermal energy – Hydro electric power – Tidal power – Wind – Biogas – Nuclear energy • Design buildings to make best use of environmental energy
  14. 14. Designing to use the Sun • Solar energy can be exploited three ways – Photo-voltaic electricity generation – Water heating – Direct solar heating of the building fabric • The last two make direct use of the greenhouse effect themselves
  15. 15. Photo-voltaic electricity generation • Light photons fall on “photo-cells”, displacing electrons and thus generating a current • Efficiency low and cost high • Pay back periods only economic due to government sponsored “feed in tariffs” • They don’t work in the dark • Energy very difficult to store
  16. 16. Solar Water heating • Black painted water pipes under glass are heated by direct solar radiation using the greenhouse effect • Pay back still very long in UK climate but should become standard fitting on all new houses.
  17. 17. Direct solar heating of the building fabric • Exploit solar energy to the maximum – Consider building orientation – Exploit the greenhouse effect for building heating – Control excessive solar heating through shading – Store day time solar heat in mass construction for night time use
  18. 18. Orientation: the sun is in the south… • Position building and locate windows to maximise solar gain. • Build heavy masonry walls to store the heat to re-emit during the night
  19. 19. Orientation: the sun is high in summer, low in winter
  20. 20. Orientation: the sun is high in summer, low in winter
  21. 21. Orientation: the sun is high in summer, low in winter
  22. 22. Orientation: the sun is high in summer, low in winter
  23. 23. Orientation: the sun is high in summer, low in winter
  24. 24. The Brise soleil
  25. 25. Geothermal energy for individual buildings • High temperature geothermal energy – Dependent on hot rocks close to the surface – Not viable in the UK but used intensively in Iceland • Low temperature “ground source” heat – Exploits the temperature differences between the atmosphere and the sub- surface ground – Concentrates low quality heat using “heat pump” technologies
  26. 26. Ground source heat • UK air temperature varies between -10 and +30ºC • 1.5 metres below ground the temperature is constant around 10ºC • This temperature difference can be exploited for heating or cooling. 1.5m 10ºC constant temp -10ºC>+30ºC
  27. 27. Simplest ground source heating • Build underground; earth sheltered houses
  28. 28. Technical exploitation of ground source heat • “Pump” the heat to the surface • To be effective, air- conditioning technology must be exploited, in reverse. • “Heat pumps” concentrate low grade heat to get higher temperatures 1.5m 10ºC constant temp Large coiled pipe full of refrigerant fluid in the ground Pump and valve form the “heat pump” which concentrates the heat Small coiled pipe full of refrigerant fluid in the building
  29. 29. Wind energy • Wind generation of electricity is renewable and non- polluting (when generating) but… • It is intermittent – Where do you get power from when it is not running? • It is highly dependent on high wind speeds
  30. 30. Is there enough wind energy to be practically useful? • The theoretical energy output is proportional to the wind speed cubed – If the wind speed doubles, the theoretical energy output goes up eight times (2x2x2) – If the wind speed halves, the theoretical output falls to an eighth (2/2/2) • High steady wind speeds are needed for useful energy generation • Domestic scale installations in lowland areas simply cannot deliver useful quantities of energy.
  31. 31. Biogas generated from waste • Fermenting organic waste generates methane, a main constituent of natural gas. • Digesting farm waste generates gas and solid residue is a good fertiliser • Food waste can be digested in urban locations to generate biogas and reduce quantity of waste • Gas can be burned to generate electricity or fed directly into the gas supply network
  32. 32. Summary • Solar energy can be exploited for heat/hot water, but electricity generation is still in its infancy. • Wind power is ineffective at domestic scale • Significant quantities of environmental energy can be harvested through good building design • Biogas generation can potentially provide fuel or energy, but needs to be fairly large scale to be significant.

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