Solar Cell

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Solar Cell

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Solar Cell

  1. 1. Solar Cell (Photovoltaics) 발표자 : 20075418 Ju Dae-Hyun Solar Cell (PV) Light Electricity
  2. 2. Nonrenewable Enargy 재생에너지원 (Renewable Energy) 일회용에너지원 (Nonrenewable Energy) Renewable
  3. 3. What is a Solar Cell? <ul><li>A structure that converts solar energy directly to DC electric energy. </li></ul><ul><ul><li>It supplies a voltage and a current to a resistive load (light, battery, motor). </li></ul></ul><ul><ul><li>Power = Current x Voltage=Current 2 x R= Voltage 2 /R </li></ul></ul><ul><li>It is like a battery because it supplies DC power. </li></ul><ul><li>It is not like a battery because the voltage supplied by the cell changes with changes in the resistance of the load. </li></ul>
  4. 4. Basic Physics of Solar Cells <ul><li>Silicon (Si) is from group 4 of the period table. When many Si atoms are in close proximity, the energy states form bands of forbidden energy states. </li></ul><ul><li>One of these bands is called the band gap(Eg) and the absorption of light in Si is a strong function of Eg. </li></ul>
  5. 5. <ul><li>The Sun daily provides about 10 000 times more energy to the Earth than we consume </li></ul><ul><li>Photovoltaic technology directly converts solar energy into electricity </li></ul><ul><li>No moving parts – no noise – no emissions – long lifetime </li></ul><ul><li>Large industrial potential - cost reductions needed </li></ul><ul><li>Feedstock for PV industry is silicon - the second most abundant element in the crust of the Earth </li></ul> The Sun as Energy Source
  6. 6. Solar Energy status <ul><li>Market is exploding </li></ul><ul><li>The solar industry is very profitable </li></ul><ul><li>Lack of highly purified silicon (polysilicon) </li></ul><ul><li>Cost of solar electricity is too high, R&D focus on reducing cost and increasing efficiency </li></ul>
  7. 7. Actual Growth vs. Historic Forecasts Actual market development
  8. 8. Solar Energy status <ul><li>Market is exploding </li></ul><ul><li>The solar industry is very profitable </li></ul><ul><li>Lack of highly purified silicon (polysilicon) </li></ul><ul><li>Cost of solar electricity is too high, R&D focus on reducing cost and increasing efficiency </li></ul>
  9. 9. - Gross revenue development 159 435 857 1705 2454 0 200 400 600 800 1000 1200 1400 1600 1800 2001 2002 2003 2004 2005 (MNOK)
  10. 10. Solar Energy status <ul><li>Market is exploding </li></ul><ul><li>The solar industry is very profitable </li></ul><ul><li>Lack of highly purified silicon (polysilicon) </li></ul><ul><li>Cost of solar electricity is too high, R&D focus on reducing cost and increasing efficiency </li></ul>
  11. 11. Solar Grade Silicon Supply-Demand (MT/year)
  12. 12. Solar Energy status <ul><li>Market is exploding </li></ul><ul><li>The solar industry is very profitable </li></ul><ul><li>Lack of highly purified silicon (polysilicon) </li></ul><ul><li>Cost of solar electricity is too high, R&D focus on reducing cost and increasing efficiency </li></ul>
  13. 13. Cost reductions – existing technologies <ul><li>Thinner wafers - Wire sawing - Laser cutting and etching </li></ul><ul><li>Higher efficiencies - Semiconductor technologies on single crystal wafers (examples Sanyo / SunPower) </li></ul><ul><li>Thin film technologies (flat panel display) </li></ul>
  14. 14. Public incentives are important
  15. 15. Cost goals for third generation solar cells Efficiency and cost projections for first-, second- and third generation photovoltaic technology (wafers, thin-films, and advanced thin-films, respectively) Source: University of New South Wales
  16. 16. Next generation technology <ul><li>Silicon nanostructures Bandgap engineering of silicon. </li></ul><ul><li>Applications could be tandem solar cells and energy selective contacts for hot carrier solar cells. </li></ul><ul><li>Fabrication of silicon nanostructures consisting of quantum well and quantum dot super lattices to achieve band gap control </li></ul>
  17. 17. <ul><li>Up/Down converters Luminescent materials that: </li></ul><ul><li>EITHER absorb one high energy photon and emit more than one low energy photon just above the bad gap of the solar cell (down-conversion) </li></ul><ul><li>OR that absorb more than one low energy photon below the band gap of the cell and emit one photon just above the band gap (up-conversion). </li></ul>Next generation technology (cont.)
  18. 18. Understanding cell efficiency
  19. 19. <ul><li>Hot carrier Cells This concept tackles the major PV loss mechanism of thermalisation of carriers. </li></ul><ul><li>The purpose is to slow down the rate of photoexcited carrier cooling caused by phonon interaction in the lattice to allow time for the carriers to be collected whilst they are still hot, and hence increasing the voltage of a cell. </li></ul>Next generation technology (cont.)
  20. 20. <ul><li>Thermoelectric solar cells Application of the concept of energy –selective electron transport used in hot carrier solar cells, to develop thermo electrics and thermo-ionics devices. </li></ul>Next generation technology (cont.)
  21. 21. The PV Value Chain (multi-crystalline) Polysilicon Wafer Solar Cell Solar Module Chemical Process (purification) Casting Cutting Surface Treatment Assembly Systems Installation Operation
  22. 22. Prices are actually increasing
  23. 23. How does solar energy work? Solar Electric or Photovoltaic Systems convert some of the energy in sunlight directly into electricity. Photovoltaic (PV) cells are made primarily of silicon, the second most abundant element in the earth's crust, and the same semiconductor material used for computers. When the silicon is combined with one or more other materials, it exhibits unique electrical properties in the presence of sunlight. Electrons are excited by the light and move through the silicon. This is known as the photovoltaic effect and results in direct current (DC) electricity. PV modules have no moving parts, are virtually maintenance-free, and have a working life of 20 - 30 years . Silicon Solar cell
  24. 24. Photovoltaics Most current solar cells are photovoltaic Typically made from silicon or amorphous silicon. Typical efficiency ~ 12%. Best efficiency ever in laboratory: ~30%. Theoretical maximum, including concentrating light: 43% Generic design: doped pn junction. Photons come in and photoionize donors. Built-in electric field at junction causes carriers to flow, building up a potential (voltage) btw the p and n sides. Clearly one can play with different band gap systems to arrive at materials with different absorption spectra. Also, good mobility of charge essential for this to work well - trapping of charge or poor mobility will kill efficiency.
  25. 25. Principle p-n Junction Diode. Silicon Solar cell Ref. Soft Condensed Matter physics group in univ. of Queenland
  26. 28. Poly-Si Solar cell Making process 기판준비 : Si ingot  330  m  2cm x 2cm Surface cleaning Texturing : chemical v-groove p-n junction : POCl 3 (900 ºC ) ITO increasing minorty carrier correction, ARC
  27. 29. Back Surface Field Deposition Al and Ag ohmic-contact Forward surface Electrode Anti-reflection coating (ARC) TiO 2 deposition
  28. 30. H 2 diffusion dangling bond H2 bonding  Decreasing recombination Measure H 2 H 2 H 2 H 2
  29. 31. - An individual PV cell typically produces between 1 and 2 watts Solar Cell, Module, Array
  30. 32. <ul><li>decrease the area of solar cell material being used in a system </li></ul>Concentrator collectors
  31. 33. <ul><li>Flat-plate collectors typically use </li></ul><ul><li>large numbers or areas of cells </li></ul><ul><li>that are mounted on a rigid, flat surface. </li></ul><ul><li>substrate ; metal, glass, plastic </li></ul><ul><li>They are simpler to design and fabricate. </li></ul><ul><li>They do not require special optics, specially designed cells, or </li></ul><ul><li>mounting structures that must track the sun precisely. </li></ul><ul><li>plus, flat-plate collectors can use all the sunlight </li></ul>Flat-Plate Systems
  32. 34. Uses for Solar Energy
  33. 35. Main Application Areas – Off-grid Solar Home Systems Space Water Pumping Telecom
  34. 36. Main Application Areas Grid Connected Residential Home Systems (2-8 kW) PV Power Plants ( > 100 kW) Commercial Building Systems (50 kW)
  35. 37. <ul><li>Solar energy will become the most important and cost-efficient energy source in the future. </li></ul><ul><li>The present lack of silicon feedstock is promoting a rapid development of next generation technology. </li></ul><ul><li>Immediate actions are taken to cut thinner wafers and increase cell efficiencies for crystalline silicon. </li></ul><ul><li>New thin film technologies are being developed </li></ul><ul><li>Stronger influence from semiconductor industry will accelerate the development of better technologies </li></ul><ul><li>Nanosilicon and other third generation technologies may offer a long-term solution for the future solar energy technology. </li></ul>Conclusions

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