ME 500 Test 2

  1. 2 uses of solar energy
    1) solar thermal energy

    2) solar photovoltaics
  2. Photovoltaics advantages
    • reliability
    • low operating costs
    • modularity
    • low construction costs
  3. photovoltaics disadvantages
    • high initial cost
    • variability
    • lack of infrastructure
    • increased storage costs
  4. Photovoltaic systems convert energy into electricity on a _____-_____device
  5. PV materials
    • silicon
    • gallium arsenite crystals
    • polycrystalline copper
  6. Semiconductor
    material with electrical conductivity
  7. Doping
    • performance increase (electrical behavior)
    • impurities
  8. p-type semiconductor
    • doped with boron
    • deficit of electrons (holes)
  9. n-type semiconductor
    • doped with phosphorus
    • surplus of electrons
  10. semiconductor band structure
    Image Upload 1
  11. intrinsic semiconductor
    • undoped
    • i-type
  12. extrinsic semiconductor
  13. Band (energy) gap
    -energy difference between the top of valence band to bottom of conduction band

    -energy required to promote electrons into conduction band
  14. Isc and Voc
    • Short circuit current
    • open current voltage
  15. silicon solar cell structure
    Image Upload 2
  16. photodiode
    photodetector capable of converting light into current or voltage
  17. Photocurrent is a combination of:
    dark current and light current
  18. P-N junction diagram
    Image Upload 3
  19. Fermi level
    highest occupied molecular orbit in valence band
  20. Reverse bias
    Image Upload 4
  21. Forward bias
    Image Upload 5
  22. Diode
    A 2 terminal electrical component
  23. Anode vs Cathode
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  24. I0
    measure of recombination in a device
  25. I-V characteristics of a p-n junction diode (graph)
    Image Upload 7
  26. Maximum power graph
    Image Upload 8
  27. Fill Factor
    -measure of sharpness of knee in I_V curve

    -Indicates 1) how well junction was made in the cell 2) how low the series resistance is
  28. Fill Factor Equation
    Image Upload 9
  29. Calculate Pmax
  30. Calculate max efficiency
  31. Calculate cell area
  32. Latitude
    Angular distance north or south of earth's equator
  33. Glazing purpose
    allows solar radiation to enter the collector but not reflect out
  34. Components of a solar panel
    Image Upload 10
  35. Heat loss (conduction) equation
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    Image Upload 12
  36. Solar Ponds
    • -bottom has high optical absorption
    • -absorbs solar energy
    • -vertical salinity gradient
  37. Active solar heating
    uses solar energy to heat a fluid, then transfer the heat directly to the space
  38. passive solar heating
    -walls, windows, and floors are made to collect store and distribute solar energy

    -no mechanical or electrical devices
  39. Conservatory
    energy store is the building itself (sunspace)
  40. Trombe wall
    solar radiation warms the store and is radiated into the house
  41. direct gain
    if the building is massive enough, and the heating system is responsible, the gains are useful
  42. solar pond diagram
    Image Upload 13
  43. force diagram
    Image Upload 14
  44. wind energy physics
    the kinetic energy of the air in motion
  45. calculate wind power
    Image Upload 15
  46. wind turbine naming comvention
    named on the basis of the way the wind flows over airfoils and their geometrical configuration
  47. airfoil diagram
    Image Upload 16
  48. solidity
    the fraction of the swept area that is solid
  49. measure of turbine rotation speed
    • -rotation speed [rpm], N
    • -angular velocity [rad/s], ω
  50. Tip speed
    tangental velocity of the rotor at the tip of blades, U [m/s]

    Image Upload 17
  51. Calculate max thrust
    Image Upload 18
  52. Calculating torque
    • Tmax = FmaxR
    • T = CTTmax
  53. Power extraction efficiency decrease
    • -blades too close together 
    • -blades rotating too fast
    •     -> blades in turbulent air
    • vice-verse
    •     -> air passes without interfering with a blade
  54. Betz limit
    maximum fraction of the power in the wind that can be extracted

  55. Blade pitch angle
    equal to the relative wind angle minus the angle of attack (β)
  56. Zero set pitch
    the setting angle of the blade causes the chord to be in line with a tangent to the circular path of rotation
  57. wind energy advantages
    • -renewable
    • -ubiguitous
  58. wind energy disadvantages
    • -variable
    • -low density source
    •    -> high initial cost
    • -distance from area to land center
  59. wind
    • -flow of gases on a large scale
    • -caused by pressure difference
  60. Earth's atmospheric circulation diagram
    Image Upload 19
  61. Pressure weather effects
    • -isobars -> equal P
    • -high P -> fine weather, little wind
    • -low P -> changeable windy weather, precipitation
  62. Sea breeze vs land breeze
    • sea breeze:
    •     -daytime
    •     -land heats up quickly

    • land breeze:
    •     -night
    •     -land cools off quickly
  63. Lenticular clouds
    stationary lens shaped clouds, perpendicular to wind direction
  64. Mountain valley winds
    -hills and valleys distort airflow by increasing friction (between atmosphere and land)

    -wind deflection occurs (barrier jet)
  65. Mountain valley winds diagram
    Image Upload 20
  66. Sun
    • -ball of plasma
    • -fusion reactor
    • -92% hydrogen, 8% helium
  67. electromagnetic spectrum
    range of EM radiation from short λ to long λ
  68. Insolation
    solar radiation at the surface of the earth
  69. direct vs diffuse radiation
    • direct:
    •   -amount of radiation on a surface perpendicular to the sun


      -indirect radiation from sky & from other surface objects
  70. Insolation measurement
    -Pyronometer (solarimeter)

    -voltage proportional to total incident light energy is produced
  71. Rooftop solar water heater
    • 1. Pumped
    •    -needs heat exchanger

    2. Thermosyphon
  72. Heat exchanger
    uses heat transfer to transfer heat from fluid on one side of a barrier to a fluid on the other side
  73. Pumped solar water heater diagram
    Image Upload 21
  74. Solar collectors
    1. Heat pipe evacuated tube

    2. Line-focus collectors

    3. Parabolic dish collectors
  75. Wind mill
    reduces a solid or coarse substance into minute grains by grinding
  76. How is the electric field generated in p-n junctions?
    The dissimilar semiconductors at the junction. The electrons move in one direction and the protons in another.
  77. Bias
    An external voltage applied to a P-N junction
  78. Equilibrium band structure
    Image Upload 22
  79. Reverse biased band structure
    Image Upload 23
  80. Forward biased band structure
    Image Upload 24
  81. Thermosyphon solar heater
    Image Upload 25
  82. Components of a solar panel
    -black painted steel plate bonded with copper tubing


  83. Solar collector application
    • -domestic water heating
    • -domestic space heating
  84. Heat pipe evacuated tube collectors
    -the vacuum enables the liquid to boil at a much lower temperature 

    -when the solar radiation hits the surface of the absorber, the liquid turns to hot vapor and rises to the top

    Image Upload 26
  85. line-focus collectors
    -a parabolic trough focuses to a higher energy focal line rather that a focal point 

    -water flows through center

    -generates steam for electricity generation

    Image Upload 27
  86. parabolic dish collectors
    • -focus the suns energy on a small (focal) point
    • -dish has mirror like absorbers at the focal point

    Image Upload 28
  87. Solar power tower
    • -sunlight is concentrated from the mirrors 
    • -molten salt is pumped through the receiver and heated
    • -pumped through the steam generator and creates steam

    Image Upload 29
  88. Solar chimney
    • -passive solar energy
    • -sun heats chamber and warm air rises at high velocity through turbines

    Image Upload 30
  89. Stall
    a loss of lift and torque and the stalled regions of the blades
  90. Axial interference factor
    the factor that takes into account the wind being slowed down as a result of power extraction
  91. measure of performance of air foils
    lift to drag ratio
  92. airfoil pressure distribution
    low pressure is created on the upper surface and high pressure on the lower surface. The pressure differences causes aerodynamic lift
  93. Comparing wind turbines of different characteristics
    • using tip speed ratio
    • λ=U/V=wr/V
    • λ changes between 6 to 20
  94. VAWT and HAWT comparison (solidity, rotors, loading, sizing)
    • -VAWT have greater solidity
    • -VAWT have heavier and more expensive rotor
    • -HAWT have shorter lifetime
    • -VAWT don't experience gravitational loads
  95. Best places for wind farms
    • -coastal areas
    • -tops of rounded hills
    • -open plains and gaps in mountains
    • -average wind speed of 25 km/h
  96. Calculate Fmax using Bernolli eqn
    • Bernoulli equation:
    • Image Upload 31

    • Assume ρ=constant, z=constant
    • Image Upload 32

    • Static pressure difference
    • Image Upload 33

    • Max value of ΔP occurs as Vd approaches to zero
    • Image Upload 34

    Image Upload 35
Card Set
ME 500 Test 2
The set of cards that cover the second test in ME 500, clean energy systems