Renewable energy course#05


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Renewable energy course#05

  1. 1. Flat Plate Solar Collectors  In wide use for domestic household hot-water heating and for space heating, where the demand temperature is low  To preheat the heat transfer fluid before entering a field of higher-temperature concentrating collectors  Basic parts: A full-aperture absorber - a sheet of high-thermal- conductivity metal with tubes or ducts either integral or attached. Its surface is painted or coated to maximize radiant energy absorption and in some cases to minimize radiant emission  Transparent or translucent cover sheets - glazing, let sunlight pass through to the absorber but insulate the space above the absorber to prohibit cool air from flowing into this space.  An insulated box - provides structure and sealing and reduces heat loss from the back or sides of the collector.
  2. 2. Flat Plate Solar Collector
  3. 3. Absorber Plate 3- Functions: absorb the maximum possible amount of solar irradiance, conduct this heat into the working fluid at a minimum temperature difference, and lose a minimum amount of heat back to the surroundings. Absorption. Surface coatings having high absorptance for short- wavelength (visible) light, are used. Appear dull or "flat," absorbing radiation from all directions. Either paint or plating is used, typically absorb over 95 percent of the incident solar radiation. Fin Heat Removal. Metal sheet acts as fin to bring absorbed heat into the fluid. Heat conducted to tubes or ducts that contain the heat-transfer fluid - a liquid (water or water with antifreeze) or gas (air). Important design criterion - high heat transfer capability at low ΔT between absorber plate and working fluid. Require pumping power and expensive absorber plate material. Liquid absorber plates - a flat sheet of metal with tubes spaced 10-25 cm apart and attached (integral, brazed or press fitted).
  4. 4. Good ‘tube and sheet’ absorber:  The fin should be thick to minimize ΔT required to transfer heat to its base (tube).  Tubes should not be spaced too far apart  Tubes should be thin-walled and of high-thermal-conductivity material.  The fin (absorber sheet) must be made of material with high thermal conductivity.  Tube should be brazed or welded to the absorber sheet to minimize thermal contact resistance.  Tube and absorber sheet should be of similar material to prevent galvanic corrosion between them.  For air as HTF, back side of the absorber plate forms one surface of a duct and heat is transferred through the absorber sheet to the air over the entire back surface of the absorber. A thin absorber sheet of high-thermal-conductivity material desired. The internal air passage must allow high airflow at the back of the absorber without producing a high pressure drop across the collector, which will cause high pumping power for fans supplying the air.
  5. 5. Emittance. Since the temperature of the absorber surface is above Tamb, the surface re-radiates some of the heat it has absorbed. This loss mechanism is a function of the emittance of the surface for low- temperature, long-wavelength (infrared) radiation. Dilemma - many coatings that enhance the absorption of sunlight (short-wavelength radiation) also enhance the long wavelength radiation loss from the surface - for most dull black paints. A class of coatings, mostly produced by metallic plating processes, produce an absorber surface that is a good absorber of short-wavelength solar irradiance but a poor emitter of long- wavelength radiant energy. Flat-plate absorbers that have selective surfaces typically lose less heat when operating at high temperature. However, the absorptance of selective coatings is seldom as high as for non-selective coatings, and a tradeoff must be made based on whether the increased high- temperature performance overshadows the reduced low-temperature performance and expense of the selective coating.
  6. 6. Cover Sheets  One or more transparent or translucent cover sheets to reduce convective heat loss  Convective loss not completely eliminated due to convective current between the absorber and the cover sheet  External convection cools the cover sheet, producing a net heat loss from the absorber  Heat loss is further reduced due to thermal resistance of the added air space & Green House Effect Number of Covers. From none to three or more Collectors with no cover sheet have high efficiencies at near ambient temperature (e.g. swimming pools with ΔT < 10 o C) - incoming energy is not lost by absorption or reflection by the cover sheet  Increases in the number of cover-sheets increases the temperature at which the collector can operate (or permits a given temperature to be reached at lower solar irradiance)  One or two cover sheets are common - triple glazed collectors used for extreme climates  Each added cover sheet increases the collection efficiency at high temperature but decreases efficiency at low temperatures
  7. 7. Cover Sheets For regions of average mid-latitude temperatures and solar radiation  collectors with no glazing generally used for applications to 32ºC  single-glazed collectors are used for applications to 70ºC  double-glazing is used in applications above 70ºC  collector efficiency increases with increasing solar irradiance level but decreases with increasing operating temperature Materials. Tempered glass with low iron content and 3.2-6.4 mm thickness is used as outer cover sheet due to superior resistance to the environment,  Surface may be either smooth, making the glass transparent, or with a surface pattern, making it translucent. Both types have a transmittance of around 90 per cent.  Plastic cover sheets are sometimes used for the second cover sheet when two sheets are required. Glass also does not transmit UV radiation and thus protects the plastic  Rigid sheets of acrylic-or fiberglass-reinforced polymers or stretched films of polyvinyl fluoride are used  A major draw back of this scheme is the potential for overheating the plastic sheet at collector stagnation (no-flow) temperatures
  8. 8. Advantages  Absorb energy coming from all directions above the absorber (both beam and diffuse solar irradiance)  Do not need to track the sun  Receive more solar energy than a similarly oriented concentrating collector, but when not tracked, have greater cosine losses  May be firmly fixed to a mounting structure, and rigid plumbing may be used to connect the collectors to the remainder of the system  To increase their output, they may be repositioned at intervals or placed on a single- or two-axis tracking mechanism They absorb both the direct and the diffuse components (~ 10% of the normal) of solar radiation on cloudless days  On a cloudy day almost all of the available solar irradiance is diffuse
  9. 9. Collectible Solar Radiation Comparison Between Flat-Plate and Concentrating Collectors   Annual Average Daily Solar Radiation (MJ/m2 ) Collector Albuquerque Madison Two-axis tracking flat- plate collector (direct plus diffuse) 31 19.5 Fixed, latitude-tilt flat- plate collector (direct plus diffuse) 23 15 Two-axis tracking concentrator (direct only) 26.5 14
  10. 10. Collector Performance Orientation  Azimuth  South facing – for a fixed surface in the northern hemisphere  If the industrial demand is greater in the morning the azimuth may be rotated to the east  It is generally accepted that the azimuth of a fixed field may be rotated up to 15 degrees from south and not make a significant difference in the overall energy collection  Tilt.  Most logical tilt angle for the fixed flat-plate collector is to tilt equal to the latitude angle  The noontime sun will only vary above and below this position by a maximum angle of 23.5 degrees  However if the demand is greater in the winter months, tilting may be more towards the horizon while accepting the summer energy loss  Collector tilt optimization is not critical and that even horizontal surfaces may be an appropriate design choice if the cost of installation is considerably less for this orientation
  11. 11. Total (global) irradiation on a south-facing tilted surface
  12. 12. Efficiency Measurement  Energy collection efficiency is normally determined by testing collector performance  Test data are correlated with a parameter comprised of the collector temperature rise above ambient divided by the solar irradiance  Collector temperature used for flat-plate collector performance correlation is normally the temperature of the heat-transfer fluid entering the collector, not the average fluid temperature  Must specify the fluid flow rate at which the measurements were made  Recommended test flow rate for a liquid collector is 0.02 kg/hr (14.7 lb/hr ft2) and for an air collector, 0.01 m3/s m2 (1.97 cfm/ft2) at atmospheric pressure.  Aperture irradiance is the global (total) solar irradiance measured in the plane of the collector  some ground reflection if the collector is tilted from the horizontal as is usually the case
  13. 13. Typical Performance of Flat Plate Collectors Fr = Heat Removal Efficiency ηopt = Optical Efficiency UL = Heat Loss Coefficient
  14. 14. Comparison with Parabolic Troughs  Treadwell (1979) used TMY (Typical Meteorological Year) weather data for 26 sites  A field of single glazed flat-plate collectors with selective absorber surfaces compared with a field of commercial parabolic trough concentrators  Both horizontal and latitude-tilt south-facing orientations for the flat-plate collectors were considered  Both north-south and east-west tracking axis orientations considered for the parabolic trough collectors  The typically higher optical efficiency of the flat-plate collector compensated only partially for the higher thermal efficiency of the concentrators  Over a full year’s operation, the north-south trough orientation and the latitude-tilt flat-plate orientations provided the most energy  Troughs and flat-plate collectors have equivalent performance at about 49ºC in the southwestern region, and at 66ºC in most of the southeastern region.
  15. 15. Temperature Contours of Equal Performances for Flat Plate Collectors & Parabolic Trough Concentrators
  16. 16. Industrial Process Heat Systems in USA Using Flat-Plate Collectors (Hot Water) Company Process Application Temperature (ºC) Area (m2 ) Anhauser-Busch, Inc. Beer pasteurization 60ª 427 Aratex Services, Inc. Heat process water 50 -70 624 Berkeley Meat Co. Sanitation 82 232 Campbell Soup Co. Preheat can wash water 91 372 Coca-Cola Bottling Co. Bottle washing NAª 881 Easco Photo Film processing 46 NA General Extrusion, Inc. Solution heating 71-82ª 409 Iris Images Film processing 24-38 59
  17. 17. Jhirmack Enterprises, Inc. Preheat boiler water 71-93 622 Mary Kay Cosmetics Sanitizing 60 305 Riegel Textile Corp. Heat dye-beck water 88ª 621 Spicer Clutch (Dana) Parts washing 54 87 Gilroy Foods, Inc. Preheat drier air/ boiler feedwater 90 553 Gold Kist, Inc. Preheat drier air b 82 1217 LaCour Kiln Services Lumber drying 82 234 Lamanuzzi & Pantaleo Raisin drying 62 1951 Company Process Application Temperature (ºC) Area (m2 )
  18. 18. Evacuated Tube Designs
  19. 19. Solar Ponds  The least expensive type of solar collector  Primarily for large industrial applications - cost decreases considerably with increases in size Shallow Ponds:  Consist of a group of collectors made of black plastic liners lying on top of insulation that has been laid on flat graded ground  At least one translucent cover sheet (un-seamed, weather-able plastic sheets) above water bag, supported by side curbs  Water is pumped into the collectors from underground storage tank  Can attain temperatures of up to 60º  Heated water pumped to an industrial demand or a
  20. 20. Shallow Pond Solar Collector 4m x 200 m
  21. 21. Salt-Gradient Ponds  Employs a salt concentration gradient to suppress natural convection  Heated water holds more dissolved salt than does cooler water  Salty, heated water is heavier - remains at the bottom of the solar pond Three zones (1) Surface convective zone - low-salinity water, ~ 0.2-0.4 m thick (2) Non-convective/salinity-gradient zone - salt concentration increases with depth ~ 1.0-1.5 m thick (3) Storage zone - bottom - uniformly high salt concentration ~ 1-3 m thick  Hot brine is drawn from the storage zone and pumped through a heat exchanger and back to the storage zone  For Rankine cycle, condenser cooling water is drawn off the top of the pond and passed through the condenser and back to the surface, where it cools 
  22. 22. Salt Gradient Pond
  23. 23. If the Solar Radiation Intensity on the horizontal surface is 600 watts and the Sun’s altitude angle is 30o , while a reflector is tilted at an angle of 85o from the horizontal direction, what will be the combined intensity of the reflected and incident light on the horizontal surface ? 30o 85o I Horizontal Surface ReflectorSolar Altitude Tilt Angle Quiz
  24. 24. Thermal Collector Capture and Loss Mechanisms Energy balance on a solar collector absorber or receiver is; Quseful = Eopt – QLoss (W) Quseful - Rate of ‘useful’ energy leaving the absorber (W) Eopt - Rate of optical (short wavelength) radiation incident on absorber (W) QLoss - Rate of thermal energy loss from the absorber (W) ‘Useful’ energy is the rate of energy being added to a heat transfer fluid (HTF) Quseful = m● Cp (Tout - Tin) (W) m● - mass flow rate of HTF (kg/s) Cp - specific heat of HTF (J/kg.K) Tout - temperature of HTF leaving the absorber T - temperature of HTF entering the absorber
  25. 25. Optical Energy Capture Einc = Ia Aa (W) Ia - Solar irradiance entering the collector aperture (global (total) or direct (beam))(W/m2 ) Aa - Aperture area of the collector (m2 ) Rate of optical (short wavelength) energy reaching the absorber or receiver is: Eopt = Γ ρ α τ Ia Aa Γ - Capture fraction (fraction of reflected energy entering or impinging on receiver) ρ - Reflectance of any intermediate reflecting surfaces τ - Transmittance of any glass or plastic cover sheets or windows α - Absorptance of absorber or receiver surface The first two terms above apply only to concentrating collectors
  26. 26. Four important mechanisms that reduce the amount of solar energy that is incident on the collector aperture; imperfect reflection, imperfect geometry, imperfect transmission and imperfect absorption  Capture fraction is a measure of both the quality of the shape of the reflecting surface, and the size of the receiver. A poorly shaped concentrator, or a receiver too small will make this number considerably less than 1.0  Properly designed concentrators have capture fractions > 0.95, and silver/glass mirrors can have a reflectance of 0.94 and new aluminum reflecting surfaces have a reflectance of about 0.86.  The transmittance is the average overall transmittance and represents the total reduction in transmitted energy in the solar spectrum by all covers  Transmittance of the cover also depends on the wavelength of light passing through it. Glass for example transmits most radiation in the visible spectrum, but does not transmit much in the infrared region
  27. 27.  Plastic covers have high transmittance values at very long wavelengths  Absorption term represents the fraction of solar energy incident upon the surface, that is absorbed (the remainder being reflected). A good black surface can have an absorption > 0.98, however, as surfaces degrade, this value can decrease  For most real surfaces, the absorption varies as a function of the wavelength of the incident energy. ‘selective surfaces’ have a higher absorptance in the visible spectrum than at longer wavelengths, thereby reducing thermal radiation loss
  28. 28. Heat Loss Mechanisms QLoss = QConvection + QRadiation + QConduction  The balance between heat removal and heat loss defines the operating temperature of the collector  For concentrating collectors, when not enough heat is being removed, the temperature of the absorber can increase to its melting temperature Approximate Convection Loss QConvection = hc Ar (Tr – Ta) hc - Average overall convective heat transfer coefficient (W/m2 .K) Ar - Surface area of receiver or absorber (m2 ) Tr - Average temperature of receiver (K) T - Ambient air temperature (K)
  29. 29. Radiation Loss  Important for collectors operating at temperatures only slightly above ambient  Becomes dominant for collectors operating at higher temperatures QRadaition = ε σ Ar (Tr 4 – Tsky 4 ) ε - Emittance of the absorber surface σ - Stefan-Boltzmann constant (5.670 × 10-8 W/m2 K4 ) Tsky- Equivalent black body temperature of the sky (K) Black, Vertical Surface in Free Air at 25o C. Radiation Convection
  30. 30. Conduction Loss QConduction = K Ar (Tr – Ta) / Δx K - Equivalent average conductance (W/m.K) Δx - Average thickness of insulating material  Usually small compared to convection and radiation losses  In flat-plate collectors, the sides and back surface of the absorber plate should incorporate good insulation (low k) and the insulation should be thick enough to render this heat loss insignificant.
  31. 31. Selective Surfaces From radiation heat transfer theory - for black body and gray surfaces, the absorptance equals the emittance However for all surfaces, Kirchoff’s Law states that they are equal only for radiation at a specific wavelength, not as an average property integrated over a spectrum Kirchoff’s law αλ = ελ  Subscript indicates that these are ‘spectral’ properties and must be integrated over all wavelengths  If the spectrums are different, the integrated properties can be different. In solar collectors, the spectrum of the energy being absorbed is from a 6,050K black body emitter with peak intensity at a wavelength of 0.48 microns. The spectrum of the energy being emitted by the absorber / receiver is defined by the temperature of the absorber surface
  32. 32.  if the receiver surface temperature is 80o C, the peak intensity is at a wavelength of 8.21 microns.  Selective surfaces have a high absorptance (and emittance) for short wavelength (visible) light and have low average absorptance and emittance for long wavelength radiation (thermal or infra-red radiation).  They do not violate Kirchoff’s law, however, we say that they have ‘high absorptance and low emittance’ meaning high absorption for short wavelength radiation, and low emittance for long wavelength radiation. The end result is a surface that absorbs solar energy well, but does not radiate thermal energy very well
  33. 33. Selective Coating
  34. 34. Selective Coatings Consider a hypothetical surface with 0.95 absorptance at wavelengths shorter than 5 microns and 0.25 for longer wavelengths. Since 99.5% of solar energy occurs at wavelengths below 5 microns, the effective absorptance of such a surface is 0.965 The integrated emittance for this hypothetical surface depends on its temperature. If this surface is 80o C, 99.1% of its radiant energy is at wavelengths above 5 microns and the integrated emittance for this surface is 25.6% On the other hand, If the absorber surface is at a temperature of 700o C as is typical for receivers in parabolic dish concentrating collectors, only 43.6 % of its radiated energy is at wavelengths above 5 microns and the integrated emittance is 64.5%. Black Chrome. Tyically, a thin (2-3 μm thick) black chrome coating (α= 0.95) is electro-deposited on a mild steel receiver tube that has been electroplated with 25 μm of bright nickel (ε=0.25)
  35. 35. Photovoltaic Panel Capture and Loss Mechanisms  An energy balance on a photovoltaic panel provides less useful information to the solar energy system designer  The PV cell efficiency decreases with increases in panel temperature  Rate of heat loss from the panel should be high rather than low Pelectric = I x v = Eopt - Qloss Physical limit to the fraction of useful energy that can be produced from the incident optical radiation 1 – 30%, requiring that the rest of the 70% to 99% of the incident energy, be lost through heat loss mechanisms Optical Energy Capture Eopt = Γ ρ α τ Ia Aa For a concentrating photovoltaic panel
  36. 36. PV Panel Performance
  37. 37.  At low values of load resistance, the current is a maximum and the voltage across the cell approaches zero. The current output at zero voltage is short-circuit current, Isc - a function of the size of the PV cell, and the number of cells connected in parallel.  Isc is also directly proportional to the level of solar irradiance - PV cells can be used as transducers to measure solar irradiance  As the load resistance increases, the current decreases slightly until the cell can no longer maintain a high current level, and it falls to zero - open-circuit voltage, Voc. Note that Voc varies only a small amount as a function of solar irradiance (except at very low levels)  A single silicon PV cell produces Voc of slightly over 0.55 volts  Peak Power Point (PPP) As the load resistance increases from the Isc condition, the voltage rises until the I-V curve starts falling to the open circuit point. There is a point along the curve where the maximum power is generated which occurs just as the I-V
  38. 38. Peak Power Point of PV at Different Solar Irradiance ~ 80% of Voc – peak power trackers
  39. 39. PV Temperature Loss ~ -4% Voc and +0.5% Isc for a 10o C change in cell temperature
  40. 40. Collector Efficiency ηcol = Quseful / Ia Aa Optical Efficiency ηopt = Γ ρ τ α Flat-plate Collectors ηcol = m● cp (Tout – Tin) / Ig Aa Where Ig is global Irradiance Concentrating Collectors ηcol = m● cp (Tout – Tin) / Ib cos θi Aa Where Ib is direct beam Irradiance Concentrating PV Collectors ηcol = I . V / Ib cos θi Aa
  41. 41. Collector Efficiency Models – Flat Plate
  42. 42. Collector Efficiency Models – Versus Inlet Temp. - Flat Plate
  43. 43. Collector Efficiency Models – Versus Global Irradiance - Flat Plate
  44. 44. Collector Efficiency Models – Parabolic Trough
  45. 45. Collector Efficiency Models – PV
  46. 46. Collector Efficiency Models – Versus Voltage -PV
  47. 47. Measuring Collector Performance Collector test standards specify both the experimental setup and the testing procedure  Testing is performed only on clear days when the solar irradiance level is high and constant  Prior to taking measurements, hot HTF is circulated through the absorber or receiver to bring it up to the test temperature  For a flat-plate collector, the test flow rate is generally specified by the test procedure in use  In case of parabolic trough testing, turbulent flow is maintained within the receiver tube to ensure good heat transfer between the fluid and the wall of the receiver tube  A measurement is made only when the collector is at steady state, which is indicated by a constant rise in heat transfer fluid as it flows through the receiver
  48. 48. Thermal Performance Measurements  Collector aperture is aligned as close as possible to normal to the incident direct (beam) solar irradiance  Once data are obtained with the aperture normal to the sun, testing is repeated, usually only at one temperature, to determine the effect of varying angles of incidence on collector performance 3 – Procedures for Performance Measurement 1. Collector Balance 2. System Balance 3. Heat Loss Measurement
  49. 49. Inlet and Outlet Temperatures and flow rate measured Rate of change of temperature of insulated water reservoir measured First, rate of optical energy collected is measured near ambient temp. Most Common Test for Flat Plate and Parabolic Trough Then heat loss is measured at different temperatures in shade using a heater 1 2 3
  50. 50. Incident Angle Modifier - Ki Ratio of collector efficiency at any angle of incidence, to that at normal incidence Ki = ηopt, θi / ηopt, n = a θi + b θi 2 ηcol = Ki ηopt,n
  51. 51. Concentrator Optics  Parabolic Trough  Parabolic Dish  Central Receivers  Fresnel Lens
  52. 52. Concentration Ratio Collector Stagnation Temperature - The receiver temperature at which convective and radiation heat loss from the receiver = absorbed solar energy Optical Concentration Ratio (CRo): The averaged irradiance (Ir) integrated over the receiver area (Ar), divided by the insolation incident on the collector aperture. CRo = [⌠ Ir dAr / Ar ] / Ia Geometric Concentration Ratio (CRg): The area of the collector aperture Aa divided by the surface area of the receiver A CR = A / A
  53. 53. Flat plate concentrated collector Concentration Ratios ~ 2-3
  54. 54. Parabolic Geometry y2 = 4 f x with origin at V Sin2 θ /Cos θ = 4 f / r in polar coordinates with origin at V p = 2 f / (1 + cos ψ) with origin at F
  55. 55. Segments of a parabola having a common focus F and the same aperture diameter ψrim
  56. 56. h = d2 / 16 f d f tan ψrim = 1 / [(d/8h) - (2h/d)] tan (ψrim / 2) = 1 / 4(f/d) f/d = (1 + cos ψrim ) / 4sin ψrim ψrim A = 2 d h / 3 Arc length = s = [ d √ (4h/d)2 + 1 / 2] + 2f ln [4h/d + √ (4h/d)2 + 1] s
  57. 57. Paraboloid The surface formed by rotating a parabolic curve about its axis is called a paraboloid of revolution. Solar concentrators having a reflective surface in this shape are often called parabolic dish concentrators. X2 + Y2 = 4fz In rectangular coordinates with the z-axis as the axis of symmetry Z = a2 / 4f In cylindrical coordinates, where a is the distance from the z-axis
  58. 58. circular differential area strip on the paraboloid dAs = 2 π a √ dz2 + da2 (m2 ) = 2 π a √ 1 + (a / 2f)2 da (m2 )
  59. 59. Parabolic Trough
  60. 60. Circular Mirror Parallel rays reflected from a circular mirror pass through a line drawn through the center of the circle and parallel to the incident rays A circular mirror is symmetrical with respect to rotations about its center
  61. 61. Parabolic Mirror A parabolic mirror is not symmetrical to rotations about its focal point. If the incident beam of parallel rays is even slightly off normal to the mirror aperture, beam dispersion occurs, resulting in spreading of the image at the focal point. For a parabolic mirror to focus sharply, therefore, it must accurately track the motion of the sun.
  62. 62. Angles for reflection from a cylindrical (or spherical) mirror – θ1 = θ2 = θ3 Point PF is termed the paraxial focus. As increases, the reflected ray crosses the line below PF. The spread of the reflected image as θ3 increases, is termed spherical aberration. For practical applications, if the rim angle ψrim of a cylindrical trough is kept low (<20-30o ), spherical aberration is small and a virtual line focus trough is achieved
  63. 63. Focusing of parallel rays of light using circular mirrors with different rim angles
  64. 64. Optical analysis of parabolic concentrators
  65. 65. Reflection of a light ray from a parabolic mirror dAs = l ds l = either length of a differential strip on the surface of a parabolic trough along the direction of the focal line, or circumference of the differential ring on the surface of a parabolic dish ds = p sin(dψ)/ cos(ψ/2)
  66. 66. Total radiant flux reflected from a differential area to the point of focus: dΦ = dAs Ib cos (ψ/2) = l p Ib dψ (for small ψ) = 2 f l Ib dψ / (1 + cos ψ) as p = 2 f / (1+ cos ψ) dΦPT = 2 f l Ib dψ / (1 + cos ψ) for Parabolic Trough dΦPD = 8π Ib f2 sin ψ dψ/ (1 + cos ψ)2 for Parabolic Dish as l = 2πp sin ψ
  67. 67. Specular Reflectance of Mirrors Silver
  68. 68. Back Surface Reflectors
  69. 69. Snell’s Law s-polarized light – Electric field is in the plane of the interface p-polarized light - Electric field is in a perpendicular direction to s-polarized
  70. 70. Freznel Equations Reflection Coefficients for S-Polarized and P-Polarized light For mixed light From 2-sides of a glass sheet 2R/(1 + R)
  71. 71. Air-Glass Reflectance Versus Angle of Incidence
  72. 72. Transmittance of borosilicate glass with antireflection coating
  73. 73. Freznel Lens Concentrator