Break Down Absorptance Material Emittance (𝜺) Temperature Comments (𝜶𝒑) (°C) Black Silicon 0.86 - 0.94 0.83 0.89 350 Silicon Binder – Paint Black Copper Patinates with 0.85 - 0.9 0.08 0.12 450 – over Copper Moisture Black Chrome Stable at High 0.92 0.94 0.07 0.12 450 – – Over Nickel Temperatures Cover Plate: A cover plate for a collector should have a high transmittance for solar radiation and should not detoriate with time. The material most commonly used is glass. A 0.32 cm thick sheet of window glass ( iron content, 0.12 percent ) transmits 85 percent of solar energy at normal incidence. And all glass is practically opaque to long-wavelength radiation emitted by the absorber plate. Some plastic materials can be used for collector glazing. They are cheaper and lighter than glass and, because they can be used in very thin sheets, they often have higher transmittance. However, they are not as durable as glass and they often degrade with exposure to ultraviolet radiation or high temperatures [12]. Table 3.2: Characteristics of material for cover plate [12]. Polyvinyl Fiber glass Test Polyester Polycarbonate Fluoride reinforced Solar 92 - 94 85 82 - 89 77 - 90 Transmission, % Maximum Operating Temp 110 100 120-135 90 (°C) Length of Life in 5 4 ---- 7 - 20 Years Thickness (mm) 1 0.025 3.2 1 Enclosure and Insulation: The collector enclosure is usually made from steel, aluminum or fiber glass. And order to prevent heat from escaping through the back of the collector, a layer of insulation is placed behind the absorber plate. Table 3.3: Characteristics of material for insulation [12] Thermal Material Density (𝒌𝒈𝒎𝟑 ) Conductivity at Temperature Limits
Material Absorptance (𝜶𝒑) Emittance (𝜺) Break Down Temperature (°C) Comments Black Silicon Paint 0.86 - 0.94 0.83 – 0.89 350 Silicon Binder Black Copper over Copper 0.85 - 0.9 0.08 – 0.12 450 Patinates with Moisture Black Chrome Over Nickel 0.92 – 0.94 0.07 – 0.12 450 Stable at High Temperatures Cover Plate: A cover plate for a collector should have a high transmittance for solar radiation and should not detoriate with time. The material most commonly used is glass. A 0.32 cm thick sheet of window glass ( iron content, 0.12 percent ) transmits 85 percent of solar energy at normal incidence. And all glass is practically opaque to long-wavelength radiation emitted by the absorber plate. Some plastic materials can be used for collector glazing. They are cheaper and lighter than glass and, because they can be used in very thin sheets, they often have higher transmittance. However, they are not as durable as glass and they often degrade with exposure to ultraviolet radiation or high temperatures [12]. Table 3.2: Characteristics of material for cover plate [12]. Test Polyvinyl Fluoride Polyester Polycarbonate Fiber glass reinforced Solar Transmission, % 92 - 94 85 82 - 89 77 - 90 Maximum Operating Temp (°C) 110 100 120-135 90 Length of Life in Years 5 4 ---- 7 - 20 Thickness (mm) 1 0.025 3.2 1 Enclosure and Insulation: The collector enclosure is usually made from steel, aluminum or fiber glass. And order to prevent heat from escaping through the back of the collector, a layer of insulation is placed behind the absorber plate. Table 3.3: Characteristics of material for insulation [12] Material Density (𝒌𝒈𝒎𝟑 ) Thermal Conductivity at Temperature Limits
99078149-Solar-Collectors-Understanding.docx