ME 556 Solar Energy Conversion

Lecture 9

Radiative Properties:

Selective Surfaces & Transparent Materials

Calculating Total EmittanceAssuming no direction effects

f is the Black Body fraction for a particular wavelength band

Ideal Selective Surface

Program to calculate band radiation

http://energy.sdsu.edu/testcenter/testhome/javaapplets/planckRadiation/blackbody.html

Real Selective Surfaces• Put a thin layer of good absorber on a poor emitter (thin film

coating)• Put very small metal particles on the surface (black chrome or

black gold)• Alter the surface roughness with small cavities

Real Selective Surface

Specular Reflectors

Radiation on Transparent Media

Snell’s and Fresnel’s Laws

Only treats one surface

Polarization

NOTE: The bars shown on the polarizer in Figure 1 are for illustration only. Actual polarizers can be made with very fine wires that resemble bars, but then they would run the other way (horizontal bars allow vertically polarized light to pass)

Reflected light is often Polarized

LCD Display