Solar Energy: Conversion into Electricity

How Solar Energy is Generally Used:

What about the Direct Conversion into Electricity?

Two Choices:
• Heat Water into Steam
• Turn photons into electrons

Water Into Steam:

Photons into Electrons: PhotoVoltaic Devices

• Charge Generation --> Photoelectric Effect

• When photons stike a metal, their energy is used to liberate loosely bound electrons and therefore induce a current
• Efficiency of this process depends upon the material
• This is the principle behind many digital cameras, otherwise known as CCD cameras . These kinds of cameras are used in astronomy to take digital pictures

Most commonly used material is Silicon:

• Abundant on Earth because it comes directly from Stars
• Has four outer (valence) electrons to bond silicon atoms together in a crystal
• Under normal circumstances, there are no free electrons available in silicon to conduct electricity
• The conduction band is empty:

Schematic structure of energy bands in Silicon:

Hence, if a silicon atom receives at least 1.11 Electron Volts from some source, a valence electron will move to the conduction band.

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The Electronic Universe Project

e-mail: nuts@moo.uoregon.edu