Capturing Energy from Light and Waste Heat

Brief discussion on photovoltaic (PV) effect

Historically, light falling on a selenium-coated iron produced a small voltage. The thin selenium coating forms a light sensitive crystal P/N junction having electrical properties of a diode at the coating interface. Visible light (400 to 700nm) energy is sufficient to move electrons in the crystal structure such that a current flows. Latter in PV history Silicone crystal junctions were found to have a higher current flow. Additionally it was discovered that impurities could change the Si crystal to N or P type silicone. Diffusion of phosphoric compounds in silicon results in N type silicon.  Aluminum and boron impurities are used for P type silicon (holes). 

Brief discussion on thermoelectric effect

The thermoelectric effect is due to electric charge carriers that develop at the interface of dissimilar conductive metals for example iron /nickel. . In order for chargers to flow a potential voltage develops that is proportional to a temperature difference. The temperature difference between a hot side and a cold side is needed in order that electric charge carriers flow resulting in an electric current flow. The thermoelectric effect is more apparent in solid state devices that have P and N impurities in there crystal structure since these charge carriers apparently flow with the heat flux between the hot and cold junctions. This effect is also called the "Seebeck" effect

    Sb and Sa are Seebeck coefficients, T temperature, and V voltage

 Thermoelectric devices are used today mainly as sensors for measuring temperate A.K.A. thermocouples. 

Energy Carriers

Energy carriers are divided into two classes' kinetic energy and energetic materials.

Kinetic energy is difficult to store. It is energy in motion; some examples are heat, light, electricity, it is always going from a higher potential to a lower potential such that a system will return to equilibrium. The entropy of such a system is always increasing. Entropy being defined as an increasing level of randomness   

Energetic materials are systems that store energy. Energetic materials are better able to store energy since they are close to equilibrium, however they are still subject to entropic forces and degrade with respect to time. Examples of energetic materials are materials that reduce to lower energy state materials such as hydrogen, coal, gasoline, explosives, and nuclear, thermonuclear materials.  In the broad sense of this definition even a hydroelectric power plant is considered an energetic material and a carrier of energy. since the system stores energy.