Photovoltaic

The Photovoltaic Effect (The creation of voltage or electric current in a material upon exposure to light) is the basic physical process through which a photovoltaic cell converts sunlight into electricity.

The Photovoltaic Effect

Sunlight is composed of photons which are packets of solar energy. These photons contain different amounts of energy that correspond to the different wavelengths of the solar spectrum. When photons strike a photovoltaic cell, they may be reflected or absorbed, or they may pass right through. The absorbed photons generate electricity.

Solar cells utilize silicon as a semiconductor material. The cells are then assembled into a solar module that converts sunlight directly into electricity. When sunlight is absorbed by the silicon material, solar energy knocks the electrons free in the silicon crystal structure, allowing the electrons to flow through the silicon material to generate electricity. Converting light (photon) into electricity (voltage) is called the photovoltaic effect.

A p-n junction is formed by placing p-type and n-type semiconductors next to one another. The p-type, with one less electron, attracts the surplus electron from the n-type to stabilize itself. Thus the electricity is displaced and generates a flow of electrons, otherwise known as electricity.

When sunlight hits the semiconductor, an electron springs up and is attracted toward the n-type semiconductor. This causes more negatives in the n-type semiconductors and more positives in the p-type, thus generating a higher flow of electricity. This is the photovoltaic effect.

History of the Photovoltaic Effect

- In 1839 French scientist Edmond Becquerel discovers the photovoltaic effect while experimenting with an electrolytic cell made up of two metal electrodes placed in an electricity-conducting solution—electricity-generation increased when exposed to light.

- In 1932 Audobert and Stora discover the photovoltaic effect in cadmium sulfide (CdS).

- In 1953 Dr. Dan Trivich, Wayne State University, makes the first theoretical calculations of the efficiencies of various materials of different band gap widths based on the spectrum of the sun.

- In 1954 Photovoltaic technology is born in the United States when Daryl Chapin, Calvin Fuller, and Gerald Pearson develop the silicon photovoltaic (PV) cell at Bell Labs—the first solar cell capable of converting enough of the sun’s energy into power to run everyday electrical equipment. Bell Telephone Laboratories produced a silicon solar cell with 4% efficiency and later achieved 11% efficiency.

- In 1955 Western Electric began to sell commercial licenses for silicon photovoltaic (PV) technologies. Early successful products included PV-powered dollar bill changers and devices that decoded computer punch cards and tape.

A complete timeline from 7th Century B.C. to 2001 A.D. may be found HERE.

From Photovoltaic Cell to Solar Panel

As mentioned the nominal output voltage of a typical silicon PV cell is about 0.5 volts. In order to make them useful for practical applications the voltage must be significantly increased. This is accomplished by connecting PV cells together in series.

As shown, four 0.5 volt cells connected in series, + to - will add up to two volts. The current from a PV cell is proportional to the area of the cell collecting the light. PV cells can be connected in parallel to furnish more current but several complicating factors put this beyond the scope of this discussion.

A hint for the final stage may be found HERE