RENEWABLE ENERGY

Solar Power

Converting Sunlight Into Electricity

Photovoltaic modules, commonly called solar modules, are the key components used to convert sunlight into electricity. Solar modules are made of semiconductors that are very similar to those used to create integrated circuits for electronic equipment. The most common type of semiconductor currently in use is made of silicon crystal. Silicon crystals are laminated into n-type and p-type layers, stacked on top of each other. Light striking the crystals induces the “photovoltaic effect,” which generates electricity. The electricity produced is called direct current (DC) and can be used immediately or stored in a battery. For systems installed on homes served by a utility grid, a device called an inverter changes the electricity into alternating current (AC), the standard power used in residential homes.

Power Generation Using the P-N Gate

High purity silicon crystals are used to manufacture solar cells. The crystals are processed into solar cells using the melt and cast method. The cube-shaped casting is then cut into ingots, and then sliced into very thin wafers.


Processing Wafers

Silicon atoms have four "arms." Under stable conditions, they become perfect insulators. By combining a small number of five-armed atoms (with a surplus electron), a negative charge will occur when sunlight (photons) hits the surplus electron. The electron is then discharged from the arm to move around freely. Silicon with these characteristics conducts electricity. This is called an n-type (negative) semiconductor, and is usually caused by having the silicon 'doped' with a boron film.

In contrast, combining three-armed atoms that lack one electron results in a hole with an electron missing. The semiconductor will then carry a positive charge. This is called a p-type (positive) semiconductor, and is usually obtained when phosphorous is doped into the silicon.



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.