Solar Energy and the Photovoltaic Cell

A photovoltaic cell, often called a solar cell, converts light directly into electricity through the photovoltaic effect. Most cells are made from silicon, a semiconductor treated so that one layer carries a slight surplus of electrons and the adjacent layer a deficit, forming a junction. When photons of sunlight strike the cell, they free electrons within the silicon, and the built-in electric field at the junction drives these electrons through an external circuit, producing a direct current.

A single cell generates only a small voltage, around half a volt, so many cells are wired together and sealed behind glass to form a solar panel, or module. Modules are in turn grouped into arrays sized to the energy needed. Because cells produce direct current, a household solar system usually includes an inverter to convert the output to alternating current, along with mounting hardware and, in stand-alone systems, batteries to store energy for use after dark.

The electricity a panel produces depends on the intensity of sunlight, the angle of the panel, temperature, and the efficiency of the cells, which for common commercial silicon modules is typically in the range of fifteen to twenty percent. Solar power is a renewable resource that produces no emissions during operation, and its use has grown as cell costs have fallen. Do-it-yourself solar projects range from small panels charging batteries for lights and gadgets to full rooftop installations feeding a home or the grid. Solar thermal collectors, by contrast, capture the sun's heat rather than generating electricity directly.

Frequently asked questions

How does a solar cell make electricity?

Sunlight knocks electrons loose in a semiconductor, and the electric field at the cell's junction pushes them through a circuit, creating a direct current. This is the photovoltaic effect.

What is the difference between a cell, a panel, and an array?

A cell is the basic unit producing about half a volt. Many cells joined together form a panel or module, and several panels wired together make an array.

Why do solar systems need an inverter?

Solar cells produce direct current, while household wiring and the grid use alternating current. An inverter converts the panel output so it can power normal appliances.