How photovoltaics works

A Few Basics about 'electricity' producing solar panels: Photovoltaics

Solar electric or "Photovoltaic" systems convert sunlight directly into electricity. Energy converts from photons (light) to electrons (electricity).

Photovoltaic (PV) cells are made primarily of silicon. Silicon is the second most abundant element on Earth. When silicon is pigmented with one or more other materials, it gains special electrical properties. Some kinds of pigmented silicon is used to create transistors and computer semiconductors. Other silicon combinations are used to create PV cells.

When PV cells are exposed to sunlight, the silicon absorbs some of the light. Electrons in the silicon become energized by the photons. The excited electrons move through the silicon in a predictable pattern, allowing us to "harvest" the electrons as usable direct current (DC) electricity. This process is known as the photovoltaic effect.

Single PV cells create small amounts of electricity. A PV module connects a number of PV cells together, to provide a greater capacity for generating electric power. PV modules have no moving parts, are virtually maintenance-free, and have a working life of 20 to 30 years.

There are three basic categories of photovoltaic systems with several types in each category:

Crystalline silicon Flat Plate PV modules

Crystalline silicon Flat Plate PV modules include single crystal silicon and polycrystalline silicon which is either grown or cast from molten silicon and later sliced into PV cells. They are then assembled onto a flat surface; no lenses are used. These PV modules are the most commonly used and widely developed PV technology.

Strengths: This PV technology has the greatest overall output (per area).

Weaknesses: Crystalline silicon cells are rigid and prone to breaking under physical stress.

Thin Film systems

They are produced by depositing a thin layer of photovoltaic material to a substrate like glass or metal. This group includes amorphous silicon like the kind found in calculators and watches.

Strengths: Thin Film systems are inherently cheaper to produce than crystalline silicon versions.

Weaknesses: Thin Film systems are not as efficient as Crystalline silicon.

Optical Concentrators

Concentrators use a lens or mirror system to concentrate sunlight on the PV cells to increase electrical output. These PV modules use much less of the expensive silicon material than the other PV technologies.

Strengths: Optical concentrator PV modules are produced more cheaply than the other PV module types.

Weaknesses: Optical concentrator PV modules require direct-sunlight to work well. These PV modules usually must track the sun throughout the day. Adding a tracking-system increases costs and adds risk from the tracking-system breaking. These concentrator panels do not work well under cloudy weather conditions.

more info

You can find more information on Photovoltaic Solar Electric Panels from the U.S. Department of Energy at: http://www.eere.energy.gov/RE/solar_photovoltaics.html (opens in new window)

The web's free encyclopedia Wikipedia explains how PV works also.