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Department of Energy Resources

Photovoltaics
EERE Solar Technologies Program

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Photovoltaics (Solar Power)

Solar cells, also called photovoltaics (PV) by solar cell scientists, have been used economically to power everything from watches and calculators to individual homes where it is expensive or impossible to send electricity through power lines. As consumers become more interested in this technology, an increasing number of power companies are now experimenting with using PV to meet some of their power needs.

A photo of two technicians outside on a sunny day surrounded by rows of photovoltaic arrays.

Photovoltaic technologies, like these flat-plate crystalline silicon arrays, can produce electricity even on cloudy days.
Photo credit: Sacramento Municipal Utility District

PV technologies produce electricity directly from sunlight. When sunlight strikes a solar cell, its semiconductor materials absorb a portion of that light. If the energy from the absorbed light strikes electrons in the outer shell of an atom, these electrons are freed from their parent atoms. Free electrons can then travel into a circuit in the form of electricity.

The most common PV device available today is made from rigid, crystalline silicon solar cells (although other materials can also be used). About 40 of these cells are typically combined to produce a flat module, and about 10 of these modules are mounted to form a PV array, which can measure up to several meters on a side. PV arrays can be mounted at a fixed angle facing south, or they can be mounted on a tracking device that follows the sun, allowing them to capture the most sunlight over the course of a day.

Where It's Available

The solar resource across the United States is ample for PV systems because they use both direct and scattered sunlight. However, the amount of power generated by a PV system at a particular site depends on how much of the sun's energy reaches it. Thus, PV systems, like all solar technologies, function most efficiently in the southwestern United States, which receives the greatest amount of solar energy.

Solar Radiation MapMap of Average Daily Solar Radiation per Month in the United States (PDF 72 KB) (Download Adobe Reader)

This map shows the solar resource for PV.