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OWOE - Solar Power - How do photovoltaic cells work to generate electricity?
  Video 1 - US Dept of Energy - Energy 101: Solar PV
Video 1 - US Dept of Energy - Energy 101: Solar PV
Video 2 - How PV cells produce electricity
Figure 1 - Photovoltaic cells, modules and arrays (DOE)
How do photovoltaic cells work to generate electricity?

Photovoltaic (PV) solar cells contain semiconductor materials that give off electrons when they absorb solar energy. When light shines on a PV cell, the energy from the absorbed light excites the electrons in the atoms of the PV cell semiconductor material. With this new energy, the electrons escape from their normal positions in the atoms and are captured within an electrical circuit created by sandwiching two layers of the silicon semiconductors. See Videos 1 and 2 for more detail on how PV cells generate electricity.

Crystalline silicon PV cells are the most common photovoltaic cells in use today, although cadmium telluride is being used as a cheaper but less efficient substitute. Researchers are also looking into a number of other materials with the goal of making more efficient and less expensive cells (for example see OWOE: A new solar PV material - perovskite).

An individual PV cell produces about 1-2 watts of power. Multiple PV cells are connected to create solar modules, and multiple modules are connected into solar panels or arrays. (See Figure 1) Although photovoltaic cells work best on sunny days, they can also produce electricity when it is cloudy. However, they will not produce electricity in the dark.

A typical 150 watt solar module for a home rooftop solar system is about 10 square feet (approximately 1 meter square) in size and can be expected to produce about 0.75 kW-hours every day assuming 5 hours of sunshine per day and 15% solar energy conversion efficiency. The average home in the United States uses approximately 30 kW-h of electricity per day. This would require about 400 square feet total of solar modules. See OWOE:What is the average size of a rooftop solar system?).

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