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What Are Passive and Active Solar Energy Systems?

Humans can capture solar energy directly from the sun through passive and active solar energy systems. Ancient people used passive solar energy systems by building their houses out of stone or clay, which absorbed the sun’s heat during the day and stayed warm after dark, providing heat throughout the night. Builders today use similar methods for passively capturing solar energy.

For example, they construct houses with large double- or triple-paned windows that get direct sunlight to capture and magnify the sun’s warmth. The effect is similar to but more powerful than what happens to your car on a sunny day: The air inside becomes much warmer than the air outside because the windows let in the sun’s energy and trap it, gradually raising the temperature.

Other effective methods of passive solar energy capture include using stone flooring and walls with thick insulation to keep the energy in buildings. With carefully placed windows and other architectural techniques, passive solar energy systems can be an effective way to heat buildings.

Active solar energy systems use the same principles as passive systems except that they use a fluid (such as water) to absorb the heat. A solar collector positioned on the roofs of buildings heats the fluid and then pumps it through a system of pipes to heat the whole building.

Photovoltaic cells, or solar panels, are slightly more involved than passive or active solar energy systems. They convert sunlight to electricity by using thin sheets of silicon. These thin sheets are inexpensive and can be added to roof tiles. People in remote areas such as mountain tops and islands often use photovoltaic cells to generate electricity in their homes and businesses.

This figure illustrates how solar panels capture sunlight and generate electricity.

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The good news about solar energy is that the sun is always available. The bad news is that depending on the system, solar energy may be too expensive for widespread consumer use. Even so, technological advances continue to lower the costs of using solar energy systems for electricity, so that may change in the future.

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