How Much Power Does a Solar Panel Generate?

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Solar panels produce electric power according to their size, efficiency and how much sunlight they receive. For homeowners and small businesses, roof-mounted panels are a typical option. Solar panels rated at 100 to 200 watts cover about 10 square feet (1 square meter). The power you get from a 100-watt solar panel depends on how much sunlight it receives, and on a daily basis the total power is much less than the rated wattage.

Solar panel roofs at Solar Settlement in Germany
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Facts

There are three main types of solar panels for home and business applications. Each type is a trade-off in energy efficiency and manufacturing costs. Solar panels are semiconductors that collect sunlight and convert it into electricity. This is called the photovoltaic effect. The amount of power a solar panel can generate depends on how much sunlight it receives, how efficiently it can convert the sunlight into electricity, and how big the solar panel is.

A larger solar panel will create more power. Wiring several solar panels together is the way to get the 120 volts required to run most household appliances, and more appliances need more amps to run. Volts times amps equals watts, or power. A typical high-end solar panel produces around 180 watts in bright sunlight. Tax credits may be available to consumers that install solar panels (http://www.energystar.gov/index.cfm?c=tax_credits.tx_index#s4).

Solar panel array on Mt. Laguna, CA.
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History

The first useful solar panels were invented in Bell Laboratories in 1954. Once used mostly for spacecraft and satellites, solar panels are now used for many applications including powering homes. Advances in the production of silicon, materials used for "doping" the semiconductor, increasing absorption, and anti-reflective techniques and more have all led to increased efficiency.

The International Space Station with solar panel arrays
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Considerations

Engineers design solar panels to make the most energy out of sunlight. Most of the sunlight that strikes a solar panel is not converted to electricity- it has to be the right wavelength (color) and it has to be absorbed (not reflected). Typical panels available for home or commercial use have efficiencies less than 20 percent, meaning only 20 percent of the power of the sunlight reaching the solar panel is converted to electricity. This is already figured into the rated wattage for a solar panel. Electric power is rated over time by watts per hour, or kilowatt hours.

Photovoltaic cells to be used in solar panel construction
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Potential

The power a solar panel can achieve and the power it delivers are two different matters. If a given panel is rated at 180 watts, then it will perform up to that level in the brightest sunlight (1,000 watts per square meter). However, unless you live on the Equator, your solar panel will not receive that much sunlight. The amount of sunlight that reaches the ground in your region (called "insolation," averaged in watts per square meter) divided industry-standard bright sunlight (1000 watts per square meter) will tell you what fraction of the rated wattage your panel will produce.

A simpler method is to find the number of "peak sun hours" your location receives each day. Any reputable vendor will have this information. A peak sun hour is one hour of 1,000 watts per square meter sunlight (http://photovoltaics.sandia.gov/docs/glossary.htm). Most locations in the United States receive less than six peak sun hours per day. You can predict how much power a given solar panel can generate by multiplying the watt rating of a solar panel by the number of peak sun hours for your location. Note that the sun hours will vary by season, and are lowest during the winter.

Photovoltaic panels cover facade of apartment building in Berlin, Germany
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Practical Considerations

Factors other than the maximum potential of your solar panel have to be considered. Is your panel in full sunlight? Is it positioned properly to attain the maximum exposure? Cloud cover will reduce the power by up to 30 percent or more. Snow and dust will limit the amount of light that reaches the panel and reduce power output.

Predicting the 24-hour performance of a panel in a given location can be estimated by noting its power production during the noon hour (brightest sunlight) and assuming approximately 20 percent of that power will be produced each hour averaged over a 24-hour period.

Farm with solar panel roof
Patrick Lux/Getty Images News/Getty Images

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