Solar energy

At the equator, the Sun provides approximately 1000 watts per square meter on Earth's surface.

Solar energy is energy that is present in sunlight. It has been used for thousands of years in many different ways by people all over the world. As well as its traditional human uses in heating, cooking, and drying, it is used today to make electricity where other power supplies are absent, such as in remote places and in space. It is becoming cheaper to make electricity from solar energy and in many situations it is now competitive with energy from coal or oil. It can also be used for heating, drying and cooking.

Solar energy is used today in a number of ways:

Energy from the Sun

The top diagram shows how the strength of sunlight is less nearer the Earth's poles.
The lower map shows how much solar energy hits the Earth's surface after clouds and dust have reflected and absorbed some solar energy.
In the bottom diagram, the dark disks represent the hypothetical land area needed to be covered in eight percent efficient solar panels trapping solar insolation to provide for the Earth's human population's electric energy use in the year 2003.

After passing through the Earth's atmosphere, most of the Sun's energy is in the form of visible light and infrared light radiation. Plants convert the energy in sunlight into chemical energy (sugars and starches) through the process of photosynthesis. Humans regularly use this store of energy in various way, as when they burn wood or fossil fuels, or when simply eating plants, fish and animals.

Solar radiation reaches the Earth's upper atmosphere with the power of 1366 watts per square meter (W/m2). [1] Since the Earth is round, the surface nearer its poles is angled away from the sun and receives much less solar energy than the surface nearer the equator.

The first diagram shows how solar energy varies at different latitudes because of this tilting away from the sun.

The second diagram shows how much of the Sun's energy is left after clouds and dust in the air have blocked some of it. [2]

At present, solar cell panels convert, at best, about 15% of sunlight hitting them into electricity. [3]

The dark disks in the third diagram on the right are imaginary examples of the amount of land that, if covered with 8% efficient solar panels, would produce slightly more energy in the form of electricity than the world needed in 2003. [4]


Types of technologies

Many technologies have been developed to make use of solar radiation. Some of these technologies make direct use of the solar energy (e.g to provide light, heat, etc.), while others produce electricity.

Solar cooking

Solar cooking uses the sun as the source of energy instead of standard cooking fuels such as charcoal, coal or gas. Solar cookers are an inexpensive and environmentally sound alternative to traditional ovens. By using the Sun as their source of energy, solar cookers allow people to allocate more of their resources towards food and other necessities by reducing the need to purchase conventional fuels. They are becoming widely used in areas of the developing world where deforestation is an issue, financial resources to purchase fuel are limited, and where open flames would pose a serious risk to people and the environment.

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References

  1. {{cite web | title=Solar Spectra: Standard Air Mass Zero | date=17 October [[172006-10-17 | work=NREL Renewable Resource Data Center | url=http://rredc.nrel.gov/solar/spectra/am0/ASTM2000.html | accessdate=2006-10-17 }}
  2. The average global irradiance calculated from satellite data collected from 1991 to 1993. For example, in North America the average insolation at ground level over an entire year (including nights and periods of cloudy weather) lies between 125 and 375 W/m² (3 to 9 kWh/m²/day).NREL: Dynamic Maps, GIS Data, and Analysis Tools - Solar Maps
  3. A solar panel in the contiguous United States on average delivers 19 to 56 W/m² or 0.45 - 1.35 (kW·h/m²)/day.us_pv_annual_may2004.jpg. National Renewable Energy Laboratory, US. Retrieved on 4 September 2006.
  4. International Energy Agency - Homepage

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