shaoyang
Sunday, August 19, 2007
Solar power
Solar power (also known as solar energy) uses
Solar Radiation emitted from our
sun. Solar power, a
renewable energy source, has been used in many traditional technologies for centuries, and is in widespread use where other power supplies are absent, such as in remote locations and in
space.
Solar radiation reaches the Earth's upper
atmosphere at a rate of
1366 watts.
Solar radiation is
reflected and 16% is
absorbed resulting in a peak
irradiance at the
equator of 1,020 W/m².
[2] Average atmospheric conditions (
clouds,
dust,
pollutants) further reduce insolation by 20% through reflection and 3% through absorption.
[3] Atmospheric conditions not only reduce the quantity of insolation reaching the Earth's surface but also affect the quality of insolation by
diffusing incoming light and altering its spectrum.
After passing through the Earth's atmosphere, most of the sun's energy is in the form of
visible and
Infrared radiations. Plants use solar energy to create chemical energy through
photosynthesis. Humans regularly use this energy burning wood or
fossil fuels, or when simply
eating the plants.
A recent concern is
global dimming, an effect of pollution that is allowing less sunlight to reach the Earth's surface. It is intricately linked with pollution particles and
global warming, and it is mostly of concern for issues of
global climate change, but is also of concern to proponents of solar power because of the existing and potential future decreases in available solar energy. The order of magnitude is about 4% less solar energy available at sea level over the timeframe of 1961–90, mostly from increased reflection from clouds back into outer space.
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 design in architecture involves the use of appropriate solar technologies to maintain a building’s environment at a comfortable temperature through the sun's daily and annual cycles. It may do this by storing solar energy as heat in the walls of a building, which then acts to heat the building at night. Another approach is to keep the interior cool during a hot day by designing in natural convection through the building’s interior.
Solar hot water systems use sunlight to heat water. Solar hot water systems were used extensively in the United States up to the 1920s until replaced by relatively cheap and more reliable conventional heating fuels. The economic advantage of conventional heating fuels has varied over time resulting in periodic interest in solar hot water; however, solar hot water and heating technologies have yet to show the sustained momentum they lost in the 1920s. That being said, the recent spikes and erratic availability of conventional fuels has resulted in a renewed interest in solar heating technologies.
On a technical level, solar water heating is particularly appropriate for low temperature applications (100-150F). This advantage has been successfully applied to heating swimming pools where solar water heating can economically increase pool use. Solar water heating is also used in stand alone or hybrid domestic water heating systems.
Solar cells, also referred to as photovoltaic cells, are devices or banks of devices that use the
photovoltaic effect of
semiconductors to generate electricity directly from sunlight. Until recently, their use has been limited because of high manufacturing costs. One cost effective use has been in very low-power devices such as
calculators with
LCDs. Another use has been in remote applications such as roadside emergency telephones, remote sensing,
cathodic protection of pipe lines, and limited "off grid" home power applications. A third use has been in powering orbiting
satellites and
spacecraft.
To take advantage of the incoming electromagnetic radiation from the sun, solar panels can be attached to each house or building. The panels should be mounted perpendicular to the arc of the sun to maximize usefulness. The easiest way to use this electricity is by connecting the solar panels to a
grid tie inverter. However, these solar panels may also be used to charge batteries or other
energy storage device. Solar panels produce more power during summer months because they receive more
sunlight. The cost payback time may take over 10 years depending on the cost of grid electricity and tax rebates.
Total
peak power of installed PV is around 3,700 MW as of the end of 2005. This is only one part of solar-generated electric power.
Declining manufacturing costs (dropping at 3 to 5% a year in recent years) are expanding the range of cost-effective uses. The average lowest retail cost of a large
photovoltaic array declined from $7.50 to $4 per watt between 1990 and
2005. With many jurisdictions now giving tax and rebate incentives, solar electric power can now pay for itself in five to ten years in many places. "Grid-connected" systems - those systems that use an
inverter to connect to the
utility grid instead of relying on batteries - now make up the largest part of the market.
In 2003, worldwide production of solar cells increased by 32%.Between 2000 and 2004, the increase in worldwide solar energy capacity was an annualized 60%. 2005 was expected to see large growth again, but shortages of refined
silicon have been hampering production worldwide since late 2004. Analysts have predicted similar supply problems for 2006 and 2007。
The first solar "cars" were actually tricycles or quadricycles built with bicycle technology. The solar array consists of hundreds of photovoltaic solar cells converting sunlight into electricity. The cells are wired together into strings while strings are often wired together to form a panel. Panels normally have voltages close to the nominal battery voltage. The main aim is to get as many cells in as small a space as possible. Designers encapsulate the cells to protect them from the weather and breakage.
Designing a solar array is more than just stringing bunch of cells together. A solar array acts like a lot of very small batteries all hooked together in series. The total voltage produced is the sum of all cell voltages. The problem is that if a single cell is in shadow it acts like a diode, blocking the flow of current for the entire string of cells. To correct against this, array designers use by-pass diodes in parallel with smaller segments of the string of cells, allowing current to flow around the non-functioning cell(s). Another consideration is that the battery itself can force current backwards through the array unless there are blocking diodes put at the end of each panel.
The power produced by the solar array depends on the weather conditions, the position of the sun and the capacity of the array. At noon on a bright day, a good array can produce over 2 kilowatts (2.6 hp).Some cars have employed free standing or integrated sails to harness wind energy.
11:23 PM
This is our school logo.Very Nice is't it?