ENERGY FROM THE SUN
The sun has produced energy for billions of years. Solar energy is the sun’s rays (solar radiation) that reach the earth.
Solar energy can be converted into other forms of energy, such as heat and electricity. In the 1830s, the British astronomer John Herschel used a solar thermal collector box (a device that absorbs sunlight to collect heat) to cook food during an expedition to Africa. Today, people use the sun's energy for lots of things.
Solar energy can be converted to thermal (or heat) energy and used to:
Heat water – for use in homes, buildings, or swimming pools.
Heat spaces – inside greenhouses, homes, and other buildings.
Solar energy can be converted to electricity in two ways:
Photovoltaic (PV devices) or “solar cells” – change sunlight directly into electricity. PV systems are often used in remote locations that are not connected to the electric grid. They are also used to power watches, calculators, and lighted road signs.
Solar Power Plants - indirectly generate electricity when the heat from solar thermal collectors is used to heat a fluid which produces steam that is used to power generator. Out of the 15 known solar electric generating units operating in the United States at the end of 2006, 10 of these are in California, and 5 in Arizona. No statistics are being collected on solar plants that produce less than 1 megawatt of electricity, so there may be smaller solar plants in a number of other states.
The major disadvantages of solar energy are:
The amount of sunlight that arrives at the earth's surface is not constant. It depends on location, time of day, time of year, and weather conditions.
Because the sun doesn't deliver that much energy to any one place at any one time, a large surface area is required to collect the energy at a useful rate.
PHOTOVOLTAIC ENERGY
Photovoltaic energy is the conversion of sunlight into electricity. A photovoltaic cell, commonly called a solar cell or PV, is the technology used to convert solar energy directly into electrical power. A photovoltaic cell is a nonmechanical device usually made from silicon alloys.
Sunlight is composed of photons, or particles of solar energy. These photons contain various amounts of energy corresponding to the different wavelengths of the solar spectrum. When photons strike a photovoltaic cell, they may be reflected, pass right through, or be absorbed. Only the absorbed photons provide energy to generate electricity. When enough sunlight (energy) is absorbed by the material (a semiconductor), electrons are dislodged from the material's atoms. Special treatment of the material surface during manufacturing makes the front surface of the cell more receptive to free electrons, so the electrons naturally migrate to the surface.
When the electrons leave their position, holes are formed. When many electrons, each carrying a negative charge, travel toward the front surface of the cell, the resulting imbalance of charge between the cell's front and back surfaces creates a voltage potential like the negative and positive terminals of a battery. When the two surfaces are connected through an external load, electricity flows.
The photovoltaic cell is the basic building block of a photovoltaic system. Individual cells can vary in size from about 1 centimeter (1/2 inch) to about 10 centimeter (4 inches) across. However, one cell only produces 1 or 2 watts, which isn't enough power for most applications. To increase power output, cells are electrically connected into a packaged weather-tight module. Modules can be further connected to form an array. The term array refers to the entire generating plant, whether it is made up of one or several thousand modules. The number of modules connected together in an array depends on the amount of power output needed.
The performance of a photovoltaic array is dependent upon sunlight. Climate conditions (e.g., clouds, fog) have a significant effect on the amount of solar energy received by a photovoltaic array and, in turn, its performance. Most current technology photovoltaic modules are about 10 percent efficient in converting sunlight. Further research is being conducted to raise this efficiency to 20 percent.
The photovoltaic cell was discovered in 1954 by Bell Telephone researchers examining the sensitivity of a properly prepared silicon wafer to sunlight. Beginning in the late 1950s, photovoltaic cells were used to power U.S. space satellites (learn more about the history of photovaltaic cells). The success of PV in space generated commercial applications for this technology. The simplest photovoltaic systems power many of the small calculators and wrist watches used everyday. More complicated systems provide electricity to pump water, power communications equipment, and even provide electricity to our homes.
Some advantages of photovoltaic systems are:
Conversion from sunlight to electricity is direct, so that bulky mechanical generator systems are unnecessary.
PV arrays can be installed quickly and in any size required or allowed.
The environmental impact is minimal, requiring no water for system cooling and generating no by-products.
Photovoltaic cells, like batteries, generate direct current (DC) which is generally used for small loads (electronic equipment). When DC from photovoltaic cells is used for commercial applications or sold to electric utilities using the electric grid, it must be converted to alternating current (AC) using inverters, solid state devices that convert DC power to AC.
Historically, PV has been used at remote sites to provide electricity. In the future PV arrays may be located at sites that are also connected to the electric grid enhancing the reliability of the distribution system.
SOLAR THERMAL HEAT
Solar thermal(heat) energy is often used for heating swimming pools, heating water used in homes, and space heating of buildings. Solar space heating systems can be classified as passive or active.
Passive space heating is what happens to your car on a hot summer day. In buildings, the air is circulated past a solar heat surface(s) and through the building by convection (i.e. less dense warm air tends to rise while more dense cooler air moves downward) . No mechanical equipment is needed for passive solar heating.
Active heating systems require a collector to absorb and collect solar radiation. Fans or pumps are used to circulate the heated air or heat absorbing fluid. Active systems often include some type of energy storage system.
Solar collectors can be either nonconcentrating or concentrating.
1) Nonconcentrating collectors – have a collector area (i.e. the area that intercepts the solar radiation) that is the same as the absorber area (i.e., the area absorbing the radiation). Flat-plate collectors are the most common and are used when temperatures below about 200o degrees F are sufficient, such as for space heating.
2) Concentrating collectors – where the area intercepting the solar radiation is greater, sometimes hundreds of times greater, than the absorber area.
SOLAR THERMAL POWER PLANTS
Solar thermal power plants use the sun's rays to heat a fluid, from which heat transfer systems may be used to produce steam. The steam, in turn, is converted into mechanical energy in a turbine and into electricity from a conventional generator coupled to the turbine. Solar thermal power generation works essentially the same as generation from fossil fuels except that instead of using steam produced from the combustion of fossil fuels, the steam is produced by the heat collected from sunlight. Solar thermal technologies use concentrator systems due to the high temperatures needed to heat the fluid. The three main types of solar-thermal power systems are:
Parabolic trough – the most common type of plant.
Solar dish
Solar power tower
SOLAR ENERGY AND THE ENVIRONMENT
Solar energy is free, and its supplies are unlimited. Using solar energy produces no air or water pollution but does have some indirect impacts on the environment. For example, manufacturing the photovoltaic cells used to convert sunlight into electricity, consumes silicon and produces some waste products. In addition, large solar thermal farms can also harm desert ecosystems if not properly managed.
Last Revised: November 2007
Sources: Energy Information Administration, Electric Power Annual, Form EIA-860, Annual Electric Generator Report database, 2006.
http://www.eia.doe.gov/kids/energyfacts/sources/renewable/solar.html
-Valentia
Saturday, June 21, 2008
Monday, June 2, 2008
Friday, May 23, 2008
Solar Power Uses
Solar power is used a number of different ways, of course. There are two very basic kinds of solar energy:
Solar thermal energy collects the sun's warmth through one of two means: in water or in an anti-freeze (glycol) mixture.
Solar photovoltaic energy converts the sun's radiation to usable electricity.
Two kinds of solar energy and Five ways they can be used.
Here are the five most practical and popular ways that solar energy is used:
Small independent solar photovoltaic systems. We see these used everywhere, from calculators to garden lights. Portable units can be used for everything from RV appliances while single panel systems are used for traffic signs and remote monitoring stations.
Solar pool heating. Running water in direct circulation systems through a solar collector is a very practical way to heat water for your pool or hot tub.
Solar thermal energy using glycol to heat water. In this method (indirect circulation), glycol is heated by the sun's rays and the heat is then transferred to water in a hot water tank. This method of collecting the sun's energy is more practical now than ever. In areas as far north as Edmonton, Alberta, solar thermal to heat water is economically sound. It can pay for itself in three years or less.
Integrating solar photovoltaic energy into your home or business power. In many parts of the world, solar photovoltaics is an economically feasible way to supplement the power of your home. In Japan, photovoltaics are competitive with other forms of power. In the US, new incentive programs make this form of solar energy ever more viable in many states. An increasingly popular and practical way of integrating solar energy into the power of your home or business is through the use of building integrated solar photovoltaics.
Large independent photovoltaic systems. If you have enough sun power at your site, you may be able to go off grid. You may also integrate or hybridize your solar energy system with wind power or other forms of renewable energy to stay 'off the grid.'
http://www.thesolarguide.com/solar-power-uses/
- Xin Yun
Solar thermal energy collects the sun's warmth through one of two means: in water or in an anti-freeze (glycol) mixture.
Solar photovoltaic energy converts the sun's radiation to usable electricity.
Two kinds of solar energy and Five ways they can be used.
Here are the five most practical and popular ways that solar energy is used:
Small independent solar photovoltaic systems. We see these used everywhere, from calculators to garden lights. Portable units can be used for everything from RV appliances while single panel systems are used for traffic signs and remote monitoring stations.
Solar pool heating. Running water in direct circulation systems through a solar collector is a very practical way to heat water for your pool or hot tub.
Solar thermal energy using glycol to heat water. In this method (indirect circulation), glycol is heated by the sun's rays and the heat is then transferred to water in a hot water tank. This method of collecting the sun's energy is more practical now than ever. In areas as far north as Edmonton, Alberta, solar thermal to heat water is economically sound. It can pay for itself in three years or less.
Integrating solar photovoltaic energy into your home or business power. In many parts of the world, solar photovoltaics is an economically feasible way to supplement the power of your home. In Japan, photovoltaics are competitive with other forms of power. In the US, new incentive programs make this form of solar energy ever more viable in many states. An increasingly popular and practical way of integrating solar energy into the power of your home or business is through the use of building integrated solar photovoltaics.
Large independent photovoltaic systems. If you have enough sun power at your site, you may be able to go off grid. You may also integrate or hybridize your solar energy system with wind power or other forms of renewable energy to stay 'off the grid.'
http://www.thesolarguide.com/solar-power-uses/
- Xin Yun
Sunday, May 11, 2008
SUMMARY OF WHAT WE COVERED SO FAR
-the operation of a solar panel
-how light energy from the sun is converted into solar energy for use
-the needs for solar energy
-pros and cons of using solar energy
-whether solar energy could become the main energy source in the future
-an insight into whether people might becom reliant on the use of solar energy
-the use of solar energy
any more to add on?
-the operation of a solar panel
-how light energy from the sun is converted into solar energy for use
-the needs for solar energy
-pros and cons of using solar energy
-whether solar energy could become the main energy source in the future
-an insight into whether people might becom reliant on the use of solar energy
-the use of solar energy
any more to add on?
yuzhen
Friday, May 9, 2008
Solar cell physics -- the photovoltaic effect, applied
Sunlight is composed of photons, which can be thought of as "packets" of energy (the amount of energy in a photon being proportional to the frequency of its light). When photons strike a solar cell, the vast majority are either reflected or absorbed (some really high-energy photons will blow right through, but they're of no concern here). When a photon is absorbed, its energy is transferred to the semiconductor -- in particular, to an electron in an atom of the cell. If enough energy is transferred, the electron can escape from its normal position associated with that atom. In the process, the electron causes a hole (i.e., an empty spot where the electron used to be) to form. Each photon with enough energy will normally free exactly one electron, and one hole. Note that both electrons and holes are mobile, and as such can be current carriers.
Figure 1. The effect of the electric field in a PV cell (diagram courtesy of How Stuff Works )
The simplest solar cells have 3 active layers -- a top junction layer (made of N-type semiconductor ), an absorber layer (a P-N junction), and a back junction layer (made of P-type semiconductor). Thanks to the P-N junction, the cell has it's own built-in electric field. This electric field provides the voltage needed to force electrons and holes freed by light absorption to flow in their own directions (the electrons to the N-type side, and the holes to the P-type side). If we provide an external current path, electrons will flow through this path to their original (P-type) side to unite with holes the electric field sent there, doing work for us along the way. The electron flow provides the current, and the cell's electric field causes a voltage. With both current and voltage, we have power, which is just the product of the two.
Figure 2. Operation of a photovoltaic cell (diagram courtesy of How Stuff Works )
After a moment's thought, you can see that two additional layers must be present in a solar cell --electrical contact layers -- to allow electric current to flow out of and into the cell. The electrical contact layer on the face of the cell where light enters is generally present in some grid pattern and is composed of a good conductor such as a metal. The grid pattern does not cover the entire face of the cell since grid materials, though good electrical conductors, are generally not transparent to light. Hence, the grid pattern must be widely spaced to allow light to enter the solar cell but not to the extent that the electrical contact layer will have difficulty collecting the current produced by the cell. The back electrical contact layer has no such restrictions -- it need simply provide an electrical contact and thus covers the entire back surface of the cell.Additionally, an antireflective coating is generally applied to the top of the cell to reduce reflection losses, and a cover plate of some kind is often installed to protect the cell from damage while out in the real world.
After a moment's thought, you can see that two additional layers must be present in a solar cell --electrical contact layers -- to allow electric current to flow out of and into the cell. The electrical contact layer on the face of the cell where light enters is generally present in some grid pattern and is composed of a good conductor such as a metal. The grid pattern does not cover the entire face of the cell since grid materials, though good electrical conductors, are generally not transparent to light. Hence, the grid pattern must be widely spaced to allow light to enter the solar cell but not to the extent that the electrical contact layer will have difficulty collecting the current produced by the cell. The back electrical contact layer has no such restrictions -- it need simply provide an electrical contact and thus covers the entire back surface of the cell.Additionally, an antireflective coating is generally applied to the top of the cell to reduce reflection losses, and a cover plate of some kind is often installed to protect the cell from damage while out in the real world.
- Yee Ting
Monday, April 28, 2008
city residential home uses
Recent years have seen rapid growth in the number of installations of PV on to buildings that are connected to the electricity grid. This area of demand has been stimulated in part by government subsidy programmes (especially Japan and Germany) and by green pricing policies of utilities or electricity service providers (e.g. in Switzerland and the USA). The central driving force though comes from the desire of individuals or companies to obtain their electricity from a clean, non-polluting, renewable source for which they are prepared to pay a small premium.In these grid-connected systems, a PV System supplies electricity to the building and any day-time excess may be exported to the grid. Batteries are not required because the grid supplies any extra demand. However, if you want to be independent of the grid supply you will need battery storage to provide power outside daylight hours. Solar PV modules can be retrofitted on to a pitched roof above the existing roof-tiles, or the tiles replaced by specially designed PV roof-tiles or roof-tiling systems. If you are planning to put a PV system on to a building and have it connected to the grid supply there are likely to be local regulations that need to be met, and permission required from your utility or electricity service provider. The level of credit for any exported electricity will vary depending on local schemes in place.
industrial uses
For many years, Solar Energy has been the power supply of choice for Industrial applications, where power is required at remote locations. This means in these applications that solar power is economic, without subsidy. Most systems in individual uses require a few kilowatts of power. The examples are powering repeater stations for microwave, TV and radio, telemetry and radio telephones.Solar energy is also frequently used on transportation signalling e.g. offshore navigation buoys, lighthouses, aircraft warning lights on pylons or structures, and increasingly in road traffic warning signals. Solar is used to power environmental and situation monitoring equipment and corrosion protection systems (based on impressing a current) for pipelines, well-heads, and bridges or other structures. As before, for larger electrical loads it can be cost effective to configure a hybrid power system that links the PV with a small diesel generator. Solar's great benefit here is that it is highly reliable and requires little maintenance so it's ideal in places that are hard to get to.
yuzhen
Recent years have seen rapid growth in the number of installations of PV on to buildings that are connected to the electricity grid. This area of demand has been stimulated in part by government subsidy programmes (especially Japan and Germany) and by green pricing policies of utilities or electricity service providers (e.g. in Switzerland and the USA). The central driving force though comes from the desire of individuals or companies to obtain their electricity from a clean, non-polluting, renewable source for which they are prepared to pay a small premium.In these grid-connected systems, a PV System supplies electricity to the building and any day-time excess may be exported to the grid. Batteries are not required because the grid supplies any extra demand. However, if you want to be independent of the grid supply you will need battery storage to provide power outside daylight hours. Solar PV modules can be retrofitted on to a pitched roof above the existing roof-tiles, or the tiles replaced by specially designed PV roof-tiles or roof-tiling systems. If you are planning to put a PV system on to a building and have it connected to the grid supply there are likely to be local regulations that need to be met, and permission required from your utility or electricity service provider. The level of credit for any exported electricity will vary depending on local schemes in place.
industrial uses
For many years, Solar Energy has been the power supply of choice for Industrial applications, where power is required at remote locations. This means in these applications that solar power is economic, without subsidy. Most systems in individual uses require a few kilowatts of power. The examples are powering repeater stations for microwave, TV and radio, telemetry and radio telephones.Solar energy is also frequently used on transportation signalling e.g. offshore navigation buoys, lighthouses, aircraft warning lights on pylons or structures, and increasingly in road traffic warning signals. Solar is used to power environmental and situation monitoring equipment and corrosion protection systems (based on impressing a current) for pipelines, well-heads, and bridges or other structures. As before, for larger electrical loads it can be cost effective to configure a hybrid power system that links the PV with a small diesel generator. Solar's great benefit here is that it is highly reliable and requires little maintenance so it's ideal in places that are hard to get to.
yuzhen
Wednesday, April 23, 2008
Popularity of Solar Energy
The Popularity of Solar Power Homes
Most people are aware of what solar power is and how it works, but for some people it is still a new issue.
Solar power homes are now more popular than ever, and for a few different reasons. Cutting costs is one of the first things that usually attract homeowners to solar power, but certainly not the only thing. Solar power homes are also great for the environment because they are not using fossil fuels and other forms of energy and so they are not polluting the environment.
Once a homeowner has switched over to solar power they will usually never complain or have any regrets, but the biggest issue is actually getting people to recognize the benefits offered to them by solar power and getting them to make the switch.
When something this good comes along most people assume that it is too good to be true, which is why the number of solar power homes in the world when compared to those with regular electricity is still very low.
If you are considering retrofitting your home with solar power but not yet sure, here are a few things you should know. For one you need to understand that solar power is only possible when there is sunlight available, so on rainy and cloudy days your solar powered applications will not be working.
This is obviously a serious problem in some cases but the fact is that it is one of very few problems overall, which is what you really want to keep in mind.
Also remember that for optimal operation, the panels used for your home will need direct sun for at least three hours mid-afternoon each day, and so therefore you want to make sure that they are situated in an ideal location at your home where they are going to be able to receive this daily sunlight.
Solar power experts suggest that homeowners who want to convert their houses to solar power homes should start by using solar energy to heat the pool. This is a very quick and easy step towards becoming completely dependent on solar power, and so it will definitely be one of the best first moves that you can make.
Solar power homes are quickly becoming all the rage, especially when you take issues like global warming which are facing the world today into consideration, and understand how much you and the world around you will be benefitting by you integrating solar energy into your life as much as possible.
http://www.linkroll.com/solar-power-house/the-popularity-of-solar-power-homes.php
-Valentia
Most people are aware of what solar power is and how it works, but for some people it is still a new issue.
Solar power homes are now more popular than ever, and for a few different reasons. Cutting costs is one of the first things that usually attract homeowners to solar power, but certainly not the only thing. Solar power homes are also great for the environment because they are not using fossil fuels and other forms of energy and so they are not polluting the environment.
Once a homeowner has switched over to solar power they will usually never complain or have any regrets, but the biggest issue is actually getting people to recognize the benefits offered to them by solar power and getting them to make the switch.
When something this good comes along most people assume that it is too good to be true, which is why the number of solar power homes in the world when compared to those with regular electricity is still very low.
If you are considering retrofitting your home with solar power but not yet sure, here are a few things you should know. For one you need to understand that solar power is only possible when there is sunlight available, so on rainy and cloudy days your solar powered applications will not be working.
This is obviously a serious problem in some cases but the fact is that it is one of very few problems overall, which is what you really want to keep in mind.
Also remember that for optimal operation, the panels used for your home will need direct sun for at least three hours mid-afternoon each day, and so therefore you want to make sure that they are situated in an ideal location at your home where they are going to be able to receive this daily sunlight.
Solar power experts suggest that homeowners who want to convert their houses to solar power homes should start by using solar energy to heat the pool. This is a very quick and easy step towards becoming completely dependent on solar power, and so it will definitely be one of the best first moves that you can make.
Solar power homes are quickly becoming all the rage, especially when you take issues like global warming which are facing the world today into consideration, and understand how much you and the world around you will be benefitting by you integrating solar energy into your life as much as possible.
http://www.linkroll.com/solar-power-house/the-popularity-of-solar-power-homes.php
-Valentia
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