Solar Panels

What they are:
A typical house solar array - http://inhabitat.com/sunpower-new-super-efficient-solar-panels/
A typical house solar array - http://inhabitat.com/sunpower-new-super-efficient-solar-panels/

Solar panels are becoming a popular sight amongst residences across Europe and North America. The changing econom ismaking solar technology much easier and cheaper for the public to own this relatively new form of electrical power generation.
To understand the physics behind solar technology, one must first have a practical understanding of what solar panels actually are. To begin, solar panels are a form of active solar power, a term used to describe a solar panels use of light photons emitted from the sun. When placed into direct sunlight, solar panels will produce electricity. The solar cells, also known as photovoltaic cells, are the core converters in solar panels and are arranged atop the solar panel in a grid-like manner to maximize surface area and organization.


History:
Antoine-César Becquerel - http://library.thinkquest.org/C006439/scientists/
Antoine-César Becquerel - http://library.thinkquest.org/C006439/scientists/


The devlopment of the solar cell stems from the work of the French experimental physicist Antoine-César Becquerel back in the 19th century. In 1839, Becquerel discovered the photovoltaic effect while experimenting with an electrolytic cell containing two metal electrodes, but he could not explain what was happening. Then the 19 year old found that certain metals and solutions would produce small amounts of electric current when exposed to light.

In 1877, Charles Fritts constructed the first true solar cells by using junctions formed by coating the semiconductor selenium with an ultrathin, nearly transparent layer of gold. Fritts' devices were very inefficient, transforming less than 1 percent of the absorbed light into electrical energy, but they were a start.
Albert Einstein in 1905 - http://www.spaceandmotion.com/quantum-theory-albert-einstein-quotes.htm
Albert Einstein in 1905 - http://www.spaceandmotion.com/quantum-theory-albert-einstein-quotes.htm


Substantial improvements in solar cell efficiency had to wait for a better understanding f the physical principles involved in their design, provided by Albert Einstein in 1905 and Schottky in 1930. By 1927 another metal semiconductor-junction solar cell, in this case made of copper and the semiconductor copper oxide, had been demonstrated. By the 1930s both the selenium cell and the copper oxide cell were being employed in light-sensitive devices, such as photometers, for use in photography. These early solar cells, however, still had energy conversion efficiencies of less than 1 percent.

Solar cell efficiency finally saw substantial progress with the development of the first silicon cell by Russell Ohl in 1941. In 1954, three other American researchers, G.L. Pearson, Daryl Chapin, and Calvin Fuller, demonstrated a further-refined silicon solar cell capable of 6% energy conversion efficiency in direct sunlight. By the late 1980s silicon cells, as well as those made of gallium arsenide, with efficiencies of more than 20% had been fabricated. In 1989 a concentrator solar cell, a type of device in which sunlight is concentrated onto the cell surface by means of lenses, achieved an efficiency of 37% thanks to the increased intensity of the collected energy. The most efficient solar cell known to date achieved 42.4% efficiency.

How They Work:
Before the explanation of how a solar panel converts solar energy into electricity can be explained, you need to understand what a Photovoltaic Cell is (otherwise called a PV Cell). A photovoltaic cell is the core of a solar panel, where a semiconductor within the PV cell reacts with the light and generates electricity. A photovoltaic cell is seen on the front of a solar panel, the PV cells are the "black squares" you see. Those squares are a combination of even more smaller squares of PV cells (depending on which type of solar panel it is) creating a form of grid of PV cells. This grid is called a Photovoltaic Module. It is here that the chemistry occurs, within these PV cells of a solar panel.
With the knowledge of what a PV cell is, the explanation can begin. Where the simplest way to explain how solar panels work is that: light goes in, electricity comes out; however, the process is much more advanced than just that. Assuming that everything is prepared (solar panel installed, sun is up, etc) the process begins with the suns UV rays. The light coming from the sun are made up of the unit "photons" (a term used to describe rays of light) which bombards the surface of the PV cells leading to a continuous series of collisions. These collisions can occur because photons can, according to the Theory of Light, "carry energy and momentum" and can also have "particle-like interactions with electrons and other particles". The constant collisions between the photon and PV cell causes the breaking of electron pairs that have taken place between the thousands of Si atoms within each cell. As a result of the this bond being broken, one of the electrons are let loose leaving behind a "hole" in the grid which is to be occupied by the oncoming photons. The electron will then seek for a "hole" even deeper within the PV cell; however, if the presence of another hole is not close enough to the loose electrons area of influence then it will be guided by an electric field (generated by two closely placed, oppositely charged semiconductors) to a secondary route where the electrons will travel through this path to the positive side of the cell where it will re-pair with the holes that the electric field had sent to the positive side. As the electrons continually flow in this manner, provided that photons are still bombarding the PV cell, it will produce an electron current; a current of electrons. And so long as the semiconductors remain in place, the electric field will still be there and produce voltage. So, with the presence of voltage and current in a cell, electricity is produced within the PV cell. While the energy is being generated by the PV cell, the backboard of the solar panel (which is made out of metal) acts as a conductor which transports a fraction of the electricity produced into an electrical grid where it is distributed and used.

Types:

There are multiple variations of a solar panel in the world, consisting mainly of the following 4 types: Monocrystalline Silicon Panels, Polycrystalline Silicon Panels, String Ribbon Silicon Panels, and Amorphous Silicon Panels.
All of these variations have one thing in common, they all use Silicon as their semiconductors; however, that’s where they end. Each variation gathers electricity at different rates and each have there own ups and downs compared to each other.
Monocrystalline Solar Panel http://sopraypv.com/p_view.asp?pid=333
Monocrystalline Solar Panel http://sopraypv.com/p_view.asp?pid=333

Monocrystalline Silicon Panels: This panel consists of a large single sheet of Silicon (a single large PV cell) that has increased conductivity capabilities due to additional metal sheets applied to its frame and structure. It is due to this factor that this type of solar panel is claimed to have the highest electricity return rate of 14% to 18%. While it can be said that this is the most efficient form of solar panel technology, it is also the most expensive due to how the structure is made by one large continuous sheet of Silicon.
Polycrystalline Solar Panel http://www.solar-water-heater.us/Products/5w-300w-solar-panels-C5/Poly-Solar-Panel-Hes-180-48p-Polycrystalline-Solar-Panel-P107.htm
Polycrystalline Solar Panel http://www.solar-water-heater.us/Products/5w-300w-solar-panels-C5/Poly-Solar-Panel-Hes-180-48p-Polycrystalline-Solar-Panel-P107.htm


Polycrystalline/Multi-crystalline Silicon Panels: The polycrystalline/multi-crystalline silicon panels are created in the same manner as a Monocrystalline panel, just that due to the financial costs of a Monocrystalline panel the polycrystalline panel was created. This panel is much cheaper to buy and maintain unlike Monocrystalline panels. The poly- panels are made up of multiple PV cells rather than one large PV cell. While this panel is slightly less efficient than the mono- panel (12% to 14% return rate compared to mono-‘s 14% to 18%) it has proven more practical as it is much simpler and cheaper to fix a poly- panel than it is a mono- panel.
String Ribbon Panel http://edbpr.net/image_spruce_evergreen190.gif
String Ribbon Panel http://edbpr.net/image_spruce_evergreen190.gif


String Ribbon Silicon Panels: The String Ribbon panel is manufactured with the polycrystalline panel in mind, where the String Ribbon panels go even farther as to make PV cells even smaller but in greater numbers where there are "strings" of PV cells which make up a single poly- PV cell where there are dozens of poly- PV cells making up a full solar panel, so it is effectively a poly- panel only broken down into even smaller PV cell size where it is claimed to be even cheaper in manufacturing costs. The String Ribbon panels return rate is similar to the poly- panels: ~ 12%-14%.
Amorphous Solar Panel http://image.made-in-china.com/2f0j00HBCTjNAMkYgs/Thin-Film-Amorphous-Silicon-Solar-Panel.jpg
Amorphous Solar Panel http://image.made-in-china.com/2f0j00HBCTjNAMkYgs/Thin-Film-Amorphous-Silicon-Solar-Panel.jpg

Amorphous Silicon Panel: Lastly, there is the Amorphous Silicon panel, where this type of panel is considered obsolete by today’s standard of solar technology where the amorphous panel returns a meagre rate of 5% to 6%. What makes this so ineffective is because the amorphous panel does not follow the same structure as the crystalline silicon panels. Where instead of having all the PV cells made out of Silicon the amorphous panel uses a thin layer of Silicon coated on the top of another conductive metal, such as copper. This panel is the cheapest of them all and the least efficient.

Construction:
The solar panel is essentially made up of layers of materials that work together to protect, produce, amplify, generate and preserve the system in place to generate the electricity. I will go through the different layers that solar panels have and what purpose they serve. The first and most basic layer is the glass on top. The only purpose of this glass is to let the sunlight through but yet protect the cells from weathering like rain, hail and snow. The second layer is the actual silicon or photovoltaic cells which produce the electricity. These are thin sheets that are 4" by 4" roughly. These thin sheets cover the whole surface of the solar panel and are what actually produce the power. They are connected electronically by a metal conductor that can relay the power to the control box. The layer beneath the voltaic cells is what holds them in place. It’s a layer of thermally conductive cement which allows the heat to dissipate. This layer is necessary because of the great heat produced by solar panels. The voltaic cells are black and absorb heat and since there is lot of electron movement it also gets hotter that way. The final layer is the frame which supports the whole unit and holds the system rigid and acts as the framework to old it all together.

Technological Advances:
One-axis solar tracker - http://www.enerquest.ca/products
One-axis solar tracker - http://www.enerquest.ca/products

There have been many technological advances in solar energy production. One of the earliest advances was the use of solar trackers.These devices act as moving stands for solar panels and move along with the sun from sunrise to sunset. The two types of physical trackers are one-axis and dual-axis trackers. One-axis trackers stay at the same vertical angle, but rotate around the post to follow the sun. The vertical angle is set manually to match the angle of the sun for the current season; closer to flat for summertime and at a steep angle for winter, with the exact angle dependant on your latitude. Dual-axis trackers change the vertical angle as well as the horizontal angle automatically.

The next major advancement came with the introduction of high-voltage solar panels and arrays. Previously, solar panels could only deliver 12 to 24 volts each, so it was necessary to place multiple panels in series to create a useful voltage level to run home power systems. With the introduction of high-voltage solar panels, fewer panels are needed to create voltages exceeding 120 volts to power home appliances. These high voltage panels can be connected in parallel to increase the output current.
Internal workings of an MPPT system - http://www.solarchargecontroller.com/solar-controllers/maximum-power-point-tracking-charge-controllers-explained/
Internal workings of an MPPT system - http://www.solarchargecontroller.com/solar-controllers/maximum-power-point-tracking-charge-controllers-explained/


Maximum Power Point Tracking controllers are a new breed of controller that can increase the output of any solar panel by 15-20 percent by trading volts for amps and vice versa to adjust the array output to changing whether conditions. They also accept high voltage inputs directly, so allowing 100-135 volt outputs to be a common figure for solar panel arrays. The results are greatly increased output on overcast days and greatly increased output when the sun is not hitting the panels at an optimum angle. MPPT makes expensive mechanical trackers less and less cost effective.

One of the most common and newest additions to solar technology is solar roof shingles. These inexpensive panels do not create as much power as their larger, more specialized counterparts, but can be wired in large arrays covering a house roof to counter their lower power output. Solar roof shingles are much less expensive than full-sized independent panels. Because of the low price of mounting and operating smaller roof shingle panels, they have become a popular choice of solar products amongst urban communities where large solar arrays would not fit.

Limitations

As mentioned in the types of solar panels section, there are limits of how well they will perform. By today’s standard the return rate of electricity gathered from the sun is 12% to 18%, which varies from panel to panel types. Where only until recently have we been able to develop even more superior solar technology converting up to 40.7%, this is a high tech development team though, so it is far from being used by the general public. Aside from the efficiency issues, there are no other limits as to how much electricity a solar energy may produce. However, in time the technology will develop to the point where solar panels will reach the %100 mark, but that is in the distant future.


Social and Econmical Impacts:
There are only a few social and economical impacts of the solar panel as it is just an alternate way of producing power. Something like an electric car may have larger social and economical impacts as it deals directly with society who would be working directly with the car. Although the main impact of the solar panel on society would be the clean energy that is produced. This technology is very expensive so initial costs to set up either a personal system or a large one for a community would be large but once installed they are practically maintenance free and the electricity produced would offset the cost of the panels. A small improvement that could also be considered is the quality of life. The quality of life would improve from less coal burning plants and the cleaner air that would be present and allow for a greater quality of life. Although they have been praised for there environmentally sound operation there is still the issue that when there is no sun you are not producing power. In a small personal household operation this could be troublesome in the fact that when no sun is out you would have to pay for power from the grid just as anyone else would. This also means on a larger scale the grid that runs off solar panels would have to have a backup alternate source for power generation. The biggest two impacts on the society though are the fact that they are a clean source of power and that the initial start up cost is large but beyond that they are a good choice as long as one can afford it.



Environmental Impacts

Solar panels do not produce environmental damage during their operational life. The main source of tribulations comes from the production and disposal of solar panels. During the manufacturing process to create solar products, workers are exposed to dangerous chemicals and gases such as Cadmium, Arsenic, Silicon dust and Chlorine gas. Silicon tetrachloride also becomes an issue of the environment around a disposed solar panel since it is toxic and can pollute. None of these potential hazards is much different in quality or magnitude from the innumerable hazards people face routinely in an industrial society. Through effective regulation, the dangers can very likely be kept at a very low level.

The large amount of land required for utility-scale solar power plants-approximately one square kilometer for every 20-60 megawatts generated poses an additional problem, especially where wildlife protection is a concern. But this problem is not unique to solar power plants. Generating electricity from coal actually requires as much or more land per unit of energy delivered if the land used in strip mining is taken into account. Large central power plants are not the only option for generating energy from sunlight, however, and are probably among the least promising. Because sunlight is dispersed, small-scale, dispersed applications are a better match to the resource. They can take advantage of unused space on the roofs of homes and buildings and in urban and industrial lots. And, in solar building designs, the structure itself acts as the collector, so there is no need for any additional space at all.

Alternatives

Obviously with a large start up cost and the fact that solar panels do not work when there is no sun, there is a need for some alternative source of power when solar is not available. For a small household operation a great combination is wind power and solar power. These two working together have a larger time frame that power can be generated. When both are not available the power can be taken from the grid but when both of these technologies work together it reduces the power you are taking from the grid and hence the cost of electricity. Another alternative is just to take your power from the grid if you cannot afford the initial start up of a solar panel system. This may not be environmentally clean way to produce electricity but it is reliable and you have no maintenance to worry about. On a large scale a community could use a nuclear power plant or a hydroelectric power plant. These ways of producing power are clean and are better than coal producing power plants which emit greenhous gasses into the environment.


Works Cited

Brower, Michael. "Environmental Impacts of Renewable Energy Technologies." 26 October 2002. Union of Concerned Scientists. 25 April 2011 <www.ucsusa.org>.

Seale, Eric. "Solar Cells." 9 July 2003. Solarbotics. 24 April 2011 <www.solarbotics.net>.

"Solar Panels." 2010. Energy Bible. 24 April 2011 <www.energybible.com>.

"Solar Power." 8 February 2008. Force Field. 24 April 2011 __www.otherpower.com__.








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