Friday, February 27, 2009

Czochralski, Float-Zone and Ribbon Silicon

Czochralski Silicon
In the Czochralski process, a seed crystal is dipped into a crucible of molten silicon and withdrawn slowly, pulling a cylindrical single crystal as the silicon crystallizes on the seed.

Float-Zone Silicon
The float-zone process produces purer crystals than the Czochralski method, because they are not contaminated by the crucible used in growing Czochralski crystals. In the float-zone process, a silicon rod is set atop a seed crystal and then lowered through an electromagnetic coil. The coil's magnetic field induces an electric field in the rod, heating and melting the interface between the rod and the seed. Single-crystal silicon forms at the interface, growing upward as the coils are slowly raised.

Once the single-crystal rods are produced, by either the Cz or FZ method, they must be sliced or sawn to form thin wafers. Such sawing, however, wastes as much as 20% of the valuable silicon as sawdust, known as "kerf." The resulting thin wafers are then doped to produce the necessary electric field. They are then treated with a coating to reduce reflection, and coated with electrical contacts to form functioning PV cells.

Ribbon Silicon
Although single-crystal silicon technology is well developed, the Czochralski and float-zone processes are complex and expensive (as are the ingot-casting processes discussed under multicrystalline silicon). Another group of crystal-producing processes, however, goes by the general name of "ribbon growth." These single crystals may cost less than other processes, because they form the silicon directly into thin, usable wafers of single-crystal silicon. These methods involve forming thin crystalline sheets directly, thus avoiding the slicing step required of cylindrical rods.

One "ribbon growth" technique—edge-defined film-fed growth—starts with two crystal seeds that grow and capture a sheet of material between them as they are pulled from a source of molten silicon. A frame entrains a thin sheet of material when drawn from a melt. This technique does not waste much material, but the quality of the material is not as high as Cz and FZ silicon.

Thursday, February 26, 2009

All About Silicon

Silicon—used to make some the earliest photovoltaic (PV) devices—is still the most popular material for solar cells. Outranked only by oxygen, silicon is also the second-most abundant element in the Earth's crust. However, to be useful as a semiconductor material in solar cells, silicon must be refined to a purity of 99.9999%.

In single-crystal silicon, the molecular structure—which is the arrangement of atoms in the material—is uniform, because the entire structure is grown from the same crystal. This uniformity is ideal for transferring electrons efficiently through the material. To make an effective PV cell, however, silicon has to be "doped" with other elements to make it n-type and p-type.

Semicrystalline silicon, in contrast, consists of several smaller crystals or grains, which introduce boundaries. These boundaries impede the flow of electrons and encourage them to recombine with holes to reduce the power output of the solar cell. However, semicrystalline silicon is much less expensive to produce than single-crystalline silicon. So researchers are working on other ways to minimize the effects of grain boundaries.

Single-Crystal Silicon
The most widely used technique for making single-crystal silicon is the Czochralski process, in which a seed of single-crystal silicon contacts the top of molten silicon. As the seed is slowly raised, atoms of the molten silicon solidify in the pattern of the seed and extend the single-crystal structure.

After growing the silicon ingot, we must saw it into thin wafers for further processing into PV cells.

To create silicon in a single-crystal state, we must first melt high-purity silicon. We then cause it to reform or solidify very slowly in contact with a single crystal "seed." The silicon adapts to the pattern of the single-crystal seed as it cools and gradually solidifies. Not surprisingly, because we start from a seed, we say that this process is "growing" a new rod (often called a "boule") of single-crystal silicon out of molten silicon.

Several different processes can be used to grow a boule of single-crystal silicon. The most established and dependable processes are the Czochralski (Cz)method and the float-zone (FZ) technique. We also discuss "ribbon-growth" techniques.

Wednesday, February 25, 2009

The Advantages of Using a Photovoltaic System

There are many unique advantages to using a photovoltaic system instead of a conventional power source. A photovoltaic system can be designed to be used in various applications. Some of the applications consist of operational requirements. A modular photovoltaic system is both transportable and expandable. Two attractive features of the photovoltaic system is environmental compatibility and energy independence. Another advantage of using the photovoltaic system is that there is no noise or pollution created when the system is in operation. The biggest advantage of installing a fully operational photovoltaic source is that sunlight is free energy. On top of all of the advantages, once installed, photovoltaic systems have reliable long service lifetimes that require a minimal amount of maintenance. This is a perfect energy resource that people all around the globe can use for all of their energy needs.

Tuesday, February 24, 2009

The Potential of Photovoltaic Energy

Each day that we walk the earth the sun is occupied with the task of delivering free energy to the earth and its inhabitants. Many people are realizing that this free energy or the technology of photovoltaic is able to generate electricity from the sun’s energy. The power of photovoltaic is phenomenal as this form of technology has the ability to harness and store an unlimited amount, from the Sun, of electrical energy.

The most awe-inspiring statistic is that there is enough solar radiation available in locations around the globe that can meet the need of the consumers increased demands for energy. Experts have proposed that the sun creates an amount of energy reaching the surface of the earth that can provide enough electricity to take care of the needs of annual energy consumption worldwide ten thousand times over.

To create the amount of energy needed to supply the globe’s energy needs the electricity generated by a photovoltaic system would use a modest electricity output per square meter of 100kWh. This means that the solar area that would be required in order to capture the energy would take up 150 x 150 km. The largest part of the photovoltaic capture area would have to be located on the walls or roofs of buildings. This is an advantage of photovoltaic energy because a capture area would not use extra land.

Monday, February 23, 2009

Energy Payback Time for Photovoltaic Technologies

The length of deployment that is required for a photovoltaic system is measured by the length of energy payback time. This means that a photovoltaic system must generate a total amount of energy that is equal to the amount of energy that is used to produce the electricity. According to engineer studies a low energy payback time is found with a roof mounted photovoltaic system.

Energy payback time is valued according to three different factors. The first factor is the amount of illumination or sunlight the system receives. The second factor is the way in which the photovoltaic system converts efficiency. The third factor deals with the type of manufacturing technology that is utilized to make solar or photovoltaic cells.

There are three approaches to the manufacturing of solar cells, commercially, according to developments in manufacturing technology. The most popular approach to processing discrete cells is by using silicon ingots in the form of wafers. The conductors or ingots is what develops the highly intensive energy process. The conductors are usually either multi or single crystalline.

A recent development in the approach of saving energy is the processing of discrete cells that originate from the multicrystalline ribbons. Another approach that has been developed is to deposit layers of silicon materials that are non-crystalline on a substrate that is inexpensive. The last mentioned approach is considered to be the least energy intensive of all of the manufacturing approaches for photovoltaic devices used for commercial purposes.

Another form of technology that is used in solar or photovoltaic energy uses amorphous silicon cells. The silicon cells are then deposited on ribbon made from stainless steel. Cells consisting of cadmium telluride is deposited onto glass. Then alloy cells made from copper indium gallium are deposited on stainless steel substrates or glass. These are some of the latest ways in which photovoltaic devices generate electricity. There have been recent studies that have established grid-tied EPBT systems, battery-free that are used when creating new and improved photovoltaic module technologies.

Friday, February 20, 2009

Information on Photovoltaic Physics

Literally, photovoltaic is translated to mean light-electricity. This is exactly what photovoltaic devices and materials do. These types of devices and materials are responsible for converting light energy into an electrical power resource. This type of energy system was first developed in the year 1839.Solar cells or photovoltaic cells (PV cells) are considered to be a device that produces electricity. Semiconductor material is what PV cells are made from. The PV cells range in size from smaller than a postage stamp to several feet long. Different sized PV arrays can be connected to modules in order to create power output. The factors that determine how much electricity is generated depends on the consumer’s needs and the amount of sunlight that is made available in a specific location. A Photovoltaic system consists of mounting hardware, electrical connections, batteries and power conditioning equipment. The batteries are used for the storing of solar energy so the power source produces electricity when the sun is not shining. There are numerous items that a PV system is a power source for. Some of the smaller items powered by solar power are wristwatches and calculators. Other items that can be powered through this energy source are appliances, water pumps, lights and communication satellites. In recent year’s traffic and road signs have been powered by photovoltaic energy. This is a very inexpensive form of electricity.To understand the physics of photovoltaic energy one must know that crystalline silicon is a very common material used as a conductor. The crystalline material is the chief material that converts the suns rays in to solar energy. The solar energy is created at an atomic level. As the material captures the sun’s rays energy is converted into cells. These cells are used to generate electricity to be either used right away or stored for later use when there is a demand.

Thursday, February 19, 2009

The Definition of Photovoltaics

Photovoltaic energy or a solar electric system generates electricity naturally and efficiently. To understand how photovoltaic power harnesses electricity one must first understand the basic underlying physics and the design of a photovoltaic device. This is a fully functional system that can be used as a renewable resource in generating electric power.

The DOE or the Solar Energy Technologies Program of the United States Department of Energy is constantly adding to the expertise and knowledge of the field of photovoltaic energy. As improvements are made in technology, in the field of solar energy, there is an abundance of power derived from the energy of the sun. Photovoltaic technology studies how the sun’s energy can essentially work for us as a power source.

Wednesday, February 18, 2009

Using Solar Energy in Your Home - Q & A

Can I get rid of the electric company?
Yes, but that is called off grid and not as cost effective as grid tied solar. With off grid you need a battery bank. Batteries are expensive and last about seven years at most. Think of the power company as a 100% efficient battery that never goes bad.

If the power goes out will a grid tied solar system produce electricity?
No, if you want electricity in the event of a power failure you need a hybrid system solar system with battery back- up or a back-up generator.

Can a grid tied solar system be installed somewhere other than a roof?
Yes, there are ground mounts, pole tops and trackers. Trackers follow the sun and produce up to 24% more electricity from the same amount of panels.

Will the electric company buy my excess if my system produces more than I use?
Yes, but they will pay you less than it is worth. A properly designed grid tied solar system will not produce more than you consume.

How long will a grid tied solar system last?
About 30 years. The panels themselves are typically warranted for 25 years.
How long does it take to have solar installed on my home?
Typically, a solar home installation can be completed within three to six weeks depending on the company installing the system.

How do we know if solar is right for our home?
Using specialized equipment, solar technicians can come to your home and take precision readings from your location and produce a report that will show any potential shading issues with your location. Although electricity from Photovoltaic (PV) systems is still more expensive than electricity from the utility grid, demand from PV technology systems has the potential to expand rapidly and become a significant part of the national energy supply, as additional advancements are made and grid parity is reached.

What are the key advantages of PV technology?
PV cells are modular and light, have no moving parts, have no direct impact on the environment and require minimal maintenance. In theory, they are available anywhere in the world, can be installed and operated in areas of difficult access and are an easy route to a power source for the developing world. In addition, they have a long life and durability as well as low operating costs.

What is the future potential of PV technology?
Photovoltaic electricity generation has a low energy density per hectare and its efficiency does not depend on the size of a photovoltaic plant. This makes it extremely suitable for a wide range of applications. Photovoltaic systems can be used in small, decentralized plants as well as in larger, central power plants; they can be built in sizes from cm2 up to km2 and can be used in many different types of locations.

Tuesday, February 17, 2009

Does the "Sunshine" State have a Sufficient Solar Resource to Support Solar Energy Applications?

While it is true that the desert southwest has the largest solar resource in the continental U.S., this does not mean that Florida has a poor resource. Consider the following map that compares the solar resource for 2-kilowatt photovoltaic residential applications across the entire U.S.:

This image comes from a study the Florida Solar Energy Center conducted on the performance of 2-kW photovoltaic (PV) systems installed on highly efficient homes across the country. The results capture all aspects of PV system performance, including the temperature effect on cell performance as well as the efficiency of the conversion from DC to AC power through the inverter. The map clearly shows that the desert southwest has the largest solar resource in the continental U.S., but Florida is not very far behind with 85% of the maximum PV resource of any location in the country (7.2 kWh/day out of a maximum of 8.5 kWh/day). Consumers should note that many parts of the country that have more state financial incentives have a much poorer solar resource, making Florida a very cost-effective location for using solar energy.

Monday, February 16, 2009

The Solar Industry Will Produce Millions of Jobs

With the rapid rise of the solar energy industry continues, job opportunities also begin to expand. The American Council for an Energy-Efficient Economy estimates that 1.1 million jobs could be created in the next 10 years through investments in energy efficiency technology. These jobs are contributing to the US economy as photovoltaic (PV) company’s site their manufacturing facilities near the expanding market grounds.

The US continues to be a fertile ground for the solar industry with many world leading solar companies taking up residence in the US. Many of the states continue to implement strong solar programs, further helping the US become a magnet for PV companies and manufacturers.

Outsourcing of solar manufacturing is not the way to go.

Manufacturing high quality technical products will ultimately raise the cost of solar panels. It is therefore important to have knowledgeable, experienced talent for the fabrication process and foreign labor in this area is not less expensive. Keeping solar manufacturing in the US not only will help lower the cost per kilowatt but also create millions of jobs for manufacturers, distributors and installers. Another benefit of keeping solar manufacturing domestic is the lower cost on shipping, thus further benefiting the environment. It creates a smaller carbon footprint of the product.

Friday, February 13, 2009

Using Fiber Lasers to Process Thin-Film Solar Cells

The solar industry as a whole has been looking at different opportunities to reduce the cost per watt of solar panel cells to make solar energy more cost efficient. Currently thin-film solar cells seem to be the most cost effective way to eliminate demand on limited fossil fuels. Many companies have reported $2.50/watt, others say that they can bring down the per watt cost to close to the one dollar mark. To become competitive, the cost per watt needs to be reduced to less than one dollar.

Current industry leaders are looking at fiber lasers to help make the one dollar per watt mark a near future reality. There are three major areas fiber lasers are reducing production costs of thin-film solar panels.

• Fiber lasers would be used to scribe through the various unaligned thin-film layers on glass or flexible substrates with high speed precision and less energy consumption than current methods. Fiber lasers offer the industry needed precision and control and allows solar cell manufacturers the ability to scribe through the thin-film layers without penetrating the substrate allowing for higher efficient manufacturing.

• Currently the thin-film devices are produced in very large sizes, approximately 1 meter square. These large thin film devices can be divided into 200 smaller electrically connected series. This subdivision and patterning would occur after each layer is deposited. Fiber laser systems are designed to control the depth of each scribe and create higher yields resulting in less waste. With the glass substrates as the base, fiber laser systems will also be able to take advantage of the substrate transparency and scribe from the rear.

• Fiber lasers can be used to mark the solar cells with alpha-numeric’s, barcodes and 2-D matrix to help track the solar cell and panels through its process. This is going to be a very important part of the entire solar industry and only fiber lasers will be able to mark these cells with the speed and efficiency needed.

The fast growing solar and fiber laser industries seem to be the perfect match for each other. The solar industry is trying to reduce the cost of creating solar panels while increasing energy and fiber laser systems are the most cost and energy efficient solution.