December 21, 2009
By: Admin
Category: Solar Cells
Glitter-sized Solar Photovoltaics Produce Competitive Results
Adventures in microsolar supported by microelectronics and MEMS techniques
Representative thin crystalline-silicon photovoltaic cells – these are from 14 to 20 micrometers thick and 0.25 to 1 millimeter across.
Sandia National Laboratories scientists have developed tiny glitter-sized photovoltaic cells that could revolutionize the way solar energy is collected and used.
The tiny cells could turn a person into a walking solar battery charger if they were fastened to flexible substrates molded around unusual shapes, such as clothing.
The solar particles, fabricated of crystalline silicon, hold the potential for a variety of new applications. They are expected eventually to be less expensive and have greater efficiencies than current photovoltaic collectors that are pieced together with 6-inch- square solar wafers.
The cells are fabricated using microelectronic and microelectromechanical systems (MEMS) techniques common to today’s electronic foundries.
Sandia lead investigator Greg Nielson said the research team has identified more than 20 benefits of scale for its microphotovoltaic cells. These include new applications, improved performance, potential for reduced costs and higher efficiencies.
“Eventually units could be mass-produced and wrapped around unusual shapes for building-integrated solar, tents and maybe even clothing,” he said. This would make it possible for hunters, hikers or military personnel in the field to recharge batteries for phones, cameras and other electronic devices as they walk or rest.
Sandia project lead Greg Nielson holds a solar cell test prototype with a microscale lens array fastened above it. Together, the cell and lens help create a concentrated photovoltaic unit.
Even better, such microengineered panels could have circuits imprinted that would help perform other functions customarily left to large-scale construction with its attendant need for field construction design and permits.
Said Sandia field engineer Vipin Gupta, “Photovoltaic modules made from these microsized cells for the rooftops of homes and warehouses could have intelligent controls, inverters and even storage built in at the chip level. Such an integrated module could greatly simplify the cumbersome design, bid, permit and grid integration process that our solar technical assistance teams see in the field all the time.”
For large-scale power generation, said Sandia researcher Murat Okandan, “One of the biggest scale benefits is a significant reduction in manufacturing and installation costs compared with current PV techniques.”
Part of the potential cost reduction comes about because microcells require relatively little material to form well-controlled and highly efficient devices.
From 14 to 20 micrometers thick (a human hair is approximately 70 micrometers thick), they are 10 times thinner than conventional 6-inch-by-6-inch brick-sized cells, yet perform at about the same efficiency.
100 times less silicon generates same amount of electricity
“So they use 100 times less silicon to generate the same amount of electricity,” said Okandan. “Since they are much smaller and have fewer mechanical deformations for a given environment than the conventional cells, they may also be more reliable over the long term.”
Another manufacturing convenience is that the cells, because they are only hundreds of micrometers in diameter, can be fabricated from commercial wafers of any size, including today’s 300-millimeter (12-inch) diameter wafers and future 450-millimeter (18-inch) wafers. Further, if one cell proves defective in manufacture, the rest still can be harvested, while if a brick-sized unit goes bad, the entire wafer may be unusable. Also, brick-sized units fabricated larger than the conventional 6-inch-by-6-inch cross section to take advantage of larger wafer size would require thicker power lines to harvest the increased power, creating more cost and possibly shading the wafer. That problem does not exist with the small-cell approach and its individualized wiring.
From left to right, Sandia researchers Murat OKandan, Greg Nielson, and Jose Luis Cruz-Campa, hold samples containing arrays of microsolar cells.
Other unique features are available because the cells are so small. “The shade tolerance of our units to overhead obstructions is better than conventional PV panels,” said Nielson, “because portions of our units not in shade will keep sending out electricity where a partially shaded conventional panel may turn off entirely.”
Because flexible substrates can be easily fabricated, high-efficiency PV for ubiquitous solar power becomes more feasible, said Okandan.
A commercial move to microscale PV cells would be a dramatic change from conventional silicon PV modules composed of arrays of 6-inch-by-6-inch wafers. However, by bringing in techniques normally used in MEMS, electronics and the light-emitting diode (LED) industries (for additional work involving gallium arsenide instead of silicon), the change to small cells should be relatively straightforward, Gupta said.
Each cell is formed on silicon wafers, etched and then released inexpensively in hexagonal shapes, with electrical contacts prefabricated on each piece, by borrowing techniques from integrated circuits and MEMS.
Offering a run for their money to conventional large wafers of crystalline silicon, electricity presently can be harvested from the Sandia-created cells with 14.9 percent efficiency. Off-the-shelf commercial modules range from 13 to 20 percent efficient.
A widely used commercial tool called a pick-and-place machine — the current standard for the mass assembly of electronics — can place up to 130,000 pieces of glitter per hour at electrical contact points preestablished on the substrate; the placement takes place at cooler temperatures. The cost is approximately one-tenth of a cent per piece with the number of cells per module determined by the level of optical concentration and the size of the die, likely to be in the 10,000 to 50,000 cell per square meter range. An alternate technology, still at the lab-bench stage, involves self-assembly of the parts at even lower costs.
Solar concentrators — low-cost, prefabricated, optically efficient microlens arrays — can be placed directly over each glitter-sized cell to increase the number of photons arriving to be converted via the photovoltaic effect into electrons. The small cell size means that cheaper and more efficient short focal length microlens arrays can be fabricated for this purpose.
High-voltage output is possible directly from the modules because of the large number of cells in the array. This should reduce costs associated with wiring, due to reduced resistive losses at higher voltages.
Other possible applications for the technology include satellites and remote sensing.
The project combines expertise from Sandia’s Microsystems Center; Photovoltaics and Grid Integration Group; the Materials, Devices, and Energy Technologies Group; and the National Renewable Energy Lab’s Concentrating Photovoltaics Group.
Involved in the process, in addition to Nielson, Okandan and Gupta, are Jose Luis Cruz-Campa, Paul Resnick, Tammy Pluym, Peggy Clews, Carlos Sanchez, Bill Sweatt, Tony Lentine, Anton Filatov, Mike Sinclair, Mark Overberg, Jeff Nelson, Jennifer Granata, Craig Carmignani, Rick Kemp, Connie Stewart, Jonathan Wierer,
George Wang, Jerry Simmons, Jason Strauch, Judith Lavin and Mark Wanlass (NREL).
The work is supported by DOE’s Solar Energy Technology Program and Sandia’s Laboratory Directed Research & Development program, and has been presented at four technical conferences this year.
The ability of light to produce electrons, and thus electricity, has been known for more than a hundred years.
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August 29, 2009
By: Admin
Category: Solar Cells
Solar Photovoltaic: Future Energy Sources
In general, energy sources are categorized into two parts namely non-renewable energy and renewable energy. Fossil energy sources are among the first group that the bulk of activity in the world using these conventional energy.
It is no doubt that the solar photovoltaic is one source of environmentally friendly energy and is very promising in the future, because there is no pollution produced during the process of energy conversion, and more widely available source of energy in nature, namely the sun.
Fundamental issues in solar cell technology is a very low efficiency in turning solar energy into electrical energy, which to date the highest efficiency can be achieved no more than 20%, and even then in a laboratory scale.
For that in developed countries, research on solar cell is a very big concern, especially with the issue of environmental clean.
From light into electricity
In a simple solar photovoltaic consists of the p-type and n junction semiconductor material (pn junction semiconductor) that if by the sun there will be a flow of electrons, electron flow is well known as the electric current flow. While the structure of the solar cell is as shown in Figure 1.
Figure 1. Structure of a thin layer of solar photovoltaic in general
The main part of the energy changes of sunlight to electricity is the absorber, however, each layer is also very influential on the efficiency of the solar cell. Sunlight consists of various types of electromagnetic waves in a spectrum can be seen in figure 2. Therefore here absorber is expected to absorb as much solar radiation derived from sunlight.
Figure 2. The spectrum of solar radiation
More detail can be explained that the sun consists of a photon-photon, if it happen to solar cell surface material (absorber), will be absorbed, reflected or simply passed (see Figure 3), and only photons with certain energy level that will liberate electrons from atomic bonds, so that electrical current flows. Energy levels is called band-gap energy which is defined as the amount of energy required to discharge electrons out of its covalent bond so that there electric current flow. To free electron from its covalent bond, photon energy (hc/v) must be slightly larger or above than the band-gap energy. If the photon energy is too much of the energy band-gap, then the extra energy will be converted in the form of heat in a solar cell. Therefore it is important to the solar cell to regulate the materials used, namely by modifying the molecular structure of the semiconductor used.
Figure 3. Radiative transition of solar photovoltaic
Of course, that the efficiency of solar cell can be high if the photons from sunlight to be absorbed that as much, then reduce reflection and increase recombination and conductivity of the material.
To be able to make that a photon is absorbed can be as much, then the absorber must have an energy band-gap with a wide range, making it possible to absorb sunlight so energy has a variety of these. One of the many materials being studied are known CuInSe2 is one of the direct semiconductor.
So many advantages of solar photovoltaic as described above was not a polemic and not just stop, saying there was a solar photovoltaic is true when the energy change process there is no pollution produced, but have we calculated how much pollution has been generated in the process manufacturing, small compared to the resulting efficiency. Now the challenge here is indeed how to increase efficiency, which would affect its economic value.
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June 03, 2009
By: Admin
Category: General
Solar Products
Solar products are easily installed and do not require any wire hookup. You can move them around as the seasons change or as you experiment with different looks to your garden, paths, flowerbeds, pool, deck or dock. Consider solar powered path lights for a beautiful incandescent effect on your garden path. How about some gentle solar garden lights for the highlights in your garden – or a cluster of solar light sticks for a beautiful effect. Solar patio lights make your outdoor gathering space warm and inviting and most come with both amber and white light settings. Solar pool lights create an exquisite effect as they float on either pool or pond, throwing a soft glow onto the water’s surface. Solar power can also do the job when more direct lighting is required: for instance a solar flood light provides strong illumination for security and solar post lights provide a classic look but can also provide strong white light if needed.
Solar products are innovative mechanisms that help conserve energy, thus, help maintain the ecosystem. Solar products are environmentally friendly and are usually cost effective as well. Today, there are several solar power products in the market for our home and office use. Solar products include items such as solar hot water heaters, solar heating systems, solar panels, solar flashlights, small radios, solar calculators, solar battery chargers, solar lanterns, solar lighting, solar car batteries and much more.
Solar products are perfect for campers, hikers or anyone who spends lots of time outdoors. Thin-film photovoltaic technology is perfect for charging many consumer products, solar cell designs are a proven success currently being used in space, military equipment, and large grid systems.
Solar products are currently growing at over 25% annually. Sales of thin film solar products are growing at over 33% annually. Most analysts project that thin film solar markets will continue to grow faster than traditional silicon wafer markets. In order for the solar industry to supply the amount of solar product needed to meet market demand, exponential growth rates will become endemic for at least the next decade.
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June 03, 2009
By: Admin
Category: General
New Solar Technology Trends Around the World
Executive Summary about Solar Technology by Philip Richards
In the business of solar energy, the U.S. has not been the biggest buyer of solar power. While the U.S. does quite well exporting solar panels and solar technology, there are many Americans who still find the cost of panels very prohibitive. As the price of solar energy decreases, Europe has had a much higher demand for solar power than anywhere else in the world. Many European universities and campuses have rebuilt their dorms to run off solar energy. Most water heaters in Europe are solar-powered, even if the home doesn’t have a full solar panel system.
In Europe, it’s not just small residential power systems that are leading the way in solar energy dependence. Specifically, Italy, Greece and the Czech Republic are the newest customers of solar power systems. These countries have begun to purchase so much solar energy that their borders have seen changes in tariffs for solar panels. Japan, who’s also been at the forefront of solar panel imports, has picked up solar panel buying as the cost of gas and electricity rises. There are entire neighborhoods in Japan outfitted with residential solar power panels. For example, the neighborhood of Iwaki New Town has about 46 homes outfitted with full private solar power panels. Japan also uses solar energy in surprising places. Japan is the only country to power most of its vending machines with solar energy. Sharp, one of the largest solar panel producing companies in Japan estimates that by 2010, Japan will produce 4.8 million kWh of solar energy.
The Race For New Solar Technology Is On
Executive Summary about Solar Technology by Winifred Churchill
Companies around the world are beginning to seriously consider the POWER of solar power.
- In Mexico a solar dish is being tested. The expanding and contracting hydrogen gas drives pistons which power a generator which creates electricity.
- A new thin-film technology is being used on the windows of high-rise apartment buildings and skyscrapers to collect the sun’s power for use in the buildings. It is attractive and not nearly as expensive as regular solar panels.
- Thin-film is attracting major manufacturers around the world.
- New solar technology is using crystalline silicon cells for solar power panels.
One criticism of solar energy is that it cannot be relied upon for a steady supply of energy, but there are projects underway which are addressing that issue. In short, solar technology is going the way of the computer industry or cell phones. Now you get the same functionality available in personal computers on tiny cell phones. The new silicon cells for solar panels may bring a similar revolution to solar power making it a reliable, clean source of energy.
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