Cost Boundary in Silicon Solar Panel
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International Journal of Chemical Engineering and Applications, Vol. 2 , No. 5 , October 2011 Cost Boundary in Silicon Solar Panel V.K.Sethi, Mukesh Pandey, and Priti Shukla high-efficiency, high-output concentrator solar cells work in Abstract—Photovoltaic is a solar power technology that uses areas with minimal cloud cover, independent of temperature solar cells or solar photovoltaic arrays to convert light directly or latitude into electricity with no emission of dangerous gases and with Most solar-cell technology is silicon based. There are least amount of industrials waste. Solar cells are a key three primary types of silicon solar cells, each named after technology in the drive toward cleaner energy production. the crystalline structure of the silicon used during Unfortunately, solar technology is not yet economically competitive and the cost of solar cells needs to be brought fabrication: down. Growth of the photovoltaic (PV) market is still • Mono-crystalline silicon has a single and continuous constrained by high initial capital costs of PV. One way to crystal lattice structure with practically zero defects or overcome this problem is to reduce the amount of expensive impurities. semiconductor material used. The materials cost and manufacturing cost of thin-film solar is much lower than wafer • Poly-crystalline silicon, also called poly-silicon, comprises based and drops much faster than wafer based in large-scale discrete grains, or crystals, of mono-crystalline silicon that manufacturing, but thin-film solar cells tend to have lower create regions of highly uniform crystal structures performance compared with conventional solar cells. separated by grain boundaries. Developments in PV technologies may lead to cheaper systems at the likely expense of life expectancy and efficiency. Cost • Amorphous silicon is an entirely non-crystalline form of boundaries are required for future PV technologies to compete silicon that can be thought of as grains the size of the effectively within the current PV market.[ B. Azzopardi, 1 individual atoms. ].Micro- and nano-enabled thin-film photovoltaics provide an Crystalline Si’s relatively high efficiency has, however, a attractive-and increasingly cost-competitive-clean-tech negative correlation with temperature. The hotter it gets, the alternative to carbon-based energy solution. less electricity it produces. Most crystalline Si solar cells decline in efficiency by 0.50%/°C. Thus, it is particularly Index Term—Nanodefect, Nanowire, Breakthroughs suitable for cooler climates. Mono crystalline Si wafers, cut from grown cylindrical ingots, make the most productive cells, with efficiencies I. INTRODUCTION ranging from 20-24%. The crystal lattice is continuous and As more people become aware of the problems associated there are no grain boundaries. Polycrystalline Si wafers are with greenhouse-gas emissions, the demand for sources of cut from cast, square ingots. Due to the presence of grain clean energy goes up. As the demand for high-quality solar- boundaries, they achieve about half the efficiency of single- cell feedstock exceeds supply and drives prices upwards, crystal cells. Many commercialized solar cells incorporate cheaper but dirtier alternative feedstock materials are being amorphous silicon and poly-silicon, which have acceptable developed [Tonio Buonassis2]. c-Si has the advantage of conversion efficiency and cost much less than mono- maturity, material stability, the highest conversion crystalline silicon. efficiencies (the percentage of the sun’s energy converted into electricity), and an already-established global manufacturing infrastructure. But, thin-film PV has many advantages, too: It is lightweight, requires relatively minuscule amounts of active semiconducting materials, and can be applied on a variety of substrates, including plastics, flexible steel, composites, and building materials. High- relatively minuscule amounts of active semiconducting materials, and can be applied on a variety of substrates, including plastics, flexible steel, composites, and building Fig. 1 Schematic illustration of a silicon solar cell (a-Si:H) sandwiched between aluminum (Al) and transparent indium tin oxide (ITO) electrical materials. High-efficiency crystalline silicon cells are well contacts. Aluminum nanoparticles on the top (gray) enhance the absorption suited for cooler, high-latitude environments. Thin films are of light. more cost effective in warmer, brighter climates, while very The process developed by Naseem, known as topdown aluminum-induced crystallization, creates poly-silicon with crystal grains 30 times larger than grains currently produced Manuscript received March 28, 2011, revised September 19, 2011. Dr. V. K. Sethi is with HOD Energy, School of Energy Environment & in the photovoltaic industry. Standard poly-silicon contains Management , U.I.T, R.G.P.V. Bhopal, India. grains of 0.5 to 1 micrometer, which is one-100th the Dr. Mukesh Pandey is with School of Energy Environment & diameter of a human hair. Naseem’s process yielded a grain Management , U.I.T, R.G.P.V. Bhopal, India. Ms. Priti Shukla is with Technocrate Institute of Technology, Bhopal, size up to 150 micrometers, which is important because the India. (e-mail: [email protected], Mobile: 9893135065). performance of a photovoltaic device is limited primarily by 372 International Journal of Chemical Engineering and Applications, Vol. 2 , No. 5 , October 2011 defects at the boundaries of crystal grains. Increasing the feedstock, the development of low-cost ‘solar-grade silicon’ size of crystal grains decreases the number of boundaries. (SoG-Si) has been proposed, which contains much higher Traditional processing of silicon-based cells requires a concentrations of deleterious transition metal impurities. heating temperature of 1,000 degrees Celsius to cause the Many studies have shown that transition metals can silicon to reach a crystalline state. Naseem’s method of decrease the minority carrier diffusion length—a key converting amorphous silicon into poly-silicon can be done parameter for determining the efficiency of solar-cell at temperatures between 100 and 300 degrees Celsius, devices. An entirely new approach is needed to make cost- which saves time, materials and energy effective solar cells from low-cost, abundant, but impurity- rich feedstock. The concept proposed in this study opens a new and II. MANUFACTURING COST OF SOLAR CELL exciting opportunity to recover low quality silicon for A. Monocrystalline Cells commercially viable solar-cell material. This concept is not necessarily limited to annealing, it could also be extended to Monocrystalline cells are the most costly from a appropriate engineering during crystal growth. As material manufacturing standpoint. The raw material is expensive performance is vary on the distribution of the interstitial and there are a limited number of manufacturers. With metals, metal clusters and metal precipitates, and not only rectangular wafers cut from cylindrical ingots, there is a by total metal concentrations, even heavily contaminated substantial waste of refined Si. Improved manufacturing techniques are making wafers thinner and larger, and materials can show dramatic enhancements through optimized gridlines are obscuring less surface area, nanodefect engineering. The defect engineering could be improving efficiencies. Techniques for roughening the complemented by the existing solar-cell processing surface area, including building pyramidal structures, techniques such as gettering or hydrogen passivation, which increase the effective surface area as well. Si ink can be expected to improve the material performance. Even technologies can also incrementally improve cell efficiency. further metal-rich SoG-Si, which would be much cheaper and far more abundant than current silicon feedstock B. Polycrystalline Cells material, has the real potential to produce cost-effective Polycrystalline Si is much less expensive to produce; solar cells, provided metal nanodefects are engineered wafers are cut from large, rectangular blocks produced by correctly.[ Tonio Buonassisi 2]. carefully cooling and solidifying molten Si. In the market, there is a definite trend towards polycrystalline products as technological advances lessen the effects of grain IV. SOLAR CELLS CAN BE MADE THINNER AND LIGHTER boundaries. Sun Power, the world’s largest producer of Si WITH THE HELP OF ALUMINUM PARTICLES solar cells, has set records with its monocrystalline Metallic nanoparticles can direct light better into the solar technology, recently achieving 24.2% efficiency. However, cell and prevent light from escaping. In conventional ‘thick- Sun Power is increasingly investing in its polycrystalline film’ solar cells, the nanoparticles would have little effect product lines, anticipating the need to meet skyrocketing because all the light is absorbed by the film due to its demands with lower-cost manufacturing solutions. thickness. For thin films, however, the nanoparticles can C. Thin Films make a big difference. Their scattering increases the Thin-film photovoltaic solutions are gaining ground duration the light stays in the film, bringing the total quickly and are expected to capture up to 30% of solar panel absorption of light up to a level comparable with that for market share by 2013 . Production costs are significantly conventional solar cells. The strategy allows us to reduce less than with crystalline products for a variety of reasons: the production costs of solar