renewable energy?

3 Comments

1. partha.d s says:

   September 17, 2009 at 12:20 pm

   Solar Cell – Renewable and Cleanest Energy Source:

   Solar cell is a semiconductor device that converts the energy of sunlight into electric energy. These are also called ‘photovoltaic cell’. Solar cells do not use chemical reactions to produce electric power, and they have no moving parts.

   Photovoltaic solar cells are thin silicon disks that convert sunlight into electricity. These disks act as energy sources for a wide variety of uses, including: calculators and other small devices; telecommunications; rooftop panels on individual houses; and for lighting, pumping, and medical refrigeration for villages in developing countries. In large arrays, which may contain many thousands of individual cells, they can function as central electric power stations analogous to nuclear, coal-, or oil-fired power plants. Arrays of solar cells are also used to power satellites; because they have no moving parts that could require service or fuels that would require replenishment, solar cells are ideal for providing power in space.

   A. Most photovoltaic cells consist of a semiconductor pn junction, in which electron-hole pairs produced by absorbed radiation are separated by the internal electric field in the junction to generate a current, a voltage, or both, at the device terminals. Under open-circuit conditions (current I = 0) the terminal voltage increases with increasing light intensity, and under short-circuit conditions (voltage V = 0) the magnitude of the current increases with increasing light intensity. When the current is negative and the voltage is positive, the photovoltaic cell delivers power to the external circuit.

   B. Characteristics of a Solar Cell – The usable voltage from solar cells depend on the semiconductor material. In silicon it amounts to approximately 0.5 V. Terminal voltages is only weakly dependent on light radiation, while the current intensity increases with higher luminosity. A 100 cm² silicon cell, for example, reaches a maximum current intensity of approximately 2 A when radiated by 1000 W/m². The output (product of electricity and voltage) of a solar cell is temperature dependent. Higher cell temperatures lead to lower output, and hence to lower efficiency. The level of efficiency indicates how much of the radiated quantity of light is converted into useable electrical energy.

   C. Cell Types: One can distinguish three cell types according to the type of crystal: monocrystalline, polycrystalline and amorphous. To produce a monocrystalline silicon cell, absolutely pure semiconducting material is necessary. Monocrystalline rods are extracted from melted silicon and then sawed into thin plates. This production process guarantees a relatively high level of efficiency.

   The production of polycrystalline cells is more cost-efficient. In this process, liquid silicon is poured into blocks that are subsequently sawed into plates. During solidification of the material, crystal structures of varying sizes are formed, at whose borders defects emerge. As a result of this crystal defect, the solar cell is less efficient.
   If a silicon film is deposited on glass or another substrate material, this is a so-called amorphous or thin layer cell. The layer thickness amounts to less than 1µm (thickness of a human hair: 50-100 µm), so the production costs are lower due to the low material costs. However, the efficiency of amorphous cells is much lower than that of the other two cell types. Because of this, they are primarily used in low power equipment (watches, pocket calculators) or as facade elements.

   D. Efficiency: Solar cell efficiencies vary from 6% for amorphous silicon-based solar cells to 42.8% with multiple-junction research lab cells. Solar cell energy conversion efficiencies for commercially available multicrystalline Si solar cells are around 14-16%. The highest efficiency cells have not always been the most economical — for example a 30% efficient multijunction cell based on exotic materials such as gallium arsenide or indium selenide and produced in low volume might well cost one hundred times as much as an 8% efficient amorphous silicon cell in mass production, while only delivering about four times the electrical power.
   To make practical use of the solar-generated energy, the electricity is most often fed into the electricity grid using inverters (grid-connected PV systems); in stand alone systems, batteries are used to store the energy that is not needed immediately.

   E. Advantages of solar energy: Solar cells are long lasting sources of energy which can be used almost anywhere. They are particularly useful where there is no national grid and also where there are no people such as remote site water pumping or in space. Solar cells provide cost effective solutions to energy problems in places where there is no mains electricity. Solar cells are also totally silent and non-polluting. As they have no moving parts they require little maintenance and have a long lifetime. Compared to other renewable sources they also possess many advantages; wind and water power rely on turbines which are noisy, expensive and liable to breaking down.

   Rooftop power is a good way of supplying energy to a growing community. More cells can be added to homes and businesses as the community grows so that energy generation is in line with demand. Many large scale systems currently end up over generating to ensure that everyone has enough. Solar cells can also be installed in a distributed fashion, i.e. they don’t need large scale installations. Solar cells can easily be installed on roofs, which mean no new space is needed and each user can quietly generate their own energy.

   F. Disadvantages of solar cells: The main disadvantage of solar energy is the initial cost. Most types of solar cell require large areas of land to achieve average efficiency. Air pollution and weather can also have a large effect on the efficiency of the cells. The silicon used is also very expensive and the problem of nocturnal down times means solar cells can only ever generate during the daytime. Solar energy is currently thought to cost about twice as much as traditional sources (coal, oil etc). Obviously, as fossil fuel reserves become depleted, their cost will rise until a point is reached where solar cells become an economically viable source of energy. When this occurs, massive investment will be able to further increase their efficiency and lower their cost.

   For further information please refer
   http://www.environmentengineering.blogspot.com
2. wizz says:

   September 17, 2009 at 12:20 pm

   focusing on which area do you want to give your speech…..

   do you want to give it in any college or to invoke environmental awareness……. if in colleges . u can frankly speak the pros aswell as cons.. but in a awareness camp u wil have to suppress the practical hurdles in the way of solar.. coz once they hear that the people will stop listening to you..

   as a beginner you can go throught the below site which mainly gives only the pros of Solarr energy
   http://www.getsolar.com

   wikipedia is also a good source..

   solar technology mainly constitutes of solar panels+solar charge controller+battery +inverter

   there are different types of solar panels
   crystalline solar panels
   polycrystalline
   amorphous
   thin film nowadays into CIGS (copper Indium Gallium Selenide)
   and few Dye based in the lab..

   other
   is solar thermmal
   concentrated solar photovoltaic ( further in to solar sterling engines .. solar dish etc)

   efficiency of the solar energy not only depend up on the conversion of solar panels but also on the efficiency of batteries, inverters.. availability of sunlight etc..
   the system itself uses a percent of energy for conversion and transfer so the solar system is always sized to 30% more than required

   regarding panels in the market the most efficient crystalline panels have a conversion efficiency of 21.9%.. latest record is 23% but not in to the market

   still the thin films come to 7%

   concentrated solar is having more conversion efficiency but is applicable for power generation…not for household..

   solar thermal is also efficient but in large scale only..

   solar energy or wind energy though said green is not 100% green coz all these uses batteries which is a major constraint in increasing the solar cost and will have to replace 2-3 during 20-25 yers period of solar panel or up to 5 times in tropical and humid climates……… and most of these batteries are not recycleable.. there few and also few to enter market but they cost too much and if used solar or wind will never reach anywhere in the near future…

   solar is still a infant and has a long way to go… but to tell solar and hydrogen is the future of renewable energy. we have to wait another 25 years for solar to become feasible without rebates…. if any miracle did not happen……. also hydrogen is another one inlab eventhough many are experimenting few vehicles on road..

   lot of people have come ahead and experiment in many different ways to bring solar cost effecting… and if they are not really boasting like the people who did before then we can se soalr maturing very fast… but all those are in labs.. whichevr have told in 2 yrs awill only come out in 6-8 years if without any miracle…..

   concnetrated solar by magnifying the light is one such promising technology.. few companies including IBM is experimenting this….. the constraint there is the enormous heat generated when magnifying lights.. how to keep the materials cool is the major issue here.. as we need to reduce the area of usage. reduce silicon content and also improve efficiency..

   high cost is hindering growth of such energy forms as well as the storage technology is to improve a lot……

   conversion technology and generation are basic things and are same in all panels .. some chages in sterling, thermal and concentrated.. basics remains same

   dont belive what the sites have written……most are hypes..
   suppressing the practical constarints… for common people all these are far away..

   even rebates are given by indian govt.. i hope for above 10KW….
   solar or wind cannot be considered as a base form of energy,.. there always we need nuclear.. hydel or coal… all three are inevitebale… we cannot avoid nuclear from emotional point of view…. if we want our economy to grow.. we need energy we need power… good modes of transportation.. communication……. better roads…. everything…. there is no are where energ is coming in to accound…. as sai din bagwad gita or in energy conservation rule.. the trasformation from one to another takes place..
   all these big words about the green energy and green envirnon ment is due to the increase in price of oil.. which was the major element in the industrial revolution which has brought our world to this stage.. there is no energy utilized like oil.. all our growth was on that..and also will be for many more years.. but will have to pay more and more and more

   once the usage of our renewable forms of energy inceases.. the cost will strip down.. and a stage will come where it is competetive in few areas which will reduce the current demand of oil and hence its price a bit…. but still the run fo oil wont be over when price is les more coutries will be able to afford and increse its demand…. so the oil run will be a roution from now… big nations can afford and run solar.. but if they use it more effectively the pric eof solar will come to standstiill or less which will be utilized by energy hungry countries like our India and neighbouring china for their growth.. this something which the others dont want

   what we can help is the unwanted usage and wastage of our resources… awareness is to be made in area.. to one and all… the real awareness shouldbe focussed here..

   dear the average enrgy generated depend on the .. requirement all components solar energy is costly and will be sized according to the requirement…
   a 100watt panels generates 100 watts at peak ie at noon time.. when there is maximum sunlight.. so it depends how many equipments u want to run on these.. also what is the area available 4 u at ur rooftop or at ur backyard.. its like u have proper sunshine for say 6 hours in ur area so the generation will be 600W in a day… te generation at other time will be very less..
   the amorphous silicon panels are effective in this matter.. they keeps generating with lesser light also.. if u have more area u can go for a-silicon panels or thin sheets.. coz the efficiency is less.. so to generate same amount of energy u need larger area of such panels than the crystalline ones
   with 100W ..u can light a 100W bulb for max one hr..
3. Shadow Guy says:

   September 17, 2009 at 12:20 pm

   http://www.greenwithfreedom.com