Solar power – Sustainable green energy to protect our economy and environment BY PARTHA DAS SHARMA

1. Introduction - Originally developed for energy requirement for orbiting earth satellite – Solar Power – have expanded in recent years for our domestic and industrial needs. Solar power is produced by collecting sunlight and converting it into electricity. This is done by using solar panels, which are large flat panels made up of many individual solar cells. It is most often used in remote locations, although it is becoming more popular in urban areas as well.

There is, indeed, enormous amount of advantages lies with use of solar power specially, in the context of environmental impact and self-reliance. However, a few disadvantages such as its initial cost and the effects of weather conditions, make us hesitant to proceed with full vigor. We discuss below the advantages and disadvantages of Solar Power:

2. Advantages of Solar power -

(a) The major advantage of solar power is that no pollution is created in the process of generating electricity. Environmentally it the most Clean and Green energy. Solar Energy is clean, renewable (unlike gas, oil and coal) and sustainable, helping to protect our environment.

(b) Solar energy does not require any fuel.

(c) It does not pollute our air by releasing carbon dioxide, nitrogen oxide, sulfur dioxide or mercury into the atmosphere like many traditional forms of electrical generation does.

(d) Therefore Solar Energy does not contribute to global warming, acid rain or smog. It actively contributes to the decrease of harmful green house gas emissions.

(e) There is no on-going cost for the power it generates – as solar radiation is free everywhere. Once installed, there are no recurring costs.

(f) It can be flexibly applied to a variety of stationary or portable applications. Unlike most forms of electrical generation, the panels can be made small enough to fit pocket-size electronic devices, or sufficiently large to charge an automobile battery or supply electricity to entire buildings.

(g) It offers much more self-reliance than depending upon a power utility for all electricity.

(h) It is quite economical in long run. After the initial investment has been recovered, the energy from the sun is practically free. Solar Energy systems are virtually maintenance free and will last for decades.

(i) It’s not affected by the supply and demand of fuel and is therefore not subjected to the ever-increasing price of fossil fuel.

(j) By not using any fuel, Solar Energy does not contribute to the cost and problems of the recovery and transportation of fuel or the storage of radioactive waste.

(k) It’s generated where it is needed. Therefore, large scale transmission cost is minimized.

(l) Solar Energy can be utilized to offset utility-supplied energy consumption. It does not only reduce your electricity bill, but will also continue to supply your home/ business with electricity in the event of a power outage.

(m) A Solar Energy system can operate entirely independently, not requiring a connection to a power or gas grid at all. Systems can therefore be installed in remote locations, making it more practical and cost-effective than the supply of utility electricity to a new site.

(n) The use of solar energy indirectly reduces health costs.

(o) They operate silently, have no moving parts, do not release offensive smells and do not require you to add any fuel.

(p) More solar panels can easily be added in the future when your family’s needs grow.

(q) Solar Energy supports local job and wealth creation, fuelling local economies.

3. Disadvantages of Solar power –

(a) The initial cost is the main disadvantage of installing a solar energy system, largely because of the high cost of the semi-conducting materials used in building solar panels.

(b) The cost of solar energy is also high compared to non-renewable utility-supplied electricity. As energy shortages are becoming more common, solar energy is becoming more price-competitive.

(c) Solar panels require quite a large area for installation to achieve a good level of efficiency.

(d) The efficiency of the system also relies on the location of the sun, although this problem can be overcome with the installation of certain components.

(e) The production of solar energy is influenced by the presence of clouds or pollution in the air. Similarly, no solar energy will be produced during nighttime although a battery backup system and/or net metering will solve this problem.

(f) As far as solar powered cars go – their slower speed might not appeal to everyone caught up in today’s fast track movement.

4. Solar Cell – 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.

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.

* 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.

* 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.

* 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.

* Advantages of solar cells: 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.

* 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.

5. Nanoparticle with carbon nanotubes based solar cells – more efficient and practical -Experts have demonstrated a way to significantly improve the efficiency of solar cells made using low-cost, readily available materials, including a chemical commonly used in paints. The researchers added single-walled carbon nanotubes to a film made of titanium-dioxide nanoparticles. This process doubles the efficiency of cell for converting ultraviolet light into electrons when compared with the performance of the nanoparticles alone. Titanium oxide is a main ingredient in white paint.

Such cells are appealing because nanoparticles have a great potential for absorbing light and generating electrons. But so far, the efficiency of actual devices made of such nanoparticles has been considerably lower than that of conventional silicon solar cells. That’s largely because it has proved difficult to harness the electrons that are generated to create a current. In fact, when electrons generated by absorbing light by titanium –oxide, absence of carbon nanotubes with the titanium-oxide particles make the electrons jump from particle to particle before reaching an electrode. On the path many electrons do not able to reach the electrode, thus fail to generate an electrical current. The carbon nanotubes “collect” the electrons and provide a more direct route to the electrode, improving the efficiency of the solar cells.

The new carbon-nanotube with titanium –oxide nanoparticle system is not yet a practical solar cell, as titanium oxide only absorbs ultraviolet light; most of the visible spectrum of light is reflected rather than absorbed. Researchers have also demonstrated ways to modify the nanoparticles to absorb the visible spectrum.

Several other groups of researchers are exploring approaches to improve the collection of electrons within a cell, including forming titanium-oxide nanotubes or complex branching structures made of various semiconductors. Using carbon nanotubes as a conduit for electrons from titanium oxide is a novel idea, and once it is successful the cheaper variety of efficient solar cells can be developed.

More research is needed towards development of efficient solar cells, as solar energy is renewable, clean and unlike grain based bio-fuel, solar energy is not agriculture based thus do not utilize farm land and do not hamper food production.

6. Desert Solar Power – Future of environmentally clean and sustainable Energy -

A recent renewed interest in alternative energy technologies has revitalized interest in solar thermal technology, a type of solar power that uses the sun’s heat rather than its light to produce electricity. Although the technology for solar thermal has existed for more than two decades, projects have languished while fossil fuels remained cheap. But solar thermal’s time may now have come — and mirrored arrays of solar thermal power plants, hopefully, will soon bloom in many of the world’s deserts.

Large desert-based power plants concentrate the sun’s energy to produce high-temperature heat for industrial processes or to convert the solar energy into electricity. It is quite interesting to note that, as per the recent reports on Solar Power, the resource calculations show that just seven states in the U.S. Southwest can provide more than 7 million MW of solar generating capacity, i.e., roughly 10 times that of total electricity generating capacity of U.S. today from all sources.

In US, as per report, four more concentrating solar technologies are being developed. Till now, parabolic trough technology (i.e., tracking the sun with rows of mirrors that heat a fluid, which then produces steam to drive a turbine) used to provide the best performance at a minimum cost. With this technology, as per the report, since the mid-1980s nine plants, totaling about 354 MW, were operating reliably in California’s Mojave Desert. Natural gas and other fuels provide supplementary heating when the sun is inadequate, allowing solar power plants to generate electricity whenever it is needed. In addition, in order to extend the operating times of solar power plants new heat-storing technologies are being developed as well.

Realizing the advantages of solar energy and seeing the success of desert solar power installed, several solar power plants are now being planned in the U.S. Southwest. Renewed Governmental supports and rising fossil fuel prices including natural gas, lead to new interest in concentrating solar power among many entrepreneurs. Efficiency of concentrating solar technologies has also been improved substantially, since then. While earlier trough plants needed a 25 percent natural gas-fired backup, the new improved plants will require only about 2 percent backup. As per recent news in US, utilities in states with large solar resources such as Arizona, California, Nevada, and New Mexico etc., are considering installation of solar dish systems on a larger scale. As per the latest estimation, within the next decade more than 4,000 MW of central solar plants will be installed. It’s quite encouraging!!

Concentrating Solar Technologies -

(i) Parabolic trough technologies track the sun with rows of mirrors that heat a fluid. The fluid then produces steam to drive a turbine.

(ii) Central receiver (tower) systems use large mirrors to direct the sun to a central tower, where fluid is heated to produce steam that drives a turbine. Parabolic trough and tower systems can provide large-scale, bulk power with heat storage (in the form of molten salt, or in hybrid systems that derive a small share of their power from natural gas).

(iii) Dish systems consist of a reflecting parabolic dish mirror system that concentrates sunlight onto a small area, where a receiver is heated and drives a small thermal engine.

(iv) Concentrating photovoltaic systems (CPV) use moving lenses or mirrors to track the sun and focus its light on high-efficiency silicon or multi-junction solar cells; they are potentially a lower-cost approach to utility-scale PV power. Dish and CPV systems are well suited for decentralized generation that is located close to the site of demand, or can be installed in large groups for central station power.

7. Development of new technology making solar power economically competitive -

We all know that solar power is excellently exhilarating. Just put a sheet or a panel exposing sun and everyday, for total life span of the device, we get power at free of cost. No fuel, no maintenance botheration and no cost incurred. It is a renewable resource – no raw material requirement. Sun may disappear behind a few clouds for a few minutes, disappear completely at night, or for hours during the winter, we can always expect it to come back in full force. Apart, solar power is completely non-polluting, green sustainable energy – throughout its life – free. Unlike oil, solar power does not emit any greenhouse gases into the atmosphere. It is silent powered – no noise pollution.

There are so many advantages of solar power. Unfortunately, the size of the initial investment keeps the cost of solar generated power higher than the cost of coal. It may be worth noting here that, if environmental costs of burning coal taken into account, the solar power is already slightly more economical. But we are not taxing carbon (yet) so we have to make solar power cheaper. At present, solar cells are not cheap. However, technology is improving, and it will continue to improve as the cost of other forms of power increase. There are few of the finest examples that are working to bring solar power to at par with grid. Below some of these technologies are briefed:

a. Most expensive part of a traditional photovoltaic array is the silicon wafers. To solve this cost problem (and also the problem of the environmentally wasteful process of creating the silicon crystals) several people are concentrating the sunlight thousands of times onto an extremely small solar panel. They decrease the amount of solar material needed by thousands of times, and produce just as much power.

Technologies collectively known as concentrating photovoltaic are starting to enjoy their day in the sun, thanks to advances in solar cells, which absorb light and convert it into electricity, and the mirror- or lens-based concentrator systems that focus light on them. The technology could soon make solar power as cheap as electricity from the grid. The idea of concentrating sunlight to reduce the size of solar cells – and therefore to cut costs -has been around for decades. The result is solar power that is nearly as cheap (if not as cheap) as coal.

The thinking behind concentrated solar power is simple. Because energy from the sun, although abundant, is diffuse, generating one gigawatt of power (the size of a typical utility-scale plant) using traditional photovoltaic requires a four-square-mile area of silicon. A concentrator system would replace most of the silicon with plastic or glass lenses or metal reflectors, requiring only as much semiconductor material as it would take to cover an area of much smaller in size. Moreover, because of decrease in the amount of semiconductor needed makes it affordable to use much more efficient types of solar cells. The total footprint of such plant, including the reflectors or lenses, would be only two to two-and-a-half square miles.

The big problem of this technology is very hot piece of silicon. You have to keep the silicon cool, even with sunlight magnified 2000 times on it. Otherwise the silicon will melt, and it’s all over. Scientists are working prototypes already and are hoping to go commercial in the coming years.

b. Another solution to the problem of limited and expensive crystalline silicon is to just not use it. This is why there are so many solar startups right now working on solar technology using non-crystalline silicon or other thin-film solutions. Many have already broken out of the lab and into manufacturing. One of the leading technologies, not using expensive crystalline silicon is ‘Nano-solar’ prints. Nano-solar prints it’s mixture of several elements in precise proportions onto a metal film. The production is fast, simple and cheap, at least for now. Some fear that shortages in indium will bring a halt to nano-solar’s cheap printing days. Though scientists make some efficiency sacrifices when compared to crystalline silicon, they are so much cheaper to produce that they might soon even beat coal in cost per watt.

The advantages of ‘Nano-solar’ prints are, they are super cheap, ultra-adaptable solar panels that can be printed on the side of pretty much anything, promising solar power anywhere you want it. At the present condition, they still slide under coal’s $2.1-a-watt energy cost, though they’re not mass produced at the scale needed to bring it to the 30-cents-a-watt level.

c. While the first two options provide the most efficient path to solar electricity, but converting photons directly into electrons, a less efficient, though simpler, option might turn out to be the real cost-effective. Simply by focusing hundreds or even thousands of mirrors onto a single point, scientists are hoping to create the kind of heat necessary to run a coal fired power plant, but without use of coal. The heat would boil water which would then be used to turn turbines. In other words, it is nothing but, concentrated thermal solar power, which concentrates the heat from the sun to power turbines or sterling engines.

The advantage of such a system is converting the existing steam turbines being produced for traditional power plants, and the rest of the technology just involves shiny objects and concrete. The problems however, are these things too hot to handle. The material holding the boiler has to be able to withstand the extreme heat that these installations can produce. That kind of material, that won’t melt or degrade under such extreme heat, can be quite expensive.

d. Researchers reveal solar power breakthrough – To rival electricity grid in five years:
The cost of electricity generated by solar power cells is falling so fast, it is likely to provide a serious alternative to the national grid within five years.
Scientists demonstrated that solar cells are now capable of converting 43 percent of the sunlight hitting them into electricity.
However, the demonstration did not use regular silicon-based solar cells, which are much cheaper and more likely to be in popular use.
Rather, the demonstration cells require sunlight to be split into five different frequencies, or ‘colours’, with each colour sent to a different cell.
In contrast, the efficiency record with regular silicon-based solar cells stands at just 25 percent.
Significance of the new system is that, as the intensity of light is increased, the efficiency of the demonstration cells improves.
For more refer: http://www.itnews.com.au/News/154653,researchers-reveal-solar-power-breakthrough.aspx

8. Conclusion – Solar power technology is improving consistently over time, as people begin to understand the benefits offered by this incredible technology. As our oil reserves decline, it is important for us to turn to alternative sources for energy. Therefore, it would be better that converting some of the world’s energy requirements to solar power are in the best interest of the worldwide economy and the environment. Since we all are aware of the power of the sun and the benefits we could get from it.

Now, the cost of solar power is quite high. In fact, for solar energy to achieve its potential, desert solar power plant construction costs will have to be further reduced via technology improvements, economies of scale, and streamlined assembly techniques. Development of economic storage technologies can also lower costs significantly. According to renewable energy department, a desert solar power plant covering 10 square miles of desert has potential to produce as much power as the Hoover Dam of US produces. Thus, desert-based power plants can provide a large share of the nation’s commercial energy needs.

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