Advantages and disadvantages of solar power

Advantages
The 89 petawatts of sunlight reaching the earth's surface is plentiful compared to the 15 terawatts of average power consumed by humans. Additionally, solar electric generation has the highest power density (global mean of 170 W/m2) among renewable energies.
Solar power is pollution free during use. Production end wastes and emissions are manageable using existing pollution controls. End-of-use recycling technologies are under development.
Facilities can operate with little maintenance or intervention after initial setup. Solar electric generation is economically competitive where grid connection or fuel transport is difficult, costly or impossible. Examples include satellites, island communities, remote locations and ocean vessels.

When grid connected, solar electric generation can displace the highest cost electricity during times of peak demand (in most climatic regions), can reduce grid loading, and can eliminate the need for local battery power for use in times of darkness and high local demand; such application is encouraged by net metering. Time-of-use net metering can be highly favorable to small photovoltaic systems.
Grid connected solar electricity can be used locally thus minimizing transmission/distribution losses (approximately 7.2%).

Once the initial capital cost of building a solar power plant has been spent, operating costs are low when compared to existing power technologies.).
Financially speaking, there are rebate advantages if you live in a state that offers rebates such as California, New York, New Jersey, and Arizona.

Disadvantages
Solar electricity is expensive compared to grid electricity.

Limited power density: Average daily insolation in the contiguous U.S. is 3-9 kW·h/m2 usable by 7-17.7% efficient solar panels.
To get enough energy for larger applications, a large number of photovoltaic cells is needed. This increases the cost of the technology and requires a large plot of land.
Like electricity from nuclear or fossil fuel plants, it can only realistically be used to power transport vehicles by converting light energy into another form of stored energy (e.g. battery stored electricity or by electrolysing water to produce hydrogen) suitable for transport.
Solar cells produce DC which must be converted to AC when used in currently existing distribution grids. This incurs an energy loss of 4-12%.

Availability of solar energy
There is no shortage of solar-derived energy on Earth. Indeed the storages and flows of energy on the planet are very large relative to human needs.
The amount of solar energy intercepted by the Earth every minute is greater than the amount of energy the world uses in fossil fuels each year.
Tropical oceans absorb 560 trillion gigajoules (GJ) of solar energy each year, equivalent to 1,600 times the world’s annual energy use.
The energy in the winds that blow across the United States each year could produce more than 16 billion GJ of electricity—more than one and one-half times the electricity consumed in the United States in 2000.

Annual photosynthesis by the vegetation in the United States is 50 billion GJ, equivalent to nearly 60% of the nation’s annual fossil fuel use.
Plants, on average, capture 0.1% of the solar energy reaching the Earth. The land area of the lower 48 United States intercepts 50 trillion GJ per year, equivalent to 500 times of the nation’s annual energy use. This energy is spread over 8 million square kilometers of land area, so that each square meter is exposed to 6.1 GJ per year. This results in potential biomass production of 6,100 GJ per square kilometer per year. Compared to the 0.1% efficiency of vegetation, roof installable amorphous silicon solar panels capture 8%-14% of the solar energy, while more expensive crystalline panels capture 14%-20%, and large scale desert mirror-concentrator heat engine based setups may capture up to 30-50%.

From wikipedia
"Alternative Energy"

Classifications of solar power technology

Solar power technologies can be classified in a number of ways.

Photovoltaic cells produce electricity directly from sunlight

Direct or Indirect

In general, direct solar power involves a single transformation of sunlight which results in a usable form of energy.
Sunlight hits a photovoltaic cell creating electricity.
Sunlight warms a thermal mass.
Sunlight strikes a solar sail on a space craft and is converted directly into a force on the sail which causes motion of the craft.
Sunlight strikes a light mill and causes the vanes to rotate as mechanical energy (little practical application has yet been found for this effect).

In a direct solar water heater the water heated in the collector is used in the domestic water system.

In general, indirect solar power involves multiple transformations of sunlight which result in a usable form of energy.

Vegetation uses photosynthesis to convert solar energy to chemical energy. The resulting biomass may be burned directly to produce heat and electricity or processed into ethanol, methane, hydrogen and other biofuels.
Hydroelectric dams and wind turbines are powered by solar energy through its interaction with the Earth's atmosphere and the resulting weather phenomena.
Ocean thermal energy production uses the thermal gradients present across ocean depths to generate power. These temperature differences are produced by sunlight.[33]
Fossil fuels are ultimately derived from solar energy captured by vegetation in the geological past.

In an indirect solar water heater the fluid heated in the collector transfers its heat through a heat exchanger to a separate domestic water system.


Passive or active

This distinction is made in the context of building construction and building services engineering.
Passive solar systems use non-mechanical techniques of capturing, converting and distributing sunlight into usable outputs such as heating, lighting or ventilation. These techniques include selecting materials with favorable thermal properties, designing spaces that naturally circulate air and referencing the position of a building to the sun.
Passive solar water heaters use a thermosiphon to circulate fluid.
A Trombe wall circulates air by natural circulation and acts as a thermal mass which absorbs heat during the day and radiates heat at night.
Clerestory windows, light shelves, skylights and light tubes can be used among other daylighting techniques to illuminate a building's interior.
Passive solar water distillers may use capillary action to pump water.
Active solar systems use electrical and mechanical components such as photovoltaic panels, pumps and fans to process sunlight into usable outputs.

Concentrating or non-concentrating

A large parabolic reflector solar furnace is located in the Pyrenees at Odeillo, French Cerdagne. It is used for various research purposes.[34]
Concentrating solar power (CSP) systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam capable of producing high temperatures and correspondingly high thermodynamic efficiencies. Concentrating solar is generally associated with solar thermal applications but concentrating photovoltaic (CPV) applications exist as well and these technologies also exhibit improved efficiencies. CSP systems require direct insolation to operate properly.[35]

Concentrating solar power systems vary in the way they track the sun and focus light.

Line focus/Single-axis
A solar trough consists of a linear parabolic reflector which concentrates light on a receiver positioned along the reflector's focal line. These systems use single-axis tracking to follow the sun. A working fluid (oil, water) flows through the receiver and is heated up to 400 °C before transferring its heat to a distillation or power generation system.[36][37] Trough systems are the most developed CSP technology. The Solar Electric Generating System (SEGS) plants in California and Plataforma Solar de Almería's SSPS-DCS plant in Spain are representatives of this technology.[38]

Point focus/Dual-axis
A power tower consists of an array of flat reflectors (heliostats) which concentrate light on a central receiver located on a tower. These systems use dual-axis tracking to follow the sun. A working fluid (air, water, molten salt) flows through the receiver where it is heated up to 1000 °C before transferring its heat to a power generation or energy storage system. Power towers are less advanced than trough systems but they offer higher efficiency and energy storage capability.[39] The Solar Two in Daggett, California and the Planta Solar 10 (PS10) in Sanlucar la Mayor, Spain are representatives of this technology.
A parabolic dish or dish/engine system consists of a stand-alone parabolic reflector which concentrates light on a receiver positioned at the reflector's focal point. These systems use dual-axis tracking to follow the sun. A working fluid (hydrogen, helium, air, water) flows through the receiver where it is heated up to 1500 °C before transferring its heat to a sterling engine for power generation.[40][39] Parabolic dish systems display the highest solar-to-electric efficiency among CSP technologies and their modular nature offers scalability. The Stirling Energy Systems (SES) and Science Applications International Corporation (SAIC) dishes at UNLV and the Big Dish in Canberra, Australia are representatives of this technology.
Non-concentrating photovoltaic and solar thermal systems do not concentrate sunlight. While the maximum attainable temperatures (200 °C) and thermodynamic efficiencies are lower, these systems offer simplicity of design and have the ability to effectively utilize diffuse insolation.[39] Flat-plate thermal and photovoltaic panels are representatives of this technology.

From wikipedia

Solar power in applications

"Alternative Energy"

Solar power (also known as solar energy) is the technology of obtaining usable energy from the light of the sun. Solar energy has been used in many traditional technologies for centuries, and has come into widespread use where other power supplies are absent, such as in remote locations and in space. Solar energy is energy deployed from the sun by nuclear reactions inside its core and outer levels.

Solar energy is currently used in a number of applications:
Heat (hot water, building heat, cooking)
Electricity generation (photovoltaics, heat engines)
Desalination of seawater.

Contents
1 Energy from the Sun

Theoretical annual mean insolation, at the top of Earth's atmosphere (top) and at the surface on a horizontal square meter.

Map of global solar energy resources. The colours show the average available solar energy on the surface during 1991 to 1993. For comparison, the dark disks represent the land area required to supply the primary energy demand in the year 2010 using currently available technology (i.e. with a conversion efficiency of 8%).


Solar radiation reaches the Earth's upper atmosphere at a rate of 1366 watts per square meter (W/m2).[1] The first map shows how the solar energy varies in different latitudes.
While traveling through the atmosphere 6% of the incoming solar radiation (insolation) is reflected and 16% is absorbed resulting in a peak irradiance at the equator of 1,020 W/m².[2] Average atmospheric conditions (clouds, dust, pollutants) further reduce insolation by 20% through reflection and 3% through absorption.[3] Atmospheric conditions not only reduce the quantity of insolation reaching the Earth's surface but also affect the quality of insolation by diffusing incoming light and altering its spectrum.


The second map shows the average global irradiance calculated from satellite data collected from 1991 to 1993. For example, in North America the average insolation at ground level over an entire year (including nights and periods of cloudy weather) lies between 125 and 375 W/m² (3 to 9 kWh/m²/day).[4] This represents the available power, and not the delivered power. At present, photovoltaic panels typically convert about 15% of incident sunlight into electricity; therefore, a solar panel in the contiguous United States on average delivers 19 to 56 W/m² or 0.45 - 1.35 (kW·h/m²)/day.[5]


The dark disks in the third map on the right are an example of the land areas that, if covered with 8% efficient solar panels, would produce slightly more energy in the form of electricity than the total world primary energy supply in 2003.[6] While average insolation and power offer insight into solar power's potential on a regional scale, locally relevant conditions are of primary importance to the potential of a specific site.
After passing through the Earth's atmosphere, most of the sun's energy is in the form of visible and Infrared radiations. Plants use solar energy to create chemical energy through photosynthesis. Humans regularly use this energy burning wood or fossil fuels, or when simply eating the plants.


A recent concern is global dimming, an effect of pollution that is allowing less sunlight to reach the Earth's surface. It is intricately linked with pollution particles and global warming, and it is mostly of concern for issues of global climate change, but is also of concern to proponents of solar power because of the existing and potential future decreases in available solar energy. The order of magnitude is about 4% less solar energy available at sea level over the timeframe of 1961–90, mostly from increased reflection from clouds back into outer space.[7]


1.1 Types of technologies


Many technologies have been developed to make use of solar radiation. Some of these technologies make direct use of the solar energy (e.g. to provide light, heat, etc.), while others produce electricity.



1.2 Solar design in architecture



Main article: Passive solar building design
Solar design in architecture involves the use of appropriate solar technologies to maintain a building’s environment at a comfortable temperature through the sun's daily and annual cycles. It may do this by storing solar energy as heat in the walls of a building, which then acts to heat the building at night. Another approach is to keep the interior cool during a hot day by designing in natural convection through the building’s interior.



1.3 Solar heating systems


Solar heating systems
Main articles: Solar hot water and Solar combisystem

Solar water heaters on a rooftop in Jerusalem, Israel
Solar hot water systems use sunlight to heat water. They may be used to heat domestic hot water, for space heating or to heat swimming pools. These systems are composed of solar thermal collectors, a storage tank and a circulation loop.[8] The three basic classifications of solar water heaters are:
Batch systems which consist of a tank that is directly heated by sunlight. These are the oldest and simplest solar water heater designs, however; the exposed tank can be vulnerable to cooldown.[9]


Active systems which use pumps to circulate water or a heat transfer fluid.
Passive systems which circulate water or a heat transfer fluid by natural circulation. These are also called thermosiphon systems.


A Trombe wall is a passive solar heating and ventilation system consisting of an air channel sandwiched between a window and a sun-facing wall. Sunlight heats the air space during the day causing natural circulation through vents at the top and bottom of the wall and storing heat in the thermal mass. During the evening the Trombe wall radiates stored heat.[10]
A transpired collector is an active solar heating and ventilation system consisting of a perforated sun-facing wall which acts as a solar thermal collector. The collector pre-heats air as it is drawn into the building's ventilation system through the perforations. These systems are inexpensive and commercial models have achieved efficiencies above 70%. Most systems pay for themselves within 4-8 years.[11]

1.4 Solar cooking


Solar Cookers use sunshine as a source of heat for cooking as an alternative to fire.
A solar box cooker traps the sun's energy in an insulated box; such boxes have been successfully used for cooking, pasteurization and fruit canning. Solar cooking is helping many developing countries, both reducing the demands for local firewood and maintaining a cleaner breathing environment for the cooks.
The first known western solar oven is attributed to Horace de Saussure in 1767, which impressed Sir John Herschel enough to build one for cooking meals on his astronomical expedition to the Cape of Good Hope in Africa in 1830.[12] Today, there are many different designs in use around the world.[13]



1.5 Solar lighting


Main articles: Daylighting and Light tube
Solar lighting or daylighting is the use of natural light to provide illumination. Daylighting directly offsets energy use in electric lighting systems and indirectly offsets energy use through a reduction in cooling load.[14] Although difficult to quantify, the use of natural light also offers physiological and psychological benefits.


Daylighting features include building orientation, window orientation, exterior shading, sawtooth roofs, clerestory windows, light shelves, Hybrid Solar Lighting[15], skylights and light tubes.[16] These features may be incorporated in existing structures but are most effective when integrated in a solar design package which accounts for factors such as glare, heat gain, heat loss and time-of-use. Architectural trends increasingly recognize daylighting as a cornerstone of sustainable design.


Daylight saving time (DST) can be seen as a method of utilising solar energy by matching available sunlight to the hours of the day in which it is most useful. DST energy savings have been estimated to reduce total electricity use in California by 0.5% (3400 MWh) and peak electricity use by 3% (1000 MW).[17] However, there is some question whether these estimates are valid. In 2000 when parts of Australia began DST in late winter, overall electricity consumption did not decrease, but the peak load increased.[18]


1.6 Photovoltaics


The solar panels (photovoltaic arrays) on this small yacht at sea can charge the 12 V batteries at up to 9 A in full, direct sunlight
Solar cells, also referred to as photovoltaic cells, are devices or banks of devices that use the photovoltaic effect of semiconductors to generate electricity directly from sunlight. Until recently, their use has been limited because of high manufacturing costs. One cost effective use has been in very low-power devices such as calculators with LCDs. Another use has been in remote applications such as roadside emergency telephones, remote sensing, cathodic protection of pipe lines, and limited "off grid" home power applications. A third use has been in powering orbiting satellites and spacecraft.


Total peak power of installed PV is around 1,700 MW as of the end of 2005.[19] This is only one part of solar-generated electric power.


Declining manufacturing costs (dropping at 3 to 5% a year in recent years) are expanding the range of cost-effective uses. The average lowest retail cost of a large photovoltaic array declined from $7.50 to $4 per watt between 1990 and 2005.[20] With many jurisdictions now giving tax and rebate incentives, solar electric power can now pay for itself in five to ten years in many places. "Grid-connected" systems - those systems that use an inverter to connect to the utility grid instead of relying on batteries - now make up the largest part of the market.
In 2003, worldwide production of solar cells increased by 32%.[21] Between 2000 and 2004, the increase in worldwide solar energy capacity was an annualized 60%.[22] 2005 was expected to see large growth again, but shortages of refined silicon have been hampering production worldwide since late 2004.[23] Analysts have predicted similar supply problems for 2006 and 2007.[24]


1.7 Solar thermal electric power plants




Solar Two, a concentrating solar power tower (an example of solar thermal energy applied to electrical power production).
Main article: Solar thermal energy
Solar thermal energy can be focused on a heat exchanger, and converted in a heat engine to produce electric power or applied to other industrial processes.


1.7.1 Power towers


Power towers use an array of flat, movable mirrors (called heliostats) to focus the sun's rays upon a collector tower (the target). The high energy at this point of concentrated sunlight is transferred to a working fluid for conversion to electrical energy in a heat engine, or in some instances, stored for nighttime usage, in order to provide a more continuous output.





1.7.2 Parabolic troughs

A long row of parabolic mirrors concentrates sunlight on a tube filled with a heat transfer fluid (usually oil). As with the power tower, this heated oil is used to power a conventional steam turbine, or stored for nighttime use. The largest operating solar power plant, as of 2007, is one of the SEGS parabolic trough systems in the Mojave Desert in California, USA (see Solar power plants in the Mojave Desert).


1.7.3 Concentrating collector with steam engine

Solar energy converted to heat in a concentrating collector can be used to boil water into steam (as is done in nuclear and coal power plants) to drive a steam engine or steam turbine. The concentrating collector can be a trough collector, parabolic collector, or power tower.


1.7.4 Concentrating collector with Stirling engine

Solar energy converted to heat in a concentrating (dish or trough parabolic) collector can be used to drive a Stirling engine, a type of heat engine which uses a sealed working gas (i.e. a closed cycle) and does not require a water supply.
Until recently, a solar Stirling system held the record for converting solar energy into electricity (30% at 1,000 watts per square meter).[25] Such concentrating systems produce little or no power in overcast conditions and incorporate a solar tracker to point the device directly at the sun. That record has been broken by a so-called concentrator solar cell produced by Boeing-Spectrolab which claims a conversion efficiency of 40.7 percent.[26]


1.7.5 Solar updraft tower

A solar updraft tower (also known as a solar chimney, but this term is avoided by many proponents due to its association with fossil fuels) is a relatively low-tech solar thermal power plant where air passes under a very large agricultural glass house (between 2 and 8 km in diameter), is heated by the sun and channeled upwards towards a convection tower. It then rises naturally and is used to drive turbines, which generate electricity.


1.7.6 Energy tower



An energy tower is an alternative proposal to the solar updraft tower. It is driven by spraying water at the top of the tower, evaporation of water causes a downdraft by cooling the air thereby increasing its density, driving wind turbines at the bottom of the tower. It requires a hot arid climate and large quantities of water (seawater may be used) but does not require the large glass house of the solar updraft tower.


1.8 Solar pond



A solar pond is simply a pool of water which collects and stores solar energy. It contains layers of salt solutions with increasing concentration (and therefore density) to a certain depth, below which the solution has a uniform high salt concentration. It is a relatively low-tech, low-cost approach to harvesting solar energy. The principle is to fill a pond with 3 layers of water:
A top layer with a low salt content.
An intermediate insulating layer with a salt gradient, which sets up a density gradient that prevents heat exchange by natural convection in the water.
A bottom layer with a high salt content which reaches a temperature approaching 90 degrees Celsius.
The layers have different densities due to their different salt content, and this prevents the development of convection currents which would otherwise transfer the heat to the surface and then to the air above. The heat trapped in the salty bottom layer can be used for heating of buildings, industrial processes, generating electricity or other purposes. One such system is in use at Bhuj, Gujarat, India[27] and another at the University of Texas El Paso.[28]


1.9 Solar chemical


Solar chemical is any process that harnesses solar energy by absorbing sunlight and using it to drive an endothermic or photoelectrochemical chemical reaction. Prototypes, but no large-scale systems, have been constructed.
One approach has been to use conventional solar thermal collectors to drive chemical dissociation reactions. Ammonia can be separated into nitrogen and hydrogen at high temperature and with the aid of a catalyst, stored indefinitely, then recombined later to release the heat stored. A prototype system was constructed at the Australian National University[29].
Another approach is to use focused sunlight to provide the energy needed to split water via photoelectrolysis into its constituent hydrogen and oxygen in the presence of a metallic catalyst such as zinc.[30]. Other research in this area has focused on semiconductors, and on the use of examined transition metal compounds, in particular titanium, niobium and tantalum oxides [31]. Unfortunately, these materials exhibit very low efficiencies, because they require ultraviolet light to drive the photoelectrolysis of water. Current materials also require an electrical voltage bias for the hydrogen and oxygen gas to evolve from the surface, another disadvantage. Current research is focusing on the development of materials capable of the same water splitting reaction using lower energy visible light.
Solar thermal energy also has the potential to be used directly to drive chemical processes that require significant amounts of process heat, including at high temperatures that can be otherwise quite hard to attain[32].

From wikipedia

Alternative energy

Solar power plant

Solar thermal energy is a technology for harnessing solar power for practical applications from solar heating to electrical power generation. Solar thermal collectors, such as solar hot water panels, are commonly used to generate solar hot water for domestic and light industrial applications. Solar thermal energy is used in architecture and building design to control heating and ventilation in both active solar and passive solar designs. This article is devoted primarily to solar thermal electric power plants; that is, solar power plants that generate electricity by converting solar energy to heat, to drive a thermal power plant. These plants include the Solar Energy Generating Systems, Nevada Solar One, and Solar Tres. The article on photovoltaics reviews solar power generation by means of solar electric panels.

Concentrated solar power (CSP) plants
Where temperatures below about 95°C are sufficient, as for space heating, flat-plate collectors of the nonconcentrating type are generally used. The fluid-filled pipes can reach temperatures of 150 to 220 degrees Celsius when the fluid is not circulating.
A concentrating collector intercepts the same amount of solar radiation as a flat-plate collector of the same area, but contains a parabolic reflector that focuses the energy onto the surface of an absorber of much smaller area. This concentration of energy heats the absorber to a much higher temperature than that produced in the flat-plate type. Whilst the amount of energy remains the same, the higher temperature enables the system to generate electrical or mechanical energy more efficiently. This is because the maximum theoretical efficiency of any heat engine increases as the temperature of its heat source increases.

Parabolic trough designs
Main article: Trough concentrator

Sketch of a Parabolic Trough Collector
Parabolic trough power plants are the most successful and cost-effective CSP system design at present. They use a curved trough which reflects the direct solar insolation onto a hollow tube running along above the trough. The whole trough tilts through the course of the day so that direct insolation remains focused on the hollow tube for as long as the sun shines. A fluid, normally thermal oil, passes through the tube and becomes hot. Full-scale parabolic trough systems consist of many such troughs laid out in parallel over a large area of land. A solar thermal system using this principle is in operation in California in the United States, called the SEGS system.[1] At 350 MW, it is currently not only the largest operational solar thermal energy system, but the largest solar power system of any kind. SEGS uses oil to take the heat away: the oil then passes through a heat exchanger, creating steam which runs a steam turbine. The 64MW Nevada Solar One plant also uses this design. Other parabolic trough systems, which create steam directly in the tubes, are under development; this concept is thought to lead to cheaper overall designs, but the concept is yet to be commercialized.

Plastic Lens Design
International Automated Systemshas evidently produced a thin plastic focusing lens. Once installed, IAUS's lenses need no further adjustment. It operates on heat and produces heat as a byproduct. This energy can be stored using a chemical regeneration process held in a continuous cycle. This chemical, in turn, is then used to create steam when there is no sun.

Power tower designs
Main article: Solar power tower

Solar Two, a concentrating solar power plant.
Power towers (also know as 'central tower' power plants or 'heliostat' power plants) use an array of flat, moveable mirrors (called heliostats) to focus the sun's rays upon a collector tower (the target). The high energy at this point of concentrated sunlight is transferred to a substance that can store the heat for later use. The more recent heat transfer material that has been successfully demonstrated is liquid sodium. Sodium is a metal with a high heat capacity, allowing that energy to be stored and drawn off throughout the evening. That energy can, in turn, be used to boil water for use in steam turbines. Water had originally been used as a heat transfer medium in earlier power tower versions (where the resultant steam was used to power a turbine). This system did not allow for power generation during the evening. Examples of heliostat based power plants are the 10 MWe Solar One (later called Solar Two), and the 15 MW Solar Tres plants. Neither of these are currently used for active energy generation. In South Africa, a solar power plant is planned with 4000 to 5000 heliostat mirrors, each having an area of 140 m².[2]

Dish designs
A dish system uses a large, reflective, parabolic dish (similar in shape to satellite television dish). It focuses all the sunlight that strikes the dish up onto to a single point above the dish, where a thermal collector is used to capture the heat and transform it into a useful form. Dish systems, like power towers, can achieve much higher temperatures due to the higher concentration of light which they receive. Typically the dish is coupled with a Stirling engine in a Dish-Stirling System, but also sometimes a steam engine is used. These create rotational kinetic energy that can be converted to electricity using an electric generator.[3] [4] [5].

Fresnel Reflectors
A linear Fresnel reflector power plant uses a series of long, narrow, shallow-curvature (or even flat) mirrors to focus light onto one or more linear absorbers positioned above the mirrors. Recent prototypes of these types of systems have been built in Australia (CLFR[6]) and Belgium (SolarMundo). These systems aim to offer lower overall costs by sharing a heat-absorbing element between several mirrors (as compared with trough and dish concepts), while still using the line-focus geometry that allows reduced complexity in the tracking mechanism (as compared with central towers). The absorber is stationary and so fluid couplings are not required (as in troughs and dishes). The mirrors also do not need to support the absorber, so they are structurally simpler. When suitable aiming strategies are used (mirrors aimed at different absorbers at different times of day), this can allow a denser packing of mirrors on available land area.
A Multi-Tower Solar Array (MTSA) concept, that uses a point-focus Fresnel reflector idea, has also been developed,[7] but has not yet been prototyped.

Conversion rates from solar energy to electrical energy
Of these technologies the solar dish/stirling has the highest energy efficiency (the current record is a conversion efficiency of 40.7% of solar energy). A single solar dish-Stirling engine installed at Sandia National Laboratories’ National Solar Thermal Test Facility produces as much as 25 kW of electricity, while its footprint is a hundred times smaller than Spain's solar updraft tower pilot plant. [8] . Solar trough plants have been built with efficiencies of about 20%.
The Concentrated Solar Power (CSP) Plant using the parabolic trough principle called the SEGS system, in California in the United States,[9] produces 330 MW, and it is currently the largest solar thermal energy system in operation. Furthermore, Southern California Edison announced an agreement to purchase solar powered Stirling engines from Stirling Energy Systems over a twenty year period and in quantities (20,000 units) sufficient to generate 500 megawatts of electricity. [10] Stirling Energy Systems announced another agreement with San Diego Gas & Electric to provide between 300 and 900 megawatts of electricity.[11]
The gross conversion efficiencies (taking into account that the solar dishes or troughs occupy only a fraction of the total area of the power plant) are determined by net generating capacity over the solar energy that falls on the total area of the solar plant. The 500-megawatt (MW) SCE/SES plant would extract about 2.75% of the insolation (1 kW/m²; see Solar power for a discussion) that falls on its 4,500-acres (18.2 km²).[12] For the 50 MW AndaSol Power Plant [13] that is being built in Spain (total area of 1,300×1,500 m = 1.95 km²) gross conversion efficiency comes out at 2.6%

From wikipedia

Solar panel

The solar panel here refer to a photovoltaic module which is an assembly of solar cells used to generate electricity. In all cases, the panels are typically flat, and are available in various heights and widths.

An array is a group of solar-thermal panels or photovoltaic (PV) modules; the panels can be connected either in parallel or series depending upon the design objective. Solar panels typically find use in residential, commercial, institutional, and light industrial applications.
Solar-thermal panels saw widespread use in Florida and California until the 1920s when tank-type water heaters replaced them. A thriving manufacturing business soon dwindled. However, solar-thermal panels are still in production, and are common in portions of the world where energy costs, and solar energy availability, are high.

Recently there has been a surge toward large scale production of PV modules. In parts of the world with significantly high insolation levels, PV output and their economics are enhanced. PV modules are the primary component of most small-scale solar-electric power generating facilities. Larger facilities, such as solar power plants typically contain an array of reflectors (concentrators), a receiver, and a thermodynamic power cycle, and thus use solar-thermal rather than PV.

The largest solar panel in the world is under construction in the south of Portugal. A 116-megawatt facility covering a 250-hectare south-facing hillside in the southern Alentejo region and it will produce electricity for 25,000 households.[1]

From wikipedia

Solar cell (2)

Solor cells has been developed in three generations

First
The first generation photovoltaic, consists of a large-area, single layer p-n junction diode, which is capable of generating usable electrical energy from light sources with the wavelengths of sunlight. These cells are typically made using a silicon wafer. First generation photovoltaic cells (also known as silicon wafer-based solar cells) are the dominant technology in the commercial production of solar cells, accounting for more than 86% of the solar cell market.

Second
The second generation of photovoltaic materials is based on the use of thin-film deposits of semiconductors. These devices were initially designed to be high-efficiency, multiple junction photovoltaic cells. Later, the advantage of using a thin-film of material was noted, reducing the mass of material required for cell design. This contributed to a prediction of greatly reduced costs for thin film solar cells. Currently (2007) there are different technologies/semiconductor materials under investigation or in mass production, such as amorphous silicon, poly-crystalline silicon, micro-crystalline silicon, cadmium telluride, copper indium selenide/sulfide. Typically, the efficiencies of thin-film solar cells are lower compared with silicon (wafer-based) solar cells, but manufacturing costs are also lower, so that a lower price in terms of $/watt of electrical output can be achieved. Another advantage of the reduced mass is that less support is needed when placing panels on rooftops and it allows fitting panels on light materials or flexible materials, even textiles.

Third
Third generation photovoltaics are very different from the other two, broadly defined as semiconductor devices which do not rely on a traditional p-n junction to separate photogenerated charge carriers. These new devices include photoelectrochemical cells, Polymer solar cells, and nanocrystal solar cells.
Companies working on third generation photovoltaics include Xsunx, Konarka Technologies, Inc., Nanosolar and Nanosys. Research is also being done in this area by the USA's National Renewable Energy Laboratory (http://www.nrel.gov/).

From wikipedia

Solar cell/Photovoltaic cell

A solar cell or photovoltaic cell is a device that converts light energy into electrical energy. Sometimes the term solar cell is reserved for devices intended specifically to capture energy from sunlight, while the term photovoltaic cell is used when the light source is unspecified.

Fundamentally, the device needs to fulfill only two functions: photogeneration of charge carriers (electrons and holes) in a light-absorbing material, and separation of the charge carriers to a conductive contact that will transmit the electricity. This conversion is called the photovoltaic effect, and the field of research related to solar cells is known as photovoltaics.
Solar cells have many applications. They have long been used in situations where electrical power from the grid is unavailable, such as in remote area power systems, Earth-orbiting satellites and space probes, consumer systems, e.g. handheld calculators or wrist watches, remote radiotelephones and water pumping applications. More recently, they are starting to be used in assemblies of solar modules (photovoltaic arrays) connected to the electricity grid through an inverter, often in combination with a net metering arrangement.
Solar cells are regarded as one of the key technologies towards a sustainable energy supply

From wikipedia

Nuclear Power

Sustainable energy sources that aren't renewable are those whose stock is not replenished, but for which the presently available stocks are expected to last for as long as human civilization cares to use them.
These energy sources are derived from nuclear energy, as other forms of stored energy found on Earth do not have sufficient energy density to supply humanity indefinitely.
Fission power uses the nuclear fission of heavy elements to release energy that drives a heat engine. Primary challenges with the use of fission power are the production of small quantities of highly-radioactive waste in the form of spent fuel, larger quantities of less-radioactive waste in the form of activated structural material, and (for use as a long-term power source) the need to perform intensive processing of highly-radioactive fuel bundles, both to reclaim unused fuel in spent fuel rods, and to reclaim plutonium 239 and uranium 233 that have been bred from uranium 238 and thorium 232, respectively.
Fusion power uses the nuclear fusion of isotopes of hydrogen to release energy that drives a heat engine. Primary challenges with the use of fusion power are that the technology required to build a useful fusion power plant are still under development, and that substantial quantities of radioactive waste in the form of activated structural material is produced.
Fission power's long-term sustainability depends on the amount of uranium and thorium that is available to be mined. Estimates for fuel reserves vary widely, but if breeder reactors and fuel reprocessing are assumed, tend to be tens of thousands of years or longer (uranium is approximately as common in Earth's crust as tin or zinc (2 ppm), and thorium as common as lead (6 ppm)).
Fusion power's long-term sustainability depends on the amount of lithium that is available to be mined (for deuterium-tritium fusion), or the amount of deuterium available in seawater (for deuterium-deuterium fusion). Lithium is a reasonably common component of Earth's crust, being about 10 times as common as thorium (65 ppm). Deuterium (a hydrogen isotope) occurs wherever hydrogen is found (principally in water), at about 150 ppm. As it can be extracted easily from seawater, economically viable reserves of deuterium are for practical purposes unlimited.


Technical sustainability of nuclear power
Discussions are re-emerging on proper classification of nuclear energy under such umbrella terms as "renewable" and "sustainable" These attributes bring moral gains or eligibility for development aid under various jurisdictions.
The primary argument in favor of "renewable" status is the relatively inexhaustible supply of fuel available (uranium and thorium for fission or hydrogen for fusion). See also: Renewable energy, Nuclear power section.
Proponents, such as environmentalists James Lovelock, Patrick Moore (Greenpeace co-founder), Stewart Brand (creator of The Whole Earth Catalog), and Norris McDonald (president of the AAEA), also claim that nuclear power is at least as environmentally friendly as traditional sources of renewable energy, making it the best future solution to global warming and the world's growing need for energy. They note that nuclear power plants produce little carbon dioxide emissions and claim that the radioactive waste produced is minimal and well-contained, especially compared to fossil fuels. [3]
In 2001, professors Jan Willem Storm van Leeuwen and Philip Smith released a study which argued that, though nuclear plants don't produce any CO2 directly, the energy required for the rest of the nuclear fuel cycle (uranium mining, enrichment, transportation) and power plant life cycle (construction, maintenance, decommissioning) leads to significant carbon dioxide emissions, especially as usage of lower-grade uranium becomes necessary.[4] In 2000, however, Frans H. Koch of the International Energy Agency reported that, although it is correct that the nuclear life cycle produces greenhouse gases, these emissions are actually less than the life cycle emissions of other renewables, like solar and wind, and drastically less than fossil fuels.[5]

Political sustainability of nuclear power
The use of nuclear power is political and controversial because of the problem of storing radioactive waste for indefinite periods, the potential for severe radioactive contamination by accident or sabotage, and the possibility that its use could in some countries lead to the proliferation of nuclear weapons.

Serious nuclear accidents which have occurred include the 1986 Chernobyl disaster, the 1979 Three Mile Island accident, the 1957 Windscale fire, and the 1957 Mayak accident. The nuclear power industry went into a period of decline for some years following the Chernobyl and Three Mile Island accidents (see Nuclear power controversy).
Some critics of nuclear energy argue that deployment of nuclear reactors in many countries would accelerate the proliferation of nuclear weapons technology that has many links with civilian use of nuclear materials. Some nuclear reactors (especially heavy water moderated reactors) create the materials necessary for these weapons.
The issue of fuel reprocessing and/or long-term repository of nuclear waste materials also remains contentious. Very few countries have developed waste depositories for high-level radioactive waste (see: Yucca Mountain Repository USA; Gorleben Germany; Forsmark, Sweden).
Due to opposition to nuclear power many countries (Austria, Italy, Sweden, Germany) have effectively banned further development of nuclear energy showing a clear lack of political sustainability under present conditions. Some other countries, such as Australia, have never built a nuclear power station

From wikipedia

Renewable energy sources

Renewable energy sources are those whose stock is rapidly replenished by natural processes, and which aren't expected to be depleted within the lifetime of the human species. In most cases, these energy sources have technical challenges to overcome before they are economically competitive with conventional methods of electricity generation. Approaches to overcoming these challenges are a field of active research, and are described on the relevant generation method pages.
The well-known renewable energy options can be classified by the natural process that provides their energy:
Direct solar energy:
Solar cells use semiconductors to directly convert sunlight into electricity. Primary challenges with their use are low efficiency, energy-intensive manufacture, and power variability due to weather and nightfall.
Solar thermal plants use concentrated sunlight as a heat source to power a heat engine which generates electricity. Primary challenges with their use are manufacture and maintenance of large mirror arrays and power variability due to weather and nightfall.
Solar updraft tower plants use sunlight to heat a contained mass of air, setting up convection currents that cause air to exit through a chimney from which power is tapped. Primary challenges with their use are low efficiency, construction and maintenance of the large structures required, and power variability due to weather (a Solar updraft tower has enough heat capacity to function through night).
Indirect solar energy:
Ocean thermal energy conversion uses the temperature difference between the warmer surface of the ocean and the cooler lower depths to drive a heat engine. The primary challenges with ocean thermal energy conversion's use are low efficiency and the construction and maintenance of large structures in a sea environment.
Wind power uses wind turbines to draw energy from large-scale motion of air. The primary challenges with wind power's use are the large areas required to produce useful amounts of electricity, and power variability due to weather.
Hydroelectricity uses dams to draw energy from the flow of water from high-altitude areas to areas with lower altitudes. Primary challenges with hydroelectricity's use are the environmental damage caused by the construction of dams, and the scarcity of remaining sites for power generation.
Wave power uses floats to extract mechanical energy from the motion of waves. Primary challenges with wave power's use are the large areas required to produce useful amounts of electricity, and disruption of coastal environments.
Biofuel uses products of plants, animals, or bacteria to provide fuels that can be used in a manner similar to fossil fuels. The primary challenge with biofuel's use is the availability of suitable feedstock in sufficient quantity for large-scale adoption. The environmental and economic benefits of non-cellulosic ethanol have been heavily critiqued by many, including Brad Ewing of Environmental Economics & Sustainable Development[1] and Lester R. Brown of Earth Policy Institute[2]
Radioactive decay within the Earth:
Geothermal power uses the temperature difference between the earth's surface and its interior to drive a heat engine, generally at a location such as a hot spring where the heat has been transported most of the way to the surface by natural processes. The primary challenge with geothermal power's use is low power generation efficiency for most sites.
Rotation of the Earth:
Tidal power uses dams to draw energy from the changes in water height due to tides produced by the gravitational influences of the moon and sun as Earth rotates. The primary challenges with tidal power's use are the large area required to produce useful amounts of electricity, and disruption of coastal environments.
Processes powered by solar energy will be renewed for as long as the sun remains on the main sequence (approximately 5 billion years). Processes powered by radioactive decay within the Earth will be renewed for time comparable to the half-life of uranium 238 (4.5 billion years) and thorium 232 (14 billion years). Processes powered by the Earth's rotation will last until the Earth becomes tidally locked to the Sun (though tidal acceleration would eject the moon from Earth orbit earlier). Both of these would take longer than the expected lifetime of the sun to occur.

Solid biomass

Solid biomass

Sugar cane residue can be used as a biofuel
Direct use is usually in the form of combustible solids, either wood, the biogenic portion of municipal solid waste or combustible field crops. Field crops may be grown specifically for combustion or may be used for other purposes, and the processed plant waste then used for combustion. Most sorts of biomatter, including dried manure, can actually be burnt to heat water and to drive turbines.
Sugar cane residue, wheat chaff, corn cobs and other plant matter can be, and is, burnt quite successfully. The net Carbon Dioxide emissions that are added to the atmosphere by this process are only from the fossil fuel that is consumed to plant, fertilize, harvest and transport the biomass. Processes to grow perenials such as switchgrass, miscanthus, and willow, field pelletize and co-fire with coal for electricity generation are being studied and appear to be economically viable. [8] Co-firing this cellulosic biomass with coal to make electricity is more effective for reducing carbon dioxide emmissions to the atmosphere than using it to make ethanol.
Solid biomass can also be gasified, and used as described in the next section.

Liquid biofuel

Liquid biofuel

Information on pump, California.
Liquid biofuel is usually either a bioalcohol such as ethanol or a bio-oil such as biodiesel and straight vegetable oil. Biodiesel can be used in modern diesel vehicles with little or no modification to the engine and can be made from waste and virgin vegetable and animal oil and fats (lipids). Virgin vegetable oils can be used in modified diesel engines. In fact the Diesel engine was originally designed to run on vegetable oil rather than fossil fuel. A major benefit of biodiesel is lower emissions. The use of biodiesel reduces emission of carbon monoxide and other hydrocarbons by 20 to 40 percent. In some areas corn, cornstalks, sugarbeets, sugar cane, and switchgrasses are grown specifically to produce ethanol (also known as grain alcohol) a liquid which can be used in internal combustion engines and fuel cells. Ethanol is being phased into the current energy infrastructure. E85 is a fuel composed of 85% ethanol and 15% gasoline that is sold to consumers.
In the future, there might be bio-synthetic liquid fuel available. It can be produced by the Fischer-Tropsch process, also called Biomass-To-Liquids (BTL).[7]

Biofuel

Biofuel

Plants use photosynthesis to grow and produce biomass. Also known as biomatter, biomass can be used directly as fuel or to produce liquid biofuel. Agriculturally produced biomass fuels, such as biodiesel, ethanol and bagasse (often a by-product of sugar cane cultivation) can be burned in internal combustion engines or boilers. Typically biofuel is burned to release its stored chemical energy. Research into more efficient methods of converting biofuels and other fuels into electricity utilizing fuel cells is an area of very active work

Nuclear power

Nuclear power

'Renewable energy', as a term in modern usage, was invented just before the energy crisis of 1973.[48] More recent arguments in favor of classifying nuclear power as renewable are based largely on the potential amount of raw materials that may become available for nuclear fission and its low environmental impact. In 1983, the physicist Bernard Cohen calculated the useful lifetime of nuclear power in the billions of years — longer than the life of the sun itself (which ultimately powers other renewables), remarking that this should qualify it as a renewable resource, too.[49] Nuclear energy has also been referred to as "renewable" by the President of the United States George W. Bush[50] and David Sainsbury, former Parliamentary Under-Secretary of State for the House of Lords.[51]
Inclusion of nuclear power under the "renewable energy" classification could render nuclear power projects eligible for development aid under various jurisdictions. However, no legislative body has yet included nuclear energy under any legal definition of "renewable energy sources" for provision of development support (see: Renewable energy development). Similarly, statutory and scientific definitions of renewable energies usually exclude nuclear energy. In England and Wales there is a Non-Fossil Fuel Obligation, which provides support for renewable energy.[52] Nuclear power production was also subsidised by this obligation from 1990 until 2002.

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