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Wind Power

Wind is a form of solar energy. Wind power all starts with the sun. When the sun heats up a certain area of land, the air around that land mass absorbs some of that heat. At a certain temperature, that hotter air begins to rise very quickly because a given volume of hot air is lighter than an equal volume of cooler air. 

Air Circulation

Faster-moving (hotter) air particles exert more pressure than slower-moving particles, so it takes fewer of them to maintain the normal air pressure at a given elevation When that lighter hot air suddenly rises, cooler air flows quickly in to fill the gap the hot air leaves behind. That air rushing in to fill the gap is wind.

If you place an object like a rotor blade in the path of that wind, the wind will push on it, transferring some of its own energy of motion to the blade. This is how a wind turbine captures energy from the wind.

Principles of Wind Power Plant

The terms wind energy or wind power describe the process by which the wind is used to generate mechanical power or electricity. Wind turbines convert the kinetic energy in the wind into mechanical power. This mechanical power can be used for specific tasks (such as grinding grain or pumping water) or a generator can convert this mechanical power into electricity.

So how do wind turbines make electricity? Simply stated, a wind turbine works the opposite of a fan. Instead of using electricity to make wind, like a fan, wind turbines use wind to make electricity. The wind turns the blades, which spin a shaft, which connects to a generator and makes electricity. Take a look inside a wind turbine to see the various parts.

Inside The Wind Turbine

Inside The Wind Turbine

Anemometer:

Measures the wind speed and transmits wind speed data to the controller.

Blades:
Most turbines have either two or three blades. Wind blowing over the blades causes the blades to "lift" and rotate.

Brake:
A disc brake, which can be applied mechanically, electrically, or hydraulically to stop the rotor in emergencies.

Controller: 

The controller starts up the machine at wind speeds of about 8 to 16 miles per hour (mph) and shuts off the machine at about 55 mph. Turbines do not operate at wind speeds above about 55 mph because they might be damaged by the high winds.

Wind Farm

Gear box:

Gears connect the low-speed shaft to the high-speed shaft and increase the rotational speeds from about 30 to 60 rotations per minute (rpm) to about 1000 to 1800 rpm, the rotational speed required by most generators to produce electricity. The gear box is a costly (and heavy) part of the wind turbine and engineers are exploring "direct-drive" generators that operate at lower rotational speeds and don't need gear boxes.

Generator:
Usually an off-the-shelf induction generator that produces 60-cycle AC electricity.

High-speed shaft:
Drives the generator.

Low-speed shaft:
The rotor turns the low-speed shaft at about 30 to 60 rotations per minute.

Nacelle:
The nacelle sits atop the tower and contains the gear box, low- and high-speed shafts, generator, controller, and brake. Some nacelles are large enough for a helicopter to land on.

Pitch:
Blades are turned, or pitched, out of the wind to control the rotor speed and keep the rotor from turning in winds that are too high or too low to produce electricity.

Wind Turbines Offshore

Rotor:
The blades and the hub together are called the rotor.

Tower:
Towers are made from tubular steel (shown here), concrete, or steel lattice. Because wind speed increases with height, taller towers enable turbines to capture more energy and generate more electricity.

Wind direction:
This is an "upwind" turbine, so-called because it operates facing into the wind. Other turbines are designed to run "downwind," facing away from the wind.

Wind vane:
Measures wind direction and communicates with the yaw drive to orient the turbine properly with respect to the wind.

Yaw drive:
Upwind turbines face into the wind; the yaw drive is used to keep the rotor facing into the wind as the wind direction changes. Downwind turbines don't require a yaw drive, the wind blows the rotor downwind.

Yaw motor:
Powers the yaw drive.

Types of Wind Turbines

Modern wind turbines fall into two basic groups: the horizontal-axis variety, as shown in the photo above, and the vertical-axis design, like the eggbeater-style Darrieus model, named after its French inventor. 

Horizontal-axis wind turbines (HAWT) typically either have two or three blades. These three-bladed wind turbines are operated "upwind," with the blades facing into the wind.

Vertical-axis wind turbines (VAWTs)

Vertical-axis wind turbines (VAWTs) are pretty rare. The only one currently in commercial production is the Darrieus turbine.  

In a VAWT, the shaft is mounted on a vertical axis, perpendicular to the ground. VAWTs are always aligned with the wind, unlike their horizontal-axis counterparts, so there's no adjustment necessary when the wind direction changes; but a VAWT can't start moving all by itself -- it needs a boost from its electrical system to get started. 

Instead of a tower, it typically uses guy wires for support, so the rotor elevation is lower. Lower elevation means slower wind due to ground interference, so VAWTs are generally less efficient than HAWTs. On the upside, all equipment is at ground level for easy installation and servicing; but that means a larger footprint for the turbine, which is a big negative in farming areas.

Size of Wind Turbines

3.6 MW Wind Power Plant

Utility-scale turbines range in size from 100 kilowatts to as large as several megawatts. Larger turbines are grouped together into wind farms, which provide bulk power to the electrical grid.

Single small turbines, below 100 kilowatts, are used for homes, telecommunications dishes, or water pumping. Small turbines are sometimes used in connection with diesel generators, batteries, and photovoltaic systems. These systems are called hybrid wind systems and are typically used in remote, off-grid locations, where a connection to the utility grid is not available.

Wind Turbine Size Compared with a Man

Solar Wind Bridge Consept

The hybrid system (combining solar and wind power) proposed allows for a continuous production of Energy. The project is based on the idea of utilizing the space between the pillars of the existing viaducts to house a system of wind-powered turbines which will be integrated into the structure.

The solar park is conceived as a green “promenade”, along which there alternate panoramic viewing points and entirely self-sufficient solar greenhouses. As with city farms, visitors to the park will be able to stop and buy the local produce grow in these greenhouses.

The asphalt will be substituted with a technological road surface of a kind already in use in the USA (“solar roadways”). The road surface itself will, therefore, collect energy as a part of a power-generating system composed of a dense grid of solar cells coated with a transparent ad highly resistant form of plastic.

The entire system is capable of producing around 40 million kWh per annum – enough energy to provide power for approximately 15.000 families.

This Solar Wind concept is the brainchild of designers Francesco Colarossi, Giovanna Saracino and Luisa Saracino, who came second in a competition to dream up a bridge spanning the Italian areas of Bagnara and Scilla.

Solar Roadways

Reference Books: Wind Power

Wind Turbine Technology: Fundamental Concep... by David A. Spera	Wind-Diesel and Wind Autonomous Energy Syst...	Reaping the Wind: How Mechanical Wizards, V... by Peter Asmus

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Rock Music Fans

There are many uses for fuel cells — right now, all of the major automakers are working to commercialize a fuel cell car. Fuel cells are powering buses, boats, trains, planes, scooters, forklifts, even bicycles. There are fuel cell-powered vending machines, vacuum cleaners and highway road signs. Miniature fuel cells for cellular phones, laptop computers and portable electronics are on their way to market. Hospitals, credit card centers, police stations, and banks are all using fuel cells to provide power to their facilities. Wastewater treatment plants and landfills are using fuel cells to convert the methane gas they produce into electricity. Telecommunications companies are installing fuel cells at cell phone and radio. The possibilities are endless. 

Fuel Cell as Power Source in Remote Location

Fuel cells are very useful as power sources in remote locations, such as spacecraft, remote weather stations, large parks, rural locations, and in certain military applications. A fuel cell system running on hydrogen can be compact and lightweight, and have no major moving parts. Because fuel cells have no moving parts and do not involve combustion, in ideal conditions they can achieve up to 99.9999% reliability. This equates to around one minute of down time in a two year period.

Since electrolyzer systems do not store fuel in themselves, but rather rely on external storage units, they can be successfully applied in large-scale energy storage, rural areas being one example. In this application, batteries would have to be largely oversized to meet the storage demand, but fuel cells only need a larger storage unit (typically cheaper than an electrochemical device).

One such pilot program is operating on Stuart Island in Washington State. There the Stuart Island Energy Initiative has built a complete, closed-loop system: Solar panels power an electrolyzer which makes hydrogen. The hydrogen is stored in a 500 gallon tank at 200 PSI, and runs a Reli On fuel cell to provide full electric back-up to the off-the-grid residence.

Fuel Cell in Residential Applications

In residential applications, small fuel cell power plants could be installed for the production of both electricity and heat or hot water for the home. 

In addition to homes in developed countries, where the market may first develop, an ideal application for fuel cells is to provide power to remote residential entities that have limited or no access to primary grid power, thereby delaying, if not eliminating, the necessity of expensive, maintenance intensive transmission line installations. These applications will be more common in developing countries, where fuel cells can provide electricity in regions gradually as development warrants and allows.

Fuel Cell in Data Centers

The propagation of  Data Centers through out the U.S. and the developed world, is a sign of continued growth in the digital age and also a significant burden on grid generation and transmission capacity. The power use density for these facilities can be in excess of 100 watts per square foot resulting in very high electrical demands for a relatively small facility. These same facilities are extremely dependent on premium quality and highly reliability power.

The potential for cogeneration at these facilities is low, however the development of the Data Center Campus concept allows cogeneration to be implements beyond the confines of the Data Center in surrounding process, office, or hospitality relate buildings. The waste heat of a fuel cell can be converted to chilled air through the absopbtion chilling process, a definite need for such a data center facility.

In 1999, the First National Bank of Omaha (FNBO) - the nation's largest privately owned bank-installed a 800-kw fuel-cell system as the primary power source for its new 200,000 square foot Technology Center's critical loads. This bank is the nation's seventh largest credit card transaction processor, handling over three million transactions per day, 365 days a year. According to officials at the bank, a single one-hour blackout could cost FNBO's credit card operation as much as $6 million in lost business.
 

Fuel Cell in Transportation

There are numerous prototype or production cars and buses based on fuel cell technology being researched or manufactured by motor car manufacturers.

The GM 1966 Electrovan was the automotive industry's first attempt at an automobile powered by a hydrogen fuel cell. The Electrovan, which weighed more than twice as much as a normal van, could travel up to 70 mph for 30 seconds.

The 2001 Chrysler Natrium used its own on-board hydrogen processor. It produces hydrogen for the fuel cell by reacting sodium borohydride fuel with Borax, both of which Chrysler claimed were naturally occurring in great quantity in the United States. The hydrogen produces electric power in the fuel cell for near-silent operation and a range of 300 miles without impinging on passenger space. Chrysler also developed vehicles which separated hydrogen from gasoline in the vehicle, the purpose being to reduce emissions without relying on a nonexistent hydrogen infrastructure and to avoid large storage tanks.

In 2005 the British firm Intelligent Energy produced the first ever working hydrogen run motorcycle called the ENV (Emission Neutral Vehicle). The motorcycle holds enough fuel to run for four hours, and to travel 100 miles in an urban area, at a top speed of 50 miles per hour. In 2004 Honda developed a fuel-cell motorcycle which utilized the Honda FC Stack.

In 2007, the Revolve Eco-Rally (launched by HRH Prince of Wales) demonstrated several fuel cell vehicles on British roads for the first time, driven by celebrities and dignitaries from Brighton to London's Trafalgar Square. Fuel cell powered race vehicles, designed and built by university students from around the world, competed in the world's first hydrogen race series called the 2008 Formula Zero Championship, which began on August 22, 2008 in Rotterdam, the Netherlands.

After this first race, Greenchoice Forze from the university of Delft (The Netherlands) became leader in the competition. Other competing teams are Element One (Detroit), HerUCLAs (LA), EUPLAtecH2 (Spain), Imperial Racing Green (London) and Zero Emission Racing Team (Leuven).

In 2008, Honda released a hydrogen vehicle, the FCX Clarity. Meanwhile there exist also other examples of bikes and bicycles with a hydrogen fuel cell engine.

A few companies are conducting hydrogen fuel cell research and practical fuel cell bus trials. Daimler AG, with thirty-six experimental units powered by Ballard Power Systems fuel cells completing a successful three-year trial, in eleven cities, in January 2007. There are also fuel cell powered buses currently active or in production, such as a fleet of Thor buses with UTC Power fuel cells in California, operated by SunLine Transit Agency. The Fuel Cell Bus Club is a global cooperative effort in trial fuel cell buses.

The first Brazilian hydrogen fuel cell bus prototype began operation in São Paulo during the first semester of 2009. The hydrogen bus was manufactured in Caxias do Sul and the hydrogen fuel will be produced in São Bernardo do Campo from water through electrolysis. The program, called "Ônibus Brasileiro a Hidrogênio" (Brazilian Hydrogen Autobus), includes three additional buses.


The Type 212 submarines of the German and Italian navies use fuel cells to remain submerged for weeks without the need to surface.

 

Fuel Cell Fueling stations

The first public hydrogen refueling station was opened in Reykjavík, Iceland in April 2003. This station serves three buses built by Daimler Chrysler that are in service in the public transport net of Reykjavík. The station produces the hydrogen it needs by itself, with an electrolyzing unit (produced by Norsk Hydro), and does not need refilling: all that enters is electricity and water. Royal Dutch Shell is also a partner in the project. The station has no roof, in order to allow any leaked hydrogen to escape to the atmosphere.

The California Hydrogen Highway is an initiative by the California Governor to implement a series of hydrogen refueling stations along that state. These stations are used to refuel hydrogen vehicles such as fuel cell vehicles and hydrogen combustion vehicles. As of July 2007 California had 179 fuel cell vehicles and twenty five stations in operation, and ten more stations have been planned for assembly in California. However, there have already been three hydrogen fueling stations decommissioned.

South Carolina also has a hydrogen freeway in the works. There are currently two hydrogen fueling stations, both in Aiken and Columbia, SC. Additional stations are expected in places around South Carolina such as Charleston, Myrtle Beach, Greenville, and Florence. According to the South Carolina Hydrogen & Fuel Cell Alliance, the Columbia station has a current capacity of 120 kg a day, with future plans to develop on-site hydrogen production from electrolysis and reformation. The Aiken station has a current capacity of 80 kg. There is extensive funding for Hydrogen fuel cell research and infrastructure in South Carolina. The University of South Carolina, a founding member of the South Carolina Hydrogen & Fuel Cell Alliance, received 12.5 million dollars from the United States Department of Energy for its Future Fuels Program.

Japan also has a hydrogen highway, as part of the Japan hydrogen fuel cell project. Twelve fueling stations have been built in 11 cities in Japan. Canada, Sweden and Norway also have hydrogenhydrogen highways implemented.

Reference Books

Modern Electric, Hybrid Electric, and Fuel Cell Vehicles

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Solar energy is the most promising clean energy source for new generations. Sun has been shinning for about 5 billion years (without malfunctions) and it will continue shinning for another 4 to 5 billion years.

Solar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation, along with secondary solar powered resources such as wind and wave power, hydroelectricity and biomass, account for most of the available renewable energy on earth. Only a minuscule fraction of the available solar energy is used.

Solar power is the conversion of sunlight into electricity, either directly using photovoltaics (PV), or indirectly using concentrated solar power (CSP). CSP systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. PV converts light into electric current using the photoelectric effect.

Solar Cells

Solar Cell used in Skylab

Though it sounds unusual at first, it is a fact that solar cells represent a very important part of information technology revolution in the last few decades. Without solar cells there wouldn't be so many communication satellites, which found the information technology revolution. The consequences are fast development in the field of information technologies and computer sciences, Internet etc. Data and voice transfer possibilities, which are offered to you by modern communications techniques, were made possible by a small piece of silicon in the form of a solar cell.

First solar cells

A physical phenomenon allowing light-electricity conversion - photovoltaic effect, was discovered in 1839 by the French physicist Alexandre Edmond Becquerel. Experimenting with metal electrodes and electrolyte he discovered that conductance rises with illumination.

Willoughby Smith discovered photovoltaic effect in selenium in 1873. In 1876, with his student R. E. Day, William G. Adams discovered that illuminating a junction between selenium and platinum also has a photovoltaic effect. These two discoveries were a foundation for the first selenium solar cell construction, which was built in 1877. Charles Fritts first described them in detail in 1883.

In 1918, a Polish scientist Jan Czochralski discovered a method for monocrystalline silicon production, which enabled monocrystalline solar cells production. The first silicon monocrystalline solar cell was constructed in 1941.

The photovoltaic effect in other materials was observed in 1932 in cadmium-selenide (CdS). Nowadays, CdS belongs among important materials for solar cells production.

In 1963, Sharp Corporation developed the first usable photovoltaic module from silicon solar cells. The biggest photovoltaic system at the time, the 242 W module field was set up in Japan. A year later, in 1964, Americans applied a 470 W photovoltaic field in the Nimbus space project.

Photovoltaics (PV)

The term photovoltaics derives from the Greek word "phos" meaning light and the word "volt" (named by Alessandro Volta). Photovoltaics is a science, which examines light-electricity conversion, respectively, photon energy-electric current conversion. In other words it stands for light-current conversion. Both direct and diffuse solar radiation take part of the process. The light to current conversion takes place within solar cells, which can be amorphous, poly- crystalline or single-crystal, according to their structure.

• Single-crystal cells are made in long cylinders and sliced into round or hexagonal wafers. While this process is energy-intensive and wasteful of materials, it produces the highest-efficiency solar cells—as high as 25 percent in some laboratory tests. Because these high-efficiency solar cells are more expensive, they are sometimes used in combination with concentrators such as mirrors or lenses. Concentrating systems can boost efficiency to almost 30 percent. Single-crystal accounts for 29 percent of the global market for PV.
• Polycrystalline cells are made of molten silicon cast into ingots or drawn into sheets, then sliced into squares. While production costs are lower, the efficiency of the solar cells is lower too—around 15 percent. Because the solar cells are square, they can be packed more closely together. Polycrystalline solar cells make up 62 percent of the global PV market.
• Amorphous silicon (a-Si) is a radically different approach. Silicon is essentially sprayed onto a glass or metal surface in thin films, making the whole module in one step. This approach is by far the least expensive, but it results in very low efficiencies—only about five percent.

Photovoltaic Cells

The basic PV or solar cell typically produces only a small amount of power. To produce more power, solar cells (about 40) can be interconnected to form panels or modules. PV modules range in output from 10 to 300 watts. If more power is needed, several modules can be installed on a building or at ground-level in a rack to form a PV array. About 10–20 PV arrays can provide enough power for a household.

Application Example

Most common application of solar cells applies to pocket calculators power supply, parking meters power supply and similar appliances. Solar-module consists of many solar cells, which are electrically connected and placed between glass and tedlar plate, and framed by an (usualy) aluminium frame. A number of solar-modules and other components (batteries, charge regulators, and inverters) can form large photovoltaic systems.

The first PV system applications developed were applied as an energy source for satellites and later for orbital stations in space. Nowadays, photovoltaic systems are applied as an energy source in many cases. Most commonly applied photovoltaic systems can be found in remote and rural areas where no public grid is available. However, quite often grid-connected systems are constructed in urban areas.

Photovoltaic systems are an excellent solution to electricity production regardless of your whereabouts - even at high latitudes of Himalayas or in Antarctica photovoltaic systems have been build. According to loads connected to the system and to the basic design principles, the following photovoltaic systems are used - direct coupled photovoltaic systems (systems without batteries - water pumping systems for example), standalone photovoltaic systems, grid-connected photovoltaic systems, hybrid systems (e.g. PV - wind or PV - diesel systems), concentrator photovoltaic systems. The applications below depict use of photovoltaic systems as an energy source in many interesting ways. 

Photovoltaic Power Plants

Photovoltaic power plants - Solar modules are nowadays parts of large standalone or grid-connected systems. Large photovoltaic power plants (MW range) have beeing constructed in Germany, Spain, USA, Italy, Netherlands etc. Worldwide more than 250 large PV power plants with peak power 1 MWp or more (each plant) are connected to the public grid(s).

Building Integrated Photovoltaics

Building integrated photovoltaics - Acronym of BIPV (Building Integrated Photovoltaics) refers to photovoltaic systems integrated with an object's building phase. It means that they are built/constructed along with an object. They are also planned together with the object. Yet, they could be built later on. Due to specific task cooperation of many different experts, such as architects, civil engineers and PV system designers, is necessary.

Photovoltaic Noise Barrier

Noise barriers - An efficient way of noise prevention by application of photovoltaic modules was first demonstrated in Switzerland in 1989. Later, the solution was applied also in some other European countries. Noise prevention is also a research subject of several projects conducted in European Union. Different photovoltaic noise barriers can be built considering motorway features, barrier construction, the height of the barrier, and other factor influence (environment etc.).

Reference Books:

Solar Electricity Handbook, 2010 Edition

Photovoltaics: Design and Installation Manual

Practical Handbook of Photovoltaics

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The modern technology used for burning coal to generate electricity has evolved over a period of more than a century and until awareness grew of the environmental damage coal burning could produce, the coal-fired power station developed in a single direction. The basic principle underlying this type of power station is to burn coal in air and capture the heat released to raise steam for driving a steam turbine. The rotation of this steam turbine, in turn, drives a generator; the net result is electricity.

The traditional coal-fired power plant comprises two basic components. The first component is a furnace boiler designed to burn the coal and capture the heat energy released using a system of circulating water and steam. The second part of the system is a steam turbine generator which converts the heat energy captured by the steam into electrical energy. In other words, chemical energy held within the coal is first translated into heat energy and then into mechanical energy, and finally into electrical energy. Modern plants also include additional units to remove dust and acid emissions from the flue gases before they are released into the atmosphere.

 

Boiler

A power plant boiler is a device for converting the chemical energy in coal into heat energy and then transferring that heat energy to a fluid, steam. The efficiency of a coal-fired power plant increases as the pressure and temperature of the steam increases. This has led to a demand for higher temperatures and pressures as technology has developed and this has required, in turn, the development of materials with higher performance under increasingly stressful conditions. The most advanced boilers develop steam with a pressure of around 250bar and a temperature of 600°C.

Early boilers were made from iron, but as the demands on the system increased, special steels were used that could resist the conditions encountered in the power plant. These now dominate in modern boilers. Even so, oxygen dissolved in the water circulating within the boiler pipes can cause serious corrosion in steel at the elevated temperatures and pressures to which it is exposed, so the boiler water must be deoxygenated.

The first part of the boiler is a furnace in which combustion takes place. In the most common type of boiler, pulverised coal is injected with a stream of air into the furnace in a continuous process through a device known as a burner. The coal burns, producing primarily carbon dioxide while incombustible mineral material (ash) falls to the bottom of the furnace where it can be removed (some is also carried away by the hot combustion gases).

The heat generated during combustion (the temperature at the heart of the furnace may be as high as 1500°C) is partly radiant and partly convective, the latter carried off by the hot combustion gases. The radiant heat is collected at the walls of the furnace where water is circulated in pipes. Covective heat in the combustion gases is captured in bundles of tubes containing either water or steam which are placed in the path of the flue gas as it exits the furnace.

In a conventional boiler there is a drum positioned appropriately within the steam–water system containing both water and steam so that steam can develop as the temperature of the fluid rises. The most advanced designs, however, operate at such high temperatures and pressures that they do not pass through a stage in which water and steam co-exist. In these boilers the water turns directly to steam within the water tubes. This type of boiler exploits what is called a supercritical cycle, called so because the thermodynamic fluid (the water) enters what is known as the supercritical phase without passing through a condition in which both water and steam co-exist.

The boiler watertubes in the exhaust gas path are frequently divided into a number of different sections. (These sections have names, such as economiser, reheater or superheater.) The water or steam passes through them is a specific order determined by the design of the steam cycle. Traditional pulverised-coal boilers have been built with outputs of up to 1000MW.

Steam turbine

The steam turbine is the primary mechanical device in most conventional coal-fired power stations. Its job is to convert the heat energy contained in the steam exiting the boiler into mechanical energy, rotary motion. The steam turbine first appeared in power applications at the end of the nineteenth century. Before that steam power was derived from steam-driven piston engines.

The steam turbine is something of a cross between a hydropower turbine and a windmill. It, like them, is designed to extract energy from a moving fluid. The fluid is water, the same as the hydro turbine. In the case of a hydro turbine the water remains in the liquid phase and neither its volume nor its temperature changes during energy extraction. In the case of the steam turbine, energy extraction is from a gas, steam, rather than a liquid and involves both the pressure and the temperature of the fluid falling. This has a profound effect on the turbine design.

Both hydro and steam turbines exist in two broad types: there are impulse turbines which extract the energy from a fast-moving jet of fluid and reaction turbines which are designed to exploit the pressure of a fluid rather than its motion. A hydro turbine will be of one design or the other. In a steam turbine the two principles may be mixed in a single machine and they may even be mixed in a single turbine blade.

It is impossible to extract all the energy from steam using a turbine with a single set of turbine blades. Instead, a steam turbine utilises a series of sets of blades, called stages. Each stage is followed by a set of stationary blades (usually called nozzles) which control the steam flow to the next stage.

A single steam turbine stage consists of a set of narrow blades projecting from a central hub. (In concept, it is something like a steam windmill.) Ten or more sets of blades can be mounted on a single steam turbine shaft. This combination of shaft and blades is called a rotor. The turbine stages are separated by carefully designed stationary blades, or nozzles, which control the flow of steam from one set of rotating blades to the next. The precise shape of the blades in each set determines whether that set is impulse or reaction, or a cross between the two. The hub, blades and nozzles are enclosed in a close-fitting case to maintain the steam pressure.

In a steam turbine impulse stage, energy is extracted at constant pressure while the velocity of the steam falls as it flows across the blades. The steam is then expanded through a stationary control stage to increase its velocity again before energy is extracted from another set of impulse blades. In a steam turbine reaction stage, by contrast, both pressure and velocity of the steam fall as energy is extracted by the rotating blades.

Steam exiting the power plant boiler is at a high temperature and a high pressure. Both temperature and pressure fall as the steam passes through the turbine. The greater the temperature drop and the greater the pressure drop, the more energy can be captured from the steam. Consequently the most efficient power plants condense the steam back to water at the end of the turbine.

Even with a modern design it is impossible to capture all the energy from the steam efficiently with a single multiple-stage turbine. Coal-fired power plants use several. These are usually divided into high-, medium- and low-pressure turbines. The blades in these turbines get larger (longer) as the pressure drops; in fact, the low-pressure turbine may comprise several turbines operating in parallel to gain the most energy without making a single turbine impossibly large. All the turbines may be mounted on a single shaft, but it is common for the low-pressure turbines to be on a separate shaft rotating at a lower speed to reduce the forces exerted at the blade tips. Multiple turbines of this type can have aggregate outputs of over 1000MW.

As with boilers, the demands of modern power plant design have led to the development and introduction of high-performance materials that can cope with the extreme conditions encountered within a steam turbine. The high-pressure turbine blades have to be able to withstand extremes of both temperature and pressure and have to be able to resist the abrasive force of steam. At the low-pressure end of the turbine train the large size of the turbines means that the blade tip speeds are enormous, again requiring specially designed materials to withstand the centrifugal forces exerted on them.

A refinement which improves the overall efficiency is to return the steam to the boiler after it has passed through the high-pressure turbine, reheating it before delivering it to the medium-pressure turbine. Most modern steam turbine plants use this single reheat design (multiple reheat is also possible).

The theoretical maximum efficiency of a coal-fired power station is determined by the temperature difference between the steam entering the high-pressure turbine and the steam exiting the low-pressure turbine. The greater this temperature difference, the more energy can be extracted. With the most advanced technology, utilising the best boiler materials to achieve the highest-steam temperatures and pressures, a maximum efficiency of around 43–45% can be achieved. New supercritical designs may eventually push this as high as 55%. In the near future, however, the best that is likely to be achieved is something between 47% and 49%.

Generators

The turbine shaft, or shafts if there is more than one, are coupled to a generator which converts the rotary mechanical motion into the electrical energy that the plant is designed to provide. Generators, like steam turbines, first appeared during the nineteenth century. All utilise a coil of a conducting material, usually copper moving in a magnetic field to generate electricity.

The generators used in most power stations, including coal-fired power stations, are designed to deliver an alternating current (AC) to a power grid. An AC current is preferred because it allows the voltage to be raised or lowered easily using a transformer. For transmission of power over long distances it is preferable to use a very high voltage and a low current. The voltage is then reduced with a transformer before delivery to the consumer.

The need to generate an AC voltage determines the speed at which the generator rotates. This must be an exact multiple of the grid frequency (normally grids operate at either 50 or 60Hz). For grids operating at 50Hz the traditional generator speed is 50 cycles per second, or 3000rpm. The equivalent 60Hz machine rotates at 3600rpm. This speed, in turn, determines the operating speed of the steam turbine. Large low-pressure steam turbines may operate at half these speeds.

Generators may be as large as 2000MW, and large generators are normally built to suit a particular project. Modern generators operate with an efficiency of greater than 95%. The remaining 5% of the mechanical input energy from the turbine is usually lost as heat within the generator windings and magnetic components. Even though the percentage is small, this still represents an enormous amount of energy; perhaps 50MW in a 1000-MW machine. Hence generators require very efficient cooling systems in order to prevent them overheating. Avariety of cooling mediums are used, including hydrogen which is extremely efficient because of its low density and high specific heat.

The broad outline of generator design has changed little over a century. However new materials have improved efficiencies. The latest developments involve the use of superconducting materials to reduce energy and increase efficiencies.

Coal Fired Steam Power Plant Video

Coal-Fired Steam Power Plant Reference Books:

Steam Plant Operation

Steam Turbines: Theory and Design

Steam Plant Calculations Manual,...

 

Power Plant Engineering

     

There are many renewable energy sources in the world such as hydrogen, solar, wind, biomass, hydropower, and geothermal energy. Many people think that hydrogen will be the most important fuel of the future because it meets so many requirements of a good energy system. Experts agree the ideal energy system should include the characteristics listed below:

• should rely on domestic energy sources.
• should be able to utilize a variety of energy sources.
• should produce few harmful pollutants and greenhouse gas emissions.
• should be energy efficient (high energy output from the energy input).
• should be accessible (easy to find, produce or harness).
• should result in stable energy prices.

Hydrogen is a versatile energy carrier that can be used to power nearly every end-use energy need. The fuel cell — an energy conversion device that can efficiently capture and use the power of hydrogen — is the key to making it happen.

• Stationary fuel cells can be used for backup power, power for remote locations, distributed power generation, and cogeneration (in which excess heat released during electricity generation is used for other applications).
• Fuel cells can power almost any portable application that typically uses batteries, from hand-held devices to portable generators.
• Fuel cells can also power our transportation, including personal vehicles, trucks, buses, and marine vessels, as well as provide auxiliary power to traditional transportation technologies. Hydrogen can play a particularly important role in the future by replacing the imported petroleum we currently use in our cars and trucks.

What Is A Fuel Cell

A fuel cell is a device that produces a chemical reaction between substances, generating an electric current in the process. It is an electrochemical energy conversion device. Everyone uses another electrochemical energy conversion device, i.e. a battery. A battery contains substances that produce an electric current as they react. When all of the substances have reacted, the battery is dead; it must be replaced or recharged.

With a fuel cell, the substances (in this case, hydrogen and oxygen) are stored outside of the device. As long as there is a supply of hydrogen and oxygen, the fuel cell can continue to generate an electric current, which can be used to power motors, lights, and other electrical appliances.

Why Fuel Cells?

Fuel cells directly convert the chemical energy in hydrogen to electricity, with pure water and potentially useful heat as the only byproducts.

• Hydrogen-powered fuel cells are not only pollution-free, but also can have two to three times the efficiency of traditional combustion technologies.
• A conventional combustion-based power plant typically generates electricity at efficiencies of 33 to 35 percent, while fuel cell systems can generate electricity at efficiencies up to 60 percent (and even higher with cogeneration).
• The gasoline engine in a conventional car is less than 20% efficient in converting the chemical energy in gasoline into power that moves the vehicle, under normal driving conditions. Hydrogen fuel cell vehicles,which use electric motors, are much more energy efficient and use 40-60 percent of the fuel’s energy — corresponding to more than a 50% reduction in fuel consumption, compared to a conventional vehicle with a gasoline internal combustion engine. 

In addition, fuel cells operate quietly, have fewer moving parts, and are well suited to a variety of applications.

How Do Fuel Cells Work?

A single fuel cell consists of an electrolyte sandwiched between two electrodes, an anode and a cathode. Bipolar plates on either side of the cell help distribute gases and serve as current collectors.

There are many types of fuel cells, but the most important technology for transportation applications is the polymer electrolyte (or proton exchange) membrane or PEM cell. A PEM fuel cell converts hydrogen and oxygen into water, producing an electric current during the process.

In a Polymer Electrolyte Membrane (PEM) fuel cell, which is widely regarded as the most promising for light-duty transportation, hydrogen gas flows through channels to the anode, where a catalyst causes the hydrogen molecules to separate into protons and electrons.  The anode is the negative side of the fuel cell. The anode has channels to disperse the hydrogen gas over the surface of the catalyst. Hydrogen gas under pressure enters the fuel cell on the anode side and reacts with the catalyst.

The polymer electrolyte membrane (PEM) is a specially treated material that conducts positive ions (protons), but blocks electrons from flowing through the membrane.  While the protons are conducted through the membrane to the other side of the cell, the stream of negatively-charged electrons follows an external circuit to the cathode. This flow of electrons is electricity that can be used to do work, such as power a motor.

On the other side of the cell, oxygen gas, typically drawn from the outside air, flows through channels to the cathode.  The cathode is the positive side of the fuel cell. It has channels to distribute oxygen gas to the surface of the catalyst. The oxygen reacts with the catalyst and splits into two oxygen atoms. Each oxygen atom picks up two electrons from the external circuit to form an oxygen ion (that combines with two hydrogen ions (2H+) to form a water molecule (H2O). This union is an exothermic reaction, generating heat that can be used outside the fuel cell.

The power produced by a fuel cell depends on several factors, including the fuel cell type, size, temperature at which it operates, and pressure at which gases are supplied. A single fuel cell produces approximately 1 volt or less — barely enough electricity for even the smallest applications. To increase the amount of electricity generated, individual fuel cells are combined in series to form a stack. (The term “fuel cell” is often used to refer to the entire stack, as well as to the individual cell.) Depending on the application, a fuel cell stack may contain only a few or as many as hundreds of individual cells layered together. This “scalability” makes fuel cells ideal for a wide variety of applications, from laptop computers (50-100 Watts) to homes (1-5kW), vehicles (50-125 kW), and central power generation (1-200 MW or more).

What Is Hydrogen?

Hydrogen is the simplest element known to exist. An atom of hydrogen has oneproton and one electron. It is the lightest element and a gas at normaltemperature and pressure. Hydrogen is also the most abundant gas in the universe and the source of all the energy we receive from the sun. Hydrogen has the highest energy content of any common fuel by weight, but the lowest energy content by volume.

The sun is basically a giant ball of hydrogen and helium gases. In the sun.s core, the process of fusion is continually taking place. During fusion, the protons of four hydrogen atoms combine to form one helium atom with two protons and two neutrons, releasing energy as radiation.

This radiant energy is our most important energy source. It gives us light and heat and makes plants grow. It causes the wind to blow and the rain to fall. It is stored as chemical energy in fossil fuels. Most of the energy we use originally came from the sun.s radiant energy.

Hydrogen as a gas (H2), however, doesn’t exist naturally on earth. It is found only in compound form. Combined with oxygen, it is water (H2O). Combined with carbon, it forms organic compounds such as methane (CH4), coal, and petroleum. It is found in all growing things. biomass. Hydrogen is also an abundant element in the earth.s crust.

How Is Hydrogen Made?

Since hydrogen gas is not found naturally on earth, it must be manufactured. There are many ways to do this. The fact that hydrogen can be produced using so many different domestic resources is an important reason why it is a promising energy carrier. In a hydrogen economy, we will not need to rely on a single resource or technology to meet our energy needs.

Steam Reforming

Industry produces hydrogen by steam reforming, a process in which high-temperature steam separates hydrogen atoms from carbon atoms in methane (CH4), as shown below.

     CH + H2O (steam)  ---> 3H + CO
     CO + H2O (steam) ---> CO2 + H2

Today, most of the hydrogen produced by steam reforming isn.t used as fuel but in industrial processes. Steam reforming is the most cost-effective way to produce hydrogen today and accounts for about 95 percent of the hydrogen produced in the U.S. Because of its limited supply, however, we cannot rely on natural gas to provide hydrogen over the long term. Instead, we will need to produce hydrogen using other resources and technologies, such as those listed below.

Electrolysis

One way to make hydrogen is by electrolysis.splitting water into its basic elements hydrogen and oxygen. Electrolysis involves passing an electric current through water (H2O) to separate the water molecules into hydrogen (H2) and oxygen (O2) gases.

The electricity needed for electrolysis can come from a power plant, windmill, photovoltaic cell or any other electricity generator. If the electricity is produced by renewable energy or nuclear power, there is no net increase in greenhouse gases added to the atmosphere. Hydrogen produced by electrolysis is extremely pure, but it is very expensive because of equipment costs and other factors. On the other hand, water is renewable and abundant in many areas.

Technological advances to improve efficiency and reduce costs will make electrolysis a more economical way to produce hydrogen in the future.

Photoelectrochemical Production

Photoelectrolysis uses sunlight to split water into hydrogen and oxygen. A semiconductor absorbs energy from the sun and acts as an electrode to separate the water molecules.

Biomass Gasification

In biomass gasification, wood chips and agricultural wastes are super-heated until they turn into hydrogen and other gases. Biomass can also be used to provide the heat.

Photobiological Production

 Scientists have discovered that some algae and bacteria produce hydrogen under certain conditions, using sunlight as their energy source. Experiments are underway to find ways to induce these microbes to produce hydrogen efficiently.

Coal Gasification With Carbon Sequestration

 In this process, coal is gasified (turned into a gas) with oxygen under high pressure and temperature to produce hydrogen and carbon monoxide (CO). Steam (H2O) is added to the CO to produce hydrogen and carbon dioxide (H2 and CO2). The carbon dioxide is captured and sequestered (stored) to prevent its release into the atmosphere.

Nuclear Thermochemical

In this experimental process, the heat from a controlled nuclear reaction is used to decompose water into hydrogen and oxygen in a series of complex chemical reactions.

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