Electricity generation”Electricity generation is the process of generating electric power from sources of primary energy. For electric utilities in the electric power industry, it is the first stage in the delivery of electricity to end users, the other stages being transmission, distribution, energy storage and recovery, using pumped-storage methods.A characteristic of electricity is that it is not a primary energy freely present in nature in remarkable amounts and it must be produced.
Production is carried out in power plants. Electricity is most often generated at a power station by electromechanical generators, primarily driven by heat engines fueled by combustion or nuclear fission but also by other means such as the kinetic energy of flowing water and wind. Other energy sources include solar photovoltaics and geothermal power.Methods of generating electricity:Several fundamental methods exist to convert other forms of energy into electrical energy. The turboelectric effect, piezoelectric effect, and even direct capture of the energy of nuclear decay Betavoltaics are used in niche applications, as is direct conversion of heat to electric power in the thermoelectric effect. Utility-scale generation is done by rotating electric generators, or by photovoltaic systems.
A very small proportion of electric power distributed by utilities is provided by batteries.Generators:Electric generators transform kinetic energy into electricity. This is the most used form for generating electricity and is based on Faraday’s law. It can be seen experimentally by rotating a magnet within closed loops of a conducting material (e.g.
copper wire). Almost all commercial electrical generation is done using electromagnetic induction, in which mechanical energy forces a generator to rotate.Electrochemistry:Electrochemistry is the direct transformation of chemical energy into electricity, as in a battery. Electrochemical electricity generation is important in portable and mobile applications. Currently, most electrochemical power comes from batteries. Primary cells, such as the common zinc–carbon batteries, act as power sources directly, but many types of cells are used as storage systems rather than primary generation systems. Open electrochemical systems, known as fuel cells, can be used to extract power either from natural fuels or from synthesized fuels.
Osmotic power is a possibility at places where salt and fresh water merges.Photovoltaic effect:The photovoltaic effect is the transformation of light into electrical energy, as in solar cells. Photovoltaic panels convert sunlight directly to electricity. Although sunlight is free and abundant, solar electricity is still usually more expensive to produce than large-scale mechanically generated power due to the cost of the panels.
Low-efficiency silicon solar cells have been decreasing in cost and multifunction cells with close to 30% conversion efficiency are now commercially available. Over 40% efficiency has been demonstrated in experimental systems.5 Until recently, photovoltaic were most commonly used in remote sites where there is no access to a commercial power grid or as a supplemental electricity source for individual homes and businesses.
Recent advances in manufacturing efficiency and photovoltaic technology, combined with subsidies driven by environmental concerns, have dramatically accelerated the deployment of solar panels. Installed capacity is growing by 40% per year led by increases in Germany, Japan, and the United States.Pumped-storage hydroelectricity:Pumped-storage hydroelectricity (PSH), or pumped hydroelectric energy storage (PHES), is a type of hydroelectric energy storage used by electric power systems for load balancing. The method stores energy in the form of gravitational potential energy of water, pumped from a lower elevation reservoir to a higher elevation. Low-cost surplus off-peak electric power is typically used to run the pumps. During periods of high electrical demand, the stored water is released through turbines to produce electric power. Although the losses of the pumping process makes the plant a net consumer of energy overall, the system increases revenue by selling more electricity during periods of peak demand, when electricity prices are highest.
Pumped-storage hydroelectricity allows energy from intermittent sources (such as solar, wind) and other renewable, or excess electricity from continuous base-load sources (such as coal or nuclear) to be saved for periods of higher demand. The reservoirs used with pumped storage are quite small when compared to conventional hydroelectric dams of similar power capacity, and generating periods are often less than half a day.Pumped storage is the largest-capacity form of grid energy storage available, and, as of 2017, the DOE Global Energy Storage Database reports that PSH accounts for over 96% of all active tracked storage installations worldwide, with a total installed nameplate capacity of over 168 GW. The round-trip energy efficiency of PSH varies between 70%–80%, with some sources claiming up to 87%.
The main disadvantage of PSH is the specialist nature of the site required, needing both geographical height and water availability. Suitable sites are therefore likely to be in hilly or mountainous regions, and potentially in areas of outstanding natural beauty, and therefore there are also social and ecological issues to overcome. Many recently proposed projects, at least in the U.S., avoid highly sensitive or scenic areas, and some propose to take advantage of “Brownfield” locations such as disused minesAt times of low electrical demand, excess generation capacity is used to pump water into the upper reservoir.
When there is higher demand, water is released back into the lower reservoir through a turbine, generating electricity. Reversible turbine/generator assemblies act as a combined pump and turbine generator unit (usually a Francis turbine design).Types: natural or man-made reservoirsIn open-loop systems, pure pumped-storage plants store water in an upper reservoir with no natural inflows, while pump-back plants utilize a combination of pumped storage and conventional hydroelectric plants with an upper reservoir that is replenished in part by natural inflows from a stream or river. Plants that do not use pumped-storage are referred to as conventional hydroelectric plants; conventional hydroelectric plants that have significant storage capacity may be able to play a similar role in the electrical grid as pumped storage by deferring output until needed.Hydropower:Hydropower or water power (from Greek: ????, “water”) is power derived from the energy of falling water or fast running water, which may be harnessed for useful purposes. Since ancient times, hydropower from many kinds of watermills has been used as a renewable energy source for irrigation and the operation of various mechanical devices, such as gristmills, sawmills textile mills, trip hammers, dock cranes, domestic lifts, and ore mills. A trompe, which produces compressed air from falling water, is sometimes used to power other machinery at a distance.
In the late 19th century, hydropower became a source for generating electricity. Cragside in Northumberland was the first house powered by hydroelectricity in 18783 and the first commercial hydroelectric power plant was built at Niagara Falls in 1879. In 1881, street lamps in the city of Niagara Falls were powered by hydropower.Since the early 20th century, the term has been used almost exclusively in conjunction with the modern development of hydroelectric power.
International institutions such as the Bank view hydropower as a means for economic development without adding substantial amounts of carbon to the atmosphere, but dams can have significant negative social and environmental impacts.Hydropower typesHydropower is used primarily to generate electricity. Broad categories include:Conventional hydroelectric, referring to hydroelectric dams.Run-of-the-river hydroelectricity, which captures the kinetic energy in rivers or streams, without a large reservoir and sometimes without the use of dams.Small hydro projects are 10 megawatts or less and often have no artificial reservoirs.
Micro hydro projects provide a few kilowatts to a few hundred kilowatts to isolated homes, villages, or small industries.Conduit hydroelectricity projects utilize water which has already been diverted for use elsewhere; in a municipal water system, for example.Pumped-storage hydroelectricity stores water pumped uphill into reservoirs during periods of low demand to be released for generation when demand is high or system generation is low.Pressure buffering hydropower use natural sources (waves for example) for water pumping to turbines while exceeding water is pumped uphill into reservoirs and releases when incoming water flow isn’t enough.What is renewable energy?Generally speaking, the world’s energy resources (all the energy we have available to use) fall into two types called fossil fuels and renewable energy:Fossil fuels are things like oil, gas, coal, and peat, formed over hundreds of millions of years when plants and sea creatures rot away, fossilize, and get buried under the ground, then squeezed and cooked by Earth’s inner pressure and heat.
Fossil fuels deliver about 80–90 percent of the world’s energy.Renewable energy means energy completed from the wind, ocean waves, solar power, biomass (plants grown especially for energy), and so on. It’s called renewable because, in theory, it will never run out. Renewable sources presently make available about 10–20 percent of the world’s energy.
Solar Energy:Introduction:Solar energy is an important, clean, cheap and abundantly available renewable energy. It is received on Earth in cyclic, intermittent and dilute form with very low power density 0 to 1 kW/m2.Solar energy received on the ground level is affected by atmospheric clarity, degree of latitude, etc. For design purpose, the variation of available solar power, the optimum tilt angle of solar flat plate collectors, the location and orientation of the heliostats should be calculated.Essential subsystems in a solar energy plant:Solar collector or concentrator: It receives solar rays and collects the energy. It may be of following types:Flat plate type without focusingParabolic trough type with line focusingParaboloid dish with central focusingFresnel lens with centre focusingHeliostats with centre receiver focusingEnergy transport medium: Substances such as water/ steam, liquid metal or gas are used to transport the thermal energy from the collector to the heat exchanger or thermal storage. In solar PV systems energy transport occurs in electrical form.Energy storage: Solar energy is not available continuously.
So we need an energy storage medium for maintaining power supply during nights or cloudy periods. There are three major types of energy storage: a) Thermal energy storage; b) Battery storage; c) Pumped storage hydro-electric plant.Energy conversion plant: Thermal energy collected by solar collectors is used for producing steam, hot water, etc. Solar energy converted to thermal energy is fed to steam-thermal or gas-thermal power plant.Power conditioning, control and protection system: Load requirements of electrical energy vary with time. The energy supply has certain specifications like voltage, current, frequency, power etc.
The power conditioning unit performs several functions such as control, regulation, conditioning, protection, automation, etc.Solar Energy:Introduction:Solar energy is an important, clean, cheap and abundantly available renewable energy. It is received on Earth in cyclic, intermittent and dilute form with very low power density 0 to 1 kW/m2.
Solar energy received on the ground level is affected by atmospheric clarity, degree of latitude, etc. For design purpose, the variation of available solar power, the optimum tilt angle of solar flat plate collectors, the location and orientation of the heliostats should be calculated.Essential subsystems in a solar energy plant:Solar collector or concentrator: It receives solar rays and collects the energy.
It may be of following types:Flat plate type without focusingParabolic trough type with line focusingParaboloid dish with central focusingFresnel lens with centre focusingHeliostats with centre receiver focusingEnergy transport medium: Substances such as water/ steam, liquid metal or gas are used to transport the thermal energy from the collector to the heat exchanger or thermal storage. In solar PV systems energy transport occurs in electrical form.Energy storage: Solar energy is not available continuously. So we need an energy storage medium for maintaining power supply during nights or cloudy periods.
There are three major types of energy storage: a) Thermal energy storage; b) Battery storage; c) Pumped storage hydro-electric plant.Energy conversion plant: Thermal energy collected by solar collectors is used for producing steam, hot water, etc. Solar energy converted to thermal energy is fed to steam-thermal or gas-thermal power plant.Power conditioning, control and protection system: Load requirements of electrical energy vary with time.
The energy supply has certain specifications like voltage, current, frequency, power etc.The power conditioning unit performs several functions such as control, regulation, conditioning, protection, automation, etc.SOLAR COLLECTORSSolar thermal energy is the most readily available source of energy. The Solar energy is most important kind of non-conventional source of energy which has been used since ancient times, but in a most primitive manner. The abundant solar energy available is suitable for harnessing for a number of applications.
The application of solar thermal energy system ranges from solar cooker of 1 KW to power plant of 200MW. These systems are grouped into low temperature (<150oC), medium temperature (150-300oC) applications.Solar CollectorsSolar collectors are used to collect the solar energy and convert the incident radiations into thermal energy by absorbing them. This heat is extracted by flowing fluid (air or water or mixture with antifreeze) in the tube of the collector for further utilization in different applications. The collectors are classified as;Non concentrating collectorsConcentrating (focusing) collectorsNon Concentrating Collectors:In these collectors the area of collector to intercept the solar radiation is equal to the absorber plate and has concentration ratio of 1.
Flat Plate Collectors (Glaze Type) Flat plate collector is most important part of any solar thermal energy system. It is simplest in design and both direct and diffuse radiations are absorbed by collector and converted into useful heat. These collectors are suitable for heating to temperature below 100oC. Concentrating Collectors:Concentrating collector is a device to collect solar energy with high intensity of solar radiation on the energy absorbing surface.
Such collectors use optical system in the form of reflectors or refractors.These collectors are used for medium (100-300o C) and high-temperature (above 300oC) applications such as steam production for the generation of electricity. The high temperature is achieved at absorber because of reflecting arrangement provided for concentrating the radiation at required location using mirrors and lenses. These collectors are best suited to places having more number of clear days in a year.
The area of the absorber is kept less than the aperture through which the radiation passes, to concentrate the solar flux. These collectors require tracking to follow the sun because of optical system. The tracking rate depends on the degree of concentration ratio and needs frequent adjustment for system having high concentration ratio. The efficiency of these collectors lies between 50-70%.
The collectors need more maintenance than FPC because of its optical system. The concentrating collectors are classified on the basis of reflector used; concentration ratio and tracking method adoptedWIND ENERGYIntroduction:The wind turbine captures the wind’s kinetic energy in a rotor consisting of two or more blades mechanically coupled to an electrical generator. The turbine is mounted on a tall tower to enhance the energy capture. Numerous wind turbines are installed at one site to build a wind farm of the desired power generation capacity. Obviously, sites with steady high wind produce more energy over the year.Two distinctly different configurations are available for turbine design, the horizontal-axis configuration (Figure 3.
1) and the vertical-axis configuration. The horizontal-axis machine has been the standard in Denmark from the beginning of the wind power industry. Therefore, it is often called the Danish wind turbine. The vertical-axis machine has the shape of an egg beater and is often called the Darrieus rotor after its inventor. It has been used in the past because of its specific structural advantage. However, most modern wind turbines use a horizontal axis design. Except for the rotor, most other components are the same in both designs, with some differences in their placements.WIND SPEED DISTRIBUTION:Having a cubic relation with power, wind speed is the most critical data needed to appraise the power potential of a candidate site.
The wind is never steady at any site. It is influenced by the weather system, the local land terrain, and its height above the ground surface. Wind speed varies by the minute, hour, day, season, and even by the year. Therefore, the annual mean speed needs to be averaged over 10 yr or more. Such a long-term average gives a greater confidence in assessing the energy-capture potential of a site. However, long-term measurements are expensive and most projects cannot wait that long. In such situations, the short-term data, for example, over 1 yr, is compared with long-term data from a nearby site to predict the long-term annual wind speed at the site under consideration. This is known as the measure, correlate, and predict (mcp) technique.
Because wind is driven by the sun and the seasons, the wind pattern generally repeats over a period of 1 yr. The wind site is usually described by the speed data averaged over calendar months. Sometimes, the monthly data is aggregated over the year for brevity in reporting the overall “windiness” of various sites.
Wind speed variations over the period can be described by a probability distribution function.WIND SPEED PREDICTIONBecause the available wind energy at any time depends on the wind speed at that time, which is a random variable, knowing the average annual energy potential of a site is one thing and the ability to accurately predict when the wind will blow is quite another thing. For the wind farm operator, this poses difficulties in system scheduling and energy dispatching as the schedule of wind power availability is not known in advance. However, a reliable forecast of wind speed several hours in advance can give the following benefits:Generating schedule can efficiently accommodate wind generation in a timely manner.Allows the grid-connected wind farm to commit to power purchase contracts in advance for a better price.Allows investors to proceed with new wind farms and avoid the penalties they must pay if they do not meet their hourly generation targets.Therefore, development of short-term wind-speed-forecasting tools helps wind energy producers.
NWTC researchers work in cooperation with the National Oceanic and Atmospheric Administration (NOAA) to validate the nation’s wind resource maps and develop methods of short-term (1 to 4 h) wind forecasting. Previously have also proposed a new technique for forecasting wind speed and power output up to several hours in advance. Their technique is based on cross-correlation at neighboring sites and artificial neural networks and is claimed to significantly improve forecasting accuracy compared to the persistence-forecasting model.”