Electricity Generation

Electricity is produced at a an electric power plant. Some fuel source, such as coal, oil, natural gas, or nuclear energy produces heat. The heat is used to boil water to create steam. The steam under high pressure is used to spin a turbine. The spinning turbine interacts with a system of magnets to produce electricity. The electricity is transmitted as moving electrons through a series of wires to homes and business.

Electric Power Plants:

Electric Power Plants have a number of components in common and are an interesting study in the various forms and changes of energy necessary to produce electricity.

Boiler Unit: Almost all of power plants operate by heating water in a boiler unit into super heated steam at very high pressures. The source of heat from combustion reactions may vary in fossil fuel plants from the source of fuels such as coal, oil, or natural gas. Biomass or waste plant parts may also be used as a source of fuel. In some areas solid waste incinerators are also used as a source of heat. All of these sources of fuels result in varying amounts of air pollution, as well as, the carbon dioxide ( a gas implicated in global warming problems).

In a nuclear power plant, the fission chain reaction of splitting nuclei provides the source of heat.

Turbine-Generator: The super heated steam is used to spin the blades of a turbine, which in turn is used in the generator to turn a coil of wires within a circular arrangements of magnets. The rotating coil of wire in the magnets results in the generation of electricity.

Cooling Water: After the steam travels through the turbine, it must be cooled and condensed back into liquid water to start the cycle over again. Cooling water can be obtained from a nearby river or lake. The water is returned to the body of water 10 -20 degrees higher in temperature than the intake water. Alternate method is to use a very tall cooling tower, where the evaporation of water falling through the tower provides the cooling effect.

Creating Electricity using a Generator:
If a magnetic field can create a current then we have a means of generating electricity. Experiments showed that a magnetic just sitting next to a wire produced no current flow through that wire. However, if the magnet is moving, a current is induced in the wire. The faster the magnet moves, the greater the induced current.

This is the principal behind simple electric generators in which a wire loop is rotated between to stationary magnetics. This produces a continuously varying voltage which in turn produces an alternating current .

Diagram of a simple electric generator is shown on the right.

To generate electricty then, some (mechanical) mechanism is used to turn a crank that rotates a loop of wire between stationary magnets. The faster the crank turns, the more current that is generated.

In hydroelectric, the falling water turns the turbine. The wind can also turn the turbine. In fossil fuel plants and nuclear plants, water is heated to steam which turns the turbine.

Electricity Generation in Power Plants

There are many methods to generate electricity. The most common and simple method is by a battery, a very familiar household item. This is ideal for very small capacities. To meet the entire domestic, commercial and industrial demand electricity generation has to be done in a large scale in power plants.

Most of the electricity generated in the world is by using an electrical generator. An electrical generator uses the principle of Faraday to produce electricity. Faraday found that a copper coil when moved in a magnetic field produces a voltage across the coil. The electric generator consists of a magnet called the ‘rotor’, which can be rotated inside a copper coil called the 'stator' to generate electricity.

To generate electricity we have to mechanically rotate the ‘rotor’. Energy is required to rotate the generator. Energy available in various forms like coal, oil and gas has to be converted to mechanical energy to rotate the generator. This conversion can take place in many different ways. The power plant does this conversion from the primary energy source to mechanical rotation and then to electricity. A small form of this generator is what we have in our car, the alternator. The car’s engine rotates the alternator which generates power for the car. A slightly bigger version is the portable generator driven by a petrol or diesel engine, normally used as a standby in case of a mains power failure.

Moreover, in thermal power plants, a steam turbine rotates the generator. This requires the continuous flow of high-pressure steam. Burning fuels like coal, oil or gas produces heat. This heat boils the water in the boiler to produce high-pressure steam. This steam rotates the turbine, which in turn rotates the generator. Burning of other fuels like bio-mass or municipal waste also produces steam for use in the turbine. Waste heat from other process can also produce steam.

Nuclear power plants also use a steam turbine to rotate the generator. Steam generators produce steam by utilising the heat from nuclear fission taking place in a nuclear reactor. Geo-thermal power plants use the steam available from underground geo-thermal reservoirs to rotate the turbine.


It is also possible to rotate the generator directly without a steam turbine using other engines. Internal combustion engines, diesel or petrol driven, can directly turn the generators to produce electricity. The gas turbine power plant uses a gas turbine. The thrust produced from combustion of natural gas rotates the gas turbines, which in turn rotates the generator. This is something like using the thrust from the jet engines of an airplane. In Hydroelectric power plants the energy of water stored at a height in reservoirs created by dams, turn hydro turbines and connected generators to generate electricity. In a wind energy farms, force of the wind turns the wind turbines, which inturn rotates the generators attached to them to produce electricity.

There are other methods to generate electricity without a generator using electrochemical reactions. The most common is the battery in which chemical reaction converts to electricity. In a solar plant, energy from the sunlight is converted directly to electricity by using Solar cells. In a hydrogen fuel cell, chemical reaction between hydrogen and oxygen is used to generate electricity.

All types of power plants cannot be installed everywhere. Availability of the primary energy source is the primary concern. For example, the installation of Wind turbines is done only in places with consistently good wind throughout the year. Also of great concern is the efficiency of conversion from the primary source to final electric output.

The attached mindmap shows the conversion of primary energy sources to electricity.
 
Mindmap

 

Steam Turbine Electricity Generation Plants

Conventional Energy Generation

The first practical electricity generating system using a steam turbine was designed and made by Charles Parsons in 1887 and used for lighting an exhibition in Newcastle. Since then, apart from getting bigger, turbine design has hardly changed and Parson's original design would not look out of place today. Despite the introduction of many alternative technologies in the intervening 120 years, over 80 percent of the world's electricity is still generated by steam turbines driving rotary generators.

The Energy Conversion Processes

Electrical energy generation using steam turbines involves three energy conversions, extracting thermal energy from the fuel and using it to raise steam, converting the thermal energy of the steam into kinetic energy in the turbine and using a rotary generator to convert the turbine's mechanical energy into electrical energy.

  

Raising steam (Thermal Sources)

Steam is mostly raised from fossil fuel sources, three of which are shown in the above diagram but any convenient source of heat can be used.

Chemical Transformation

In fossil fuelled plants steam is raised by burning fuel, mostly coal but also oil and gas, in a combustion chamber. Recently these fuels have been supplemented by limited amounts of renewable biofuels and agricultural waste.

The chemical process of burning the fuel releases heat by the chemical transformation (oxidation) of the fuel. This can never be perfect. There will be losses due to impurities in the fuel, incomplete combustion and heat and pressure losses in the combustion chamber and boiler. Typically these losses would amount to about 10% of the available energy in the fuel.

Nuclear Power

Steam for driving the turbine can also be raised by capturing the heat generated by controlled nuclear fission. This is discussed more fully in the section on Nuclear Power.
Solar Power

Similarly solar thermal energy can be used to raise steam, though this is less common.
Geothermal Energy

Steam emissions from naturally occurring aquifers are also used to power steam turbine power plants.

The Steam Turbine (Prime Mover)

Working Principles

High pressure steam is fed to the turbine and passes along the machine axis through multiple rows of alternately fixed and moving blades. From the steam inlet port of the turbine towards the exhaust point, the blades and the turbine cavity are progressively larger to allow for the expansion of the steam.

The stationary blades act as nozzles in which the steam expands and emerges at an increased speed but lower pressure. (Bernoulli's conservation of energy principle - Kinetic energy increases as pressure energy falls). As the steam impacts on the moving blades it imparts some of its kinetic energy to the moving blades.

There are two basic steam turbine types, impulse turbines and reaction turbines, whose blades are designed control the speed, direction and pressure of the steam as is passes through the turbine.

Impulse Turbines

The steam jets are directed at the turbine's bucket shaped rotor blades where the pressure exerted by the jets causes the rotor to rotate and the velocity of the steam to reduce as it imparts its kinetic energy to the blades. The blades in turn change change the direction of flow of the steam however its pressure remains constant as it passes through the rotor blades since the cross section of the chamber between the blades is constant. Impulse turbines are therefore also known as constant pressure turbines.

The next series of fixed blades reverses the direction of the steam before it passes to the second row of moving blades.

Reaction Turbines

The rotor blades of the reaction turbine are shaped more like aerofoils, arranged such that the cross section of the chambers formed between the fixed blades diminishes from the inlet side towards the exhaust side of the blades. The chambers between the rotor blades essentially form nozzles so that as the steam progresses through the chambers its velocity increases while at the same time its pressure decreases, just as in the nozzles formed by the fixed blades. Thus the pressure decreases in both the fixed and moving blades. As the steam emerges in a jet from between the rotor blades, it creates a reactive force on the blades which in turn creates the turning moment on the turbine rotor, just as in Hero's steam engine. (Newton's Third Law - For every action there is an equal and opposite reaction

Steam Turbine Electricity Generation Plants

Conventional Energy Generation

The first practical electricity generating system using a steam turbine was designed and made by Charles Parsons in 1887 and used for lighting an exhibition in Newcastle. Since then, apart from getting bigger, turbine design has hardly changed and Parson's original design would not look out of place today. Despite the introduction of many alternative technologies in the intervening 120 years, over 80 percent of the world's electricity is still generated by steam turbines driving rotary generators.

The Energy Conversion Processes

Electrical energy generation using steam turbines involves three energy conversions, extracting thermal energy from the fuel and using it to raise steam, converting the thermal energy of the steam into kinetic energy in the turbine and using a rotary generator to convert the turbine's mechanical energy into electrical energy.


Raising steam (Thermal Sources)

Steam is mostly raised from fossil fuel sources, three of which are shown in the above diagram but any convenient source of heat can be used.
Chemical Transformation

In fossil fueled plants steam is raised by burning fuel, mostly coal but also oil and gas, in a combustion chamber. Recently these fuels have been supplemented by limited amounts of renewable biofuels and agricultural waste.

The chemical process of burning the fuel releases heat by the chemical transformation (oxidation) of the fuel. This can never be perfect. There will be losses due to impurities in the fuel, incomplete combustion and heat and pressure losses in the combustion chamber and boiler. Typically these losses would amount to about 10% of the available energy in the fuel.
Nuclear Power

Steam for driving the turbine can also be raised by capturing the heat generated by controlled nuclear fission. This is discussed more fully in the section on Nuclear Power.
Solar Power

Similarly solar thermal energy can be used to raise steam, though this is less common.
Geothermal Energy

Steam emissions from naturally occurring aquifers are also used to power steam turbine power plants.

The Steam Turbine (Prime Mover)

Working PrinciplesHigh pressure steam is fed to the turbine and passes along the machine axis through multiple rows of alternately fixed and moving blades. From the steam inlet port of the turbine towards the exhaust point, the blades and the turbine cavity are progressively larger to allow for the expansion of the steam.

The stationary blades act as nozzles in which the steam expands and emerges at an increased speed but lower pressure. (Bernoulli's conservation of energy principle - Kinetic energy increases as pressure energy falls). As the steam impacts on the moving blades it imparts some of its kinetic energy to the moving blades.



There are two basic steam turbine types, impulse turbines and reaction turbines, whose blades are designed control the speed, direction and pressure of the steam as is passes through the turbine.

Impulse Turbines

The steam jets are directed at the turbine's bucket shaped rotor blades where the pressure exerted by the jets causes the rotor to rotate and the velocity of the steam to reduce as it imparts its kinetic energy to the blades. The blades in turn change change the direction of flow of the steam however its pressure remains constant as it passes through the rotor blades since the cross section of the chamber between the blades is constant. Impulse turbines are therefore also known as constant pressure turbines.

The next series of fixed blades reverses the direction of the steam before it passes to the second row of moving blades.


Reaction Turbines

The rotor blades of the reaction turbine are shaped more like aerofoils, arranged such that the cross section of the chambers formed between the fixed blades diminishes from the inlet side towards the exhaust side of the blades. The chambers between the rotor blades essentially form nozzles so that as the steam progresses through the chambers its velocity increases while at the same time its pressure decreases, just as in the nozzles formed by the fixed blades. Thus the pressure decreases in both the fixed and moving blades. As the steam emerges in a jet from between the rotor blades, it creates a reactive force on the blades which in turn creates the turning moment on the turbine rotor, just as in Hero's steam engine. (Newton's Third Law - For every action there is an equal and opposite reaction)


 

Electric Generation Using Natural Gas

Natural gas, because of its clean burning nature, has become a very popular fuel for the generation of electricity. In the 1970s and 80s, the choices for most electric utility generators were large coal or nuclear powered plants; but, due to economic, environmental, and technological changes, natural gas has become the fuel of choice for new power plants. In fact, in 2000, 23,453 MW (megawatts) of new electric capacity was added in the U.S. Of this, almost 95 percent, or 22,238 MW were natural gas fired additions. The graph below shows how, according to the Energy Information Administration (EIA), natural gas fired electricity generation is expected to increase dramatically over the next 20 years, as all of the new capacity that is currently being constructed comes online.
There are many reasons for this increased reliance on natural gas to generate our electricity. While coal is the cheapest fossil fuel for generating electricity, it is also the dirtiest, releasing the highest levels of pollutants into the air. The electric generation industry, in fact, has traditionally been one of the most polluting industries in the United States. Regulations surrounding the emissions of power plants have forced these electric generators to come up with new methods of generating power, while lessening environmental damage. New technology has allowed natural gas to play an increasingly important role in the clean generation of electricity. For more information on the environmental benefits of natural gas, including its role as a clean energy source for the generation of electricity.

Coal & Electricity

Modern life is unimaginable without electricity. It lights houses, buildings, streets, provides domestic and industrial heat, and powers most equipment used in homes, offices and machinery in factories. Improving access to electricity worldwide is critical to alleviating poverty.

Coal plays a vital role in electricity generation worldwide. Coal-fired power plants currently fuel 41% of global electricity. In some countries, coal fuels a higher percentage of electricity.

How is Coal Converted to Electricity?

Steam coal, also known as thermal coal, is used in power stations to generate electricity.

Coal is first milled to a fine powder, which increases the surface area and allows it to burn more quickly. In these pulverised coal combustion (PCC) systems, the powdered coal is blown into the combustion chamber of a boiler where it is burnt at high temperature (see diagram below). The hot gases and heat energy produced converts water – in tubes lining the boiler – into steam.

The high pressure steam is passed into a turbine containing thousands of propeller-like blades. The steam pushes these blades causing the turbine shaft to rotate at high speed. A generator is mounted at one end of the turbine shaft and consists of carefully wound wire coils. Electricity is generated when these are rapidly rotated in a strong magnetic field. After passing through the turbine, the steam is condensed and returned to the boiler to be heated once again.

The electricity generated is transformed into the higher voltages (up to 400,000 volts) used for economic, efficient transmission via power line grids. When it nears the point of consumption, such as our homes, the electricity is transformed down to the safer 100-250 voltage systems used in the domestic market.
Efficiency Improvements

Improvements continue to be made in conventional PCC power station design and new combustion technologies are being developed. These allow more electricity to be produced from less coal - known as improving the thermal efficiency of the power station. Efficiency gains in electricity generation from coal-fired power stations will play a crucial part in reducing CO2 emissions at a global level.

Efficiency improvements include the most cost-effective and shortest lead time actions for reducing emissions from coal-fired power generation. This is particularly the case in developing countries where existing power plant efficiencies are generally lower and coal use in electricity generation is increasing. Not only do higher efficiency coal-fired power plants emit less carbon dioxide per megawatt (MW), they are also more suited to retrofitting with CO2 capture systems.

Improving the efficiency of pulverised coal-fired power plants has been the focus of considerable efforts by the coal industry. There is huge scope for achieving significant efficiency improvements as the existing fleet of power plants are replaced over the next 10-20 years with new, higher efficiency supercritical and ultra-supercritical plants and through the wider use of Integrated Gasification Combined Cycle (IGCC) systems for power generation.

A one percentage point improvement in the efficiency of a conventional pulverised coal combustion plant results in a 2-3% reduction in CO2 emissions.

Electric Reliability Information

The Form EIA-411, “Coordinated Bulk Power Supply Program Report,” collects information from the Nation's power system planners about the electricity supply, both capacity and energy, that is needed to serve current demand and for future growth.

The reported data can be used to examine such issues as: the reliability of the U.S. electricity system; projections which assess future demand growth and plans for constructing new generating and transmission facilities; and consequences of unavailable or constrained capacity on usage of the existing generation base.

Reliability of the electric power system covers three areas: the security of the electrical systems; the usage of proper operational practices that adhere to mandatory standards; and the ability to plan for adequate supply to meet future demand. Data collected on the Form EIA-411 focuses on planning for adequacy of supply. Separately, the Department of Energy collects information covering security and selected operational practices under the Form OE-417, "Electric Emergency Incident and Disturbance Report."

The information on this page includes historical (with and without projections) and current data (with projections) for the reported year:
peak load
monthly peak hour demand
net energy for load
net internal demand and planned capacity resources

Only projections, but no historical data, are reported for:
high voltage transmission line planned additions

The data provided here are aggregated by the North American Reliability Corporation (NERC) using data provided by the regional entities within NERC that oversee the development and implementation of the mandatory national and regional reliability standards. There are currently eight regions covering all of Canada and the contiguous United States plus a small part of Mexico (Baja California Norte) in North America. The data presented here is for the United States. For data years prior to 2005, 10 NERC regions are indicated, however, from 2005 on, there are 8 regions. (See maps at the top right). Users should expect some differences in geographic reporting coverage from these regional realignments.

Electric Power Flash (November 2010)

General: 
The Monthly Flash Estimates of Electric Power Data (“Flash Estimates”) is prepared by the Electric Power Division, Office of Coal, Nuclear, Electric and Alternate Fuels, Energy Information Administration (EIA), U.S. Department of Energy. Data published in the Flash Estimates are compiled from the following sources: Form EIA-826,“Monthly Electric Utility Sales and Revenues with State Distributions Report,” Form EIA-906, “Power Plant Report,” Form EIA-920, “Combined Heat and Power Plant Report,” and Form EIA-923, “Power Plant Operations Report.”

The survey data is collected monthly from a statistically-derived sample of power plants and electricity retailers. The nominal sample sizes are: for the EIA-826, approximately 450 electric utilities and other energy service providers; for the EIA-923, approximately 1,610 power plants. With the exception of stocks, a regression-based method is used to estimate totals from the sample. Essentially complete samples are collected for the Electric Power Monthly, which includes State-level values. The Flash Estimates is based on an incomplete sample and includes only national-level estimates. Stocks data for out-of-sample plants and any monthly non-respondents are estimated by bringing forward the last reported value for a plant.

Electricity from the Generation Plant to You

In 2008, the average annual electricity consumption for a U.S. residential utility customer was 11,040 kWh, an average of 920 kilowatt-hours (kWh) per month. Tennessee had the highest annual consumption at 15,624 kWh and Maine the lowest at 6,252 kWh.

About 518.5 billion kilowatt-hours (kWh) of electricity were used for cooling and ventilation by the residential and commercial sectors. Of that, about 227 billion kWh was used for cooling by the residential sector, which was about 16% of the total residential electricity consumption. About 291 billion kWh was used by the commercial sector for cooling and ventilation, which was about 22% of total commercial sector electricity consumption. Combined, that was about 17.6% of total U.S. electricity consumption in 2008. 

Capacity is a measure of how much electricity a generator can produce under specific conditions. Generation is how much electricity a generator produces over a specific period of time. For example, a generator with 1 MegaWatt (MW) capacity that operates at that capacity consistently for one hour will produce 1 MW-hour (MWh) of electricity. If it operates at only half that capacity for one hour, it will produce 0.5 MWh of electricity. Many generators do not operate at their full capacity all the time; they may vary their output according to conditions at the power plant, fuel costs, and/or as instructed from the electric power grid operator. Net generation is the amount of gross generation less the electricity used by the generating station/power plant to operate the plant, including fuel handling, boiler and cooling water pumps, pollution control equipment, plant lighting, and computers.

About 517 billion kilowatt-hours (kWh) of electricity were used for lighting by the residential and commercial sectors. This was equal to about 19% of the total electricity consumed by both of those sectors and 13.4% of total U.S. electricity consumption.

Residential lighting consumption was about 212 billion kWh, equal to about 15% of all residential electricity consumption. About 305 billion kWh was consumed for lighting by the commercial sector, which includes commercial and institutional buildings and public street and highway lighting, equal to about 23% of commercial sector electricity consumption.
 
U.S. Residential Electricity Consumption by End Use, 2008

End-Use Quadrillion
Btu Billion Kilowatt-
hours Share of Total

Space Cooling 0.77 227 16.5%
Lighting 0.72 212 15.4%
Water Heating 0.43 127 9.2%
Space Heating1 0.42 123 8.9%
Refrigeration 0.38 110 8.0%
Televisions and Set-Top Boxes 0.35 101 7.3%
Clothes Dryers 0.26 77 5.6%
Computers and Related Equipment 0.17 49 3.6%
Cooking 0.11 31 2.2%
Dishwashers 2 0.09 27 2.0%
Freezers 0.08 23 1.7%
Clothes Washers 2 0.03 10 0.7%
Other — Miscellaneous Uses 0.89 260 18.8%

Total Consumption 4.71 1,379


1 Includes fans and pumps.
2 Excludes energy for water heating.
 

Electricity Consuming Plant

1. "Consumption of electricity" is a non-scientific expression often used to describe the conversion of electrical energy to mechanical work, heat or light.

The Joule is the unit of measurement used to quantify any type of energy. One Newton-meter of mechanical work is one Joule. One foot-pound of work is 1.36 Joules. One calorie of heat is 4.18 joules. One BTU (British thermal unit) of heat is 1054 Joules.

Most electric power plants require water to operate. Nuclear and fossil fuel power plants drink over 185 billion gallons of water per day. Geothermal power plants add another 2 billion or so gallons a day. Hydropower plants use water directly to generate power. These power plants represent the single largest consumer of water among any industrial, governmental or residential activity. Since 98 percent of the water used in power plants is returned to its source, distinctions are made between use and consumption.

Water use is a measure of the amount of water that is withdrawn from an adjacent water body (lakes, streams, rivers, estuaries, etc.), passes through various components of a power plant, and is then ultimately discharged back into the original water body. Environmental concerns surrounding water use center around any chemical or physical alteration of the water body and any impacts these changes may have on the plants, fish and animals who reside in the ecosystem.

Water consumption refers to water sucked up in power plant operations that is lost, typically through evaporation. The primary concerns surrounding water consumption is how best to utilize this essential resource, especially in areas, such as deserts in the West, where water is in short supply.

2. In 2008, about 518.5 billion kilowatt-hours (kWh) of electricity were used for cooling and ventilation by the residential and commercial sectors. Of that, about 227 billion kWh was used for cooling by the residential sector, which was about 16% of the total residential electricity consumption. About 291 billion kWh was used by the commercial sector for cooling and ventilation, which was about 22% of total commercial sector electricity consumption. Combined, that was about 17.6% of total U.S. electricity consumption in 2008.

3. Capacity is a measure of how much electricity a generator can produce under specific conditions. Generation is how much electricity a generator produces over a specific period of time. For example, a generator with 1 MegaWatt (MW) capacity that operates at that capacity consistently for one hour will produce 1 MW-hour (MWh) of electricity. If it operates at only half that capacity for one hour, it will produce 0.5 MWh of electricity. Many generators do not operate at their full capacity all the time; they may vary their output according to conditions at the power plant, fuel costs, and/or as instructed from the electric power grid operator. Net generation is the amount of gross generation less the electricity used by the generating station/power plant to operate the plant, including fuel handling, boiler and cooling water pumps, pollution control equipment, plant lighting, and computers.

4. By re-directing their electricity dollars to support environmentally benign energy resources, consumers are empowered, in states that offer supply choice, to influence the existing generating resources that are deployed to meet demand. They can also support the construction of new and cleaner electricity resources that will be built to meet overall growth in demand in the future. By supporting these power options, consumers can minimize many water use and consumption impacts. Still, it should be noted that directing one's dollars to cleaner power products in no way helps remediate damages that already have occurred. Consumers can stop the construction of new hydropower facilities or alter conditions of siting and operation, but they cannot undo previous environmental degradation that occurred at existing hydropower facilities.

5. If energy is converted or transferred at a rate of one Joule per second, the rate of energy conversion is 1 watt. The speed of energy transfer or the speed of performing work is power. If power is converted at a rate of 1 watt for 1 second, 1 watt-second or 1 Joule of energy is transferred. If energy is transferred at a rate of 1000 watts for 1 hour, 1 kilowatt-hour of energy is transferred. When it comes time to pay the electric bill, the cost of electricity consumption is the cost of the kilowatt hours of energy transferred to the user and converted to mechanical work, heat or light.