BETTER TECHNOLOGY PROMOTES WIND POWER USE

BETTER TECHNOLOGY PROMOTES WIND POWER USE
On the 1920s and 1930s, farm families in the Midwest used wind to generate enough electricity to power their lights and electric motors. After rural electrification in the 1930s and 1940s, however, wind-generated electricity became much less common. Commercial interest in wind power began growing again in the 1970s when energy shortages forced utility companies to find other electricity sources. Technological advances that have cut production costs, the need to comply with clean air laws, and, most recently, concern about global warming also have spurred the interest of utilities in wind-generated electricity.

Because it's a renewable, combustion-free electricity source, wind power can play an important role in cutting emissions of carbon dioxide (CO2), the leading greenhouse gas associated with global warming, says the the American Wind Energy Association. A single utility-scale wind turbine, by displacing electric power generated by fossil fuels, can prevent the emission of 5,000 tons of heat-trapping CO2 into the atmosphere each year.

Aeronautical engineering doctoral student Robyn Ramsay, whose research deals with improving the durability and aerodynamic performance of wind turbine rotors, agrees with the wind association. As its price continues to drop, wind power will become an important electricity source and will help reduce the levels of atmospheric CO2, she predicts.

"Wind power costs have dropped 50 percent over the past decade to 5 or 6 cents per kilowatt hour -- a price that's competitive with conventionally-produced electricity in states with high fuel costs," Ramsay says. "So you see more and more power companies in California, Minnesota, Wisconsin, and other states using wind power to supplement electricity produced in power plants."

On the other hand, wind power has yet to take hold in Ohio and other states that use ample supplies of cheap natural gas or coal to generate electricity costing 3 cents per kilowatt hour.

Ramsay tests models of airfoils that represent cross-sections of turbine rotor blades in a subsonic wind tunnel at Ohio State's Aeronautical and Astronautical Research Laboratory. Her data may help other engineers design rotors that have the best aerodynamic performance and are least affected by insect debris.
"Insect debris changes the shape of rotors and can cut turbine power generation by up to 50 percent," Ramsay says. "In areas with little rain, crews with sprayer trucks wash turbine blades -- something that hikes electricity prices."

Besides advanced wind turbines, photovoltaic systems that convert solar energy into electricity and urban designs that take full advantage of sunlight and breezes also can put a dent in greenhouse gas emissions by reducing fossil fuel combustion needed to generate power.

"Urban design refers to the design of the built environment at any scale from a small green space between buildings to an entire neighborhood, for example," says Norman Booth, landscape architecture professor. "Anytime an urban environment is created, so are many microclimates - the climate around a very small, specific area such as immediately adjacent to a wall of a building. While they're small, microclimates have a big impact on the energy consumption of the building and the comfort of its occupants."

The orientation of a home on a site, as well as the site itself, can reduce by 20 to 30 percent the energy needed to heat or cool the structure. In the Midwest, people can reduce their utility costs by building a new home on that part of a site most exposed to the southern sun and protected from cold northwest winds that drive up winter heat consumption, Booth adds.

New Solar Power Technology Harnesses the Heat

New Solar Power Technology Harnesses the Heat
By Sarah Davidson, LiveScience Staff Writer


Applying the most efficient solar technology available, researchers are building a new power plant that utilizes the heat from sunlight to generate electric power.
The solar dish, as it's known, is a joint project between Stirling Energy Systems, Inc. (SES) and the National Nuclear Security Administration's Sandia National Laboratories.
Based in New Mexico, the prototype contains 82 mirrors that focus the Sun's rays, transmitting the heat energy to an engine filled with hydrogen. As the gas expands and contracts from heating and cooling, this motion drives pistons which power a generator that creates electricity.
Before January, five additional solar powered dishes and their engines are planned to boost the electricity production of the prototype to 150 kilowatts of electricity a day, enough to power 40 average households, according to researchers.
"A farm 100 miles by 100 miles in the southwestern U.S. hypothetically could provide as much electricity as is needed to power the entire country," said SES general manager Bob Liden.
The current project is not an abstract possibility for the future, however, and is actively selling electricity to power companies.
"These systems are currently grid-connected," Chuck Andraka, of Sandia Laboratory told LiveScience, "and are designed to offset peak power demands at the utility."
Commercial electricity providers use grids to supply power to regions of the country, and the grids are interconnected. Power can be fed in at practically any point and shared between providers.
Secured behind a fence to deter people and animals from approaching the test field, the mirrors have been vigorously tested to withstand vandalism. The dish is capable of operating in winds up to 35 mph. In addition to its robust design, the automated dish-engine systems are able to turn themselves off when there is no sunlight.
"These systems produce when the Sun shines only," Andraka said. "Maximum production is determined by the brightness of the Sun and ambient temperature. The more light, the more power."
Researchers hope to lower the cost of the $150,000 prototype to levels where the electricity produced by the solar dishes are comparable to that of other energy sources.
"Coal and nuclear cost 3-5 cents per kilowatt hour. Natural gas can cost anywhere from 6 to 50 cents per kilowatt hour," Andraka said. "Consumers are typically charged in the range of 8-10 cents per kilowatt hour. SES has a goal to get the cost of generation to about 6 cents per kilowatt hour."
Ideally suited for regions with sustained sunlight, 20,000 solar dish engine systems could provide electricity to utility companies throughout the southwestern United States, Andraka said.
"This is the perfect type of electricity generation for the Southwest," Liden said. "It's a renewable resource, its pollution free, and the maintenance of a solar farm is minimal."

HYDROELECTRIC POWER OPTION IN BRAZIL

THE HYDROELECTRIC POWER OPTION IN BRAZIL ENVIRONMENTAL, TECHNOLOGICAL AND ECONOMIC ASPECTS
VENTURA FILHO, Altino ITAIPU Binacional Foz do Iguaçu, Brazil
1. Introduction
This paper deals with an evaluation of Brazil's option in favor of hydroelectric power as its primary source of electric power generation.
Aspects concerning the environment, as well as technological and economic considerations in regard to the use of hydroelectric power in Brazil are commented, stressing the importance of the transmission system for the integration and the optimization of hydroelectric generation.
Reference is made to Brazil's strategy for expanding its generating system at medium term, up to the year 2015, listing the various primary sources for the generation of electric power and explaining why priority is given to continued use of the country's hydroelectric potential.


2. Electric power supply and hydroelectric power
Hydroelectric power is an important and widely used primary source for the generation of electric power. Figure 1 shows the share of each of the several primary sources in world terms and in Brazil.
Coal is the most important source used for the generation of electricity, amounting to 40% of the world total. The cost of the energy generated by means of current technology is competitive, even taking into account fuel transportation costs. The relative abundance of coal indicates that its price on the international market will remain stable. Technological evolution will be necessary, especially regarding control of emissions into the environment, and this may result in a rise of approximately 25% in investment costs. The use of mineral coal for large scale electric power generation, at medium and long term, depends basically on its economical and environmental competitiveness, when compared to the other thermal options, mainly nuclear power and natural gas.
Hydroelectric power, worldwide the second largest primary source used for electricity generation, amounts to 19% of the total production of electricity. Its use evolved in industrialized countries that took advantage of the economically and environmentally feasible portion of their total hydroelectric potential, which corresponds to a percentage between 60 and 80%. No major hydroelectric program is foreseen for these countries. Future hydroelectric expansion is more likely to occur in developing countries, where most of the hydroelectric potential is still available. Restrictions to such expansion will be related to environmental aspects of hydroelectric plants and to the limited funds available for investment in these projects, considering the large amounts necessary to meet the growing evolution of the electric systems in these countries.
Nuclear power, the third largest source used for electric power generation (17% of the total) gained in importance in the 60s and 70s. As from the 80s, programs for the installation of new units were scaled down, especially in the United States and Europe. This option has the environmental advantage of not contributing to global climatic changes, such as the greenhouse effect. Large scale nuclear generation expansion depends on public acceptance, its competitiveness with other thermal options, and upon environmental restrictions, that may be placed on conventional thermal generation sources, such as a CO2 emission tax.
Natural gas fired generation is responsible for 13% of the worldwide electricity production, and is expected to grow rapidly in the future, due to the technological progress achieved over the last decades, especially in the yield of the thermal energy/electricity conversion process in combined cycle plants, and to the fact that investment costs have been drastically reduced. Natural gas, when available, is a competitive low-cost option for electric power generation and may be implemented at short term. It is also considered the best conventional alternative for thermal power from an environmental point of view. It can, furthermore, be implemented in different modules and sizes, in cogeneration processes at consumer-end level, thereby acquiring greater energy efficiency.
The use of oil by-products for power generation is more likely to remain restricted to special situations due to the possibility of more relevant uses for this fuel, and also for strategic reasons. No large-scale worldwide programs for oil by-products fired plants are foreseen.
3. Brazil's economy and energy
Brazil is a vast country - 8.5 million square kilometers - the fifth largest in the world. Distances between its extreme boundaries - north to south, east to west - span more than 4,000 km. Its Atlantic Ocean shore extends over 7,000 km, whereas its territorial borders measure approximately 16,000 km, touching all South American countries, except Chile and Ecuador, as shown in Figure 1. Brazil's huge dimensions favor the use of the country's hydroelectric potential, due to its high energy value, as will be seen in this paper.
It is estimated that the country's population will reach 167 million inhabitants by the year 2000 (demographic density of 19.6 inhabitants/km2), with an annual growth rate of 1.2% - an increase of 2 million inhabitants per year. These figures make Brazil the fifth most populated country in the world. [1]
Brazil's Gross Domestic Product grew over the period 1970/2000 at a higher rate than its population, despite the recessive 80s. Over the period 1970/2000, the GDP rose from US$ 240 billion, to approximately US$ 850 billion (exchange rate of 1995), a yearly growth rate of 4.3%, resulting in an annual income elevation from 2,580 to 5,090 US$/inhabitant-year, over the last thirty years. Table 1 shows a breakdown of the GDP by primary, secondary and tertiary sectors for the years 1970 and 2000, and the country's urbanization level, which are important aspects affecting the overall energy growth, including electric power.
The Energy Sector took large strides forward during the period 1970/2000, due to Brazil's economic expansion, industrialization and growing urbanization. During these thirty years, the Energy Consumption x Gross Domestic Product elasticity stood at about 1.25. Table II provides a breakdown of national energy consumption by main energy types for the years 1970 and 2000. As can be seen, a major structural change occurred over these thirty years. Electricity (renewable source-hydro) shot up from 19 to 41%, the use of firewood, charcoal and sugar-cane bagasse dropped significantly (from 40 to 20%), and oil by-products use declined from 38 to 32%. Presently, renewable energy amounts to 2/3 of the total.
This large share borne by electricity is a result of its 7,1% average annual growth rate in the 1970/2000 period (from 40 TWh to 315 TWh, electric energy consumption). This rate is to be compared to the rates of growth for the economy (4.3%), the population (2.0%) and energy consumption from all sources (5.4%). The Electric Power Consumption x Gross Domestic Product elasticity in Brazil will probably reach 1.65 during the 1970/2000 period. The electricity content of the GDP is expected to rise from 0.167 in the year 1970, to 0.371 kWh/US$ of the GDP, in 2000, whereas the annual per capita electric power consumption is estimated to rise from 430 to 1,886 kWh/inhabitant-year, during this period. As the per-capita consumption figure, for the year 2000, is well below the average value for industrialized countries, it can be inferred that there is a large middle and long term (15 to 20 years) growth potential for the Brazilian electric power market.

4. Hydroelectric power in Brazil

4.1 - General remarks
Figure I shows the distribution of primary sources for electric power generation in Brazil. Hydroelectric power stands out, with 96,8% of the total. Thermal generation comprises oil by-products (1.3%), mineral coal (1.2%) and nuclear power (0.7%). Oil-fired generation is usually restricted to isolated systems in the northern part of the country, in the Amazon Region. But, occasionally, if the hydrological situation is unfavorable or there is need for peak supply, oil by-products are used for thermal generation in the National Interconnected System. Coal-fired generation is restricted to Brazil's Southern Region, and it aims at making use of this regionally available primary energy source in order to develop the technology which will be needed for medium-term generation expansion. Presently, nuclear power is generated only at Angra I plant (657 MW). In 1999, the Angra II plant (1309 MW) will be in operation.
The significant predominance of hydroelectric power, the geographical dimension of the national interconnected electrical system, the size of its market, as well as the large number of hydroelectric plants located at great distances from each other, and possessing different hydrological regimes, place Brazil in a unique worldwide situation. Two important aspects are noteworthy: one refers to hydroelectric generation itself and the other to the role of the transmission system.
In the first case, the amount of energy generation depends directly on the natural flow of rivers and the storage capacity of reservoirs. A historical analysis of the natural flows available, dating back to 1931, shows that, in general, hydrological conditions are favorable. Isolated years of low water supply were rare. Consecutive years of draught with a flow significantly lower than average were even rarer. Within a specific year, hydrology is markedly seasonal. There occur periods of strong flow - floods - at the start of the year in the main hydrographical basins.
As a result of these hydrological characteristics and the possibility of installing reservoirs for storing large volumes of water at a low cost, Brazil's hydroelectric system can regulate pluri-annual stocks for a period of about 5 years. Such regulating capacity and the electrical interconnections among hydrographical basins require a continuous time-dependent evaluation of the supply system with regard to energy generation (as opposed to thermal systems), as this generation in one particular year is conditioned by the previous hydrological behavior and its expected evolution in the following years.
The role played by the transmission in a hydroelectric system, such as the Brazilian, is of major importance. Aside from transporting the energy generated to the consumption centers, which is the basic function of transmission in thermal systems, it also permits the optimization of the hydro generation. This optimization increases the overall energy production by transferring the surplus energy surplus available in some plants to other hydrographical basins or geographical regions with unfavorable hydrological conditions. The optimized operation of the Brazilian hydroelectric system results in an increase of about 30% in energy generation, when compared to the production that would be obtained through the individual operation of the plants, without the coordination of a centralized dispatch. This, in Brazil, gives rise to a significant cost reduction for hydroelectric power generation. This distinctive characteristic of the transmission system is recognized by the legal framework of the Electric Sector, which differentiates it from transmission systems that are connected to plants and to the distribution segment.
In the Brazilian electric power system, the market supply criterion is based upon meeting average energy requirements, attributing a lower priority to peak supply. This philosophy opposes that adopted for thermal systems, which emphasizes peak demand supply. The Brazilian system adopts a criterion based on the supply of guaranteed energy with a certain deficit risk. Currently the maximum annual deficit risk considered for expanding the electric power generation in order to meet the energy requirements is 5%.
4.2 - Brazil's electrical system in the year 2000
Brazil's electrical system configuration for the year 2000, takes into account the energy supply to two different geographical areas. One is covered by the National Interconnected System, extending for 6.0 million km2, corresponding to 70% of Brazil's territory and to 98% of the country's electric power consumption. The second area comprises the nearly 400 isolated systems, mainly located in the northern region, covering 2.5 million km2, and corresponding to the remaining 2% of the total electrical power consumption.
Figure 2 shows these systems, highlighting the National Interconnected System and the interconnections among the different geographical regions of the country - north/northeast, north/south and south/southeast.
The National Interconnected System integrates a significant number of hydroelectric plants of various sizes that are often situated at great distances from each other and have, in some cases, different hydrological regimes. Therefore, plants as widely apart - about 3,000 km - as Tucuruí (8,325 MW) located on the Tocantins River, in the northern region, and Itá (1,450 MW) on the Uruguai River, in the southern region, are inter-dependent due to the different hydrological regimes, and require a coordinated operation. Table III shows Brazil's installed capacity in hydroelectric and thermal terms, for the year 2000; Table IV highlights the main characteristics of hydroelectric plants over 1,000 MW.
4.3 - Hydroelectric power generation in Brazil
Brazil's option for hydroelectric power is based on the following reasons:
Availability of Hydroelectric Resources: Brazil has a hydroelectric potential of 260 GW that can generate 1,270 TWh/year, and ranks 3rd in the world. By the year 2000, only 30% of this potential will have been used or will be under development. On the other hand, Brazil does not have the natural resources necessary for a large-scale conventional thermal electric power program, except for the mineral coal in the Southern Region, which is restricted to local use.
Competitiveness of the Hydroelectric Potential: Most of Brazil's hydroelectric potential in use by the year 2000 will have been implemented at low cost (around 1,000 US$/kW or less - roughly 20 US$/MWh). Several of these plants are located in the vicinity of consumption centers and have relatively short transmission systems, a factor that contributes to their competitiveness.
Renewable Source: Since hydroelectric power is a renewable source, it is of strategic importance to Brazil. The useful life of hydroelectric power plants is much longer than the 50 years adopted in economic evaluations. In the long run, the country's hydroelectric plants will generate electric power at a very low cost, merely to cover operation and maintenance expenses, since the investment costs will be partially or entirely amortized. In Brazil, this is already the case for a significant number of hydroelectric plants in operation that were installed since the 50's.
National Technology: Brazil masters the technology used in the various stages of hydroelectric power generation: planning, design, civil works and assembly, equipment production and operation/maintenance, as well as the management of the whole process. Therefore, the hydroelectric program is carried out with national resources, generating employment and technological development.
Environment and Multiple Uses: The hydroelectric plants in operation or under construction, except for a few, have no significant negative impact on the environment, since the most favorable sites were chosen. A noteworthy aspect is that, although most of the hydroelectric projects were planned and designed for energy generation, several of the reservoirs are also used to other ends, within a concept of multiple use of water resources.


5. Brazil's electric power prospects up to the year 2015
5.1 Electric power market
At medium and long term, the prospects of electric power consumption growth are favorable, due to the population's growth (from 167 million inhabitants in the year 2000 to nearly 200 million inhabitants in 2015), to the economic expansion, and to the availability of several energy sources, including energy integration with neighboring countries.
A long-term forecast for the economy and for the electric power market was made in the PLAN 2015 studies. Scenarios II and III of PLAN 2015 are adopted in this paper. The average annual growth rates for the economy and for the electric power consumption are shown in Table V, for the period 2000/2015. Electric power consumption in Brazil will increase from 315 TWh in the year 2000, to 630 TWh (Scenario I) or 730 TWh (Scenario II) in the year 2015. The resulting annual per capita consumption would be 3,150 or 3,650 kWh/inhabitant-year in that year.
5.2 Electric power supply
Expansion in electric power consumption requires an increase in Brazil's installed capacity from 70 GW in the year 2000, to approximately 150 or 170 GW in 2015, for the two adopted scenarios. This corresponds to an addition of 80 or 100 GW generating capacity, over the 2000/2015 period. Several different primary sources will have to be utilized for electric power generation depending, basically, on the following: availability of energy resources, competitiveness, environmental viability and the current stage of technology.
Brazil has an abundance of primary energy sources for generating electric power: hydroelectric potential, coal, uranium (nuclear power) and alternative sources (biomass, solar energy and eolic energy). On the other hand, oil and natural gas resources available in Brazil are not sufficient for a large-scale conventional thermoelectric generation expansion program.
The competitiveness evaluation of various primary sources for electric power generation is based on a 10% annual discount rate and on an useful life of 50 years for hydroelectric plants, and of 30 years for thermal plants. All costs - investment, operation/fuel and maintenance, as well as environmental - of the plants are considered. Benefits are calculated for each plant operating under optimized conditions within the interconnected system. Table VI shows the cost ranges of energy generated, in Brazil, by means of the different primary sources. As can be seen, approximately 2/3 of Brazil's hydroelectric potential is competitive with a combination of coal and nuclear power.
A reliable environmental component in generation undertakings must be founded on three basic principles: Social-Environmental Viability, Regional Insertion and Decision Process.
The "Social-Environmental Viability" of generation projects, especially hydroelectric, must be based on the following requirements: 1) an in-depth analysis of the social and environmental impacts caused by the installation and the operation of the plant: 2) restrictions considered relevant in the social-environmental field, such as preserving certain cultural values or areas of special ecological importance; 3) pinpointing favorable net benefits (positive less negative impacts).
The social-environmental viability concept of a generation project must translate itself into a satisfactory balance between the Electrical Sector's objectives - meeting its market demands at the lowest possible cost and the expectations of the social segments whose electric power demand will be met and of the local community affected by the implementation of the project.
"Regional Insertion" must take into account that the installation and the operation of a power plant causes a potential conflict between the objectives of the Electrical Sector and those of the social groups and of the economic activities affected by the project.
Regional insertion of the project should maximize the benefits for the Electrical Sector and, at the same time, develop local potentials. Thence, an effort should be made to reduce negative impacts and to promote benefits in the project's influence range. As an example, for hydroelectric plants, the following benefits may arise for the local communities: flood control, shipping, leisure activities, water supply, irrigation, fisheries, and others. One successful program with satisfactory results consists of paying royalties to the communities affected by hydroelectric plant reservoirs. These royalty funds may be invested in municipal social programs, such as education and health.
The "Decision Process", in regard to social-environmental aspects, depends on a good relationship between the Electrical Sector and society. Inter-institutional communication is of fundamental importance, in order to synchronize objectives and strategies as well as for establishing procedures that include defining the financial responsibilities of the involved entities. It is therefore a good idea for the Electrical Sector to adopt a strategy of sharing planning and decision making, transforming a power plant in a tool for regional development.
No technological restrictions hinder the expansion of generation and transmission systems in Brazil. Nevertheless, technological improvements are necessary, basically with a view to reduce costs in the following fields: mineral coal - environmental control of emissions and combustion in circulating fluidized bed; biomass - gasification of wood and use in high-yield gas-fired turbines; hydroelectric power - roller compacted concrete dams, auscultation and monitoring civil structures, automation and control of plant operation and maintenance; as well as eolic and solar generation.


5.3 Generation expansion strategy up to 2015
Considering the size of the country and the specific economic-energy features of its various regions, the electric power requirements for the year 2015, and the aspects mentioned above regarding the different energy sources, Brazil should use, for long term generation expansion, a combination of all available sources, endeavoring to optimize their composition and also to promote benefits for the national economy. The prospects for using different energy sources are listed below:
"Mineral Coal" thermal power may have an important share in the generation of electric power from 2010 on, when this option would expand in a substantially and competitively manner. The use of Brazilian mineral coal is expected to continue restricted to the Southern Region, with a circulating fluidized bed combustion technology. In other regions of the country, coal-fired thermoelectricity is likely to be based on imported fuel and conventional technology. In the years 2000/2010, PLAN 2015 propose a minimum program of national mineral coal-fired thermal units, basically in order to prepare the country for this generation alternative which will be necessary at medium term.
"Nuclear Power" is a long-term option, applicable after the competitive and environmentally viable hydroelectric potential has been exhausted. It is unknown when this will take place, since it basically depends on: the expansion scenarios of the economy and of the electric power market; the competitiveness and environmental questions of that potential; and the magnitude of the conventional thermal program. Evaluations so far indicate that this will happen after the year 2015. PLAN 2015, similarly to its stand toward mineral coal, proposes a minimum nuclear program up to the year 2015, as a way to prepare the country for this generation option that will be necessary at long term.
"Natural Gas" will be used for generating electric power in the Northern Region of Brazil where deposits compatible with the size of the foreseen thermal program are found. In other regions, especially in the south and southeast, projects for importing this fuel from Bolivia and Argentina are at the implementation stage. Natural gas generation is the best conventional thermal generation source from an environmental and competitive point of view, especially when located near consumption centers. It is beneficial to the transmission system and supply reliability. The natural gas thermal generation program is expected to develop, subject only to the availability of the fuel at an adequate price.
"Sugarcane Residues" are also an option since they are widely available, and because they can be used in cogeneration processes in the sugar and alcohol industries, with the sale of the surplus electric power to utilities, at competitive costs. "Biomass" is also highly available as fuel, especially in the Northern Region (Natural Forest). The main problems with this option are technological limitations and costs. A project for the generation of electric power by gasefying biomass and using high yield gas turbines is underway to test technology and related costs, which may cause this primary source to become a viable alternative.
"Alternative Sources "such as eolic and solar energy may be used in specific cases of isolated small systems; others, such as shale, tidal power, hydrogen, organic residues, turf and lignite are not envisaged for use by the year 2015, due to technological difficulties and cost.
"Energy Interchange with Neighboring Countries" is, in some cases, a competitive option for the supply of firm, hydroelectric or thermal energy, and for the exchange of optimization energy, aiming at the reduction of fuel used in the thermal plants and of the system's deficit risk. Several projects involving Argentina, Uruguay and Venezuela are being implemented.
"Oil By-Products" are not likely to feature in large electric power generation programs, due to their cost and to their other more relevant uses, except for certain specific circumstances in isolated systems.
Finally, "Hydroelectric Power", offers the best prospects for use in Brazil until the year 2015. It would, in fact, be beneficial to continue the hydroelectric program to assure the predominance of hydroelectricity in the supply of the electrical system in this year. Approximately half of Brazil's available hydroelectric power potential is found in the Amazon Region, at a distance of approximately 2,500 km from the principal consumption centers. In order to make use of this hydroelectric potential, long-distance transmission lines should be implemented. Studies confirm the technical-economic viability of this transmission, over 3,000 km, provided a direct current technology similar to that of the present transmission system of ITAIPU is adopted; estimated costs stand at about US$ 16.00 per MWh transmitted, including investment, operation and maintenance expenditures, and electricity losses.
In Brazil, hydroelectric power has very little negative impact on the four chief categories cited in international discussions on the deterioration of the environment: the greenhouse effect, acid deposits, destruction of the ozone layer, and the loss of biodiversity. Moreover, the use of hydroelectric power in Brazil does not contaminate water resource or the soil. Within the "regional insertion" concept of hydroelectric plants, the flooding of areas for reservoirs that caused local physical and social-economic impacts took place in a perfectly acceptable manner, with a positive balance between benefits (energy and others) and costs (economic, social and environmental).
The cost of energy generated by the Brazilian hydroelectric plants is low. This is due to three principal reasons: plants in operation, with few exceptions, were implemented at a low investment cost; integrated operation of the hydroelectric plants in the interconnected system, raises the energy generation; the investment costs are partially or totally amortized for several plants.
The reasons that lead the Brazilian generating system to be predominantly hydroelectric in the year 2000 continue valid in the context of the system's expansion. Thus, generation will continue to be mostly hydroelectric in its configuration for the year 2015, amounting to about 80% of the total electric power production. Of the additional 80 or 100 GW necessary in the 2000/2015 period, according to the scenarios outlined in PLAN 2015, approximately 60 or 75 GW will be hydroelectric.
6. Conclusions
In the 20th century, Brazil opted for hydroelectric power as the source for supplying practically the entire national electricity market. Large plants and their respective regional transmission systems began to be installed in the fifties.
This was the correct option, considering the results obtained by the Brazilian Electrical Sector. Reliable energy supply in sufficient amounts to meet consumer demand is assured from a renewable primary source that is environment-friendly, both from a local (the micro-region of the plant's location) and a global point of view. Moreover, the useful life of the hydro plants is much longer than the 50 years adopted in the economic evaluations.
The cost of the generated hydroelectric power is low and does not run the risk of rising (a risk faced in the case of thermal plants if the cost of fuel increases); in fact, it tends to drop in time, as the investment costs are partially or totally amortized for most plants.
The transmission system has very important integration and optimization roles, through the increase of the total electric energy production of the hydroelectric plants. Long transmission lines, of about 3,000 km - nowadays technically and economically feasible - will be necessary in order to use the hydroelectric potential of the country's Northern Region to supply the National Interconnected System.
In Brazil, the expansion of the generating system is expected to occur up to 2015, predominantly based on hydroelectric plants. The share of hydroelectricity in the year 2015 is estimated at about 80% of the generation system

PRODUCTION OF ELECTRIC POWER

Hydro-Electric Power Commission of Ontario was created, with Adam Beck as ... More
In Canada the 2 basic methods of producing ELECTRIC POWER are hydroelectric generation, based on the energy contained in flowing water, and thermal generation, based on the production of steam. Thermal generation may be conventional, using COAL and PETROLEUM products, or nuclear, using URANIUM in thermonuclear fission (see NUCLEAR ENERGY). Canada is abundantly supplied with most of the resources from which electric power can be generated, and Canadians are among the world's highest per capita producers and consumers of electricity.
Hydroelectric Plant No 6In the Saguenay-Lac-St-Jean region of Québec (courtesy Alcan Aluminum).
Solar EnergyMacLaren pulp and paper plant at Masson, Québec. Solar panels for pre-heating water (photo by Jim Merrithew). Canada's installed electrical generating capacity in 1994 was 114 gigawatts (GW = 109 watts): 56% derived from HYDROELECTRICITY, 18% from coal, 14% from nuclear power, 7% from oil, 4% from natural gas and 1% from other sources. Installed capacity is the amount of power that could be generated at a given instant if all power plants were working simultaneously at full capacity.
Actual production depends on the amount of time particular generators are running and on load (appliances, motors, etc) placed on the system. ELECTRIC UTILITIES build 10-25% extra capacity into their systems, above the expected maximum load, to serve as backup during emergencies and maintenance shutdowns. In 1994, total actual production in Canada was 533 508 GWh. Of this, 61% was hydroelectric, 19% nuclear, 15% coal, 3% natural gas, 1% oil and 1% other sources. The difference between the various sources' shares of capacity and production (ie, a higher proportional production from hydro and nuclear, lower from fossil fuels) reflects the economics of electric-power generation, and the pressures placed by CONSERVATION concerns on petroleum-based thermal development.

BC Hydro Generation

BC Hydro generates power by harnessing the power of moving or falling water to produce mechanical/electrical energy. BC Hydro generates over 43,000 gigawatt hours of electricity annually to supply more than 1.6 million residential, commercial and industrial customers. This power is delivered using an interconnected system of over 73,000 kilometres of transmission and distribution lines.
So how do we generate this power? The process begins before electricity even reaches customers. The steps to generating electricity from a dam and how it is transported are outlined below.
1. Hydroelectric damThere is potential energy stored in a water reservoir behind a dam. It is converted to kinetic energy when the water starts flowing down the penstock (what it is), from the dam. This kinetic energy is used to turn a turbine.
2. GeneratorThe falling water strikes a series of blades attached around a shaft which converts kinetic energy to mechanical energy, and causes the turbine to rotate. The shaft is attached to a generator, so that when the turbine turns, the generator is driven. The generator converts the turbine's mechanical energy into electric energy.
3. Step-up transformerVoltage is the pressure that makes electricity flow. Generators usually produce electricity with a low voltage. In order for the transmission lines to carry the electricity efficiently over long distances, the low generator voltage is increased to a higher transmission voltage by a step-up transformer.
4. Grid high voltage transmission linesGrid transmission lines, usually supported by tall metal towers, carry high voltage electricity over long distances.
5. Terminal StationTerminal stations control power flow on grid transmission lines and reduce the grid voltage to subtransmission voltage.
6. Subtransmission linesSubtransmission lines supply power from terminal stations to large industrial customers or distribution substations.
7. How It Is Used by the CustomerElectric energy can be sold at transmission voltage to users of large amounts who own and operate their own substations. Most customers, however, are unable to accept energy at transmission voltage, and require that it be stepped down in a transformer.
8. Distribution substationA distribution substation is a system of transformers, meters, and control and protective devices. At a substation, transmission voltage is reduced to lower voltages for distribution to residential, commercial, and small and medium industrial customers.
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LED technology

LED technology

[edit] Physical function
Like a normal diode, an LED consists of a chip of semiconducting material impregnated, or doped, with impurities to create a p-n junction. As in other diodes, current flows easily from the p-side, or cathode, to the n-side, or anode, but not in the reverse direction. Charge-carriers — electrons and electron holes — flow into the junction from electrodes with different voltages. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon.
The wavelength of the light emitted, and therefore its colour, depends on the band gap energy of the materials forming the p-n junction. In silicon or germanium diodes, the electrons and holes recombine by a non-radiative transition which produces no optical emission, because these are indirect band gap materials. The materials used for an LED have a direct band gap with energies corresponding to near-infrared, visible or near-ultraviolet light.
LEDs are usually constantly illuminated when a current passes through them, but flashing LEDs are also available. Flashing LEDs resemble standard LEDs but they contain a small chip inside which causes the LED to flash with a typical period of one second. This type of LED comes most commonly as red, yellow, or green. Most flashing LEDs emit light of a single wavelength, but multicolored flashing LEDs are available too.
LED development began with infrared and red devices made with gallium arsenide. Advances in materials science have made possible the production of devices with ever-shorter wavelengths, producing light in a variety of colors.
LEDs are usually built on an n-type substrate, with electrode attached to the p-type layer deposited on its surface. P-type substrates, while less common, occur as well. Many commercial LEDs, especially GaN/InGaN, also use sapphire substrate. Substrates that are transparent to the emitted wavelength, and backed by a reflective layer, increase the LED efficiency. The refractive index of the package material should match the index of the semiconductor, otherwise the produced light gets partially reflected back into the semiconductor, where it gets absorbed and turns into additional heat lowering the efficiency. In 2007 experiments tried to avoid multiple internal reflection by roughening the chip. Again at the surface from the package to a low refractive index medium like a glass fiber or air total internal reflection is avoided by using a sphere shaped package, with the diode in the center, so that the light rays hit the surface quite perpendicular, and anti-reflection coating may be added. The package may be cheap plastic, which may be colored, but this is only for cosmetic reasons or to improve the contrast ratio; the color of the packaging does not substantially affect the color of the light emitted.
Conventional LEDs are made from a variety of inorganic semiconductor materials, producing the following colors:
Aluminium gallium arsenide (AlGaAs) - red and infrared
Aluminium gallium phosphide (AlGaP) - green
Aluminium gallium indium phosphide (AlGaInP) - high-brightness orange-red, orange, yellow, and green
Gallium arsenide phosphide (GaAsP) - red, orange-red, orange, and yellow
Gallium phosphide (GaP) - red, yellow and green
Gallium nitride (GaN) - green, pure green (or emerald green), and blue also white (if it has an AlGaN Quantum Barrier)
Indium gallium nitride (InGaN) - near ultraviolet, bluish-green and blue
Silicon carbide (SiC) as substrate — blue
Silicon (Si) as substrate — blue (under development)
Sapphire (Al2O3) as substrate — blue
Zinc selenide (ZnSe) - blue
Diamond (C) - ultraviolet
Aluminium nitride (AlN), aluminium gallium nitride (AlGaN) - near to far ultraviolet (down to 210 nm[4])
With this wide variety of colors, arrays of multicolor LEDs can be designed to produce unconventional color patterns.[4]

[edit] Ultraviolet, blue and white LEDs

An ultraviolet GaN LED.
Blue LEDs are based on the wide band gap semiconductors GaN (gallium nitride) and InGaN (indium gallium nitride). They can be added to existing red and green LEDs to produce white light, though white LEDs today rarely use this principle.
The first blue LEDs were made in 1971 by Jacques Pankove (inventor of the gallium nitride LED) at RCA Laboratories.[5] However, these devices were too feeble to be of much practical use. In the late 1980s, key breakthroughs in GaN epitaxial growth and p-type doping by Akasaki and Amano (Nagoya, Japan) ushered in the modern era of GaN-based optoelectronic devices. Building upon this foundation, in 1993 high brightness blue LEDs were demonstrated through the work of Shuji Nakamura at Nichia Corporation.[6]
By the late 1990s, blue LEDs had become widely available. They have an active region consisting of one or more InGaN quantum wells sandwiched between thicker layers of GaN, called cladding layers. By varying the relative InN-GaN fraction in the InGaN quantum wells, the light emission can be varied from violet to amber. AlGaN aluminum gallium nitride of varying AlN fraction can be used to manufacture the cladding and quantum well layers for ultraviolet LEDs, but these devices have not yet reached the level of efficiency and technological maturity of the InGaN-GaN blue/green devices. If the active quantum well layers are GaN, as opposed to alloyed InGaN or AlGaN, the device will emit near-ultraviolet light with wavelengths around 350-370 nm. Green LEDs manufactured from the InGaN-GaN system are far more efficient and brighter than green LEDs produced with non-nitride material systems.
Most "white" LEDs in production today are based on an InGaN-GaN structure, and emit blue light of wavelengths between 450 nm – 470 nm blue GaN. These GaN-based, InGaN-active-layer LEDs are covered by a yellowish phosphor coating usually made of cerium-doped yttrium aluminum garnet (Ce3+:YAG) crystals which have been powdered and bound in a type of viscous adhesive. The LED chip emits blue light, part of which is efficiently converted to a broad spectrum centered at about 580 nm (yellow) by the Ce3+:YAG. The single crystal form of Ce3+:YAG is actually considered a scintillator rather than a phosphor. Since yellow light stimulates the red and green receptors of the eye, the resulting mix of blue and yellow light gives the appearance of white, the resulting shade often called "lunar white". This approach was developed by Nichia and was used by them from 1996 for manufacturing of white LEDs.
The pale yellow emission of the Ce3+:YAG can be tuned by substituting the cerium with other rare earth elements such as terbium and gadolinium and can even be further adjusted by substituting some or all of the aluminum in the YAG with gallium. Due to the spectral characteristics of the diode, the red and green colors of objects in its blue yellow light are not as vivid as in broad-spectrum light. Manufacturing variations and varying thicknesses in the phosphor make the LEDs produce light with different color temperatures, from warm yellowish to cold bluish; the LEDs have to be sorted during manufacture by their actual characteristics. Philips Lumileds patented conformal coating process addresses the issue of varying phosphor thickness, giving the white LEDs a more consistent spectrum of white light.

Spectrum of a "white" LED clearly showing blue light which is directly emitted by the GaN-based LED (peak at about 465 nanometers) and the more broadband stokes shifted light emitted by the Ce3+:YAG phosphor which extends from around 500 to 700 nanometers.
White LEDs can also be made by coating near ultraviolet (NUV) emitting LEDs with a mixture of high efficiency europium-based red and blue emitting phosphors plus green emitting copper and aluminum doped zinc sulfide (ZnS:Cu, Al). This is a method analogous to the way fluorescent lamps work. However the ultraviolet light causes photodegradation to the epoxy resin and many other materials used in LED packaging, causing manufacturing challenges and shorter lifetimes. This method is less efficient than the blue LED with YAG:Ce phosphor, as the Stokes shift is larger and more energy is therefore converted to heat, but yields light with better spectral characteristics, which render color better. Due to the higher radiative output of the ultraviolet LEDs than of the blue ones, both approaches offer comparable brightness.
The newest method used to produce white light LEDs uses no phosphors at all and is based on homoepitaxially grown zinc selenide (ZnSe) on a ZnSe substrate which simultaneously emits blue light from its active region and yellow light from the substrate.
A new technique just developed by Michael Bowers, a graduate student at Vanderbilt University in Nashville, involves coating a blue LED with quantum dots that glow white in response to the blue light from the LED. This technique produces a warm, yellowish-white light similar to that produced by incandescent bulbs.[7]

[edit] Organic light-emitting diodes (OLEDs)
Main article: Organic light-emitting diode

Combined spectral curves for blue, yellow-green, and high brightness red solid-state semiconductor LEDs. FWHM spectral bandwidth is approximately 24-27 nanometres for all three colors.
If the emitting layer material of an LED is an organic compound, it is known as an Organic Light Emitting Diode (OLED). To function as a semiconductor, the organic emitting material must have conjugated pi bonds. The emitting material can be a small organic molecule in a crystalline phase, or a polymer. Polymer materials can be flexible; such LEDs are known as PLEDs or FLEDs.
Compared with regular LEDs, OLEDs are lighter, and polymer LEDs can have the added benefit of being flexible. Some possible future applications of OLEDs could be:
Inexpensive, flexible displays
Light sources
Wall decorations
Luminous cloth
OLEDs have been used to produce visual displays for portable electronic devices such as cellphones, digital cameras, and MP3 players. Larger displays have been demonstrated, but their life expectancy is still far too short (<1,000 hours) to be practical.

[edit] Operational parameters and efficiency
Most typical LEDs are designed to operate with no more than 30-60 milliwatts of electrical power. Around 1999, Philips Lumileds introduced power LEDs capable of continuous use at one watt. These LEDs used much larger semiconductor die sizes to handle the large power input. Also, the semiconductor dies were mounted to metal slugs to allow for heat removal from the LED die.
One of the key advantages of LED-based lighting is its high efficiency, as measured by its light output per unit power input. White LEDs quickly matched and overtook the efficiency of standard incandescent lighting systems. In 2002, Lumileds made 5-watt LEDs available with efficacy of 18–22 lumens per watt. For comparison, a conventional 60-100 watt incandescent lightbulb produces around 15 lumens/watt. However, note that standard fluorescent lights produce up to 100 lumens/watt. (The Luminous efficiency page discusses this in more detail.)
In September 2003 a new type of blue LED was demonstrated by the company Cree, Inc. to give 24 mW at 20 mA. This produced a commercially packaged white light giving 65 lumens per watt at 20 mA, becoming the brightest white LED commercially available at the time, and over four times more efficient than standard incandescents. In 2006 they demonstrated a prototype with a record white LED efficacy of 131 lm/W at 20 mA. Also Seoul Semiconductor has plans for 135 lm/W by 2007 and 145 lm/W by 2008, which would be approaching an order of magnitude improvement over standard incandescents and better even than standard fluorescents. [5]. Nichia Corp. has developed a white light LED with efficacy of 150 lm/W at a forward current of 20 mA[6].
It should be noted that high-power (≥ 1 Watt) LEDs are necessary for practical general lighting applications. Typical operating currents for these devices begin at 350 mA. The highest efficiency high-power white LED is claimed by Philips Lumileds Lighting Co. with a luminous efficacy of 115 lm/W (350 mA).
Today, OLEDs operate at substantially lower efficiency than inorganic (crystalline) LEDs. The best efficacy of an OLED so far is about 10% of the theoretical maximum of 683, so about 68 lm/W. These claim to be much cheaper to fabricate than inorganic LEDs, and large arrays of them can be deposited on a screen using simple printing methods to create a color graphic display.

[edit] Failure modes
The most common way for LEDs (and diode lasers) to fail is the gradual lowering of light output and loss of efficiency. However, sudden failures can occur as well.
The mechanism of degradation of the active region, where the radiative recombination occurs, involves nucleation and growth of dislocations; this requires a presence of an existing defect in the crystal and is accelerated by heat, high current density, and emitted light. Gallium arsenide and aluminum gallium arsenide are more susceptible to this mechanism than gallium arsenide phosphide and indium phosphide. Due to different properties of the active regions, gallium nitride and indium gallium nitride are virtually insensitive to this kind of defects; however, high current density can cause electromigration of atoms out of the active regions, leading to emergence of dislocations and point defects, acting as nonradiative recombination centers and producing heat instead of light. Ionizing radiation can lead to creation of such defects as well, which leads to issues with radiation hardening of circuits containing LEDs (eg. in optoisolators). Early red LEDs were notable for their short lifetime.
White LEDs often use one or more phosphors. The phosphors tend to degrade with heat and age, losing efficiency and causing changes in the produced light color. Pink LEDs often use an organic phosphor formulation which may degrade after just a few hours of operation causing a major shift in output color.
High electrical currents at elevated temperatures can cause diffusion of metal atoms from the electrodes into the active region. Some materials, notably indium tin oxide and silver, are subject to electromigration. In some cases, especially with GaN/InGaN diodes, a barrier metal layer is used to hinder the electromigration effects. Mechanical stresses, high currents, and corrosive environment can lead to formation of whiskers, causing short circuits.
High-power LEDs are susceptible to current crowding, nonhomogenous distribution of the current density over the junction. This may lead to creation of localized hot spots, which poses risk of thermal runaway. Nonhomogenities in the substrate, causing localized loss of thermal conductivity, aggravate the situation; most common ones are voids caused by incomplete soldering, or by electromigration effects and Kirkendall voiding. Thermal runaway is a common cause of LED failures.
Laser diodes may be subject to catastrophic optical damage, when the light output exceeds a critical level and causes melting of the facet.
Some materials of the plastic package tend to yellow when subjected to heat, causing partial absorption (and therefore loss of efficiency) of the affected wavelengths.
Sudden failures are most often caused by thermal stresses. When the epoxy resin used in packaging reaches its glass transition temperature, it starts rapidly expanding, causing mechanical stresses on the semiconductor and the bonded contact, weakening it or even tearing it off. Conversely, very low temperatures can cause cracking of the packaging.
Electrostatic discharge (ESD) may cause immediate failure of the semiconductor junction, a permanent shift of its parameters, or latent damage causing increased rate of degradation. LEDs and lasers grown on sapphire substrate are more susceptible to ESD damage.

[edit] Considerations in use

Close-up of a typical LED in its case, showing the internal structure.


Unlike incandescent light bulbs, which light up regardless of the electrical polarity, LEDs will only light with positive electrical polarity. When the voltage across the p-n junction is in the correct direction, a significant current flows and the device is said to be forward-biased. If the voltage is of the wrong polarity, the device is said to be reverse biased, very little current flows, and no light is emitted. LEDs can be operated on an alternating current voltage, but they will only light with positive voltage, causing the LED to turn on and off at the frequency of the AC supply.
While the only 100% accurate way to determine the polarity of an LED is to examine its datasheet, these methods are usually reliable:
sign:
+
−
polarity:
positive
negative
terminal:
anode (A)
cathode (K)
leads:
long
short
exterior:
round
flat
interior:
small
large
wiring:
red
black
Less reliable methods of determining polarity are:
sign:
+
−
marking:
none
stripe
pin:
1
2
PCB:
square
round
Because the voltage versus current characteristics of an LED are much like any diode (that is, current approximately an exponential function of voltage), a small voltage change results in a huge change in current. Added to deviations in the process this means that a voltage source may barely make one LED light while taking another of the same type beyond its maximum ratings and potentially destroying it.
Since the voltage is logarithmically related to the current it can be considered to remain largely constant over the LEDs operating range. Thus the power can be considered to be almost proportional to the current. In order to keep power nearly constant with variations in supply and LED characteristics, the power supply should be a "current source", that is, it should supply an almost constant current. If high efficiency is not required (e.g. in most indicator applications), an approximation to a current source made by connecting the LED in series with a current limiting resistor to a constant voltage source is generally used.
Most LEDs have low reverse breakdown voltage ratings, so they will also be damaged by an applied reverse voltage of more than a few volts. Since some manufacturers don't follow the indicator standards above, if possible the data sheet should be consulted before hooking up an LED, or the LED may be tested in series with a resistor on a sufficiently low voltage supply to avoid the reverse breakdown. If it is desired to drive an LED directly from an AC supply of more than the reverse breakdown voltage then it may be protected by placing a diode (or another LED) in inverse parallel.
LEDs can be purchased with built in series resistors. These can save PCB space and are especially useful when building prototypes or populating a PCB in a way other than its designers intended. However the resistor value is set at the time of manufacture, removing one of the key methods of setting the LED's intensity. To increase efficiency (or to allow intensity control without the complexity of a DAC), the power may be applied periodically or intermittently; so long as the flicker rate is greater than the human flicker fusion threshold, the LED will appear to be continuously lit.
Provided there is sufficient voltage available, multiple LEDs can be connected in series with a single current limiting resistor. Parallel operation is generally problematic. The LEDs have to be of the same type in order to have a similar forward voltage. Even then, variations in the manufacturing process can make the odds of satisfactory operation low. For more information see Nichia Application Note.
Bicolor LED units contain two diodes, one in each direction (that is, two diodes in inverse parallel) and each a different color (typically red and green), allowing two-color operation or a range of apparent colors to be created by altering the percentage of time the voltage is in each polarity. Other LED units contain two or more diodes (of different colors) arranged in either a common anode or common cathode configuration. These can be driven to different colors without reversing the polarity.
LED units may have an integrated multivibrator circuit that makes the LED flash. They may also have an integrated current regulator.
Generally, for newer common standard LEDs in 3 mm or 5 mm packages, the following forward DC potential differences are typically measured. The forward potential difference depending on the LED's chemistry, temperature, and on the current (values here are for approx. 20 milliamperes, a commonly found maximum value).
Color
Potential Difference
Infrared
1.6 V
Red
1.8 V to 2.1 V
Orange
2.2 V
Yellow
2.4 V
Green
2.6 V
Blue
3.0 V to 3.5 V
White
3.0 V to 3.5 V
Ultraviolet
3.5 V
Many LEDs are rated at 5 V maximum reverse voltage.

[edit] Advantages of using LEDs
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LED schematic symbol
LEDs produce more light per watt than do incandescent bulbs; this is useful in battery powered or energy-saving devices.
LEDs can emit light of an intended color without the use of color filters that traditional lighting methods require. This is more efficient and can lower initial costs.
The solid package of an LED can be designed to focus its light. Incandescent and fluorescent sources often require an external reflector to collect light and direct it in a usable manner.
When used in applications where dimming is required, LEDs do not change their color tint as the current passing through them is lowered, unlike incandescent lamps, which turn yellow.
LEDs are ideal for use in applications that are subject to frequent on-off cycling, unlike fluorescent lamps that burn out more quickly when cycled frequently.
LEDs, being solid state components, are difficult to damage with external shock. Fluorescent and incandescent bulbs are easily broken if dropped on the ground.
LEDs have an extremely long life span. One manufacturer has calculated the ETTF (Estimated Time To Failure) for their LEDs to be between 100,000 and 1,000,000 hours [7]. Fluorescent tubes typically are rated at about 10,000 hours, and incandescent light bulbs at 1,000-2,000 hours.
LEDs mostly fail by dimming over time, rather than the abrupt burn-out of incandescent bulbs.
LEDs light up very quickly. A typical red indicator LED will achieve full brightness in microseconds; LEDs used in communications devices can have even faster response times.
LEDs can be very small and are easily populated onto printed circuit boards.
LEDs do not contain mercury, as compact fluorescent lamps do.

LEDs are produced in an array of shapes and sizes. The 5 mm cylindrical package (red, fifth from the left) is the most common, estimated at 80% of world production. The color of the plastic lens is often the same as the actual color of light emitted, but not always. For instance, purple plastic is often used for infrared LEDs, and most blue devices have clear housings. There are also LEDs in extremely tiny packages, such as those found on blinkies (not shown).

[edit] Disadvantages of using LEDs
LEDs are currently more expensive, price per lumen, on an initial capital cost basis, than more conventional lighting technologies. The additional expense partially stems from the relatively low lumen output and the drive circuitry and power supplies needed. However, when considering the total cost of ownership (including energy and maintenance costs), LEDs far surpass incandescent or halogen sources and begin to threaten compact fluorescent lamps.
LED performance largely depends on the ambient temperature of the operating environment. "Driving" a LED "hard" in high ambient temperatures may result in overheating of the LED package, eventually leading to device failure. Adequate heat-sinking is required to maintain long life. This is especially important when considering automotive, medical, and military applications where the device must operate over a large range of temperatures, and are required to have a low failure rate.
LEDs must be supplied with the correct current. This can involve shunt resistors or regulated power supplies [8].
LEDs typically cast light in one direction at a narrow angle compared to an incandescent or fluorescent lamp of the same lumen level.
The spectrum of some white LEDs differs significantly from a black-body radiator, such as the sun or an incandescent light. The spike at 460 nm and dip at 500 nm can cause the color of objects to be perceived differently under LED illumination than other light sources.
LEDs cannot be used in applications that need a sharply directive and collimated beam of light. LEDs are not capable of providing directivity below a few degrees. In such cases LASERs (or LED lasers) may be a better option.

[edit] LED applications

LED panel light source used in an experiment on plant growth. The findings of such experiments may be used to grow food in space on long duration missions.

Light sources for machine vision systems.

Flashlights and lanterns that utilize white LEDs are becoming increasingly popular due to their durability and longer battery life.

Single high-brightness LED with a glass lens creates a bright carrier beam that can stream DVD-quality video over considerable distances. The device, RONJA, can be built very simply by enthusiasts.

LED lights on a Audi S6

LED car tail lights modulated to appear dimmer.

[edit] List of LED applications
Some of these applications are further elaborated upon in the following text.
Architectural lighting
Status indicators on all sorts of equipment
Traffic lights and signals
Light source for machine vision systems, requiring bright, focused, homogeneous and possibly strobed illumination.
Exit signs
Motorcycle and Bicycle lights
Toys and recreational sporting goods, such as the Flashflight
Railroad crossing signals
Continuity indicators
Flashlights, including some mechanically powered models.
Light bars on emergency vehicles.
Elevator Push Button Lighting
Thin, lightweight message displays at airports and railway stations and as destination displays for trains, buses, trams and ferries.
Red or yellow LEDs are used in indicator and alphanumeric displays in environments where night vision must be retained: aircraft cockpits, submarine and ship bridges, astronomy observatories, and in the field, e.g. night time animal watching and military field use.
Red, yellow, green, and blue LEDs can be used for model railroading applications
Remote controls, such as for TVs and VCRs, often use infrared LEDs.
In optical fiber and Free Space Optics communications.
In dot matrix arrangements for displaying messages.
Glowlights, as a more expensive but longer lasting and reusable alternative to Glowsticks.
Grow lights composed of LEDs are more efficient, both because LEDs produce more lumens per watt than other alternatives, and also because they can be tuned to the specific wavelengths plants can make the most use of.
Movement sensors, for example in optical computer mice
Because of their long life and fast switching times, LEDs have been used for automotive high-mounted brake lights and truck and bus brake lights and turn signals for some time, but many high-end vehicles are now starting to use LEDs for their entire rear light clusters. Besides the gain in reliability, this has styling advantages because LEDs are capable of forming much thinner lights than incandescent lamps with parabolic reflectors. The significant improvement in the time taken to light up (perhaps 0.5s faster than an incandescent bulb) improves safety by giving drivers more time to react. It has been reported that at normal highway speeds this equals 1 car length increased reaction time for the car behind. Some manufacturers use the same LEDs for brake and tail lights, and dim the LEDs by modulating the current at 100 Hz or so, instead of reducing the current. This makes the LEDs flash visibly, which can distract drivers of other vehicles, and is illegal in the UK. Road Vehicles Lighting Regulations 1989
Backlighting for LCD televisions and displays. The availability of LEDs in specific colors (RGB) enables a full-spectrum light source which expands the color gamut by as much as 45%.
New stage lighting equipment is being developed with LED sources in primary red-green-blue arrangements.
Lumalive, a photonic textile
LED-based Christmas lights have been available since 2002, but are only now beginning to gain in popularity and acceptance due to their higher initial purchase cost when compared to similar incandescent-based Christmas lights. For example, as of 2006, a set of 50 incandescent lights might cost $2.00 USD, while a similar set of 50 LED lights might cost $10.00 USD. The purchase cost can be even higher for single-color sets of LED lights with rare or recently-introduced colors, such as purple, pink or white. Regardless of the higher initial purchase price, the total cost of ownership for LED Christmas lights would eventually be lower than the TCO for similar incandescent Christmas lights[citation needed] since an LED requires much less power to output the same amount of light as a similar incandescent bulb.
LED phototherapy for acne using blue or red LEDs has been proven to significantly reduce acne over a 3 month period.[citation needed]
As a medium quality voltage reference in electronic circuits. The forward voltage drop (e.g. about 1.7 V for a normal red LED) can be used instead of a Zener diode in low-voltage regulators. Although LED forward voltage is much more current-dependent than a good Zener, Zener diodes are not available below voltages of about 3 V.
Computers, for hard drive activity and power on. Some custom computers feature LED accent lighting to draw attention to a given component. Many computer manufactuers use LEDs to tell the user its current state. One example would be the Mac, which tells its user when it is asleep by fading the LED activity lights in and out in and out.

[edit] Illumination applications
LEDs used as a replacement for incandescent light bulbs and fluorescent lamps are known as solid-state lighting (SSL) - packaged as a cluster of white LEDs grouped together to form a light source. LEDs are moderately efficient; the average commercial SSL currently outputs 32 lumens per watt (lm/W), and new technologies promise to deliver up to 80 lm/W. The long lifetime of LEDs make SSL very attractive. They are also more mechanically robust than incandescent light bulbs and fluorescent tubes. Currently, solid state lighting is becoming more available for household use but is relatively expensive, although costs are decreasing. LED flashlights, however, already have become widely available.
One 6 watt LED light bulb can potentially last up to 58,500 or more hours than a 60 watt incandescent bulb, and potentially 50,000 more hours than a CFL. The cost difference between 40 incandescent light bulbs and 1 LED light bulb is only a few dollars, however, the kWh usage is significantly smaller with an LED light. Over this period of time, a significant amount of money can be saved. LEDs will also contribute by producing less waste.[9]
Recently a number of manufacturers have started marketing ultra-compact LCD video projectors that use high-powered white LEDs for the light source. Another alternative design is to use red, green, and blue LEDs in a sequential DLP design.
Incandescent bulbs are much less expensive but also less efficient, generating from about 16 lm/W for a domestic tungsten bulb to 22 lm/W for a halogen bulb. Fluorescent tubes are more efficient, providing 50 to 100 lm/W for domestic tubes (average 60 lm/W), but are bulky and fragile and require starter or ballast circuits. Compact fluorescent lamps, which include a quiet integrated ballast, are relatively robust and efficient and fit in standard light bulb sockets. They are currently the best choice for efficient household lighting[citation needed].
LEDs are now well established in applications such as traffic signals and indicator lamps for trucks and automobiles. High output LED fixtures suitable for general architectural lighting applications are beginning to appear on the market with system efficacies of up to 56 lumens per watt, which is comparable to fluorescent systems. Proponents of LEDs expect that technological advances will reduce costs such that SSL will replace incandescent and fluorescent lighting in most commercial and residential applications.
Due to their monochromatic nature, LED lights have great power advantages over white lights when a specific color is required. Unlike traditional white lights, the LED does not need a coating or diffuser that can absorb much of the emitted light. LED lights are inherently colored, and are available in a wide range of colors. One of the most recently introduced colors is the emerald green (bluish green, about 500 nm) that meets the legal requirements for traffic signals and navigation lights.
There are applications that specifically require light without any blue component. Examples are photographic darkroom safe lights, illumination in laboratories where certain photo-sensitive chemicals are used, and situations where dark adaptation (night vision) must be preserved, such as cockpit and bridge illumination, observatories, etc. Yellow LED lights are a good choice to meet these special requirements because the human eye is more sensitive to yellow light (about 500 lm/watt emitted) than that emitted by the other LEDs.
The first residence lit solely by LEDs was the "Vos Pad" in London. The entire flat is lit by a combination of white and RGB (color changing) LEDs.

[edit] Light sources for machine vision systems
Machine vision systems often require bright and homogeneous illumination, so features of interest are easier to process. LEDs are often used to this purpose, and this field of application is likely to remain one of the major application areas until price drops low enough to make signalling and illumination applications more widespread. LEDs constitute a nearly ideal light source for machine vision systems for several main reasons:
Size of illuminated field is usually comparatively small and Vision systems or smart camera are quite expensive, so cost of LEDs is usually a minor concern, compared to signaling applications.
LED elements tend to be small and can be placed with high density over flat or even shaped substrates (PCBs etc) so that bright and homogeneous sources can be designed which direct light from tightly controlled directions on inspected parts.
LEDs often have or can be used with small, inexpensive lenses and diffusers, helping to achieve high light densities and very good lighting control and homogeneity.
LEDs can be easily strobed (in the microsecond range and below) and synchronized; their power also has reached high enough levels that sufficiently high intensity can be obtained, allowing well lit images even with very short light pulses: this is often used in order to obtain crisp and sharp "still" images of fast moving parts.
LEDs come in several different colors and wavelengths, easily allowing to use the best color for each application, where different color may provide better visibility of features of interest. Having a precisely known spectrum allows tightly matched filters to be used to separate informative bandwidth or to reduce disturbing effect of ambient light.
LEDs usually operate at comparatively low working temperatures, simplifying heat management and dissipation, therefore allowing plastic lenses, filters and diffusers to be used. Waterproof units can also easily be designed, allowing for use in harsh or wet environments (food, beverage, oil industries).
LED sources can be shaped in several main configurations (spot lights for reflective illumination; ring lights for coaxial illumination; backlights for contour illumination; linear assemblies; flat, large format panels; dome sources for diffused, omnidirectional illumination).
Very compact designs are possible, allowing for small LED illuminators to be integrated within smart cameras and vision sensors.

[edit] History

[edit] Discovery
The first known report of a light-emitting solid-state diode was made in 1907 by the British experimenter H. J. Round. However, no practical use was made of the discovery for several decades.[8] Independently, Oleg Vladimirovich Losev published "Luminous carborundum [[silicon carbide]] detector and detection with crystals" in the Russian journal Telegrafiya i Telefoniya bez Provodov (Wireless Telegraphy and Telephony).[9] Losev's work languished for decades.
The first practical LED was invented by Nick Holonyak, Jr., in 1962 while he was at General Electric Company. The first LEDs became commercially available in late 1960s, and were red. They were commonly used as replacements for incandescent indicators, and in seven-segment displays, first in expensive equipment such as laboratory and electronics test equipment, then later in such appliances as TVs, radios, telephones, calculators, and even watches. These red LEDs were bright enough only for use as indicators, as the light output was not enough to illuminate an area. Later, other colors became widely available and also appeared in appliances and equipment. As the LED materials technology became more advanced, the light output was increased, and LEDs became bright enough to be used for illumination.
Most LEDs were made in the very common 5 mm T1-3/4 and 3 mm T1 packages, but with higher power, it has become increasingly necessary to get rid of the heat, so the packages have become more complex and adapted for heat dissipation. Packages for state-of-the-art high power LEDs bear little resemblance to early LEDs (see, for example, Philips Lumileds).

[edit] LED panels

The 1,500 foot long LED display on the Fremont Street Experience is currently the largest in the world.
there are two types of LED panels: conventional, using discrete LEDs, and surface mounted device (SMD) panels. Most outdoor screens and some indoor screens are built around discrete LEDs, also known as individually mounted LEDs. A cluster of red, green, and blue diodes is driven together to form a full-color pixel, usually square in shape. These pixels are spaced evenly apart and are measured from center to center for absolute pixel resolution. The largest LED display in the world is over 1,500 feet (457.2 m) long and is located in Las Vegas, Nevada covering the Fremont Street Experience.
Most indoor screens on the market are built using SMD technology — a trend that is now extending to the outdoor market. An SMD pixel consists of red, green, and blue diodes mounted on a chipset, which is then mounted on the driver PC board. The individual diodes are smaller than a pinhead and are set very close together. The difference is that the maximum viewing distance is reduced by 25% from the discrete diode screen with the same resolution.

LED panels allow for smaller sets of interchangeable LEDs to be one large display.
Indoor use generally requires a screen that is based on SMD technology and has a minimum brightness of 600 candelas per square meter (unofficially called nits). This will usually be more than sufficient for corporate and retail applications, but under high ambient-brightness conditions, higher brightness may be required for visibility. Fashion and auto shows are two examples of high-brightness stage lighting that may require higher LED brightness. Conversely, when a screen may appear in a shot on a television show, the requirement will often be for lower brightness levels with lower color temperatures (common displays have a white point of 6500 to 9000 K, which is much bluer than the common lighting on a television production set).

A large LED screen in Razorback Stadium
For outdoor use, at least 2,000 nits are required for most situations, whereas higher brightness types of up to 5,000 nits cope even better with direct sunlight on the screen. Until recently, only discrete-diode screens could achieve that brightness level. (The brightness of LED panels can be reduced from the designed maximum, if required.)
Suitable locations for large display panels are identified by factors such as line of sight, local authority planning requirements (if the installation is to become semi-permanent), vehicular access (trucks carrying the screen, truck-mounted screens, or cranes), cable runs for power and video (accounting for both distance and health and safety requirements), power, suitability of the ground for the location of the screen (if there are no pipes, shallow drains, caves, or tunnels that may not be able to support heavy loads), and overhead obstructions.

[edit] Early LED flat panel TV history
Perhaps the first recorded flat LED television screen prototype to be developed was by James P. Mitchell in 1977. The modular, scalable display was enabled by MV50 LEDs and newly available TTL (transistor transistor logic) memory addressing circuit technology. The prototype and paper was displayed at an Engineering Exposition in Anaheim May 1978, and organized by the Science Service in Washington D.C. The LED flat panel TV display received special recognition by NASA, General Motors Corporation, and area universities including The University of California Irvine, Robert M. Saunders Prof. of Engineering and IEEE President 1977. Additionally, technology business representatives from the U.S. and overseas witnessed operation of the monochromatic LED flat panel television display. The prototype remains operational. A LCD (liquid crystal display) matrix design was also presented in the accompanying scientific paper, as a future television display method using a similar scanning design method.
The early display prototype was red monochromatic. Low-cost efficient blue LEDs did not emerge until the early 1990s, completing the RGB color triad. High-brightness colors gradually emerged in the 1990s enabling new designs for outdoor signage and huge video displays for billboards and stadiums.

[edit] Multi-touch sensing
Since LEDs share some basic physical properties with photodiodes, which also use p-n junctions with band gap energies in the visible light wavelengths, they can also be used for photo detection. These properties have been known for some time, but more recently so-called bidirectional LED matrices have been proposed as a method of touch-sensing. In 2003, Dietz, Yerazunis, and Leigh published a paper[10] describing the use of LEDs as cheap sensor devices.
In this usage, various LEDs in the matrix are quickly switched on and off. LEDs that are on shine light onto a user's fingers or a stylus. LEDs that are off function as photodiodes to detect reflected light from the fingers or stylus. The voltage thus induced in the reverse-biased LEDs can then be read by a microprocessor, which interprets the voltage peaks and then uses them elsewhere. The website of Jeff Han features a video demonstrating one such implementation of an LED matrix multi-touch sensor.LED technology

[edit] Physical function
Like a normal diode, an LED consists of a chip of semiconducting material impregnated, or doped, with impurities to create a p-n junction. As in other diodes, current flows easily from the p-side, or cathode, to the n-side, or anode, but not in the reverse direction. Charge-carriers — electrons and electron holes — flow into the junction from electrodes with different voltages. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon.
The wavelength of the light emitted, and therefore its colour, depends on the band gap energy of the materials forming the p-n junction. In silicon or germanium diodes, the electrons and holes recombine by a non-radiative transition which produces no optical emission, because these are indirect band gap materials. The materials used for an LED have a direct band gap with energies corresponding to near-infrared, visible or near-ultraviolet light.
LEDs are usually constantly illuminated when a current passes through them, but flashing LEDs are also available. Flashing LEDs resemble standard LEDs but they contain a small chip inside which causes the LED to flash with a typical period of one second. This type of LED comes most commonly as red, yellow, or green. Most flashing LEDs emit light of a single wavelength, but multicolored flashing LEDs are available too.
LED development began with infrared and red devices made with gallium arsenide. Advances in materials science have made possible the production of devices with ever-shorter wavelengths, producing light in a variety of colors.
LEDs are usually built on an n-type substrate, with electrode attached to the p-type layer deposited on its surface. P-type substrates, while less common, occur as well. Many commercial LEDs, especially GaN/InGaN, also use sapphire substrate. Substrates that are transparent to the emitted wavelength, and backed by a reflective layer, increase the LED efficiency. The refractive index of the package material should match the index of the semiconductor, otherwise the produced light gets partially reflected back into the semiconductor, where it gets absorbed and turns into additional heat lowering the efficiency. In 2007 experiments tried to avoid multiple internal reflection by roughening the chip. Again at the surface from the package to a low refractive index medium like a glass fiber or air total internal reflection is avoided by using a sphere shaped package, with the diode in the center, so that the