Energy
Renewable Energy
Nonrenewable Energy
Energy
Energy is one of the most fundamental parts of our universe.
We use energy to do work. There are two types of energy, kinetic energy and potential energy. Kinetic energy is motion while potential energy is stored energy.
Different forms of potential energy are:
- Chemical energy - the energy stored in bonds of atoms and molecules
- Stored mechanical energy - the energy stored in objects by application of force
- Nuclear energy - the energy stored in the nucleus of atoms
- Gravitational energy - the energy of position or place.
Different forms of kinetic energy are:
- Electrical energy - movement of electrical charges
- Radiant energy - electromagnetic energy that travels in transverse waves
- Thermal energy - heat of internal energy in substances
- Motion energy - movement of substance from one place to another
- Sound energy - movement of energy through substances in longitudinal waves
All forms of energy are stored in different sources of energy.
Sources of Energy
- Solar Energy
- Wind Energy
- Biomass Energy
- Geothermal Energy
- Hydropower and Ocean Energy
- Fossil Fuels - Coal, Oil, Natural Gas
- Nuclear Energy
The United States currently relies heavily on coal, oil, and natural gas for its energy. Fossil fuels are nonrenewable, that is, they draw on finite resources that will eventually dwindle, becoming too expensive or too environmentally damaging to retrieve. In contrast, renewable energy resources—such as wind and solar energy—are constantly replenished and will never run out.
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Renewable Energy
Renewable energy is defined as an energy source that is naturally replaced by an on-going process at a rate greater than the rate of usage. Ultimately, almost all renewable energy comes either directly or indirectly from the sun. Renewable energy sources include solar, wind, hydro, tidal, biomass and geothermal energy.
Solar energy, can be used directly for heating and lighting the buildings, for generating electricity, and for hot water heating, solar cooling, and a variety of commercial and industrial uses.
Wind is the fuel source for wind energy. The sun's heat drives the winds, which are captured with wind turbines. Wind turbines typically generate electricity that is fed into the utility grid.
The winds and the sun's heat cause water to evaporate. This water vapor turns into rain and feeds rivers and streams. Water flowing downhill in rivers or streams can be harnessed to generate hydroelectric power.
Rain and sunlight allow plants to grow creating organic matter known as biomass. Biomass can be used to produce electricity, transportation fuels, or chemicals. The use of biomass for any of these purposes is called biomass energy.
Energy derived from the natural heat of the earth is called geothermal energy, which has a variety of uses, including electric power production, and the heating and cooling of buildings.
The gravitational pull of the moon and the sun upon the Earth cause tides in the oceans that cover more than 70% of earth surface. These tides can be harnessed to produce electricity. Additionally, the sun warms the surface of the ocean more than the ocean depths, creating a temperature difference that can be used as an energy source.
Types of renewable energy:
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Solar Energy
Solar energy is the energy derived from the sun's light to provide heat, light, hot water, electricity, and cooling for homes, business, and industry.
Solar technologies include:
More information about research in solar energy by
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Photovoltaic Cells
This process of converting light (photons) to electricity (voltage) is called the photovoltaic (PV) effect. Photovoltaic cells are made from a class of materials know as semiconductors. When sunlight is absorbed by these materials, the solar energy knocks electrons loose from their atoms, allowing the electrons to flow through the material to produce electricity.
A PV cell's performance is measured in terms of its efficiency at turning sunlight into electricity. Only certain wavelengths can be captured by PV cells and much of the total solar energy is reflected or absorbed. Because of this, a typical PV cell has an efficiency of between 15 and 20 percent, meaning only one-sixth of the sunlight striking the cell generates electricity. Improving PV cell efficiencies while holding down the cost per cell is an important goal of the PV industry, NREL researchers, and other U.S. Department of Energy (DOE) laboratories, and they have made significant progress.
Department of Energy's view Turning sunlight into electricity
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Concentrating Solar Power
There are three main types of concentrating solar power systems: parabolic-trough, dish/engine, and power tower.
Parabolic-trough systems concentrate the sun's energy through long rectangular, curved (U-shaped) mirrors. The mirrors are tilted toward the sun, focusing sunlight on a pipe that runs down the center of the trough. This heats the oil flowing through the pipe. The hot oil then is used to boil water in a conventional steam generator to produce electricity.
A dish/engine system uses a mirrored dish. The dish-shaped surface collects and concentrates the sun's heat onto a receiver, which absorbs the heat and transfers it to fluid within the engine. The heat causes the fluid to expand against a piston or turbine to produce mechanical power. The mechanical power is then used to run a generator or alternator to produce electricity.
A power tower system uses a large field of mirrors to concentrate sunlight onto the top of a tower, where a receiver sits. This heats molten salt flowing through the receiver. Then, the salt's heat is used to generate electricity through a conventional steam generator. Molten salt retains heat efficiently, so it can be stored for days before being converted into electricity. That means electricity can be produced on cloudy days or even several hours after sunset.
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Passive Solar heating and Daylighting
Today, many buildings are designed to take advantage of solar energy through the use of passive solar heating and day lighting.
In the northern hemisphere, the south side of a building always receives the most sunlight. Therefore, buildings designed for passive solar heating usually have large, south-facing windows. Materials that absorb and store the sun's heat can be built into the sunlit floors and walls. The floors and walls will then heat up during the day and slowly release heat at night, when the heat is needed most. This passive solar design feature is called direct gain.
Other passive solar heating design features include sunspaces and trombe walls. A sunspace (which is much like a greenhouse) is built on the south side of a building. As sunlight passes through glass or other glazing, it warms the sunspace. Proper ventilation allows the heat to circulate into the building. On the other hand, a trombe wall is a very thick, south-facing wall, which is painted black and made of a material that absorbs a lot of heat. A pane of glass or plastic glazing, installed a few inches in front of the wall, helps hold in the heat. The wall heats up slowly during the day. Then as it cools gradually during the night, it gives off its heat inside the building.
Many of the passive solar heating design features also provide daylighting. Daylighting is simply the use of natural sunlight to brighten up a building's interior allowing for less energy usage to light a space. To lighten up north-facing rooms and upper levels, a clerestory— a row of windows near the peak of the roof— is often used along with an open floor plan inside that allows the light to bounce throughout the building.
Of course, too much solar heating and daylighting can be a problem during the hot summer months. Fortunately, there are many design features that help keep passive solar buildings cool in the summer. For instance, overhangs can be designed to shade windows when the sun is high in the summer. Sunspaces can be closed off from the rest of the building and a building can be designed to use fresh-air ventilation in the summer.
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Solar hot water
One of the most cost effective ways to incorporate renewable technologies into a building is with a solar hot water system. A typical system will reduce the need for conventional water heating by about two-thirds, minimizing the expense of electricity or fossil fuel to heat the water and reducing the associated environmental impacts.
Most solar water heating systems for buildings have two main parts: a solar collector and a storage tank. The most common collector is called a flat-plate collector. Mounted on the roof, it consists of a thin, flat, rectangular box with a transparent cover that faces the sun. Small tubes run through the box and carry the fluid – either water or other fluid, such as an antifreeze solution – to be heated. The tubes are attached to an absorber plate, which is painted black to absorb the heat. As heat builds up in the collector, it heats the fluid passing through the tubes.
The storage tank then holds the hot liquid. It can be just a modified water heater, but it is usually larger and very well-insulated. Systems that use fluids other than water heat the water by passing it through a coil of tubing in the tank, which is full of hot fluid.
Solar water heating systems can be either active or passive, but the most common are active systems. Active systems rely on pumps to move the liquid between the collector and the storage tank, while passive systems rely on gravity and the tendency for water to naturally circulate as it is heated.
Swimming pool systems are simpler. The pool's filter pump is used to pump the water through a solar collector, which is usually made of black plastic or rubber. And of course, the pool stores the hot water. Top of Page
Wind Energy
Wind energy is both old and new. From the trireme sailing ships of the ancient Greeks, to the grain mills of pre-industrial Holland, to the latest high-tech wind turbines rising over the Minnesota prairie, humans have used the power of the wind for millennia. Today, the windmill's modern equivalent— a wind turbine— can use the wind's energy to generate electricity.
Wind Turbines
Wind turbines are mounted on towers to take advantage of faster and less turbulent wind than is available at ground level. Turbines catch the wind's energy with their propeller-like blades which are mounted on a shaft to form a rotor. When the wind blows, a pocket of low-pressure air forms on the downwind side of the blade. The low-pressure air pocket then pulls the blade toward it, causing the rotor to turn. This is called lift. The force of the lift is actually much stronger than the wind's force against the front side of the blade, which is called drag. The combination of lift and drag causes the rotor to spin, and the turning shaft spins a generator to make electricity.
Wind turbines can be used as stand-alone applications, or they can be connected to a utility power grid or even combined with a photovoltaic (solar cell) system. For utility-scale sources of wind energy, a large number of wind turbines are usually built close together to form a wind plant. Several electricity providers today use wind plants to supply power to their customers.
Stand-alone wind turbines are typically used for water pumping or communications. However, homeowners, farmers, and ranchers in windy areas can also use wind turbines as a way to cut their electric bills.
Small wind systems also have potential as distributed energy resources. Distributed energy resources refer to a variety of small, modular power-generating technologies that can be combined to improve the operation of the electricity delivery system.
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Biomass Energy
The most familiar forms of renewable energy are the wind and the sun. But biomass, energy from plants and animals, supplies almost 30 times as much energy in the United States as wind and solar power combined -- and has the potential to supply much more.
The term biomass refers to plant materials and animal wastes used for energy, especially tree and grass crops, and forestry, agricultural, and urban wastes. It is the oldest source of renewable energy known to humans, used since our ancestors learned the secret of fire.
Today, wood is still our largest biomass energy resource. But many other sources of biomass can now be used, including plants, residues from agriculture or forestry, and the organic component of municipal and industrial wastes. Even the fumes from landfills can be used as a biomass energy source.
The use of biomass energy has the potential to greatly reduce our greenhouse gas emissions. Biomass generates about the same amount of carbon dioxide as fossil fuels, but every time a new plant grows, carbon dioxide is actually removed from the atmosphere. The net emission of carbon dioxide will be zero as long as plants continue to be replenished for biomass energy purposes. These energy crops, such as fast-growing trees and grasses, are called biomass feedstocks.
We depend on biomass to provide about 3 to 4 percent of our energy in the United States and continue to expand our use of bioenergy. We're even learning more about how to produce the same high-quality materials and chemicals from biomass, such as those that presently come from petroleum.
Converting Biomass into Energy
The old way of converting biomass to energy, practiced for thousands of years, is simply to burn it to produce heat. This is still the use to which most biomass is put, in the United States and elsewhere. The heat can be used directly, for heating, cooking, and industrial processes, or indirectly, to produce electricity. The problems with burning biomass are that much of the energy is wasted and that it can cause some pollution if it is not carefully controlled.
An approach that may increase the use of biomass energy in the short term is to burn it mixed with coal in power plants. Utilities in New York and Wisconsin are experimenting with this approach as a way to reduce carbon dioxide emissions.
A number of noncombustion methods for converting biomass to energy have one thing in common -- they convert raw biomass into a variety of gaseous, liquid, or solid fuels before using it. The carbohydrates in biomass, which are compounds of oxygen, carbon, and hydrogen, can be broken down into a variety of chemicals, some of which are useful fuels. This conversion can be done in three ways:
- Thermochemical. When plant matter is heated, but not burned, it breaks down into various gases, liquids, and solids. These products can then be processed into gas and liquid fuels like methane and alcohol. Biomass gasifiers capture methane released from the plants and burn it in a gas turbine to produce electricity. Another approach is to take these fuels and run them through fuel cells, converting the hydrogen-rich fuels into electricity and water, with few or no emissions.
- Biochemical. Bacteria, yeasts, and enzymes also break down carbohydrates. Fermentation, the process used to make wine, changes biomass liquids into alcohol, which is inflammable. A similar process is used to turn corn into grain alcohol or ethanol, which is mixed with gasoline to make gasohol. Also, when bacteria break down biomass, methane and carbon dioxide are produced. This methane can be captured, in sewage treatment plants and landfills, for example, and burned for heat and power.
- Chemical. Biomass oils, like soybean and canola oil, can be chemically converted into a liquid fuel similar to diesel fuel, and into gasoline additives. Cooking oil from restaurants, for example, has been used as a source to make "biodiesel" for trucks. Biomass is also used to make gas additives like ETBE and MTBE, which reduce air emissions from cars.
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Geothermal Energy
"Geothermal" comes from the Greek words geo (earth) and therme (heat). The heat from the earth's core continuously flows outward. It transfers (conducts) to the surrounding layer of rock, known as the mantle. When temperatures and pressures become high enough, some mantle rock melts, becoming magma. Then, because it is less dense than the surrounding rock, the magma rises (convects), moving slowly up toward the earth's crust, carrying the heat from below.
Sometimes the hot magma reaches all the way to the surface, where we know it as lava. But most often the magma remains below earth's crust, heating nearby rock and water - sometimes to as hot as 700˚ F. Some of this hot geothermal water travels back up through faults and cracks and reaches the earth's surface as hot springs or geysers, but most of it stays deep underground, trapped in cracks and porous rock. This natural collection of hot water is called a geothermal reservoir.
Heat from the earth can be used in many ways, from large and complex to small and simple. Geothermal energy is as remote as deep wells in Indonesia and as close as the dirt in our back yards. Tapping that heat is a relatively clean and sustainable energy source.
Geothermal Electricity
In geothermal power plants steam, heat or hot water from geothermal reservoirs provides the force that spins the turbine generators and produces electricity. The used geothermal water is then returned down an injection well into the reservoir to be reheated, to maintain pressure, and to sustain the reservoir.
There are three kinds of geothermal power plants and the type of plant employed depends on the temperatures and pressures of a reservoir.
- A "dry'" steam reservoir produces steam but very little water. The steam is piped directly into a "dry" steam power plant to provide the force to spin the turbine generator. The largest dry steam field in the world is The Geysers, about 90 miles north of San Francisco. Production of electricity started at The Geysers in 1960, at what has become the most successful alternative energy project in history.
- A geothermal reservoir that produces mostly hot water is called a "hot water reservoir" and is used in a "flash" power plant. Water ranging in temperature from 300 - 700˚ F is brought up to the surface through the production well where, upon being released from the pressure of the deep reservoir, some of the water flashes into steam in a 'separator.' The steam then powers the turbines.
- A reservoir with temperatures between 250 - 360˚ F is not hot enough to flash enough steam but can still be used to produce electricity in a "binary" power plant. In a binary system the geothermal water is passed through a heat exchanger, where its heat is transferred into a second (binary) liquid, such as isopentane, that boils at a lower temperature than water. When heated, the binary liquid flashes to vapor, which, like steam, expands across and spins the turbine blades. The vapor is then recondensed to a liquid and is reused repeatedly. In this closed loop cycle, there are no emissions to the air.
DIRECT USES
Geothermal waters ranging from 50˚ F to over 300˚ F are used directly from the earth.
Space heating of individual buildings and of entire districts, is - besides hot spring bathing - the most common and the oldest direct use of nature's hot water. Geothermal district heating systems pump geothermal water through a heat exchanger, where it transfers its heat to clean city water that is piped to buildings in the district. There, a second heat exchanger transfers the heat to the building's heating system. The geothermal water is injected down a well back into the reservoir to be heated and used again. The first modern district heating system was developed in Boise, Idaho. (In the western U.S. there are 271 communities with geothermal resources available for this use.) Modern district heating systems also serve homes in Russia, China, France, Sweden, Hungary, Romania, and Japan. The world's largest district heating system is in Reykjavik, Iceland. Since it started using geothermal energy as its main source of heat Reykjavik, once very polluted, has become one of the cleanest cities in the world.
Geothermal heat is being used in some creative ways; its use is limited only by our ingenuity. For example, in Klamath Falls, Oregon, which has one of the largest district heating systems in the U.S., geothermal water is also piped under roads and sidewalks to keep them from icing over in freezing weather. The cost of using any other method to keep hot water running continuously through cold pipes would be prohibitive. And in New Mexico and other places rows of pipes carrying geothermal water have been installed under soil, where flowers or vegetables are growing. This ensures that the ground does not freeze, providing a longer growing season and overall faster growth of agricultural products that are not protected by the shelter and warmth of a greenhouse.
GEOTHERMAL HEAT PUMPS
Animals have always known to burrow into the earth, where the temperature is relatively stable compared to the air temperature, to get shelter from winter's cold and summer's heat. People, too, have sought relief from bad weather in earth's caves. Today, geothermal heat pumps (GHP's) can take advantage of this stable earth temperature, about 45 - 58˚ F, just a few feet below the surface - to help keep our indoor temperatures comfortable. GHP's circulate water or other liquids through pipes buried in a continuous loop (either horizontally or vertically) next to a building. Depending on the weather, the system is used for heating or cooling.
Heating: Heat from the ground (the difference between the earth's temperature and the colder temperature of the air) is transferred through the buried pipes into the circulating liquid and then transferred again into the building.
Cooling: During hot weather, the continually circulating fluid in the pipes 'picks up' heat from the building - thus helping to cool it - and transfers it into the earth.
GHP's use very little electricity and are very easy on the environment. In the U.S., the temperature inside over 300,000 homes, schools and offices is kept comfortable by these energy saving systems, and hundreds of thousands more are used worldwide. The U.S. Environmental Protection Agency has rated GHP's as among the most efficient of heating and cooling technologies. Top of Page
Hydropower Energy
Hydropower is energy derived from moving or falling water. Hydroelectric power uses the kinetic energy of moving water to make electricity.
There are different types of hydropower:
- Impoundment
- Diversion
- Pumped Storage
Impoundment
The impoundment method uses dams built across a river to stop the flow of water and made reservoir. When water is released from dam, it pushes against blades in a turbine causes them to turn. The turbine spins a generator to produce electricity.
Diversion
With the diversion method, fast flowing rivers are diverted in part through a turbine set in the river or off to the side and may not require the use of dam.
Pumped Storage
In a pumped storage plant, water is pumped from a lower reservoir to a higher reservoir during off-peak times, using electricity from other types of generators. When the power is needed, it is released back into the lower reservoir through turbines. Top of Page
Non Renewable Energy
Most of our energy comes from fossil fuels: coal, oil and natural gas.
Fossil fuels were formed many hundreds of millions of year ago. At the time, the land was covered with swamps filled with huge trees, ferns and other large leafy plants. The water and seas were filled with algae. As the trees and plants died, they sank to the bottom of the swamps and oceans and formed layers of a spongy material call peat.
Over many hundreds of years, the peat was covered by sand and clay and other minerals, which turned into a type of rock called sedimentary. More and more rock piled on top and the weight pressed down on the peat. The peat was squeezed and squeezed until the water came out of it and it eventually, over millions of years, it turned into coal, oil or petroleum, and natural gas.
Coal
Coal is a hard, black-colored rock like substance made up of carbon, hydrogen, oxygen, nitrogen and varying amounts of sulphur. There are three main types of coal - anthracite, bituminous and lignite. Anthracite coal is the hardest and has more carbon, which gives it a higher energy content. Lignite is the softest and is low in carbon but high in hydrogen and oxygen content. Bituminous is in between.
Oil and Natural Gas
Oil was formed more than 300 million years ago. Researcher says, diatoms are the source of oil. Diatoms are sea creatures the size of a pin head and they can convert sunlight directly into stored energy. When diatoms died, they fall to the sea floor and they were buried under sediment and other rock. The rock squeezed the diatoms and the energy in their bodies turned into oil under great pressure and heat. Natural gas is lighter than air and is made up mostly of gas called methane.
Methane is a simple chemical compound that is made up of carbon and hydrogen atoms. This gas is found under ground between folds of rock and in areas that are porous and contain the oils within the rock itself. Natural gas is a relatively clean burning fossil fuel, used mostly for space and water heating in buildings and running industrial processes. Increasingly, natural gas is used in combustion turbines to produce electricity.
Our nation's energy security continues to be threatened by our dependency on oil and many of the world’s oil sources are vulnerable to political instabilities, trade disputes, embargoes, and other disruptions.
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