Pushpendra
Alternate Energy Solution

By Pushpendra Singh

Abstract

Alternative sources of energy are considerably more attractive in many ways than nuclear power. These sources include solar power, wind, wave and geothermal energy. Energy efficiency is also critically important in delivering an economically and environmentally acceptable but sustainable source of energy for the 21st century. An alternative, or complementary, approach is to reward cleaner energy supply systems by paying a subsidy to balance the environmental costs of burning fossil fuels. The environmental consequences of energy production have led many nations in the world to impose stricter guidelines on the production and consumption of energy. Further, the search for new sources of energy and more efficient means of employing energy has accelerated. Researchers and engineers have been looking at alternative energy sources that do not tax the environment or deplete natural fuel reserves. Future energy development faces great challenges due to an increasing world population, demands for higher standards of living.











TABLE OF CONTENT
1. Introduction
2. Alternative Energy Sources
2.1 Solar Energy
2.2 Geothermal Energy
2.3 Wind Energy
2.4 Ocean Energy
2.5 Biomass Energy
2.6 Nuclear Energy
2.7 Hydrogen
2.8 Fuel Cell
2.9 Hydropower
2.10 Energy from fossil fuels
3. Energy Storage
4. Advantages and Disadvantages of Alternative Energy
5. Conclusion
6. References






2 Alternative Energy Sources
An Alternative Energy Source is one not commonly associated with a particular use. For example, wind power in the form of windmills has been used for hundreds of years to grind grain making it a conventional source of energy. However, using wind power to generate electricity is relatively new, and is therefore considered an alternative energy source when used for this application Examples of renewable primary energy sources include geothermal, hydropower and solar. Nonrenewable primary energy sources include natural gas, oil, coal and uranium. Secondary energy sources are products of human technology, the most common of these energy sources is electricity.
Alternative Energy Sources
Nonrenewable
Renewable

Oil sands, heavy oil
Wood/other biomass

Natural gas
Hydro-electric power

Coal
Solar energy

Shale oil
Wind energy

Gas hydrates
Wave energy

Nuclear fission
Tidal power

Geothermal1
Fusion


Ocean thermal energy conversion



SOLAR ENERGY

The sun's energy is vital to life on Earth. It determines the Earth's surface temperature and supplies virtually all the energy that drives natural global systems and cycles. Although some other stars are enormous sources of energy in the form of X-rays and radio signals, our sun releases 95% of its energy as visible light. Yet, visible light represents only a fraction of the total radiation spectrum; infrared and ultraviolet rays are also significant parts of the solar spectrum.

All renewable energies derive from the sun. There is solar, of course, but also hydrothermal, biomass, and wind. They all get their energy from the sun. The amount of sun that reaches the earth’s surface is enormous. Two weeks of sunlight over the whole earth is equal to all of the energy stored in coal, oil and natural gas. The problem is to harness it.
Each second, the sun releases an enormous amount of radiant energy in to the solar system. The Earth receives a tiny fraction of this energy; still, an average of 1367 watts (W) reaches each square meter (m2) of the outer edge of the Earth's atmosphere. The atmosphere absorbs and reflects some of this radiation, including most X-rays and ultraviolet rays. Still, the amount of sunshine energy that hits the surface of the Earth every minute is greater than the total amount of energy that the world's human population consumes. The Earth's atmosphere and cloud cover absorb, reflect, and scatter some of the solar radiation entering the atmosphere.
Solar cells












These convert solar power directly into electricity. Clean, but very expensive and polluting in the production of them. The most important parts of a solar cell are the semiconductor layers, because this is where the electron current is created. There are a number of different materials suitable for making these semi conducting layers, and each has benefits and drawbacks. Unfortunately, there is no one ideal material for all types of cells and applications. In addition to the semi conducting materials, solar cells consist of a top metallic grid or other electrical contact to collect electrons from the semiconductor and transfer them to the external load, and a back contact layer to complete the electrical circuit. Then, on top of the complete cell is typically a glass cover or other type of transparent encapsulate to seal the cell and keep weather out, and an anti reflective coating to keep the cell from reflecting the light back away from the cell.

The "photovoltaic effect" is the basic physical process through which a PVcell converts sunlight into electricity. Sunlight is composed of photons, or particles of solar energy. These photons contain various amounts of energy corresponding to the different wavelengths of the solar spectrum (see "Light and the Sun" for more about that). When photons strike a PVcell, they may be reflected or absorbed, or they may pass right through.Only the absorbed photons generate electricity. When this happens, the energy of the photon is transferred to an electron in an atom of the cell (which is actually a semiconductor). With its newfound energy, the electron is able to escape from its normal position associated with that atom to become part of the current in an electrical circuit. By leaving this position, the electron causes a "hole" to form. Special electrical properties of the PV cell-a built-in electric field provide the voltage needed to drive.
Solar cells are typically combined into modules that hold about 40 cells; about 10 of these modules are mounted in PV arrays that can measure up to several meters on a side. These flat-plate PV arrays can be mounted at a fixed angle facing south, or they can be mounted on a tracking device that follows the sun, allowing them to capture the most sunlight over the course of a day. About 10 to 20 PV arrays can provide enough power for a household; for large electric utility or industrial applications, hundreds of arrays can be interconnected to form a single, large PV system. By connecting cells together to form a solar panel we can do even more work. The typical individual silicon solar cell has the potential of generating about half a volt, but by wiring them in series or end to end you can increase the voltage. In other words, 36 individual cells will produce about 18 volts. The size of the individual cell is what determines the amount of current of amps that a solar panel can produce.
Solar energy power plants
Many power plants today use fossil fuels as a heat source to boil water. The steam from the boiling water rotates a large turbine, which activates a generator that produces electricity. However, a new generation of power plants, with concentrating solar power systems, uses the sun as a heat source. 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 (similar to a very large satellite 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.

California has an abundance of accessible solar energy resources. In terms of potential Electricity capacity, sunlight striking California could produce about 30,000 megawatts (MW) for central generation to the electricity grid and about 35,000 MW for distributed generation. For comparison, the entire California electric generation demand is currently about 65,000 MW. As of 1998, however, solar energy produces only roughly about 355 MW of electricity (about 0.3 percent of the total state electricity generation).
Solar Hot Water
The shallow water of a lake is usually warmer than the deep water. That's because the sunlight can heat the lake bottom in the shallow areas, which in turn, heats the water. It's nature's way of solar water heating.
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 usually heat the water by passing it through a coil of tubing in the tank, which is full of hot fluid.
Solar Process Heat
These technologies include ventilation air preheating, solar process heating and solar cooling.
In cold climates, heating this air can use large amounts of energy. A solar ventilation system can preheat the air, saving both energy and money. This type of system typically uses a transpired collector, which consists of a thin, black metal panel mounted on a south-facing wall to absorb the sun's heat. Air passes through the many small holes in the panel. A space behind the perforated wall allows the air streams from the holes to mix together. The heated air is then sucked out from the top of the space into the ventilation system.
Solar process heating systems are designed to provide large quantities of hot water or space heating for nonresidential buildings. A typical system includes solar collectors that work along with a pump, a heat exchanger, and/or one or more large storage tanks. The two main types of solar collectors used—an evacuated-tube collector and a parabolic-trough collector—can operate at high temperatures with high efficiency. An evacuated-tube collector is a shallow box full of many glass, double-walled tubes and reflectors to heat the fluid inside the tubes. A vacuum between the two walls insulates the inner tube, holding in the heat. Parabolic troughs are long, rectangular, curved (U-shaped) mirrors tilted to focus sunlight on a tube, which runs down the center of the trough. This heats the fluid within the tube.
The heat from a solar collector can also be used to cool a building. It may seem impossible to use heat to cool a building, but it makes more sense if you just think of the solar heat as an energy source. Your familiar home air conditioner uses an energy source, electricity, to create cool air. Solar absorption coolers use a similar approach, combined with some very complex chemistry tricks, to create cool air from solar energy. Solar energy can also be used with evaporative coolers (also called "swamp coolers") to extend their usefulness to more humid climates, using another chemistry trick called desiccant cooling
Solar ponds
One way to tap solar energy is through the use of solar ponds. Solar ponds are large-scale energy collectors with integral heat storage for supplying thermal energy. It can be use for various applications, such as process heating, water desalination, refrigeration, drying and power generation.
The solar pond works on a very simple principle. It is well-known that water or air is heated they become lighter and rise upward e.g. a hot air balloon. Similarly, in an ordinary pond, the sun’s rays heat the water and the heated water from within the pond rises and reaches the top but loses the heat into the atmosphere. The net result is that the pond water remains at the atmospheric temperature. The solar pond restricts this tendency by dissolving salt in the bottom layer of the pond making it too heavy to rise.
A solar pond has three zones. The top zone is the surface zone, or UCZ (Upper Convective Zone), which is at atmospheric temperature and has little salt content. The bottom zone is very hot, 70°– 85° C, and is very salty. It is this zone that collects and stores solar energy in the form of heat, and is, therefore, known as the storage zone or LCZ (Lower Convective Zone). Separating these two zones is the important gradient zone or NCZ (Non-Convective Zone). Here the salt content increases as depth increases, thereby creating a salinity or density gradient. If we consider a particular layer in this zone, water of that layer cannot rise, as the layer of water above has less salt content and is, therefore, lighter. Similarly, the water from this layer cannot fall as the water layer below has a higher salt content and is, therefore, heavier. This gradient zone acts as a transparent insulator permitting sunlight to reach the bottom zone but also entrapping it there. The trapped (solar) energy is then withdrawn from the pond in the form of hot brine from the storage zone.
Geothermal Energy
Geothermal energy is an alternative energy source, although it is not resourceful enough to replace more than a minor amount of the future's energy needs. Geothermal energy is obtained from the internal heat of the planet and can be used to generate steam to run a steam turbine. This in turn generates electricity, which is a very useful form of energy. These resources can be classified as low temperature (less than 90°C or 194°F), moderate
temperature (90°C - 150°C or 194- 302°F), and high temperature (greater than 150°C or
302°F). The uses to which these resources are applied are also influenced by temperature.
The highest temperature resources are generally used only for electric power generation.

Hydrothermal convection system

A permeable layer in which hot water circulates. If the temperature is high enough, we have a vapor-dominated system, where mixed water and steam exist. As the mixture is brought to higher levels, the water flashes to superheated steam, which can drive steam turbines. The used water has to be pumped back down into the ground, as it is hot and often contains toxic materials.
The second type is a hot-water system. Here the temperature is not high enough to have
only steam, and the water and steam must be separated. Plus, the water has to be pumped
back into the ground.
Hot igneous systems

These consist of hot rock that is not in contact with groundwater. Most igneous intrusions are of this type. Temperature can be well over 600°C. They have the highest amount of energy stored in them, but without the water to circulate to the surface and create electricity, they don’t do us any good in their present form. They can be drilled and then explosives at depth can create fracturing. Water can then be injected and recovered as steam. Injected water was heated to 150°C and pumped to the surface.
Moderate T ground waters
Direct use, as the name implies, involves using the heat in the water directly (without a
heat pump or power plant) for such things as heating of buildings, industrial processes,
greenhouses, aquaculture (growing of fish) and resorts. Direct use projects generally use
resource temperatures between 38°C (100°F) to 149°C (300°F). Current U.S. installed
capacity of direct use systems totals 470 MW or enough to heat 40,000 average-sized
houses.
Low T groundwater systems
We’re back to the discussion of low temperature energy needs. Most of our energy needs
is low T. Normal water is only about 13°C. This isn’t hot, but it is hotter than on a
cold winter day. So you could use the water to heat your home in the winter. And it’s a lot colder than a hot summer day. So in summer it could be used to cool a house. It is economically feasible, but the payoff is about 8 years. Ground-source heat pumps use the earth or groundwater as a heat source in winter and a heat sink in summer. Using resource temperatures of 4°C (40°F) to 38°C (100°F), the heat pump, a device which moves heat from one place to another, transfers heat from the soil to the house in winter and from the house to the soil in summer.
How do Geothermal-Energy Systems Work?
The radius of the Earth is about 4000 miles, with an internal core temperature of about 4000 degrees Celsius at the center. The mantle surrounds the outer core and is only about 45 miles below the surface, depending on location. The temperature at the mantle-surface crust boundary is about 375 degrees, Celsius. Drilling down only three miles we can reach temperatures of 100 degrees, Celsius, which is enough to boil water to run a steam-powered electric power plant. Drilling three miles through the earth is possible, but not easy, so luckily there are easier routes to access this power source, known as geothermal hotspots.
Geothermal hotspots are volcanic features which are found all around the world. Basically a hotspot is an area of reduced thickness in the mantle which transmits excess internal heat from the interior of the earth to the outer crust. These hotspots are well known for their unique effects on the surface, such as the volcanic islands of Hawaii, the mineral deposits and geysers in Yellowstone National Park, or the hot springs in Iceland. These geothermal hotspots can easily be used to generate electricity
Some systems pump hot-water into permeable sedimentary hotspots found underground and then use the steam to generate electricity. Then the used steam is condensed and sent back down to the permeable sedimentary stream. Another system utilizes volcanic magma which is still partly molten at around 650 degrees, Celsius, to boil water which would generate electricity. Also there is a system which uses hot dry rock, which is just hardened magma, but still is extremely hot. To recover this heat from these rocks, a system is used which circulates water through the rock and transfers the heat up to a steam generator. The first system listed here is not as useful as other methods because of the acidic nature of the fluids found under the ground. These acidities require a lot of maintenance and upkeep on the equipment, and this cost reduces the economic effectiveness of the system. Therefore, geothermal energy systems are more inefficient than other alternative energy sources because of the costs required in upkeep and the shortage of potential sites
Geothermal Electricity Production
Geothermal power plants, however, use steam produced from reservoirs of hot water found a couple of miles or more below the Earth's surface. There are three types of geothermal power plants: dry steam, flash steam, and binary cycle.
Dry steam power plants draw from underground resources of steam. The steam is piped directly from underground wells to the power plant, where it is directed into a turbine/generator unit. There are only two known underground resources of steam in the United States: The Geysers in northern California and Yellowstone National Park in Wyoming, where there's a well-known geyser called Old Faithful. Since Yellowstone is protected from development, the only dry steam plants in the country are at The Geysers.
Flash steam power plants are the most common. They use geothermal reservoirs of water with temperatures greater than 360°F (182°C). This very hot water flows up through wells in the ground under its own pressure. As it flows upward, the pressure decreases and some of the hot water boils into steam. The steam is then separated from the water and used to power a turbine/generator. Any leftover water and condensed steam are injected back into the reservoir, making this a sustainable resource.
Binary cycle power plants operate on water at lower temperatures of about 225°—360°F (107°—182°C). These plants use the heat from the hot water to boil a working fluid, usually an organic compound with a low boiling point. The working fluid is vaporized in a heat exchanger and used to turn a turbine. The water is then injected back into the ground to be reheated. The water and the working fluid are kept separated during the whole process, so there are little or no air emissions.
Small-scale geothermal power plants (under 5 megawatts) have the potential for widespread application in rural areas, possibly even 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.
Geothermal Heat Pumps
The shallow ground, the upper 10 feet of the Earth, maintains a nearly constant temperature between 50° and 60°F (10°–16°C). Like a cave, this ground temperature is warmer than the air above it in the winter and cooler than the air in the summer. Geothermal heat pumps take advantage of this resource to heat and cool buildings.
Geothermal heat pump systems consist of basically three parts: the ground heat exchanger, the heat pump unit, and the air delivery system (ductwork). The heat exchanger is basically a system of pipes called a loop, which is buried in the shallow ground near the building. A fluid (usually water or a mixture of water and antifreeze) circulates through the pipes to absorb or relinquish heat within the ground. In the winter, the heat pump removes heat from the heat exchanger and pumps it into the indoor air delivery system. In the summer, the process is reversed.
Wind Energy
Wind is air in motion. It is produced by the uneven heating of the earth’s surface by the sun. Since the earth’s surface is made of various land and water formations, it absorbs the sun’s radiation unevenly. When the sun is shining during the day, the air over landmasses heats more quickly than the air over water. The warm air over the land expands and rises, and the heavier, cooler air over water moves in to take its place, creating local winds. At night, the winds are reversed because the air cools more rapidly over land than over water. Similarly, the large atmospheric winds that circle the earth are created because the surface air near the equator is warmed more by the sun than the air over the North and South Poles. Wind is called a renewable energy source because wind will continually be produced as long as the sun shines on the earth. Today, wind energy is mainly used to generate electricity.
Types of Windmills
Aeration Windmill
This windmill will aerate a pond or pump water out of your pond or river to water your animals or garden. This windmill will pump out of a shallow (up to 15m) well.

Aermotor Windmill
They have been manufactured since 1888 and are the old standard of windmills. They will pump out of a well but will not aerate a pond or pump water out of the pond or river.
These styles of windmills will not produce electricity! Many people think you can buy a regular windmill to run your air conditioner, freezer, washer, dryer, etc. and you can not. This is all 240 volts A.C.
Wind Turbine
The wind turbine, also called a windmill, is a means of harnessing the kinetic energy of the wind and converting it into electrical energy. This is accomplished by turning blades called aerofoil, which drive a shaft, which drive a motor (turbine) and are e connected to a generator. the Wind turbines, like windmills, are mounted on a tower to capture the most energy. At 100 feet (30 meters) or more aboveground, they can take advantage of the faster and less turbulent wind. Turbines catch the wind's energy with their propeller-like blades. Usually, two or three blades are mounted on a shaft to form a rotor. 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 like a propeller, and the turning shaft spins a generator to make electricity.
A blade acts much like an airplane wing. 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
Wind Mill Efficiency
Windmills are turbines. The two names can be used synonymously. Turbines are a means of harnessing the fluid's power (the wind) by converting the kinetic energy of the fluid (the wind) into mechanical power (the rotating shaft) When the shaft of a w windmill is hooked up to a generator, electrical energy can be formed. The generator can be used to produce either DC or AC current. Generators that produce DC can be connected to batteries, an inverter to produce AC, or to power DC loads.An important equation used to find the wind power density, how much power is available per square meter is the equation ------------------ P = .5 pu³
where P is the wind power density in W/m2, p is the density of the air, and u³ is the cube of the wind velocity.
Windmills can not operate at 100% efficiency because the structure itself impedes the flow of the wind. The structure also exerts back pressure on the turbine blades as they act like an air foil (a wing on an airplane). In most all cases, the efficiency of the wind turbine depends on the actual wind speed. The maximum efficiency of 44% is reached in a 9 m/s wind (18 mph) and falls sharply at higher wind speeds. For a reasonable range of winds, the average efficiency is around 20%.
Ocean Energy
The ocean can produce two types of energy: thermal energy from the sun's heat, and mechanical energy from the tides and waves.
Oceans cover more than 70% of Earth's surface, making them the world's largest solar collectors. The sun's heat warms the surface water a lot more than the deep ocean water, and this temperature difference creates thermal energy. Just a small portion of the heat trapped in the ocean could power the world.
Ocean thermal energy
Ocean thermal energy is used for many applications, including electricity generation. There are three types of electricity conversion systems: closed-cycle, open-cycle, and hybrid. Closed-cycle systems use the ocean's warm surface water to vaporize a working fluid, which has a low-boiling point, such as ammonia. The vapor expands and turns a turbine. The turbine then activates a generator to produce electricity. Open-cycle systems actually boil the seawater by operating at low pressures. This produces steam that passes through a turbine/generator. And hybrid systems combine both closed-cycle and open-cycle systems.
Ocean mechanical energy
Ocean mechanical energy is quite different from ocean thermal energy. Even though the sun affects all ocean activity, tides are driven primarily by the gravitational pull of the moon, and waves are driven primarily by the winds. As a result, tides and waves are intermittent sources of energy, while ocean thermal energy is fairly constant. Also, unlike thermal energy, the electricity conversion of both tidal and wave energy usually involves mechanical devices.
A barrage (dam) is typically used to convert tidal energy into electricity by forcing the water through turbines, activating a generator. For wave energy conversion, there are three basic systems: channel systems that funnel the waves into reservoirs; float systems that drive hydraulic pumps; and oscillating water column systems that use the waves to compress air within a container. The mechanical power created from these systems either directly activates a generator or transfers to a working fluid, water, or air, which then drives a turbine/generator.
Wave Energy
Waves, particularly those of large amplitude, contain large amounts of energy. Wave energy is in effect a stored and concentrated form of solar energy, since the winds that produce waves are caused by pressure differences in the atmosphere arising from solar heating. The total power of waves breaking on the world's coastlines is estimated at 2 to 3 million megawatts. In favorable locations, wave energy density can average 65 megawatts per mile of coastline.
Several ways of classifying wave energy devices have been proposed, based on the energy extraction method, the size of the device, etc. The method adopted here uses the location of the device with respect to the shoreline, i.e. shoreline devices, near shore devices and offshore devices.
Shoreline Devices
Shoreline devices have the advantage of relatively easier maintenance and installation and do not require deep water moorings and long underwater electrical cables. The less energetic wave climate at the shoreline can be partly compensated by the concentration of wave energy that occurs naturally at some locations by refraction and/or diffraction. The three major classes of shoreline devices are the oscillating water column (OWC), the convergent channel (TAPCHAN) and the Pendulor, as shown below.
The OWC comprises a partly submerged concrete or steel structure, which has an opening to the sea below the water line, thereby enclosing a column of air above a column of water. As waves impinge on the device, they cause the water column to rise and fall, which alternately compresses and depressurizes the air column. This air is allowed to flow to and from the atmosphere through a turbine which drives an electric generator. Both conventional (i.e. unidirectional) and self- rectifying air turbines have been proposed. The axial-flow Wells turbine, invented in the 1970s, is the best known turbine for this kind of application and has the advantage of not requiring rectifying air valves. A number of OWC devices have been installed worldwide, with several of them being built into a breakwater to lower overall construction costs.
The Tap Chan comprises a gradually narrowing channel with wall heights typically 3 to 5 m above mean water level. The waves enter the wide end of the channel and, as they propagate down the narrowing channel, the wave height is amplified until the wave crests spill over the walls to a reservoir which provides a stable water supply to a conventional low head turbine. The requirements of low tidal range and suitable shoreline limit the world-wide replicability of this device.
The Pendulor device consists of a rectangular box, which is open to the sea at one end. A pendulum flap is hinged over this opening, so that the action of the waves causes it to swing back and forth. This motion is then used to power a hydraulic pump and generator. World-wide, only small devices have been deployed.
Near shore Devices
Near shore devices are situated in shallow waters (typically 10 to 25 m water depth). Again the OWC is the main type of device, with several designs having been deployed world-wide.
Offshore Devices
Offshore devices are situated in deeper water, with typical depths of more than 40 m. Several different designs having been deployed world-wide, with many more still at the design stage. Some of the representative devices that have been deployed are shown below:
The Swedish Hose pump has been under development since 1980. It consists of a specially reinforced electrometric hose (whose internal volume decreases as it stretches), connected to a float which rides the waves. The rise and fall of the float stretches and relaxes the hose thereby pressurizing sea water, which is fed (along with the output from other Hose pumps) through a non-return valve to a central turbine and generator unit.
The McCabe Wave Pump consists of three rectangular steel pontoons which move relative to each other in the waves. The key aspect of the scheme is the damper plate attached to the central pontoon, which ensures that it stays still as the fore and aft pontoons move relatively to the central pontoon by pitching about the hinges. Energy is extracted from the rotation about the hinge points by linear hydraulic pumps mounted between the central and two outer pontoons near the hinges. The device was developed to supply potable water (by reverse osmosis) but can also be used to generate electricity (via a hydraulic motor and generator).
The floating wave power vessel is a steel platform containing a sloping ramp, which gathers incoming waves into a raised internal basin. The water flows from this basin back into the sea through low-head turbines. In these respects it is similar to an offshore Tap Chan but the device is not sensitive to tidal range.
The Danish Wave Power float-pump device uses a float which is attached to a seabed mounted piston pump; the rise and fall motion of the float causes the pump to operate driving a turbine and generator mounted on the pump. The flow of water through the turbine is maintained as uni-directional through the incorporation of a non-return valve.
Biomass Energy
The biomass energy or " bioenergy " the energy from plants and plant-derived materials—since people began burning wood to cook food and keep warm. Wood is still the largest biomass energy resource today, but other sources of biomass can also be used. These include food crops, grassy and woody plants, residues from agriculture or forestry, and the organic component of municipal and industrial wastes. Even the fumes from landfills (which are methane, a natural gas) can be used as a biomass energy source

Biomass can be used for fuels and power production that would otherwise be made from fossil fuels.
Biofuels
Biomass can be converted directly into liquid fuels, called "biofuels," to help meet transportation fuel needs. The two most common types of biofuels are ethanol and biodiesel.
Ethanol is an alcohol-based alternative fuel produced by fermenting and distilling starch crops that have been converted into simple sugars. Feedstocks for this fuel include corn, barley, and wheat. Ethanol can also be produced from "cellulosic biomass" such as trees and grasses and is called bioethanol. Ethanol is most commonly used to increase octane and improve the emissions quality of gasoline . Ethanol can be blended with gasoline to create E85, a blend of 85% ethanol and 15% gasoline.
Biodiesel is made by combining alcohol (usually methanol) with vegetable oil, animal fat, or recycled cooking grease. It can be used as an additive (typically 20%) to reduce vehicle emissions or in its pure form as a renewable alternative fuel for diesel engines.
Biopower
Biopower, or biomass power, is the use of biomass to generate electricity. Biopower system technologies include direct-firing, cofiring, gasification, pyrolysis, and anaerobic digestion.
Most biopower plants use direct-fired systems. They burn bioenergy feedstocks directly to produce steam. This steam drives a turbine, which turns a generator that converts the power into electricity. Paper mills, the largest current producers of biomass power, generate electricity or process heat as part of the process for recovering pulping chemicals.
Co-firing refers to mixing biomass with fossil fuels in conventional power plants. Coal-fired power plants can use co-firing systems to significantly reduce emissions, especially sulfur dioxide emissions. Gasification systems use high temperatures and an oxygen-starved environment to convert biomass into synthesis gas, a mixture of hydrogen and carbon monoxide. The synthesis gas, or "syngas," can then be chemically converted into other fuels or products, burned in a conventional boiler, or used instead of natural gas in a gas turbine.
Biomass pyrolysis refers to a process where biomass is exposed to high temperatures in the absence of air, causing the biomass to decompose. The end product of pyrolysis is a mixture of solids (char), liquids (oxygenated oils), and gases (methane, carbon monoxide, and carbon dioxide).
Anaerobic digestion is a process by which organic matter is decomposed by bacteria in the absence of oxygen to produce methane and other byproducts. The primary energy product is a low to medium calorific gas, normally consisting of 50 to 60 percent methane.


Nuclear Energy
Nuclear processes can release a million times the energy of a chemical process. For this reason, mankind has tried to make use of this energy source for both military purposes and for power production. There are two kinds of ways that nuclear energy has been used: fission and fusion.
Nuclear Fusion
Fusion means joining smaller nuclei (the plural of nucleus) to make a larger nucleus. The sun uses nuclear fusion of hydrogen atoms into helium atoms. This gives off heat and light and other radiation. The most suitable reaction occurs between the nuclei of the two heavy forms (isotopes) of Hydrogen - Deuterium (D) and Tritium (T); eventually reactions involving just Deuterium or Deuterium and Helium (3He) may be used.
Reaction : 2H + 3H --> 4He + n.+ energy
Scientists have been working on controlling nuclear fusion for a long time, trying to make a fusion reactor to produce electricity. But they have been having trouble learning how to control the reaction in a contained space. What's better about nuclear fusion is that it creates less radioactive material than fission, and its supply of fuel can last longer than the sun.
Nuclear Fission
When a nucleus fissions, it splits into several smaller fragments. These fragments, or fission proThe sum of the masses of these fragments is less than the original mass. This 'missing' mass (about 0.1 percent of the original mass) has been converted into energy according to Einstein's equation.
Fission can occur when a nucleus of a heavy atom captures a neutron, or it can happen spontaneously.
Reaction : U235 + n -----à fission product + 2 or 3 n + 200 MeV
1 MeV (million electron volts) = 1.609 x 10 -13 joules
the natural uranium, only 0.7% is uranium 235. This meant that a large amount of uranium was needed to obtain the necessary quantities of uranium 235. plutonium 239 would have a high fission probability. However, plutonium 239 is not a naturally occurring element and would have to be made.
Nuclear Power Plants
A nuclear power plant uses uranium as a "fuel." Uranium is an element that is dug out of the ground many places around the world. It is processed into tiny pellets that are loaded into very long rods that are put into the power plant's reactor. The controlled fission occurs in core. This water from around the nuclear core is sent to another section of the power plant. Here, in the heat exchanger, it heats another set of pipes filled with water to make steam. The steam in this second set of pipes turns a turbine to generate electricity.
A typical nuclear power plant
Types of Nuclear Power Plants
Pressurized Water Reactor (PWR)
This is the most common type, with over 230 in use for power generation and a further several hundred in naval propulsion. The design originated as a submarine power plant. It uses ordinary water as both coolant and moderator. The design is distinguished by having a primary cooling circuit which flows through the core of the reactor under very high pressure, and a secondary circuit in which steam is generated to drive the turbine. Water in the reactor core reaches about 325ƒC, hence it must be kept under about 150 times atmospheric pressure to prevent it boiling. Pressure is maintained by steam in a pressurizer (see diagram). In the primary cooling circuit the water is also the moderator, and if any of it turned to steam the fission reaction would slow down.
A PWR has fuel assemblies of 200-300 rods each, arranged vertically in the core, and a large reactor would have about 150-250 fuel assemblies with 80-100 tonnes of uranium
Boiling Water Reactor (BWR)
This design (diagram next page) has many similarities to the PWR, except that there is only a single circuit in which the water is at lower pressure (about 75 times atmospheric pressure) so that it boils in the core at about 285ƒC. The steam passes through drier plates (steam separators) above the core and then directly to the turbines, which are thus part of the reactor circuit. BWR fuel assembly comprises 90-100 fuel rods, and there are up to 750 assemblies in a reactor core, holding up to 140 tonnes of uranium.
Pressurized Heavy Water Reactor (PHWR or CANDU)
It uses natural uranium (0.7% U-235) oxide as fuel, hence needs a more efficient moderator, in this case heavy water (D2O) .The moderator is in a large tank called a calandria, penetrated by several hundred horizontal pressure tubes which form channels for the fuel, cooled by a flow of heavy water under high pressure in the primary cooling circuit, reaching 290ƒC. As in the PWR, the primary coolant generates steam in a secondary circuit to drive the turbines.
Advanced Gas-cooled Reactor (AGR)
These are the second generation of British gas-cooled reactors, using graphite moderator and carbon dioxide as coolant. The fuel is uranium oxide pellets, enriched to 2.5-3.5%, in stainless steel tubes. The carbon dioxide circulates through the core, reaching 650ƒC and then past steam generator tubes outside it, but still inside the concrete and steel pressure vessel. Control rods penetrate the moderator and a secondary shutdown system involves injecting nitrogen to the coolant.
Light water graphite-moderated reactor
This is a Soviet design, developed from plutonium production reactors. It employs long (7 meter) vertical pressure tubes running through graphite moderator, and is cooled by water, which is allowed to boil in the core at 290°C, much as in a BWR. Fuel is low-enriched uranium oxide made up into fuel assemblies 3.5 meters long. With moderation largely due to the fixed graphite, excess boiling simply reduces the cooling and neutron absorption without inhibiting the fission reaction, and a positive feedback problem can arise
Thorium as a nuclear fuel
Thorium, as well as uranium, can be used as a nuclear fuel. Although not fissile itself, thorium-232 (Th-232) will absorb slow neutrons to produce uranium-233 (U-233), which is fissile. The use of thorium-based fuel cycles has been studied for about 30 years, but on a much smaller scale than uranium or uranium/plutonium cycles. Much experience has been gained in thorium-based fuel in power reactors around the world, some using high-enriched uranium (HEU) as the main fuel. In India, both Kakrapar-1 and -2 units are loaded with 500 kg of thorium fuel in order to improve their operation when newly-started. Many Concepts for advanced reactors based on thorium-fuel cycles example Light Water Reactors - With fuel based on plutonium oxide (PuO2), thorium oxide (ThO2) and/or uranium oxide (UO2) particles arranged in fuel rods.
Hydrogen
Hydrogen is the third most abundant element on the earth's surface, where it is found primarily in water (H²O) and organic compounds. It is generally produced from hydrocarbons or water; and when burned as a fuel, or converted to electricity, it joins with oxygen to again form water. Most hydrogen production today is by steam reforming natural gas. Fill vehicle fuel tanks with it instead of gasoline. Pipe it to homes for heating and cooking instead of natural gas and to generate electricity onsite instead of sending electricity through transmission lines. On a weight basis, hydrogen has nearly three times the energy content of gasoline (120 MJ/kg for hydrogen versus 44 MJ/kg for gasoline). However, on a volume basis the situation is reversed (8 MJ/liter for liquid hydrogen versus 32 MJ/liter for gasoline). On-board hydrogen storage in the range of 5-13 kg H2 is required to encompass the full platform of light-duty vehicles.
Hydrogen Properties
Hydrogen is a colorless, odorless, tasteless, and nonpoisonous gas under normal conditions on Earth. It typically exists as a diatomic molecule, meaning each molecule has two atoms of hydrogen ,this is why pure hydrogen is commonly expressed as "H2". Hydrogen is the most abundant element in the universe, accounting for 90 percent of the universe by weight. However, it is not commonly found in its pure form, since it readily combines with other elements. It is also the lightest element, having a density of 0.08988 grams per liter at standard pressure.
Hydrogen has several important chemical properties that affect its use as a fuel:
It readily combines with oxygen to form water, which is absolutely necessary for life on this planet.
It has a high energy content per weight (nearly 3 times as much as gasoline), but the energy density per volume is quite low at standard temperature and pressure. Volumetric energy density can be increased by storing the hydrogen under increased pressure or storing it at extremely low temperatures as a liquid. Hydrogen can also be adsorbed into metal hydrides.
Hydrogen is highly flammable; it only takes a small amount of energy to ignite it and make it burn. It also has a wide flammability range, meaning it can burn when it makes up 4 to 74 percent of the air by volume.
Hydrogen burns with a pale-blue, almost-invisible flame, making hydrogen fires difficult to see.
The combustion of hydrogen does not produce carbon dioxide (CO2), particulate, or sulfur emissions. It can produce nitrous oxide (NOX) emissions under some conditions.
Hydrogen can be produced from renewable resources, such as by reforming ethanol (this process emits some carbon dioxide) and by the electrolysis of water (electrolysis is very expensive).
Hydrogen Production
Hydrogen can be produced using a variety of domestic energy resources - fossil fuels, such as coal and natural gas, with carbon capture and sequestration; renewable, such as biomass, and renewable energy technologies, including solar, wind, geothermal, and hydropower; and nuclear power. Specific technologies and processes are described below.
Thermochemical Processes
Steam methane reforming: In this process, high-temperature steam is used to extract hydrogen from a methane source such as natural gas. This is the most common method of producing hydrogen; about 95 percent of the hydrogen we use today in the United States is produced using this process.
Partial oxidation: Scientists are exploring a process that produces hydrogen by simultaneously separating oxygen from air and partially oxidizing methane.
Other thermal processes: Other processes include (1) splitting water using heat from a solar concentrator, and (2) gasifying or burning biomass (i.e., biological material, such as plants or agricultural waste) to generate a bio-oil or gas, which is then reformed to produce hydrogen.
Electrolytic Processes
Electrolysis: In electrolysis, electricity is used to separate water (H2O) into hydrogen and oxygen. Current electrolysis systems are very energy intensive. The challenge is to develop low cost and more energy efficient electrolysis technologies.
Photolytic Processes
Photolytic methods: In photolysis, sunlight is used to split water. Two photolytic processes are being explored: (1) photobiological methods, in which microbes, when exposed to sunlight, split water to produce hydrogen, and (2) photoelectrolysis, in which semi-conductors, when exposed to sunlight and submersed in water, generate enough electricity to produce hydrogen by splitting the water.
Hydrogen Storage
Finding a cost-effective method of storing hydrogen on a vehicle is a challenge. While hydrogen contains more energy per weight than any other energy carrier, it contains much less energy by volume. This makes it difficult to store a large amount of hydrogen in a small space, like in a gas tank of a car.
Technologies
High-pressure tanks: Hydrogen gas can be compressed and stored in storage tanks at high pressure. These tanks must be strong, durable, light-weight, and compact, as well as cost competitive.
Liquid hydrogen: Hydrogen can be stored as a liquid. In this form, more hydrogen can be stored per volume, but it must be kept at cold temperatures (about -253°C).
Materials-based storage of hydrogen: Hydrogen can be stored within solid materials, such as powders, or liquids. Technologies under study include —
Reversible Metal Hydrides: Hydrogen combines chemically with some metals, which can result in higher storage capacity compared to high-pressure gas or liquid. These materials can be "re-filled" with hydrogen while on the vehicle.
Carbon Materials and High Surface Area Sorbents: Carbon nanotubes are examples of materials that reversibly store hydrogen. Other sorbents may be able to store hydrogen at room temperature.
Chemical Hydride Materials: Materials are under study that release hydrogen by a chemical process on the vehicle. These materials are then removed and "regenerated" off-board, either at the fueling station or at a central processing plant.
Hydrogen Fuel Cell
The fuel cell works by injecting molecular hydrogen (H2) molecules into the anode. The hydrogen molecules react with the catalyst. The catalyst is usually a thin coat of powdered platinum on carbon paper. This breaks up the hydrogen into a proton and an electron. The proton goes across the electrolyte, (remember, it only accepts protons) while the electron is fed through the circuit and goes to work, whether it be powering our oven or providing horsepower to our new automobile.
Upon finishing their job, the electrons return to the cell through the cathode. There, the catalyst assists the oxygen molecules, the hydrogen protons and the hydrogen electrons in making water. The chemical reactions are the following:
Anode:2H2 => 4H+ + 4e-
Cathode: O2 + 4H+ + 4e- => 2H2O
The whole reaction ends up looking like this:2H2 + O2 => 2H2O
This reaction only creates about 0.7 volts. Because of this, there are several cells built into a stack. This multiplies the voltage up to useable levels.
Fuel Cell

Electricity is nothing more than flowing electrons. That means that power generation is nothing more than finding out how to free electrons. Fuel cells rely on hydrogen for its electrons. There are many different fuel cells for every kind of application. But every fuel cell has the same essentials. They all have an anode (negative electrode) comprised of hydrogen gas, and a cathode (positive electrode) of oxygen. In the middle is an electrolyte that only allows protons to pass through it. In between both electrodes and the electrolyte are catalysts that facilitate the reactions
Fuel cells are an important enabling technology for the hydrogen economy and have the potential to revolutionize the way we power our nation, offering cleaner, more-efficient alternatives to the combustion of gasoline and other fossil fuels. Fuel cells have the potential to replace the internal combustion engine in vehicles and provide power in stationary and portable power applications because they are energy-efficient, clean, and fuel-flexible. Hydrogen or any hydrogen-rich fuel can be used by this emerging technology.
Types of Fuel Cells
Fuel cells are classified primarily by the kind of electrolyte they employ. This determines the kind of chemical reactions that take place in the cell, the kind of catalysts required, the temperature range in which the cell operates, the fuel required, and other factors.
Polymer Electrolyte Membrane (PEM) Fuel Cells
Polymer electrolyte membrane (PEM) fuel cells—also called proton exchange membrane fuel cells—deliver high power density and offer the advantages of low weight and volume, compared to other fuel cells. PEM fuel cells use a solid polymer as an electrolyte and porous carbon electrodes containing a platinum catalyst. They need only hydrogen, oxygen from the air, and water to operate and do not require corrosive fluids like some fuel cells. They are typically fueled with pure hydrogen supplied from storage tanks or onboard reformers.
Direct Methanol Fuel Cells
Direct methanol fuel cells (DMFCs), however, are powered by pure methanol, which is mixed with steam and fed directly to the fuel cell anode. Direct methanol fuel cells do not have many of the fuel storage problems typical of some fuel cells since methanol has a higher energy density than hydrogen—though less than gasoline or diesel fuel. Methanol is also easier to transport and supply to the public using our current infrastructure since it is a liquid, like gasoline.
Alkaline Fuel Cells
Alkaline fuel cells (AFCs) were one of the first fuel cell technologies developed, and they were the first type widely used in the U.S. space program to produce electrical energy and water onboard spacecraft. These fuel cells use a solution of potassium hydroxide in water as the electrolyte and can use a variety of non-precious metals as a catalyst at the anode and cathode. High-temperature AFCs operate at temperatures between 100°C and 250°C (212°F and 482°F). However, newer AFC designs operate at lower temperatures of roughly 23°C to 70°C (74°F to 158°F)
Phosphoric Acid Fuel Cells
Phosphoric acid fuel cells use liquid phosphoric acid as an electrolyte—the acid is contained in a Teflon-bonded silicon carbide matrix—and porous carbon electrodes containing a platinum catalyst. The chemical reactions that take place in the cell are shown in the diagram to the right.
The phosphoric acid fuel cell (PAFC) is considered the "first generation" of modern fuel cells. It is one of the most mature cell types and the first to be used commercially, with over 200 units currently in use. This type of fuel cell is typically used for stationary power generation, but some PAFCs have been used to power large vehicles such as city buses.
Molten Carbonate Fuel Cells
Molten carbonate fuel cells (MCFCs) are currently being developed for natural gas and coal-based power plants for electrical utility, industrial, and military applications. MCFCs are high-temperature fuel cells that use an electrolyte composed of a molten carbonate salt mixture suspended in a porous, chemically inert ceramic lithium aluminum oxide (LiAlO2) matrix. Since they operate at extremely high temperatures of 650°C (roughly 1,200°F) and above, non-precious metals can be used as catalysts at the anode and cathode, reducing costs.

Solid Oxide Fuel Cells
Solid oxide fuel cells (SOFCs) use a hard, non-porous ceramic compound as the electrolyte. Since the electrolyte is a solid, the cells do not have to be constructed in the plate-like configuration typical of other fuel cell types. SOFCs are expected to be around 50-60 percent efficient at converting fuel to electricity. In applications designed to capture and utilize the system's waste heat (co-generation), overall fuel use efficiencies could top 80-85 percent. Solid oxide fuel cells operate at very high temperatures—around 1,000°C (1,830°F).
Regenerative Fuel Cells
Regenerative fuel cells produce electricity from hydrogen and oxygen and generate heat and water as byproducts, just like other fuel cells. However, regenerative fuel cell systems can also use electricity from solar power or some other source to divide the excess water into oxygen and hydrogen fuel—this process is called "electrolysis."
Applications of Fuel Cells
Fuel cells have the potential to slip into every kind of electronic device. A few applications could include:
· Cars- as stated before, fuel cells the size of a printer could provide enough juice to power as well (if not better than) a combustion engine. The hydrogen for both forms of transportation may be provided through propane, methanol or natural gas.
· Personal Devices (Laptops, cell phones, hearing aides) - fuel cells have the tremendous potential to get into every electronic device we come in contact with.
· Stationary Power Production and Backup- larger-scale fuel cells could allow every city to have its own power station, rather than a centralized power grid. Power generation could become so decentralized that each housing development or apartment complex could be self-sustained with its own power. This would drastically cut down on pollution and ugly power lines. Hospitals and airports could (some already do) have backup power supplies that kick in, in the event of a power failure.
Hydropower
Flowing water creates energy that can be captured and turned into electricity. This is called hydroelectric power or hydropower. The most common type of hydroelectric power plant uses a dam on a river to store water in a reservoir. Water released from the reservoir flows through a turbine, spinning it, which in turn activates a generator to produce electricity. But hydroelectric power doesn't necessarily require a large dam.
Hydroelectric power plant
Hydroelectricity comes from the damming of rivers and utilizing the potential energy stored in the water. As the water stored behind a dam is released at high pressure, its kinetic energy is transferred onto turbine blades and used to generate electricity. This system has enormous costs up front, but has relatively low maintenance costs and provides power quite cheaply.
Another type of hydroelectric power plant—called a pumped storage plant—can even store power. The power is sent from a power grid into the electric generators. The generators then spin the turbines backward, which causes the turbines to pump water from a river or lower reservoir to an upper reservoir, where the power is stored. To use the power, the water is released from the upper reservoir back down into the river or lower reservoir. This spins the turbines forward, activating the generators to produce electricity.
Energy Storage
Helping secure a clean energy future for the nation and the world isn't just about reducing energy usage or producing clean energy. It is about how energy moves from the power source to the end user. Moving the energy from point A to point B, or storing it at the site where it will be used, are related to using our energy most effectively and wisely. Energy storage can improve the efficiency and reliability of the electric utility system by reducing the requirements for spinning reserves to meet peak power demands, making better use of efficient baseload generation, and allowing greater use of renewable energy technologies.
Energy Storage Technologies
Batteries
Batteries are the most common device used for storing electrical energy.
Advanced Batteries
Advanced battery technologies include lithium-ion, lithium polymer, nickel metal hydride, and sodium sulfur types. Advanced batteries offer much smaller "footprints" (i.e., they take up less space) than lead-acid batteries. They are typically CURRENTLY too expensive for large-scale utility applications, but are used for power quality and backup purposes at manufacturing plants. They are also used in consumer goods and automobiles. Lithium-ion batteries in laptop computers, for example, can provide twice as much operating time as conventional batteries. Sodium sulfur batteries can operate at high temperatures, and have proven safe even under extreme conditions.
Flow Batteries
Flow batteries work in a similar fashion to lead-acid batteries, but the electrolyte is stored in external containers and circulated through the battery cell stack as required. This external reservoir of rechargeable electrolyte can be as large as needed, and situated where convenient. Some flow batteries use two different kinds of electrolyte that are stored separately.
The great advantage to flow batteries is that their electrical storage capacity is limited only BY the capacity of the electrolyte storage reservoirs. They provide very high power and very high capacity batteries for load-leveling applications on the electricity grid. Zinc-bromine flow batteries are the most common type in use in the United States.
Lead-Acid Batteries
Lead-acid batteries are the most common type of battery. They are used in automobiles, and by both utilities and electricity consumers as a backup energy source for critical electricity needs.
The traditional lead-acid battery is made up of plates, lead, and lead oxide immersed in a solution consisting of 35% sulfuric acid and 65% water. This solution is called "electrolyte," and causes a chemical reaction that produces electrons. Various other elements are also used to change the density, hardness, and porosity of the plates.
A couple of variations on the traditional design have emerged:
Valve-regulated lead-acid (VRLA) batteries — are sealed and need no topping off with water, and so require less maintenance than regular lead-acid batteries.
Gel-type lead-acid batteries — are filled with a gel instead of liquid, making them much less likely to spill.

Compressed Air Energy Storage
Compressed air energy storage (CAES) is really a hybrid storage/power production system. Off-peak electricity is used to power a motor/generator that drives compressors to force air into an underground storage reservoir, such as a rock cavern or abandoned mine. When the demand for electric power peaks, the process is reversed. The compressed air is returned to the surface, heated by natural gas in combustors and run through high-pressure and low-pressure expanders to power the motor/generator to produce electricity.
In traditional gas turbines, the air that drives the turbine is compressed and heated using natural gas. CAES technology needs less gas to produce power because it uses air that has already been compressed. There is only one CAES facility operating in the United States at present.
Has high energy storage capacity compared to the alternatives. About 10 times higher per cubic meter than water.
One example (in Germany) to date:
· Storage reservoir is underground cavity in a natural salt deposit.
· The storage volume is 300,000 cubic meters.
· Sheer weight of the salt deposit is able to pressure confine the air reservoir.
· Air is compressed to 70 atm (1000 lbs per square inch)
· Compression is done by electrically driven air compressors
· System delivers 300 Megawatts for 2 hours by using the compressed air to drive a turbine
· Difficult to measure the efficiency of this system. Two major contributions to the inefficiency:

o Energy required to cool the air as it is being put into storage this is a critical requirement (see below)
o Energy required (usually from fuel) to expand the cool air taken from storage as it entries the turbine.
· Desirable design feature would be recycle the waste heat from the compression stage and use it to reheat the air during expansion stag
Flywheels
A flywheel is a cylinder that spins at very high speeds, storing kinetic (movement) energy. A flywheel can be combined with a device that operates either as an electric motor that accelerates the flywheel to store energy or as a generator that produces electricity from the energy stored in the flywheel. The faster the flywheel spins, the more energy it retains. Energy can be drawn off as needed by slowing the flywheel.
Modern flywheels use composite rotors made with carbon-fiber materials. The rotors have a very high strength-to-density ratio, and rotate in a vacuum chamber to minimize aerodynamic losses. The use of superconducting electromagnetic bearings can virtually eliminate energy losses through friction. Flywheels can discharge their power either slowly or quickly, allowing them to serve as backup power systems for low-power applications or as short-term power quality support for high-power applications. They are little affected by temperature fluctuations, take up relatively little space, have lower maintenance requirements than batteries, and are very durable.
Pumped Hydropower
Pumped hydro facilities use off-peak electricity to pump water from a lower reservoir into one at a higher elevation. When the water stored in the upper reservoir is released, it is passed through hydraulic turbines to generate electricity.
The off-peak electrical energy used to pump the water up hill can be stored indefinitely as gravitational energy in the upper reservoir. Thus, two reservoirs in combination can be used to store electrical energy for a long period of time, and in large quantities.
Supercapacitors
Supercapacitors are electrochemical storage devices that work like large versions of common electrical capacitors. They are also known as ultracapacitors or electrochemical double-layer capacitors. Unlike batteries, supercapacitors store their energy in an electrostatic field rather than in chemical form.
Batteries are charged when they undergo an internal chemical reaction. They discharge, delivering the absorbed energy, when they reverse the chemical reaction. In contrast, when a supercapacitor is charged, there is no chemical reaction. Instead, the energy is stored as a charge or concentration of electrons on the surface of a material.
Supercapacitors are capable of very fast charges and discharges, and can typically be recharged hundreds of thousands of times, unlike conventional batteries which last for only a few hundred or thousand recharge cycles. But their power is available only for a very short duration, and their self-discharge rate is much higher than with batteries. Common applications include starting diesel trucks and railroad locomotives, and in electric/hybrid-electric vehicles for transient load leveling and capturing the energy used in braking. In power systems, they are most likely to be used as bridging power sources in uninterruptible power supplies, much like flywheels.
Superconducting Magnetic Energy
Superconducting magnetic energy storage (SMES) systems store energy in the magnetic field created by the flow of direct current through a large coil of superconducting material that has been super-cooled. In low-temperature superconducting materials, electric currents encounter almost no resistance, greatly enhancing their storage capacity.
Power is available almost instantaneously from SMES systems, and very high power output is provided for a brief period of time. There are no moving parts. However, the energy content of SMES systems is small and short-lived, and the cryogenics (super-cooling technology) can be a challenge. Researchers are trying to find ways to maintain the special qualities of SMES without having to keep the systems quite so cold. Low-temperature SMES cooled by liquid helium is commercially available today, and "high temperature" (less cold) SMES cooled by liquid nitrogen is in development
Energy Density of Some Materials (KHW/kg) · Gasoline --------------> 14· Lead Acid Batteries ----> 0.04· Hydrostorage -----------> 0.3 (per meter3)· Flywheel, Steel --------> 0.05· Flywheel, Carbon Fiber -> 0.2· Flywheel, Fused Silica -> 0.9· Hydrogen ---------------> 38· Compress Air ------------> 2 (per meter3)
Energy density storage drives the choices that can be made. Technology helps to drive this. As discussed previously, energy storage in batteries is not sufficiently high to solve the basic problem