Wind power Generation

The primitive man had to use his muscle power to carry out different works in his attempt of obtaining the necessities of life. The demand for more power and the scarcity of man power and the ready availability of natural resources like wind, water, etc., might have formed the reason why the ancient man turned his attention to the utilization of these resources as sources of power; thus originated the early prime movers namely wind mill and water wheel.

Principle of wind mill:
Wind flow is created as an effect of solar heat. Winds are caused due to the absorption of solar energy on the earth surface and the rotation of earth about its own axis and around the sun. because of this, alternate heating and cooling occurs and difference in pressure is obtained and the air movement is caused.

The flowing wind which has kinetic energy is used to rotate the wind turbine which is also known as wind mill. Although wind mills have been used for more than a dozen centuries for pumping water and grinding grains, interest in large scale power generation had developed over the past 50 years.

The earth’s atmosphere is thus a marvelous solar driven heat engine. It is estimated that roughly 10 million MW of energy is continuously available in the earth’s winds.

Types of winds mills
Wind mills are classified as

• Horizontal axis type and
• Vertical axis type,  Depending on their axis of rotation.

Horizontal axis wind mills are further classified as single-bladed, double-bladed and multi-bladed types.

Horizontal axis wind mill with double blade rotor:
In the horizontal axis single blade type, the blade is of propeller type with counter weight arrangement. The double blade type gives a better performance than the single blade type.

In the double-blade type, the blade has thick cross section of an aerofoil. At the tip of the blade, the velocity is about six times the wind velocity. The blade is set at right angles to the direction of the wind. Ideally the blades should be twisted, but because of construction difficulties this is not always achieved.
The blade rotor drives a generator through a gear box. It is mounted on a bed plate attached on the top of the tower.

Blade material: the blades are made from aluminum or sheet metal. Not a single large wind turbine – generator with metal blades has operated for longer than one year without a blade failure. The suitable material required is a major problem in developing wind mills of higher power generation capacity.

With rotor, the tower is also subjected to the wind loads which may cause serious damage. Hence the structure of the tower should be so designed to withstand the wind load.

The best sites for the wind energy are found off-shore and sea coast. The second best sites are in mountains. The lowest level of wind energy is found in plains, where values are generally three or four times lower than that at the coast.

Multiblade rotor:
It is shown in image below. Rotors with more than two blades will produce high power.

Sail type blades:
It is of recent origin. The blade surface is made from cloth, nylon or plastic arranged as sail wings. There is also variation in the number of sails used.

The horizontal axis types generally have better performance than vertical types. They are mainly used for power generation and pumping water. The biggest wind mill erected for power generation is of 2500kW capacity in U.S.A.

Advantages of Wind Power Generation:

1. The wind energy is a renewable source of energy. It is free and inexhaustible.
2. The power requirements for irrigation, lighting and small industrial units can be fulfilled with the use of wind energy. Power generation on large scale using wind energy is not yet so successful, but the small wind mills will play a vital role in the present condition of power shortage.
3. It does not need transportation.
4. Like all forms of solar energy, wind power systems are non-polluting.

Disadvantages of Wind Power Generation:

1. Wind velocity is fluctuating which makes the complications in designing a wind power plant.
2. Some form of storage of wind energy is essential to maintain a constant supply of power.
3. The wind is a very hazardous, treacherous and unpredictable source of energy. Blowing in strong gusts from varying directions causing hurricanes, the wind may smash the whole plant within no time. To avoid this, special and costly designs and controls are always required.
4. It is considered suitable and economical to generate power on a small scale of order of 2 MW.
5. Power production cost with the present technology available may not compete with the conventional power generating systems. This is because, 1000s of units are required to provide the power output of one fossil-fueled plant.
6. Wind energy systems are noisy in operation. A large unit can be heard many kilometers away.

Read more...

Solar Power Plant

Basic principle of solar energy:

The sun gives out 3.7*10 ^20 MW of energy into space, out of which earth intercepts one 1.7*10^11 MW. Solar radiation is reduced in intensity in the atmosphere by clouds, dust, haze, and fog. The energy emitted by the sun in three minutes is equivalent to the world energy consumption during a year. Most of the energy we receive from the sun comes in the form of light, a short wave radiation, not all of which is visible to human eye. When this radiation strikes a solid or liquid, it is absorbed and transformed into heat energy.
The heat energy is collected in a fluid, generally water. This heat energy can be used in a solar heater or drier or can be used to run an engine. Flat plate collector or parabolic concentrated type collector is issued to collect and concentrate the solar energy and increase the temperature of the working fluid.

Applications of solar energy enjoying most success today are:

• Solar engines for water pumping.
• Solar water heaters.
• Solar cookers
• Solar furnaces.
• Photo-voltaic conversion (solar cells).
• Solar power generation.

Arrangement of solar power plant:

The Image above shows a solar power plant with a low temperature solar engine using heated water from flat plate solar collector and butane as the working fluid. This was developed in France for lift irrigation.

Solar collectors:

Flat plate collector:

In a flat plate collector, the radiation energy of sun falls on a flat surface coated with black paint having high absorbing capacity. It is placed facing the general direction of sun. The materials used for the plate may be copper, steel or aluminum. The thickness of the plate is 1 mm to 2 mm. tubing of copper is provided in thermal contact with the plate.

Heat is transferred from the absorber plate to water which is circulated in the copper tubes through the flat plate collector.

Thermal insulation is provided behind the absorber plate to prevent heat losses from the rear surface. Insulation material is generally fiber glass or mineral wool. The front cover is made up of glass and it is transparent to the in-coming solar radiation.

Cylindrical parabolic concentrator collector:

Concentrator collectors are of reflecting type utilizing mirrors. The reflecting surface may be a parabolic mirror. The solar energy falling on the collector surface is reflected and focused along a line where the absorber tube is located. As large quantity of energy falling on the collector surface is collected over a small surface, the temperature of absorber fluid is very much higher than in flat plate collector.

While flat plate collectors may be used to heat water upto 80’C (low temperature), the concentrating type of collectors are designed to heat water to medium and high temperature ranges.

Butane boilers:

The water heated in flat plate solar collector to 80’C is used for boiling butane at high pressure in the butane boiler. Boiling point of butane is about 50’C.

Turbine:

The butane vapour generated at high pressure in the boiler is used to run the vapour turbine which drives the electrical generator.

The vapour coming out of the turbine at low pressure is condensed in a condenser using water. The condensed liquid butane is fed back to the butane boiler using feed pump.

Tower concept for power generation:

Steam is generated in the boiler, which may attain a temperature upto 2000’K.

Electricity is generated by passing steam through the turbine coupled to a generator. A 50 KW plant based on this concept has been built and successfully operated in Italy.

Advantages of solar power plant:

1. Sun is essentially an infinite source of energy. Therefore solar energy is very large inexhaustible and renewable source of energy and is freely available all over the world.
2. It is environmentally very clean and is hence pollution-free.
3. It is dependable energy source without new requirements of a highly technical and specialized nature for its wide spread utilization.

Disadvantages of solar power plant:

1. It is available in a dilute form and is at a low potential. The intensity of solar energy on sunny day in India is about 1.1 KW/Square meter area. Hence very large collecting areas are required.
2. Also the dilute and diffused nature of the solar energy needs large land area for the power plant; for instance, about 30 square kilometer area is required for a solar power station to replace a nuclear plant on a 1 square kilometer site. Hence capital cost is more for the solar plant.
3. Solar energy is not available at night or during cloudy or rainy days.

Read more...

Comparison of sources of energy

Solid fuels vs. Liquid fuels:

Solid fuels produce large quantity of ash after burning, whereas liquid fuels leave no or very little ash after burning. Liquid fuels require less storage space. But they are costly as compared to solid fuels. Further they require special type of burners for their burning. Also there is danger of explosion in the case of liquid fuels.

Solid fuels vs. gaseous fuels:

Gaseous fuels do not produce ash. Also greater cleanliness is assured as smoke is practically nil. Handling of gaseous fuels is not required as they can be easily piped into the furnace. However there is danger of explosion for gaseous fuels.

Availability of source of energy:

The steam power plants depend upon coal which is exhaustible. For a hydro – power plant the availability of water depends upon the natural phenomenon of rain. Solar, wind and tidal energies are inexhaustible.

Capacity of power plant:

The capacity of power production of steam or hydro – power plant may be high. Diesel power plants are limited generation capacity.

Air pollution and radiation hazard:

In steam power plants there is nuisance of smoke and air pollution. In nuclear power plants radio-active waste is a health-hazard. Hydro-power plant has no such air or waste disposal problem.

Cost:

The capital cost of a steam power plant using coal is less than a hydro-electric power plant. However, the operating cost of a steam power plant is higher than that of a hydro-power plant. Initial cost of a nuclear power plant is the highest whereas its running cost is perhaps least of all.

Location of power plant:

Steam power stations can be located at the load Centre whereas a hydro-power plant has to be located where water is available in large quantities. The nuclear power plants are best suited for areas far remote from coal reserves and water power.

Renewable resources:

The advantages of renewable resources like hydro power, solar power, wind power and tidal power are enormously attractive. Of these, hydro-electric power is the best developed, providing 8% of the world’s energy supply in the form of very cheap electricity (1/8 and ½ of the cost of fossil fuels and nuclear generated electricity).

The major problem associated with renewable resources is our inability to store large quantities of energy either in the form of heat or as electricity. The diffuse or dilute nature of renewable resources means that large area of land or ocean is necessary to accommodate solar collectors, 30 km square for a solar power station or 1000 wind mills with 90m blades set 250m apart to replace the nuclear power plant on a square km site. The use of renewable resources can only come slowly, as the development of technologies has a very long time scale. It is a fact that the use of renewable resources such as solar, wind and tidal energy are likely to prove far less hazardous as compared to depleting fossil and fissible fuels.

Read more...

Sources of Energy

Classification: renewable and non-renewable sources.

Renewable sources are hydro-power, solar energy, wind energy, tidal or wave energy and energy from bio-mass.

Non-renewable sources include fossil fuels, viz., solid fuels, liquid fuels, gaseous fuels and nuclear fuel.

Fossil Fuels
Fossil fuels are classified as solid, liquid and gaseous as natural or prepared.

Solid fuels:
Naturally occurring solid fuels include wood, varieties of coals, viz., anthracite, bituminous and lignite (brown coal) while prepared ones include coke, charcoal etc.

Liquid Fuels:
Liquid fuels include petroleum and its derivative, namely, diesel. After the first and second shocks of oil prices, the power industry in western countries moved from oil to coal.

Gaseous fuels:
Naturally occurring gaseous fuel is natural gas which comes out of gas wells and petroleum wells. Producer gas, coal gas and blast furnace gas are prepared from gaseous fuels.

Energy stored in water:
The potential energy of water at higher level is used for the generation of electrical power. Apart from being perennial and inexhaustible source of energy, it represents the cheapest source of energy from our country. Water is renewable source of energy, as it is neither consumed nor converted into something else.

Nuclear energy:
Enormous release of energy from relatively small mass of nuclear fuel like uranium makes this source of energy of great interest. The energy liberated by nuclear fission of one kilogram of uranium is equal to the heat energy obtained by burning 4500 tons of high grade coal.

Solar energy:
The heat energy contained in the rays of sun is utilized to boil water and generate steam which can be used to drive prime movers to generate electrical powers.

Wind energy:
Wind energy can be made use of where wind at suitable velocity is available.
Tidal or wave energy:
Ocean wavers and tides contain large amount of potential energy which is also used for power generation.

Geo-thermal energy:
It is the thermal energy naturally available in the form of steam in some part of the earth below the earth surface. Generally geo-thermal steam is available in volcanic regions.

Read more...