Electrical power sources- basics: hydroelectric, thermal, nuclear, wind, solar

INTRODUCTION TO POWER PLANTS

Bulk electric power is produced by special plants known as generating stations or power plants. A generating station essentially employs a prime mover coupled to an alternator for the production of electric power. The prime mover (e.g., steam turbine, water turbine etc.) converts energy from some other form into mechanical energy. The alternator converts mechanical energy of the prime mover into electrical energy. The electrical energy produced by the generating station is transmitted and distributed with the help of conductors to various consumers.

Depending upon the form of energy converted into electrical, the generating stations are classified as under:

1.1. Steam Power Station (Thermal Station):

A generating station that converts heat energy of coal combustion into electrical energy is known as a steam power station. A steam power station basically works on the Rankine cycle. Steam is produced in the roller by utilising the heat of coal combustion. The steam is then expanded in the prime mover (i.e., steam turbine) and is condensed in a condenser to be fed into the boiler again. The steam turbine drives the alternator which converts mechanical energy of the turbine into electrical energy.

This type of power station is suitable where coal and water are available in abundance and a large amount of electric power is to be generated.

Advantages:

The fuel (i.e., coal) used is quite cheap.
Less initial cost as compared to other generating stations.
It can be installed at any place irrespective of the existence of coal. The coal can be transported to the site of the plant by rail or road.
It requires less space as compared to the hydroelectric power station.
The cost of generation is lesser than that of the diesel power station

Disadvantages:

It pollutes the atmosphere due to the production of large amount of smoke and fumes.
It is costlier in running cost as compared to hydroelectric plant.

The schematic diagram for the steam power plant is shown in figure below:

1.1.1. Choice of Site for Steam Power Stations:

In order to achieve overall economy, the following points should be considered while selecting a site for a steam power station:

(1) Supply of fuel: The steam power station shouldbelocated near the coal mines so that transportation cost of fuel is minimum. However, if such a plant is to be installed at a place where coal is not available, then care should be taken that adequate facilities exist for the transportation of coal

(2) Availability of water: As huge amend of water is required for the condenser, therefore, such, a plant should be located at the bank of a river or near a canal to ensure the continuous supply of Water.

(3) Transportation facilities: A modern steam power station often requires the transportation of material and machinery. Therefore, adequate transportation facilities must exist i.e., the plant should be well connected to other parts of the country by rail, road etc.

(4) Cost and type of land: The steam power station should be located at a place where land is cheap.

(5) Nearness to load centres: In order to reduce the transmission cost, the plant should be located near the centre of the load.

(6) Distance from populated area: As huge amount of coal is burnt in a steam power station; therefore, smoke and fumes pollute the surrounding area. This necessitates that the plant should be located at a considerable distance from the populated areas.

1.1.2. Efficiency of Steam Power Station:

The overall efficiency of a steam power station is quite low (about 29%) as huge amount of heat is lost in the condenser and heat losses occur at various stages of the plant.

(i) Thermal efficiency:

The ratio of heat equivalent of mechanical energy transmitted to the turbine shaft to the heat of combustion of coal is known as thermal energy of steam power station.

(ii) Overall efficiency:

The ratio of heat equivalent of electrical output to the heat of combustion of coal is known as overall efficiency of stem power station i.e.

Overall efficiency = Thermal efficiency x Electrical efficiency

1.1.3. Equipment of Steam Power Station:

The most important constituents of a steam power station are:

Steam generating equipment
Condenser
Prime mover
Water treatment plant
Electrical equipment

INTRODUCTION NON-CONVENTIONAL ENERGY RESOURCES

Renewable energy resources also called non-conventional energy resources that are continuously replenished by natural processes.

A renewable energy system converts the energy found in sunlight, wind, falling water, sea waves, geothermal heat, or biomass into a electrical energy.

Various forms of renewable energy resources:

Solar energy
Wind energy
Bio energy
Hydro energy
Geothermal energy
Wave and tidal energy

5.1. Solar energy:

Solar energy is the most readily available and free source of energy since prehistoric times. It is estimated that solar energy equivalent to over 15,000 times the world's annual commercial energy consumption reaches the earth every year.

India receives solar energy in the region of 5 to 7 kWh/m² for 300 to 330 days in a year. This energy is sufficient to set up 20 MW solar power plant per square kilometre land area.

Solar energy can be utilised through two different routes, as solar thermal route and solar electric (solar photovoltaic) routes. Solar thermal route uses the sun's heat to produce hot water or air, cook food, drying materials etc. Solar photovoltaic uses sun's heat to produce electricity for lighting home and building, running motors, pumps, electric appliances, and lighting.

5.2. Wind energy:

Wind energy is basically harnessing of wind power to produce electricity. The kinetic energy of the wind is converted to electrical energy. When solar radiation enters the earth's atmosphere, different regions of the atmosphere are heated to different degrees because of earth curvature. This heating is higher at the equator and lowest at the poles. Since air tends to flow from warmer to cooler regions, this causes what we call winds, and it is these airflows that are harnessed in windmills and wind turbines to produce power.

Wind power is not a new development as this power, in the form of traditional windmills for grinding corn, pumping water, sailing ships have been used for centuries. Now wind power is harnessed to generate electricity in a larger scale with better technology.

5.3. Bio Energy:

Biomass is a renewable energy resource derived from the carbonaceous waste of various human and natural activities. It is derived from numerous sources, including the by-products from the wood industry, agricultural crops, raw material from the forest, household wastes etc.

Biomass does not add carbon dioxide to the atmosphere as it absorbs the same amount of carbon in growing as it releases when consumed as a fuel. Its advantage is that it can be used to generate electricity with the same equipment that is now being used for burning fossil fuels. Biomass is an important source of energy and the most important fuel worldwide after coal, oil, and natural gas. Bio energy, in the form of biogas, which is derived from biomass, is expected to become one of the key energy resources for global sustainable development. Biomass offers higher energy efficiency through form of Biogas than by direct burning.

5.4. Tidal energy:

Tidal electricity generation involves the construction of a bar- rage across an estuary to block the incoming and outgoing tide. The head of water is then used to drive turbines to generate electricity from the elevated water in the basin as in hydro- electric dams.

Barrages can be designed to generate electricity on the ebb side, or flood side, or both. Tidal range may vary over a wide range (4.5 - 12.4 m) from site to site. A tidal range of at least 7 m is required for economical operation and for sufficient head of water for the turbines.

5.5. Ocean energy:

Oceans cover more than 70% of Earth's surface, making them the world's largest solar collectors. Ocean energy draws on the energy of ocean waves, tides, or on the thermal energy (heat) stored in the ocean. The sun warms the surface water a lot more than the deep ocean water, and this temperature difference stores thermal energy.

The ocean contains two types of energy: thermal energy from the sun's heat, and mechanical energy from the tides and waves.

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.