The term Alternative Energy is generally used to indicate non-traditional energy systems which
do not use fossil fuels and have low environmental impact. There are many non-fossil fuel based energy systems either already in use or being evolved and developed to counter the harmful effects of increasing use of fossil fuels.
We shall briefly look at the major alternative energy systems.
Solar energy
Wind energy
Tidal (Wave) Power
Biomass
Geothermal
Nuclear
Solar Power as Alternative Energy Source
Solar radiations cover a very wide spectrum of frequencies - from infrared through the visible to ultraviolet frequencies. The visible radiations give us light and the infrared radiations give us warmth.
From ancient times people have been using the solar radiation for heating - heating water and warming houses in winter. In recent years many developments have taken place; now apart from domestic hot water supply or space heating of large buildings, solar energy is being used to provide hot water and steam for industrial processes and even to supplement power generation in large thermal power stations.
Photovoltaic generation of electricity as an alternative energy source is a modern development. A photovoltaic (PV) cell is made of Silicon metal; it exhibits strong photovoltaic properties converting visible solar radiation into electricity.
Individual solar cells are small and give only a small amount of power. Now PV cells are assembled in different configurations as arrays and panels; these solar arrays and panels can be used for generating sufficient electricity for practical applications. Arrays or panels of solar cells are being used in remote and inaccessible communities to obtain clean power; they are being used to run cars, to supply power on satellites and space stations and even to supplement power generation in large power stations of hundreds of MW.
Since the year 2000 solar electric production has grown at an average rate of 40% per year and by 2007, the installed capacity is about 10.6 GW.
Wind Power as Alternative Energy Source
Wind energy for pumping water and grinding grains has been used since the medieval times. Wind energy is now mainly used for generation of electricity; wind mills drive turbines for generation of electricity which is connected into the grid of the local utility. Due to variability of wind speeds from time to time, generally wind energy supplies only a small proportion of the total utility load.
By the end of the last year, the total wind-powered generator-capacity worldwide was 94.1 GW contributing only 1% of world-wide electricity use. Wind power generation has increased by over 500% since 2000 and is expected to spiral upward.
Tidal Power as Alternative Energy Source
Tidal power utilizes the rise and fall in sea levels due to the tides. This alternative energy source had been realized by man long ago and in Europe tide mills had been in use for grinding grains over a thousand years ago. It is possible to utilize this energy for generating of electricity and efforts are on in many countries around the world to harness this energy.
Tidal energy, being derived directly from the interaction of the sun and the moon and the earth's rotation, is an inexhaustible alternative energy source. The only limitation is that it can be put to use only in select places around the world.
The two methods by which energy of the tides can be harnessed are:
The tidal stream system which will make use of moving water in much the same manner as wind energy being used by windmills; and
The barrage system which will use the difference in the height between the low and the high tide in an estuary.
Both these methods are being actively tried out in various places. Experts feel that tidal energy has a great potential as an alternative energy source. .
Biomass Power as Alternative Energy Source
Biomass refers to biological materials including trees, grass, agricultural and urban waste matter, etc. Biomass contains energy received from the sun. Chlorophyll in plants uses solar energy to convert carbon dioxide (from air) and water (from ground) into carbohydrates. When these carbohydrates are burnt they release carbon dioxide and water, and energy that had been trapped in it is released. This is as if the carbohydrates act as storage battery for solar energy - they hold the energy and release it at a later time when burnt as an effective alternative energy source in place of fossil fuels.
From time immemorial biomass has been burnt to recover sun's energy as heat. By using modern technology we can produce heat, steam and electricity from biomass more efficiently and cleanly; we can also convert it into liquid fuels or produce combustible gases from it.
In US alone, about 50 billion kWh of electricity (about 1.2% of total consumption), about four billion gallons of ethanol (about 2% of the liquid fuel used in vehicles) are produced from biomass. DOE believes that by 2030 about 20% of transportation fuel could be produced from biomass. There is obviously a vast potential for use of biomass the world over.
Geothermal Power as Alternative Energy Source
The most recent (1994) estimate of temperature at the core of earth is about 7500 deg. C. Energy obtained by tapping into the hot interior of the earth is called the geothermal energy. Geothermal energy is an alternative energy source for generation of electricity; it is also used for heating houses in cold countries, and for supplying process heat requirements.
Building a geothermal power station is expensive but the low operating costs and absence of carbon emission into atmosphere are two major benefits of this system.
Power plants based on geothermal energy fall into three types depending upon the method used:
Those plants that take steam directly from fractures/holes in the ground and drive turbines directly from this steam are called Dry steam plants.
In a Flash plant hot water, usually at more than 200 deg C, , is taken out of the ground and allowed to boil as it rises to the surface; steam is separated from it and run through turbines.
In binary plants, hot water taken from ground flows through heat exchangers, where it imparts heat to an organic fluid to boil it; this organic fluid runs through turbines driving them.
In all the three types, the remaining geothermal fluid and condensed steam are injected back into the hot rock crust to recycle.
A 1999 study shows that the worldwide geothermal electrical generation capacity using existing technologies is between 35,000 to 70,000 MW; using the new technologies it could be twice as much.
Nuclear Power as Alternative Energy Source
Popularly nuclear reaction is equated with atom bombs. However, controlled nuclear reaction is used as an alternative energy source for generation of electricity for the last 50 years. Nuclear reaction releases enormous energy which is used to raise steam as is done by burning oil or coal in conventional thermal power stations and this in turn is used to generate electricity. Today more than 50 countries are generating over 370 000 MW of electricity by using nuclear power reactors.
Constructing and maintaining nuclear power plants is expensive. Moreover they produce nuclear waste which is hazardous, and there is the potential for enormous nuclear disasters. The nuclear waste is highly toxic and can not be destroyed or recycled. Unless properly stored in a secure location it can create hazardous environment.
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