What are the Alternative Sources of Energy for Mankind?

What are the alternative sources of energy after the depletion of fossil fuels ? The fuel for future should be convenient, clean, less wasteful of energy and should be renewable so that there is no threat of its depletion. Important energy resources which may be tapped as an alternative to fossil fuels are:

(1) Wind Power:

Approximately 11 x 10²¹ Joules of solar energy are used up in generating air and water currents. In a number of countries where persistent strong winds blow, wind power has been in use since ancient times. Across the passing air current large fans are placed whose revolving motion is carried down, through a shaft to drive water pumps, wind mills, turbines etc. Wind power provides cheap, clean and inexhaustible energy to small villages, domestic establishments, small- scale industries etc. The main drawback of wind power is its erratic and irregular supply. However, there are places where strong winds blow for most of the day or nights. At these places this inexpensive, inexhaustible energy resource can be used to save power obtained from other sources by concentrating work during the periods when wind power is available.

(2) Energy from Oceans:

Oceans are vast reservoirs of water covering about three-fourth of earth’s surface. They can also be used for generation of power in following ways :

1. Tidal Energy:

Gravitational pull excercised by sun and moon causes tides to develop. Sea level rises and falls depending upon the position of sun and moon. As the sea level rises water may be diverted through suitable channels to inshore reservoirs, driving the turbines during its entry. The stored water may gradually be released driving the turbines again during the periods of low tide. In this way an inexhaustible, clean and cheap power shall be available to mankind. Total tidal energy potential has been estimated to be about 2 x 10¹⁸ Joules per year.

2. The Energy of Waves:

Air currents rubbing the ocean surface produce waves which are pushed to the shores where its energy is dissipated as waves break when they strike the shore-line. Floating propellers placed in shallow waters along the shores may be kept in a state of continuous motion by these waves. Their kinetic energy can be used to drive turbines maintained on floats or on platforms erected for the purpose in shallow waters. This will provide a cheap, clean and inexhaustible source of energy to mankind.

3. Thermal Energy of Oceans:

There is often a large temperature difference between the upper and the lower layers of sea water. In tropical regions surface waters (at 28-30°C) are warmer by 5-12°C than the layers about 1000 metres below. This temperature difference can be utilized to generate electricity with the help of some low boiling point working fluid (like liquid ammonia or propane). In reservoirs maintained on sea surface, the fluid picks up heat, evaporates and is guided through turbines. As the turbines rotate the vapours are pushed down to lower temperature zones where they cool, condense and are brought back to warm water zone to be recycled again. The concept of Ocean Thermal Energy Conversion (OTEC) was first put forth by a French Scientist as early as 1881 A.D. and has already been tested. It has a huge potential for providing clean, cheap, inexhaustible energy to the mankind.

(3) Geo-thermal Energy:

Temperature of earth increases at a rate of 20-75°C per km as w move down from earth’s surface. The heat could be used by circulating waters through pipes to raise steam and generate electricity. For satisfactory results it would be useful to drill and locate the turbines near already known hot springs or thermal springs, volcanos etc. For this reason, geothermal energy shall be of a local interest only. Still the total geothermal energy potential of the world, if properly utilized could provide about 2 ^x 10¹⁸ to 20 x 10′⁸ Joules of energy per year.

(4) Direct Use of Solar Energy:

Earth receives about 75,000 x 10″ KW of energy from sun every day. Just 0.1% of this energy is sufficient to meet the energy requirement of the entire world. At noon, the solar energy striking an area of 12,550 sq. kms if converted to electricity shall be equal to the peak power generation capacity of all power plants in the world. Only a part of the roof of an average house in India if covered with solar panels can provide sufficient energy to meet entire energy requirement of the house.

In parts of the world which receive abundant sunshine, solar heat can be used directly for heating and cooking purposes. Intense sunlight focused with reflectors which track the sun as it moves across the sky can save a large amount of energy which we use to keep space warm, heat waters and for cooking purposes. Solar energy can be converted to mechanical, chemical or electrical energy also.

Silicon solar cells can convert solar radiations directly into electricity and can be used for domestic lighting, run television sets, radio-instruments and for community lighting. These systems are costly to install, however, once installed there is little expenditure involved and the device works for years and years together.

(5) Biomass Based Energy:

Biomass has been an important source of energy for mankind since ancient times. For today’s needs, biomass is often not a convenient fuel. It has to be converted to suitable and convenient state before it can be used. Some of the important energy resources which originate basically from photosynthetic activity of green plants are:

1. Biogas:

Biogas consists mainly of methane which is produced when organic matter decays under anaerobic conditions. Cow-dung, faecal matter, and other bio-degradable wastes are allowed to decay under anaerobic conditions in digesters equipped with device to collect methane thus formed. The residue is exceedingly rich in plant nutrients which can be used as fertilizers. Methane as a fuel is pollution free, clean and cheap source of energy since it is obtained from the wastes which we have to dispose of.

2. Petroplants:

A number of plants belonging to families Euphorbiaceae, Asclepiadaceae, Apocynaceae, Convolvulaceae etc. possess hydrocarbons in their saps and latex. These can be used to produce liquid and gaseous fuels and used just as petroleum products are used. About 15 species of plants have yielded encouraging results.

3. Dendrothermal Energy:

Denuded waste lands can be used to produce fast growing shrubs and trees with high calorific value. These can be used to provide fuel-wood, charcoal, fodder, and through gasification system gases to be used where fuel-wood and charcoal is not convenient. Similarly, baggasse, the pulp and waste discarded after expulsion of juice from sugarcane during the manufacture of sugar can be used to generate energy for local use.

(6) Hydrogen as the Future Fuel for Mankind:

Like natural gas and oil, hydrogen can also provide the concentrated energy needed in domestic establishments, factories and motor vehicles. Hydrogen when burned produces 284 kilo-joules per mole of energy (or 142 kilo-joules per gm) and the product of combustion are water vapours only. 284 kilo-joules per mole.

On weight basis hydrogen is a better fuel than methane, the common constituent of natu gas. Methane produces only 55.6 kilo-joules per gm of energy as compared to hydrogen which yields 142 kilo-joules per gm of gas burnt. Hydrogen is a cleaner fuel than any other gas or oil as it produces water only upon combustion. However, the storage of hydrogen poses problems because of its low density. Its storage in pressurized tanks in liquid state makes the containers too heavy to carry.

Its storage as metal hydrides from which the gas can be recovered by heating is also expense though abundant supply of this gas occurs in the form of water (H₂0), at present hydrogen is about four to five times costly to obtain than methane. Active research is underway to produce cheaper hydrogen and develop adequate and less costly means for its storage and use. The promise of inexhaustible pollution free energy resource makes hydrogen an important energy carrier of the future.