This article throws light upon the top five non-conventional sources of energy. The sources are: 1. Solar Energy 2. Wind Energy 3. Ocean Energy 4. Geothermal Energy 5. Small Hydro-Energy.
Non-Conventional Source # 1. Solar Energy:
Utilisation of solar energy is of great importance to India, since it lies in a tropical climate region of the world where sunlight is abundant for a major part of the year. Solar energy has the greatest potential of all the sources of renewable energy and if only a small amount of this form of energy could be used, it will be one of the most important supplies of energy specially when other sources in the country have depleted. Sun is regarded as an inexhaustible source of useful energy.
The ‘solar power’ (solar power is referred to the electricity generated by solar energy) would eliminate most of the serious environmental problems associated with fossil fuel and nuclear power.
There are certain major limitations to the extensive application of solar energy such as:
(i) The intermittent and variable manner in which it arrives at the earth’s surface, and
(ii) The large area required to collect the energy.
The solar energy is effective only during the day time, and if the power supply is to be made during night, then some reservoir of energy such as storage battery or heat accumulator should be used. Solar energy cannot be used during cloudy weather and rainy season. Its intensity during winter is very less. At present harnessing, storage and use of solar energy is much more expensive than using fossil fuel.
It is believed that solar power can become economically feasible with the following aims achieved:
(a) Availability of better heat collectors
(b) Availability of improved materials and manufacturing techniques
(c) Better techniques for storage and cheap distribution of solar power.
India has the potentialities of solar and wind energy, but it needs the advanced technology to tap this potential.
Applications of Solar Energy:
Traditionally, we have been using solar energy for drying clothes and food grains, for preservation of eatables, and for obtaining salt from seawater. However, in this modern age, we have already invented several techniques for harnessing the solar energy.
Some of the important solar energy applications are:
1. Solar water heating,
2. Heating and cooling of residential buildings,
3. Solar drying of agricultural and animal products,
4. Solar distillation on a small community scale,
5. Salt manufacturing by evaporation of sea water or inland brines,
6. Solar cooking,
7. Solar pumping of water,
8. Food refrigerator,
9. Solar furnaces,
10. Solar power generation,
11. Solar photovoltaic (PV) cells, and
12. Bioconversion, wind energy, ocean thermal energy conversion, tidal energy, sea waves etc., which are indirect sources of solar energy.
Electricity can be produced from the solar energy by photovoltaic solar cells, which convert the solar energy directly to electricity. This photovoltaic technology is also used for the energisation of pump sets for irrigation, drinking water supply, and rural electrification for street lights, community TV sets, medical refrigerators, and other small power loads.
Non-Conventional Source # 2. Wind Energy:
Winds arise primarily from temperature difference of the earth’s surface resulting from unequal exposure to (or absorption of) solar radiation. Air heated by contact with a warmer surface tends to rise, and cooler air from a less heated surface flows in, to take this place; the resulting air flow constituted wind. Wind energy is thus a form of solar energy. Like direct solar energy, wind energy is also highly variable.
It is the conversion of kinetic energy of the wind into mechanical energy that can be utilized to perform useful work or to generate electricity. Wind energy is a renewable source of energy. India with its long coastline, blessed with steady winds almost throughout the year has tremendous potential of wind power.
Wind energy which is an indirect source of solar energy can be utilised to run wind mills which in turn drives a generator to produce electricity. Wind mills may be either horizontal axis wind mills or vertical axis wind mills.
Some characteristics of wind energy are as under:
1. It is a free and inexhaustible renewable source of energy,
2. Wind power systems are non-polluting, and has no adverse influence on the environment,
3. It avoid fuel provision and transport, and
4. These are economical in the rural areas which are at far remote places from existing grids.
However, following problems are associated with wind power:
1. Wind energy available is unpredictable and fluctuating in nature,
2. Wind energy systems are noisy in operation,
3. Large areas are needed to install wind farms of electrical power generators, and
4. Wind mills usually kill the birds.
Wind being an intermittent source, cannot be used as the sole source of electricity, and requires some other backup.
Wind power is a function of wind speed and therefore, the average wind speed of an area is an important factor for economically feasible power. As wind speed increases with height, therefore, power available 30 m above ground is 60% greater than at 10 m heights. Therefore wind mills need to be located at enough heights.
In India, high wind speeds are obtainable in coastal areas of Saurashtra, Maharashtra, Tamil Nadu, Kerela, Karnataka, Orissa, Andhra Pradesh, Western Rajasthan and some parts of central India. In these areas, there could be possibility of using medium and large sized wind mills for generation of electricity and feeding the same into the grid.
As a rough estimate, India has a potential of 20,000 MW of wind power. Traditionally, wind mills were used extensively in the middle ages to mill grain and lift water for land drainage and watering cattle. Wind energy converters are still used for these purposes today in some parts of the world, but the main focus of attention now lies with their use to generate electricity.
Non-Conventional Source # 3. Ocean Energy:
Solar radiation is absorbed by the seas and oceans, which causes, like the wind, ocean currents and moderate temperature gradients from the water surface downward, especially in tropical waters. The oceans and seas constitute about 70 per cent of the earth’s surface area; hence, they represent a large storage reservoir of the solar input.
The conversion of solar energy stored as heat in the ocean into electrical energy by making use of temperature difference between the warm surface water and the colder deep water. The facilities proposed for achieving this conversion are commonly referred to as OTEC (Ocean Thermal Energy Conversion) plants.
Periodic rise and fall of the water level of the sea which are carried by the action of the sun and moon on the water of the earth is known as tide. The tidal range varies from few centimeters to about 8 to 10 m in some parts of the world. The potential energy of the tides can be trapped to generate power.
Ocean and Sea Waves:
Ocean and sea waves are caused indirectly by solar energy like wind and OTEC. Wave energy drives from wind energy, which drives in turn from solar energy. Devices that convert energy from waves can therefore produce much higher power densities than solar devices. But the wave energy development is not nearly as far along as wind and tidal energy.
The hydrological cycle results in rain fall, which causes river flows that, can be trapped behind dams to even out the variations in river flows and thus become the source of hydroelectric energy.
Thus the Ocean sources of energy are:
(i) Ocean Thermal Energy Conversion (OTEC), and
(ii) Tidal energy.
(i) Ocean Thermal Energy Conversion (OTEC):
Ocean covers a little more than 70% of the earth’s surface. This makes them the largest solar energy collector and energy storage system. On an average daily basis, 60 million km2 of tropical seas absorb an amount of solar radiation equal in heat content of about 250 billion barrels of crude oil. The surface of the water acts as the collector for solar heat, while the upper layers of the sea constitutes infinite heat storage reservoir. Thus, in this indirect form of solar energy at sea, collection and storage are free.
The technology which is used to convert this heat energy contained by the upper layers of the ocean into the electrical energy is known as OTEC (Ocean Thermal Energy Conversion).
This technology makes use of the ocean’s natural thermal gradient, caused due to warm upper layers and cold lower layers of water. An OTEC system can produce significant amount of renewable power. This potential is estimated to be of the order of 10,000 GW of base load power generation.
The heat contained in the oceans, which is solar in original could be converted into electricity by utilizing the fact that the temperature difference between the warm surface water of the tropical oceans and the colder waters in depth (1000 – 1500 m) is about 20 – 25 °C. Warm surface water could be used, to heat some low boiling organic fluid (such as ammonia), the vapour of which would run a heat engine.
The exit vapour would be condensed by pumping cold water from the deeper regions. The process of OTEC requires that the warm surface water and cold water from depth, be brought into proximity so they act as the heat source and heat sink, respectively for a heat engine, without the requirement of any depletable fuel. After providing the cooling effect in the condenser, a part of the cold sea water is diverted for the development of aqua culture.
Although there is some seasonal variation in the ocean thermal resource at a given OTEC power plant location, there is little variation on day-to-day basis. OTEC systems can be used to generate electricity, desalinate seawater, provide refrigeration and air-conditioning and may help in mineral extraction from sea water. These complementary products may make the OTEC systems quite attractive to the industry and island communities.
(ii) Tidal Energy:
The water level in a sea rises and falls during tides, caused mainly by gravitational attraction of the moon and the sun on the water of solid earth and the oceans. About 70 per cent of the tide producing force is due to the moon and 30 per cent due to the sun. The moon is therefore is the major factor in the tide formation.
Surface water is pulled away from the earth on the side facing the moon, and at the same time the solid earth is pulled away from the water on the opposite side. Thus, high tides occur in these two areas (directly under the moon and diametrically opposite the earth’s surface), with low tides on intermediate points.
As the earth rotates, the position of a given area relative to the moon change, and so also do the tides. Thus, there are periodic successions of high and low tides. Therefore, the time between high tides and low tide at any given location is a little over 6 hours.
Thus, a full moon as well as no moon produces a high tide. In a period of 24 hours 50 minutes, there are therefore, two high tides and two low tides. The difference between high and low water levels is called the range of the tide. The periodic rise and fall in levels is in rhythms with daily cycle of rising and setting of sun and moon.
The potential energy developed by the water head created during high tide can be used to run the turbines, to generate electricity. Electricity produced by these tides is called tidal power. If the differential head between high tide and low tide could be utilized in operating a low head reversible hydraulic turbine, the tidal energy could be covered into electrical energy by means of an attached generator.
During high tide, the sea water flows towards the land reservoir through the openings in the dam or the barrage, and turns the turbines, generating electricity. During the low tide, as the seawater levels falls, the water from the upstream reservoir flows towards the downstream in seaward direction, again turning the turbine blades, to generate electricity.
The main problem in harnessing the tidal power is that, it is not possible to harness the tidal power along most of the coasts of the world. If the tidal range is less than about 8 metres or if narrow and enclosed bays are not available, then tidal power development becomes very uneconomical. Therefore, very few sites are available where tidal energy can be economically harnessed.
Following characteristics are to be noted regarding the tidal phenomenon:
1. The tidal are periodical phenomenon and two tides in any cycle are alike
2. In any month, the tides on the full moon and no moon days are particularly higher than the rest
3. The mean tidal range varies from place to place
4. It is free from pollution
5. It is inexhaustible, and independent of the rains
6. Tidal power plants require less area of valuable land and are located on sea shore
7. The tidal range is highly variable and therefore, the turbines have to work on a wide range of head variation. This affects the efficiency of the plant
8. High chances of machinery being get corroded due to sea water.
Non-Conventional Source # 4. Geothermal Energy:
Geothermal energy is the energy which lies embeded within the earth as heat (i.e. thermal energy) in the earth’s crust. The earth’s crust constitutes a potentially useful and almost inexhaustible source of energy. This heat is apparent from the increase in temperature of the earth with increasing depth below the surface. The eruption of hot lava from volcanoes at the surface at about 1200°C temperature, clearly shows that the deep interior parts of the earth are very hot, and may be in liquid or semi-liquid state.
From the extremely hot interior of the earth, a continuous upward current of heat flows towards the upper crust of the earth. Due to such currents, the upper 3 km portion of the earth’s crust, also contains a huge amount of heat energy, which if removed is liable to be replaced again by the new heat coming from the heat currents from the interior portion of the earth. This source of heat energy is therefore, considered as a renewable energy source.
In the natural geothermal areas, water circulating systems are continuously transporting the heat energy to the surface, and this is observed as natural hot springs, called natural geysers. These natural eruptions of hot waters with steam with temperatures reaching upto about 350°C, may occur through the cracks existing in the crystal rocks.
The utilization of geothermal energy can be made by drilling holes or wells into these natural circulation systems, and to top the geothermal fluids through these wells. The naturally erupting geyser can also be utilised for this purpose. These hot fluids (water + steam) can either be used for generation of electricity, or for direct heating purposes. For large scale use bore holes are normally sink with depth upto 1000 m, releasing steam and water at temperatures upto 200 or 300°C and pressures upto 30 kgf/cm2.
Geothermal energy is advantageous both from the point of view of conserving fossil fuel and of pollution control. The hot water coming out of the ground with steam (which has about 1/3 of the available thermal energy) is discarded because it contains about 30% dissolved salts and minerals, which can cause serious, rust damage to the turbine.
Non-Conventional Source # 5. Small Hydro-Energy:
Earlier, hydro-engineers concentrated on developing large hydel (hydro-electric) plants, but now, with the prospect of rapidly depleting fossil fuels coupled with steady rise in oil prices, attention is being given to the smaller hydel sites, previously regarded as uneconomical. Further, the advance of technology of development of turbines suitable for small heads and small discharges has increased the use of small (including micro and mini) hydel installations to a large extent.
Small hydel installations can supply significant amount of electricity in hilly and remote rural areas without a long transmission system. The total potential amount of such a resource is though poorly documented, but their usefulness is significant. Moreover, lesser gestation periods, with little or no adverse environmental impact have lent added attraction.
In India, the potential of small hydropower (SHP) is estimated to be over 15000 MW, through the exact investigations and surveys are expected to indicate a higher potential. The small hydropower is covered in the renewable energy programme. Sites suitable for low-head installations can be found everywhere in the mountain region, plains or even at the sea level.
Low head hydropower sites can be close to power consumption areas. In water logged areas like Sunderbans in Bengal or remote hilly areas such as Ladakh, low head installations are often the only source of energy. Many of these small hydropower schemes can be constructed on existing canals and irrigation system, where small heads are available. Till Jan. 2011, 801 small hydel schemes (upto 25 MW), with 2953 MW capacity have been constructed and 271 schemes with 914 MW were under construction.
Small hydropower stations are classified as under:
(a) Micro hydel schemes – upto 100 KW
(b) Mini hydel schemes – upto 2,000 KW (2 MW)
(c) Small hydel schemes – upto 25,000 KW (25 MW)
Advantages of Small Scale Hydel Schemes:
1. Takes very small time for constructing these schemes
2. The running expenditure after commissioning is almost negligible.
3. Operation and maintenance of these power stations is simple.
4. These energy sources are free from pollution.
5. Unlike the major hydel projects, these have no environmental problems, no submergence of land, no dislocation of habitation, and ecology of the region also remains unaffected.
6. These can be operated and maintained easily by engaging local people.
Limitations:
Following are the major factors responsible for slow rate of development of small hydel projects:
1. Conventional major hydel projects are still to be constructed on untapped hydro-potential in the country.
2. Non-availability of indigenous equipment for generating plants for such projects.
3. Remoteness of sites especially, in the hilly areas and adverse geological conditions in Himalayan region, where most of these plants can be constructed.
4. General lack of awareness of benefits from such plants.
With concentrated efforts it would be possible to improve the conditions and create climate for the development of small hydel projects. With the creation of Ministry of Renewable Energy Sources, efforts are now being made to emphasize on the development of small hydel projects.