This article throws light upon the Classification of Energy Resources:- 1. Primary Energy Resources 2. Secondary Energy Resources.
Classification # 1. Primary Energy Resources:
(A) (i) Conventional Sources of Energy:
Hydroelectric Energy:
Hydroelectric power (electricity from water) is the cleanest, cheapest and best means of electricity generation.
Central Electricity Authority (CEA) has indicated the hydropotential of India at-84,000 MW at 60% load factor or 1,35,500 MW at 40% load factor.
It is equivalent to 600 billion units of energy per year. But at present, only 16% or 6500 mega watt of hydroelectricity is being generated.
For generation of electricity from hydel projects, it is necessary to utilise energy produced from the descent of water from higher to lower level. In practice, a water reservoir is constructed by means of dams in a river for storage of water. High dams are built to obtain a substantial amount of hydrostatic pressure. When stored water under high pressure is released from the upper level into a water driven turbine placed at a lower level, electricity is generated (Fig. 1). The hydel projects of Jaldhaka, Panchyet and Maithon constitute typical examples.
In US, about 300 large dams generate 9.5% of its total electrical power production. In Venezuela, (South America), 10,000 mega-watt of hydroelectricity is produced which is equivalent to the production of electricity from 10 thermal power plants.
Advantages of Hydroelectricity:
1. Hydroelectricity is basically non-polluting renewable clean source of energy.
2. There is no emission of green-house gases.
3. No consumption of fuel
4. No need of high technology.
Problems in the Development of Hydroelectric Energy:
1. Land acquisition,
2. Environmental aspects,
3. Techno-economic clearance,
4. Statutory clearance,
5. Construction machinery,
6. Zero date disparity.
Limitations:
Hydroelectricity is still associated with serious problems:
1. Dams have drowned out beautiful stretch of rivers, forests, productive farm land and wild life habitat.
2. Local people become refugees as they are uprooted from their houses.
3. Capacity of the reservoir gets reduced due to siltation.
4. Since water flow from the dam is regulated as per the requirement of power, dams play havoc downstream because water level may change from extremes of near flood levels to virtual dryness and back to flood even overnight.
Many developing countries have great potential for large hydel power projects but due to certain limitations, there is a lot of opposition from Environmental Protection Organisations and people.
Nuclear Energy:
Nuclear Energy from Nuclear Fission and Nuclear Fusion:
Nuclear energy can be generated by nuclear power (fission) reactors which are based on the fission of uranium-235 nuclei by thermal neutrons.
The energy from these nuclear reactions is used to heat water in the reactor and produce steam to drive a steam turbine. Thus energy is converted into electricity.
1. Fission of 1 kg of U-235 releases energy equal to 1.7×1013 cals.
2. 1 lb of U-235 = 5 million lb of coal = 20 million lb of TNT.
3. 1 g of U-235 produces heat energy equivalent to energy produced by 3 tonne of coal or 14 barrels of crude oil.
Light water reactor (LWR), high temperature gas cooled reactor (HTGR) and fast breeder reactor (FBR) are viable for power generation. LWR consumes only U-238 and Th-232 to fissionable Pu-23.9 and Np-244.
Nuclear power contributes only 5% of total electricity generation.
Advantages of nuclear energy:
Nuclear power plants do not emit polluting gases such as CO2 and SO2 as thermal power plants do.
Limitations:
1. The major constraint in the use of nuclear fission power is the yield of large quantities of radioactive fission waste products which remain lethal for thousands of years.
2. Safe disposal methods have not been devised.
Nuclear fusion reactions are based on deuterium-deuterium and deuterium-tritium reactions. The latter is energetically more viable.
1H2 + 1H3 ——->2He4 + on1+17.6MeV
The deuterium-deuterium reaction promises an endless source of energy without any radioactive wastes, but the technological problems for harnessing fusion energy will take several years to solve.
Thermal Power:
Electricity is generated by combustion of coal in a furnace. This heat is utilised to produce steam at high temperature and pressure. Steam is then used to run a turbine which is linked with the generator producing electricity.
Coal-fired thermal power plants are operated on the above principle by mechanical rotation of the steam turbine. In India, thermal power contributes about 65000 MW of electricity, that is, 70% of the total power supply. Some of the major thermal power stations of National Thermal Power Corporation (NTPC) of India are at Singrauli and Rihand in Up Farakka in West Bengal and Talchar in Orissa. They are the major source of thermal pollutants, flyash and decreased content of dissolved oxygen.
(ii) Non-Conventional Sources of Energy:
Solar Energy (Electromagnetic Radiation from the Sun):
Sun is the source of all energy on the planet earth. It is a large nuclear reactor where hydrogen gas is continuously burning at high temperature and pressure. Solar energy originates from the thermonuclear fusion reactions occurring in sun. The energy generated by sun into the space is received on the earth as electromagnetic radiant energy. Out of the solar radiations reaching the earth, 92% consist of radiations in the range 315 nm to 1400 nm, 45% of this radiation is in the visible region, 400 nm to 700 nm. The earth
absorbs radiation mainly in the visible region and emits radiation in the infra red region (2 p to 40 p with maximum at 10 p).
Energy Output:
The value of solar flux reaching the earth’s upper atmosphere is estimated to be about 1400 watt m-2 min-1. The heat equivalent of the solar radiation reaching the earth is 2.68×1024 Joule per year. The total energy output of the sun is estimated at 3.45×1023 KWH. The average intensity of solar radiation is 2.1 to 2.5 kJ per cm2 per day in India.
Location:
India is situated between 7° N and 37° N latitudes and the prospects of using solar energy are very bright indeed. If India can trap 1% of the incident radiation, it can generate many times the energy of its actual requirement at present. But it utilises only 25 x 10-7% (13 x 107 KWH per year) of the incident solar radiation (5 x 1015 KWH per year). Only 0.5% of solar energy reaching the earth is trapped by photosynthesis which is the energy source for the ecosystem.
Production of Electricity using Solar Energy:
Solar energy can be used either by absorbing radiations to produce heat or by converting it directly into electricity by the following methods:
1. Photovoltaic Cells (Solar Cells):
Solar panels or a large number of solar cells are connected in series parallel combination to obtain the required amount of power. These cells when exposed to solar radiation give direct current (DC) which can be converted into alternating current (AC) using inverters. The silicon solar cell, developed for the space programme consists of a sandwich of n-type and p-type silicon semiconductors, the charge separation is developed across the junction between them and electricity is produced.
N-type Silicon cell (semiconductor):
When Si lattice contains an impurity of As, which contains 5 electrons in the outer shell, 4 of these electrons form bonds with Si while the fifth electron is available for conducting current. Such solids are called n-type semiconductors.
P-type Silicon cell (semiconductor):
When Si lattice contains some atoms of indium (In), with three electrons in the outer shells the covalent bonding is incomplete, some sites being vacant, which constitute positive (+ve) holes. If these holes are filled by adjacent electrons, they form other holes and by migration, they carry current. Such solids are called p-type Si cells.
If a crystal of Si is prepared such that one part is p-type (which conducts positive charge) and the other n-type (which conducts negative charge), the p-n junction will permit current from an external source of flow through it in one direction. The silicon cell produces only 15% electricity and is quite expensive since very high grade crystalline Si is required (Fig. 2).
With innovation in manufacturing process and more advanced technology, the photovoltaic power plants may produce power nearly at the same cost as traditional power plants. Experiments with vehicles run on PV cells are under way using ultra-efficient designs. Solar photovoltaic cells deteriorate due to exposure to weather. Other solar cells developed are CdS (n-type), CU2S (p-type), gallium arsenide and indium phosphide.
2. Solar Trough Collectors (Invented by Charles Abbott):
Sunlight hitting the solar trough collector is reflected onto a pipe and heat the fluid circulating through it. The heated fluid is used to boil water, thereby generating steam to run turbo generator.
3. Power Tower:
In this method, an array of sun tracking mirrors is used to focus sunlight on a large area of land onto a boiler mounted on a tower. The intense heat produces steam in the boiler which drives a turbo generator to generate electricity.
4. Solar Furnace:
Here thousands of small plane mirrors are arranged in concave reflectors which collect the solar heat and produces high temperature up to ‘3000°C.
Applications of Solar Energy:
The best application of solar energy is in heating buildings and providing hot water which in developed countries like USA, consumes about 25% of the fuel supply. Figure 3 illustrates the detailed heating system in a solar heated house. Sunlight is collected on plates on the roof and heat transferred to a circulating water system. It has been calculated, that in US, an average house with a collection area of 1300 ft2 can get its energy supply for heating and hot water in December by this method.
1. The use of solar energy is a completely benign operation. Solar energy can be used as solar heat by several gadgets such as solar cooker, solar dryer, solar water heater, solar distillation, space conditioning, green house technology, solar air crafts.
2. Solar energy can also be used as solar electricity by PVC or solar cells. Solar photovoltaic cells could be installed in remote areas in forests and deserts where installation of electric cables is cost-prohibitive.
3. Solar energy being non-polluting and non-depletable is considered as renewable energy and fits into the principle of sustainability.
4. Solar cells are widely used in electronic watches, calculators, traffic signals and artificial satellites. Because of their nonpolluting nature, solar cells are known as clean and green cells.
Limitations of Solar Energy:
1. The major constraint is that sunlight is diffuse and intermittent.
2. Density of solar energy is low as compared to oil, gas or coal etc.
3. CO2 produced while forming silicon from silica increases atmospheric temperature. Silicon dust is also an occupational hazard.
4. Cadmium is used in fabricating thin film solar cells which is carcinogenic. However, only traces of Cd are released from discarded PV panels.
Wind Energy:
Principle:
In India, wind power can be usefully exploited for the generation of electricity as there are large coastal, hill and desert areas. The concept of air plane type propeller blades turning a generator geared to shaft is applied. Wind turbines, comprising of two blades, convert kinetic energy of the wind into electrical energy.
Operation:
The flow of air against the windward side of the blades creates suction on the reverse side, which turns the rotor shaft on which the blades are mounted. This rotor turns the generator which is linked directly to the electricity grid. When the wind speed is greater than 25 m/s, a disc brake stops the turbine from operation.
The operation of the wind turbine is monitored and controlled by a computer in the bottom of the tower. The computer receives information regarding wind speed and wind direction via an anemometer and a wind wave mounted on the top of turbine housing. Currently, wind turbines have horizontal axis with high hub height (328 ft) and large rotors (180 ft). A prototype electrical generator develops 20 kW power at Rensselaur polytechnic Institute in Troy, New York.
Classification of Wind Machines:
Wind machines used for generating electricity may be classified into three categories:
1. Mini-converters with average output of 1 KWe are used to run small irrigation units, light houses and ranger stations.
2. Machines with average output of 50 KWe are used in rural industries, isolated houses, pumping of irrigation water and space heating.
3. Wind farms with average output in the range from 500 KWe to many MW supply power to electrical power grids. A modern wind farm may contain 500 wind turbines connected to a transmission grid. Wind mills used extensively in USA, England and Russia, work on the principle of converting kinetic energy of the wind to mechanical energy. By the year 2009, more than 13000 mega-watts of wind power had been installed world-wide. California alone had 1600 MW of wind power in use to provide enough electricity for over 7,50,000 homes.
Advantages of Wind Energy:
1. Wind energy is a renewable and economically competitive energy source.
2. Wind machines can be built on shore or off shore.
3. Cost effective and reliable wind power generators are now being produced.
4. Wind machines are useful in supplying electric power to remote and rural areas.
5. Dispersed wind energy systems are more environmentally benign than any other alternate source of energy.
Limitations of Wind Energy:
1. Low energy density.
2. Wind is variable, irregular and intermittent.
3. Design, manufacture and installation of wind turbines is complex due to varying atmospheric conditions where they have to operate.
4. Small units are more reliable but have higher capital cost per KWh. Large units require high technology.
5. Requires energy storage batteries which indirectly contribute to environmental pollution.
6. Requires vast open area which is generally far away from load centres.
7. Wind generators may interfere with habitats, causing noise pollution and aesthetic degradation.
Geothermal Energy:
Geothermal energy is the exploitation of heat energy from the molten core of the earth. In volcanic regions, holes can be drilled into the hot-rocks and make the rising steam from ground water to drive turbo generators to produce electric power. The high temperature (>150°C) geothermal resources are exclusively used for power generation.
The world’s largest Geothermal energy production facility exists at a location called Geysors near San Fransisco in US. In 2008, its electricity output was 14.3 billion kW, which is equivalent to the power produced by two large nuclear power plants. Similar geothermal facilities exist in Mexico, Japan, Italy and Iceland generating a total power of about 3000 MW. Geothermal sources provide more than 7% of electricity in California. Worldwide, geothermal energy amount to more than 8 million kW or about 3% of the 3180 kW used globally.
Advantages of Geothermal Energy:
1. Geothermal resources in the moderate temperature range (90°C to 150°C) can be used for space heating, for generating industrial process steam, green houses and aquaculture.
2. Coupled with heat pumps, the low temperature (< 90°C) geothermal resources are used for heating and cooling the houses.
Limitations of Geothermal Energy:
1. Natural steam vents occur only in few regions whereas hot dry rocks are available in almost all places.
2. Hot steam coming to the surface is usually contaminated with the salts and sulphur compounds. Some of these contaminants are highly corrosive to turbines.
3. SO2 pollution from a geothermal plant may be as much as that of a high sulphur coal based thermal power plant.
4. Hot brine released into surface waters may be ecologically hazardous.
Ocean Energy:
India’s first power plant generating electricity is commissioned at Vizhinjam fishing harbour in Kerala to provide energy to the extent of 150 MW in a year. The conversion of ocean thermal energy into electrical energy is about 150 MW in Andaman and Nicobar islands.
Sources of Energy from Oceans:
The biggest treasures of the world lie hidden in the sea. Oceans are, therefore, known as our last frontier.
The various methods of extracting energy from oceans are:
1. Ocean winds, Ocean waves, Ocean tides,
2. Ocean currents, Ocean geothermal power,
3. Ocean thermal energy conversion.
Energy from Ocean Waves:
Ocean waves splash on ocean shores at tremendous speed. The mechanical energy in this process can be harnessed and converted into electrical energy. In a large chamber, sea water is enclosed by oscillating water column method. Ocean waves enter the chamber through an inlet pipe and force the enclosed water upward at terrific speed. This exerts hydraulic pressure on the enclosed air which, in turn, can rotate a turbine.
It has been found that in the middle of North Atlantic Ocean, each wave per one metre height can generate 90 kW electricity whereas on the shore the waves can generate 25-75 kW. During storm, the generation level can rise upto 5 mega watt.
Limitation:
Energy production from ocean is expensive at present but it has immense potential which can be exploited in future with advanced technology.
Sea is unpredictable in energy generation at best but devastating at worst (such as when Tsunami hit in the South Pacific).
Tidal Power:
A lot of energy is inherent in the rise and fall of the tides and ocean waves. One of the simple schemes to utilise tidal energy is to construct a dam across the mouth of a bay and mount turbines in the structure. The incoming tide forming through the turbines generates power. As the tide shifts, the blades may be reversed so that outflow of water continues to generate power.
Tidal power plants are in operation in Russia, France and Nova Scotia. There are 15 locations in the world to generate tidal power. In India, the probable sites for exploration of tidal energy are Gulf of Kutchch and Sunderbans and also near Andaman, Nicobar and Lakshadeep islands.
The Bay of fundy in North America has the large tidal power plant. Tidal power plants are accompanied by the adverse environmental effects because of the dams which may trap sediments, impede the migration of marine organisms, change water circulation and cause mixing of fresh water with salt water.
Fossil Fuel Based Energy:
Coal, crude oil and natural gas are called fossil fuels because all of them some-time were living matter.
Coal (Black Diamond):
Coal is substantially more abundant than oil or gas, the total coal reserve being 7.4 x1012 metric tonne, which is equivalent to 4.7×10 22 calories. This is 1000 times more than the total world energy consumption from all other fuels.
Coal, derived from partial degradation of plants, is mainly of three types namely lignite (70% C), bituminous (80% C) and anthracite (90% C). Anthracite, a hard, clean burning, low sulphur content coal is most desirable of all the coals. Typical approximate composition of coal is
Environmental problems associated with the use of coal:
1. On combustion, coal emits SO2 which forms sulphuric acid in air and causes acid rain.
2. CO2 is also produced which is a green-house gas responsible for causing global warming.
3. Coal is less convenient to use than petroleum or natural gas.
Measures adopted to use coal:
1. Minimise impact of coal mining.
2. Remove ash and sulphur from coal prior to combustion.
3. Remove ash and SO2 from stack gas after combustion.
4. Convert coal to liquid and gaseous fuel free of ash and sulphur.
Magneto hydrodynamic (MHD) power combined with conventional steam generating units is a major breakthrough in the efficiency of coal utilization. MHD generators are produced by means of a plasma of ionized gas blasting at 2400°C through a very strong magnetic field of 50,000 gauss (Fig. 4).
The ionization of gas is carried by injecting a seed of Cs+ or K+ salts. In a coal fired MHD generator, the ultra-high temperature gas issuing through a supersonic nozzle consists of ash, NOX and SO2 which have a corrosive action on the materials used. This hot gas is then used for generating steam for a conventional steam power plant.
Coal Conversion:
Coal can be transformed into liquid, gaseous or low sulphur solid fuels, which are less polluting than coal. In South Africa, a plant converts about 10,000 tonne of coal per day to synthetic petroleum. Coking coal is first heated to make it non-coking which then undergoes carbonization and water fluidized bed gasification steps. Steam reacts with coal to produce water gas (CO + H2).
The gaseous products from bituminous coal in a synthane gasifier are 18.2% CO2, 10.5% CO, 37% H2O, 17% H2, 16% CH4 and 0.3% H2S. Calorific value of the gas is 405 Btu/ft3 as compared to 1000 Btu/ft3 for CH4. Tar, oil, water, ash and S are also produced which must be removed by water scrubbing, H2S and COS are eliminated by alkaline scrubber. Finally, high Btu gas is produced by methanation over a Ni catalyst.
High Grade Ash Free Coal:
High grade ash free coal is produced as Solvent Refined Coal (SRC) by suspending pulverized coal in a solvent by treating with 2% of its weight of H2 at 1000 psi and 450°C. The product is a semi solid with m.p. 170°C having a calorific value of 16000 Btu/lb comparable to best anthracite coal.
Methanol:
Methanol, CH3OH is a convenient liquid fuel which can be produced from coal. On a commercial scale, it is produced by the reaction of CO and H2 obtained from coal, oxygen and steam in presence of Cu based catalyst.
15% Methanol makes an excellent additive to gasoline. It has a high octane number of 106, improves fuel economy and cuts down the emission of all automotive pollutants.
Petroleum and Natural Gas:
The consumption of petroleum and natural gas is maximum in USA. The world reserve of petroleum is about 800 billion barrels, which is likely to be exhausted in the next century.
Natural gas is a better fuel than coal and petroleum since on burning, it produces less C02. For production of one unit of energy, mineral oil, coal and wood, on burning produces 35%, 75% and 85% more CO2 than natural gas.
Biomass Energy:
Biomass is the organic matter produced by plants or animals which include crop residues, wood, dung, manure, sewage and agricultural wastes etc. Biomass energy refers to the direct burning of biomass and converting it into fuel.
It is of the following types:
1. Energy Plantation (Indirect use of Solar Energy):
Solar energy is trapped by green plants through photosynthesis and converted into biomass energy Fast growing trees like cotton, wood and Leucaena, non-woody herbaceous grasses, crop plants like sugarcane, sweet sorghum, sugar beet, aquatic weeds like water hyacinth, sea weeds, carbohydrate rich potato, etc. are some of the energy plantations. They may produce energy either by burning directly or by getting converted into inflammable gas or may be converted into fuels by fermentation.
2. Petro Crops:
Certain latex containing plants like Euphorbia lathyris (Grophar or gasoline tree) and oil palms contain about 5% oil and polymeric hydrocarbons. Highest biocrude potential (10%) lies in resinous species of Compositae family. Calotropis procera (Akra) provides energy on burning comparable to that of crude oil, fuel oil and gasoline.
a. Pittosporum resiniferum (petroleum nut) and Botryococcus braunii yield an oily distillate on hydrocracking, 67% of which is diesel oil.
b. Bio-diesel, an ester based oxygenated fuel is made from vegetable oil. It has low emissions and can be blended in any ratio with petroleum diesel fuel.
c. The oily material may be burned in diesel engines directly or may be refined to form gasoline.
3. Agricultural Waste Biomass:
a. Crop residues, bagasse (sugar cane residues), coconut shells, cotton stalks, paddy husk etc. produce energy on burning.
b. At Jalkheri, Punjab, a rice straw fired thermal plant is the only plant of its kind in the world, which generates 62 million units of electricity per year.
c. Paddy husk can be converted into smokeless solid fuel briquettes suitable for use in domestic cooking, kilns and boilers.
d. Rice bran is used as a source of oil which is converted into methyl ester for use as fuel. Saw dust, by partial combustion, is converted into low calorific value producer gas for thermal power generation.
e. Plant residues along with 500 kg garbage can produce 5 KWH of electricity per hour. The garbage undergoes anaerobic digestion to produce biogas which in turn is used to produce electricity.
f. Jatropha Curcas Linn belonging to family Euphorbiaceae can be used as a substitute of diesel. Neem oil, mahua oil and soya oil can be good blends with diesel.
Environmental Implications:
The burning of coal, oil, wood, dung cakes and petroleum products create well debated environmental hazards. The fly ash requires large ash ponds and smoke causes eye and lung diseases.
Biogas (Green Energy):
Biogas is a mixture of CH4, CO2, H2, N2 and H2S. At 40% methane content, the calorific value of biogas is 3200 kcal/m3 while at 50%, it is 4500 kcal/m3. Biogas is produced by anaerobic degradation of animal wastes (sometimes plant wastes) in presence of water.
There is a vast reserve of biogas in Indian villages. Biogas plants are mainly of floating gas holder type, Fixed dome type and KVIC type. It is estimated that 1000 million tonne of animal dung per year is available from 250 million cattle population.
On an average, 10 kg of wet dung is available per animal per day, which at 66% collection efficiency, can yield 22500 million cubic metre of biogas through biogas plants. This can replace kerosene oil whereby 14000 million litre of kerosene per year can be saved in villages.
India’s Highest Biogas Plant Commissioned at Leh-Ladakh:
Spearheading the effort to tap biogas energy in remote areas, the Defence Institute of High Altitude Research (DIHAR), a constituent laboratory of the Defence Research and Development Organisation (DRDO), has commissioned India’s highest (world’s second highest) biogas plant at Leh-Ladakh at an altitude of 3500 m amsl in 2010. It has been set up in collaboration with BARC, Mumbai. The world’s highest biogas plant has been established by Nepal at Langtang valley at 3850 m amsl.
Process:
The plant is based on dual process employing partial aerobic digestion followed by anaerobic digestion. The organically rich biodegradable portion of solid waste (cattle dung, horse and poultry waste) is mixed with recycled water to form a slurry. The predigestion of slurry is accentuated by hot water and intermittent aeration.
This predigested slurry is further digested under anaerobic conditions for about 15 days followed by methanogenesis in the digester. The capacity of the biogas plant is 0.5 tonne per day and will generate 35 to 50 m3 of biogas per day during the processing of biodegradable waste. This can be fed to a gas alternator set of 25 kVA capacity to generate electricity or can be used for boiler purposes.
Advantages of using Biogas:
1. Besides being an important domestic energy source, biogas offers an environmentally clean technology.
2. There is direct supply of gas from the plant without any storage problem. 1.5 to 2.1 m3 of biogas with methane content of 60% is equivalent to 1 litre of diesel in terms of heat output.
3. Air-tight digestion of wastes prevent direct exposure to faecal pathogens and parasites.
4. Biogas slurries can produce 200 million tonne of organic manure per year which is rich in NPK and iron. It can be used in agricultural fields to improve soil fertility and crop productivity.
5. Biogas is not merely a fuel for producing green energy but it also reduces green-house gases and may qualify for green credits.
Gasohol:
Gasoline blended with upto 20% methanol or ethanol is known as gasohol. This can be used as a fuel in existing internal combustion engines (ICE). Methanol or ethanol can also be used as fuel (instead of gasoline) in suitably designed ICE. Methanol is produced by destructive distillation of wood.
Because of its photosynthetic origin, ethanol is a renewable resource. Ethanol is manufactured by fermentation of sugar resulting from the hydrolysis of cellulose in crop wastes. Brazil is the leading country in the manufacture of ethanol for fuel. This country possesses abundant source of fermentable biomass that is, Cassava or manioc.
Hydrogen Fuel Energy:
Hydrogen holds the potential to provide clean, safe, affordable and secure energy from abundant renewable and traditional energy resources.
Attributes of Hydrogen:
H2 is considered as an alternate perfect fuel for two reasons. It is renewable and is the most abundant element (93%) in the universe. Its major reserve (water) is inexhaustible. However, H2 in nature exists in combination with other elements. For hydrogen to be useful as a fuel, it must exist as free hydrogen.
Production of H2:
Hydrogen can be produced from a variety of feed-stocks including oil, coal, natural gas, biomass and water.
1. From Feed-stocks:
H2 can be produced from coal, residual oil and mainly from natural gas where the efficiency is high and production cost is low.
2. From Biomass:
High temperature is required to convert biomass into H2 and CO2.
3. From Water by Electrolysis:
In H2O, hydrogen is 11.2 percent by weight. H2 is generated directly by electrolysis of water. Electricity is passed between electrodes immersed in a conducting aqueous solution. H2 is generated at cathode and O2 at anode. The energy stored in H2 can then be reconverted into electricity using the reverse of the electrolytic cell called the fuel cell.
Extraction of Energy from Hydrogen:
1. By Fuel Cell:
A fuel cell is an electrochemical engine that converts the chemical energy contained in hydrogen molecule into electrical energy. H2 is oxidised at the cathode where electrons are produced and passed through the circuit to the anode where O2 is reduced (Fig. 5). The overall efficiency is low due to various energy barriers connected with the electrode processes.
The proton-exchange membrane is the most promising fuel cell for automotive use such as light trucks. PEM fuel cell has a low operating temperature and its power density is high for light duty vehicles. The fuel cell coupled with electric drive motors are able to move 18 metric tonne buses efficiently and reliably.
2. Energy contained in hydrogen can also be extracted by simple combustion in internal combustion engines or turbine engines.
Storage of H2:
Liquid hydrogen storage is preferred to compressed gas storage since more H2 can be stored in liquid form. Refrigerated and pressurized tanks, based on carbon adsorption system, can store massive amounts of H2.
Safety:
H2 is highly inflammable and explosive in nature. Safe handling is required for using H2 as a fuel. H2 detectors can be used to detect explosive concentrations of hydrogen.
Energy Security:
1. Using hydrogen in conjunction with fuel cells empowers countries to invest in a sustainable energy infrastructure.
2. Hydrogen fuel enables individual homes and communities to manage their own energy supply. This reduces dependence on large scale power stations and national grids etc.
3. Hydrogen also supplies more energy per unit volume than diesel or kerosene. Because of its low density, liquid H2 weighs less than petroleum based fuels. The density of gaseous hydrogen is 0.0899 g/L (air is 1.4 times more dense). Liquid hydrogen boils at -252.77°C and it has a density 70.99 g/L. With these properties, H2 has the highest energy-to-weight ratio of all fuels. 1 kg of H2 has the same amount of energy as 2.1 kg of natural gas or 2.8 kg of gasoline.
Environmental Considerations:
1. Hydrogen is the cleanest fuel available.
2. Hydrogen powered fuel cell vehicles, ICE’s, air craft gas turbine engines have zero CO2 and NOX emissions.
3. H2, a carbon free perfect fuel, can reduce green-house gas emissions.
4. To realise environmental benefits of H2, we must consider the full fuel cycle (also called well-to-wheels) from energy source to hydrogen production to end-use.
Hydrogen Act of 2005 authorises $ 3.2 billion for hydrogen and fuel cell activities intended to enable the commercial introduction of hydrogen fuel cell vehicles by 2020. Thus hydrogen, as energy source holds much promise in future.
Classification # 2. Secondary Energy Resources:
These sources do not occur in nature but are derived from primary energy resources. Examples are petrol or gasoline, electrical energy from coal burning, H2 obtained by electrolysis of H2O.
World scenario of energy:
Conventional sources of energy account for 90% of the world’s production of commercial energy. Other sources account for: Oil 39.5%, coal 30%, natural gas 19.6%, hydro-electric energy 6.7% and nuclear energy 3.9%.