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1. Introduction


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The threat posed to sustainability by greenhouse gas emissions and deterioration of the natural resource base (e.g., oil crisis, etc.) has caused worldwide concern. Sustainable development of a region depends on the health of renewable energy resources like water, vegetation, livestock, etc. The integrated development of all these components is essential for environmentally sound development of the region. The natural resource base has deteriorated considerably due to the rapid growth in population coupled with unplanned developmental activities including industrialisation and urbanisation. This also has resulted in exponential increase in fossil fuel consumption. Post-oil crises shifted the focus towards renewable resources and energy conservation. This would imply a shift to renewable energy sources from non-renewable fossil fuels, which ensures sustainability.Renewable energy resources are those having a cycling time less than 100 yr. These are the resources that are renewed by nature again and again, and their supply is not affected by the rate of consumption. Examples for renewable energy are solar, wind, hydroenergy, tidal, geothermal, biomass and energy from organic wastes such as biogas, etc. The consumption of energy for lighting, cooking, heating and other appliances by households and the service industry has shown a significant change in recent years. To understand the kind of resource used by different sectors of usage, it is important to review the energy use trends.

Coal is the predominant energy source (58%) in India, followed by oil (27%), natural gas (7%), lignite (4%), hydropower (3%) and nuclear power (0.22%). Energy consumption patterns in the Indian residential sector vary widely not only among the rural and urban areas but also across various income classes in urban areas. Approximately 86.1% rural households in India use fuel wood and dung cakes for cooking, 3.5% rural households use LPG for cooking, 50.6% of rural households use kerosene and 48.4% use electricity as a primary source of lighting. The annual average fuel wood consumption is around 270–300 million tonne, kerosene consumption is about 10.5 million tonne out of which 60% is in rural areas [1]. India’s present energy scenario calls for the effective management of all available resources in order to attain national objectives. A well-balanced fuel mix, in which all energy resources are appropriately utilised, is essential for sustainable development. Renewable energy resources, which the country has in abundance, such as solar, wind, biomass, small hydroenergy, etc., can effectively meet energy demand and are environmentally benign. About 3700MW of power-generating capacity based on renewable energy sources has been installed in the country so far. This constitutes about 3.5% of the total installed capacity [2]. Table 1 gives renewable energy potential and its achievement in India.

Energy utilisation in Karnataka considering all types of energy sources and sectorwise consumption revealed that traditional fuels such as firewood (7.440 million tonnes of oil equivalent—43.62%), agro residues (1.510 million tonnes of oil equivalent—8.85%), biogas and cowdung (0.250 million tonnes of oil equivalent—1.47%) account for 53.20% of the total energy consumption in Karnataka. In rural areas, the dependence on bioenergy to meet the domestic requirements such as cooking and water-heating purposes are as high as 80–85% [3].

Efficient use of energy is achieved when unnecessary energy conversions are avoided, as each conversion has limited efficiency and, therefore, implies a certain loss of energy as wasted heat. For instance, if secondary energy can immediately serve as final energy oreven as useful energy, substantial losses can be avoided, e.g., wind machines in irrigation or hydroturbines powering a shaft. This principle favours decentralised energy generation and is particularly relevant with new and renewable energy sources. Very high efficiencies can be achieved with cogeneration, where heat as a by-product of power is not wasted, but put to good use on the spot.

1.1. Solar energy

The Sun is by far the largest object in the solar system. It contains more than 99.8% of the total mass of the solar system. The Sun’s energy output (3.86e33 erg/s or 386 billionMW) is produced by nuclear fusion reactions. Each second, about 700 million tonnes of hydrogen is converted to about 695 million tonnes of helium and 5 million tonnes ( ¼ 3.86e33 erg) of energy in the form of gamma rays. As it travels out towards the surface, the energy is continuously absorbed and re-emitted at lower and lower temperatures so that by the time it reaches the surface, it is primarily visible light. For the last 20% of the way to the surface, the energy is carried more by convection than by radiation [4]. From the Sun’s surface, the radiation is then transferred to the whole of the solar system. An annual energy of 1.51018kWh is obtained from the Sun to the earth. This is about 10,000 times larger than the current annual energy consumption of the world. The surface temperature of the Sun is around 5503.85 1C. Energy is continuously released from the Sun by a fusion reaction, which produces 3.941023kW of power. Radiation from the Sun takes about 91 3 min to cover 93 million miles to the earth. The earth receives only a small fraction of the total power emitted by the Sun, an amount of 1.731014kW or 340W/m2 averaged over the whole earth surface. Approximately 30% is reflected back to space and 20% is absorbed by clouds, dust and ‘‘greenhouse’’ gas such as water vapour, carbon dioxide and ozone. The annual global radiation in India varies from 1600 to 2200kWh/m2, which is comparable with radiation received in the tropical and sub-tropical regions. The equivalent energy potential is about 6000 millionGWh of energy per year [5].

The total quantity of short-wave radiant energy emitted by the Sun’s disc, as well as that scattered diffusively by the atmosphere and cloud, passing through a unit area in the horizontal in unit time is referred generally as global solar radiation. Monitoring the daily global solar radiation will help in assessing the total solar energy at any location considering diurnal and seasonal variations. The global solar radiation reaching the earth’s surface is made up of two components, direct and diffuse. The sum of the direct and diffuse components reaching a horizontal surface is global radiation. Direct radiation is the part which travels unimpeded through space and the atmosphere to the surface, and diffused radiation is the part scattered by atmospheric constituents such as molecules, aerosols and clouds. In simple terms, direct radiation causes shadows and diffuse radiation is responsible for skylight [6].

India receives solar energy equivalent to more than 5000 trillionkWh/yr, which is far more than its total annual energy consumption. The daily average global radiation is around 5kWh/m2 day with the sunshine hours ranging between 2300 and 3200 per year. Though the energy density is low and the availability is not continuous, it is now possible to harness this abundantly available energy very reliably for many purposes by converting it to usable heat or through direct generation of electricity. The total solar photovoltaic (PV) capacity in India is 2490kW. A large number of solar water heaters with the collector area of about 30,000m2 have been financed till December 2002. A total collector area of 6,80,000m2 has been installed in the country so far. During the year 2002–2003, over 5000 box solar cookers were sold till 31.12.2002 making a total of 5,30,000 cookers sold in the country till date [2].

1.1.1. Global solar radiation

Computation of daily sums of global solar radiation at sites where no radiation data are available can be done through various probable relationships among the parameters such as (i) sunshine and cloudiness and (ii) extra terrestrial radiation allowing for its depletion by absorption and scattering in the atmosphere [7]. There is a relationship between solar radiation received on earth’s surface and sunshine [8]. Relation of global solar radiation is obtained by considering the influence of climatological multivariates like mean temperature (Tm), relative humidity (RH), specific humidity (SH) as follows

:

SH is used instead of RH to take care of the relatively large variation in RH and is given by

where RH as mentioned above is the relative humidity, f 1; f 2; f 3 and f 4 are empirical constants, which vary with geographical location.

1.2. Wind energy

Wind energy is another form of solar energy. Sunlight falling on the ocean and continents causes air to warm and rise, which in turn generates surface winds. Wind is affected significantly by topography, weather conditions with seasonal, daily and hourly variation, and land use pattern. The total annual kinetic energy of air movement in the atmosphere is estimated to be around 3106TWh or about 0.2% of solar energy reaching the earth [9]. Windmills are used to harness wind energy. The power of wind blowing at 25.6 km/h is about 200W/m2 of the area swept by windmill. Approximately 35% of this power can be captured by the windmill and converted to electricity. Maximum amount of wind energy can be harnessed only in windy locations like on mountaintops and coasts. Such places are suitable for the economic generation of electricity by wind power.

According to initial estimates, India’s wind power potential was assessed at around 20,000MW. It has been re-assessed at 45,000MW, assuming 1% of land availability for wind power generation in potential areas. However, the present exploitable technical potential is limited to 13,000MW, on account of the limitation of grid capacity in the State Grids. Grid penetration of more than 20% could result in grid instability. The technical potential will go up with the augmentation of grid capacity in the potential States. Karnataka has a gross potential of 6620MW and technical potential of 1120MW [2].

1.2.1. Wind speed

The annual wind speed at a location is useful as an initial indicator of the value of wind energy potential. This can be extrapolated by the following equation:

where v is the wind speed at height h in m/s, vo the wind speed at anemometer height ho in m/s, h the height at which wind speed is measured in m, ho the anemometer height (usually 10 m) and k the height exponent (0.14–0.3).

The relationship between the annual mean wind speed and the potential value of the wind energy resource as considered in India [10] is listed in Table 2.

Energy pattern factor (EPF) and power densities are computed for sites with hourly wind data. With the knowledge of EPF and mean wind speed, mean power density is computed for the locations with only hourly and monthly data. The wind power density (P) or energy flux or the power per unit area normal to the wind is expressed in W/m2. Wind power density of a stream of air with density d moving with a velocity vm is given by

where vi is the hourly wind speed during the month, Nm the number of hourly wind speed values during the month and vm the monthly mean wind speed.

1.3. Hydroenergy

Hydropower owes its position as a renewable resource, as it depends ultimately on the natural evaporation of water by solar energy and precipitation. Hydropower, large or small, remains by far the most important of the ‘‘renewables’’ for electrical power production worldwide, providing 19% of the planet’s electricity. The exploitable hydroresources in the world are enormous and the total estimated hydroelectric resources in the world are 2,261,000MW [11]. The power available is proportional to the rate of discharge of the water and is given by

where 1000 is the mass of water in kg/m3, g the acceleration due to gravity in m/s2, Z the hydraulic efficiency of the turbine expressed as fraction, H the effective head of water in m and Q the flow rate passing through the turbine in m3/s.

Hydroelectric power plants are generally located near dams or river barrages. The capacity of hydropower plants can vary between a few kW and thousands of kW. Depending on this, hydropower plants are classified as micro (up to 100 kW), mini (up to 3MW) and small (up to 25MW) plants. The small hydropower plant (SHP), i.e., up to 25MW capacity, is set to attain commercial status in the country. SHP projects are becoming economically viable with appropriate systems for evacuation/utilisation of power from the project being increasingly put in place. In India, over 4215 SHP sites have been identified with a total capacity of 10,279MW. India has an estimated SHP potential of about 15,000MW; 453 SHP projects with an aggregate installed capacity of 1,463MW have been installed. Besides, 199 SHP projects with an installed capacity of 538MW are being commissioned. A database has been created for potential sites suitable for SHP projects [2].

The Karnataka State government has so far accorded permission to private developers to establish small hydroprojects in more than 79 locations amounting to 465MW. Private developers have commissioned eight projects with an installed capacity of 49MW. Over the next 2 yr, 20 projects with a capacity of 150MW are expected to be commissioned. More than 450 million units of electrical energy have been generated from the eight small hydroprojects commissioned in the State [12].

1.4. Bioenergy

Biomass refers to the organic matter derived from biological organisms (plants, animals, algae). They are basically classified into two categories:

Biomass energy is a result of solar energy converted to biomass energy by green plants. Only green plants are capable of photosynthesis. As per an estimate, photosynthesis produces 220 billion dry tonnes of biomass per year globally, with 1% conversion efficiency [11].

The total bioenergy potential in India is about 19,500MW, including 3500MW of exportable surplus power from bagasse-based cogeneration in sugar mills and 16,000MW of grid quality power from other biomass resources. The total installed capacity in the country, as of December 31, 2002, is 468MW and projects of capacity 530MW are in various stages of implementation. Biomass gasifier of total capacity 55.105MW has so far been installed, mainly for stand-alone applications [2].

Quality of life in rural areas can be improved through the efficient use of locally available bioenergy sources by recovering the energy from cattle dung, human waste and non-woody organic wastes without losing their manurial value through biogas plants. Against an estimated potential of 12 million biogas plants, about 3.44 million family type plants have been set up so far, representing coverage of over 28% of the potential. In addition, about 4000 night soil-based and institutional biogas plants have been set up. Monitoring of these plants by the regional offices of the Ministry of Non-Conventional Energy Sources (MNES) shows an overall functionality of 86%. These plants have helped to save 44 lakh tonnes of fuelwood, produced 450 lakh tonnes of manure per year. An estimated 4.5 million people per day of employment has also been generated in the rural areas. Research and development efforts are being taken up to develop new designs and improve the efficiency of biogas plants in different geographical and climatic conditions [2].


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