Renewable Sources of Energy or Non-conventional Sources of Energy

 

Renewable Sources of Energy or Non-conventional Sources of Energy

 Renewable energy sources are also called non-conventional energy sources that are continuously replenished by natural processes. For example, solar energy, wind energy, bio-energy, hydropower etc., are some of the examples of renewable energy sources.

 A renewable energy system converts the energy found in sunlight, wind, falling-water, sea waves, geothermal heat, or biomass into a form, we can use such as heat or electricity. Most of the rmewable energy comes either directly or indirectly from sun and wind and can never be exhausted, and therefore they are called renewable. They are available in unlimited amount in nature and develop in a relatively short period of time.

However, most of the world's energy sources are derived from conventional sources-fossilfuels such as coal, oil and natural gases. These fuels are often termed non-renewable energy sources.Although, the available quantity of these fuels are extremely large, they are nevertheless finites andso will in principle 'run out at some time in the future.

Renewable energy sources are essentially flows of energy, whereas the fossil and nuclear fuels are, in essence, stocks of energy

Solar Energy

Solar energy is the most readily available and free source of energy since prehistoric times. It is mated that solar energy equivalent to over 15,000 times the world's annual commercial energy spion reaches the earth every year

I receive solar energy in the region of 5 to 7 kwh/m² for 300 to 330 days in a year. This is sufficient to set up 20MW solar power plant per square kilometre land area.Solar energy can be utilized through two different routes, as solar thermal route and solar electric (solar photovoltaic) routes. Solar thermal route uses the sun's heat to produce hot water or air for cooking food, drying materials etc. Solar photovoltaic uses sun's heat to produce electricity for lighting homes and buildings, running motors, pumps, electric appliances etc.

 

Solar Water Heaters

 

Most of the solar water heating systems have two main parts: a solar collector and a storage tank. The most common collector is called a flat-plate collector (Fig.1). It consists of a thin, flat, rectangular box with a transparent cover that faces the sun, mounted on the roof of building or home. Small tubes run through the box and carry the fluid - either water or other fluid, such as an antifreeze solution - to be heated. The tubes are attached to an absorber plate, which is painted with special coatings to absorb the heat. The heat builds up in the collector is then passed through the fluid, which is passing through the tubes.

Fig1 : Solar Flat Plate Collector

 

The last water is collected in an insulated storage tank. It is similar to water heater, but larger in size. In case of systems that use fluids, heat is passed from hot fluid to the water stored in the tank through a coil of tubes.

Solar water heating systems can be either active or passive systems. The active systems which are most common, rely on pumps to move the liquid between the collector and the storage tank. The passive systems rely on gravity and the tendency for water to naturally circulate as it is heated. A few industrial application of solar water heaters are listed below:

·       Hotels: Bathing, kitchen, washing, laundry applications

·       Dairies: Ghee (clarified butter) production, cleaning and sterilizing, pasteurization 

·       Textiles: Bleaching, boiling, printing, dyeing, curing, ageing and finishing 

·    Breweries & Distilleries: Bottle washing, wort preparation, boiler feed heating

·       Chemical/Bulk drugs units: Fermentation of mixes, boiler feed applications

·       Electroplating/galvanizing units Heating of plating baths, cleaning, decreasing application

·    Pulp and paper industries: Boiler feed applications, soaking of pulp.

Solar Cooker

Solar cooker is a device in which solar energy is used for cooking, and thus saving fossil fuels, fuel wood and electrical energy to a large extent. However, it can only be considered as a supplementary

cooking fuel and it cannot replace the fossil fuel totally. It is a simple cooking unit, ideal for domestic cooking during most of the year except during the monsoon season, cloudy days and winter months .

Box Type Solar Cookers: The box type solar cookers with a single reflecting mirror are the most popular in India. These cookers have proved immensely popular in rural areas where women spend considerable time for collecting firewood. A family size solar cooker is sufficient for 4 to 5 members and saves about 3 to 4 cylinders of LPG every year. The life of this cooker is upto 15 years. It is cheap and easily available in the market it costs around Rs.1000.

Solar Electricity Generation

 Solar Photovoltaic (PV): Photovoltaic is the technical term for solar electricity Photo mcare "light" and voltaic means "electric". PV cells are usually made of silicos, as element that naturally releases electrons when exposed to light. Amount of electrons released from silicon cells directly related to the intensity of light incident on it. The silicon cells is covered with a grid of metal that directs the electrons to flow in a path to create an electric current. This current is guided into a wire that is connected to a battery or DC appliance. Typically, one cell produces about 3,5 of govest Individual cells are connected together to form a solar panel or module, capable of producing 3 to 110 Watts power. Panels can be connected together in series and parallel to make a solar array (Fig 2), which can produce any amount of Wattage as space will allow. Modules are usually designed to supply electricity at 12 Volts. PV modules are rated by their peak Watt output at solar noon on a clear day.

fig 2. Solar Photovoltaic Array

Applications of PV Systems: The PV systems are generally used for the chimerical buildings outdoor (street) lighting rural and village lighting etc. Solar electric power systems can offer independence from the utility and offer protection during extended power failures Solar PV syste are very economical especially in the hilly and far flung areas where conventional grid power supply will be expensive to reach.

PV tracking system is an alternative to the fixed, stationary PV panels PV tracking systems are mounted and provided with tracking mechanisms to follow the sus as it moves through the sky. These tracking systems run entirely on their own power and can increase output by 40% Back-up systems are necessary since PV systems only generate electricity when the sun isshining. The two most common methods of backing up solar electric systems are connecting the system to the utility grid or storing excess electricity in batteries for use at night or on cloudy days.

Performance: The performance of a solar cell is measured in terms of its efficiency at converting sunlight into electricity. Only sunlight of certain energy will work efficiently to create electricity, and1.58Environmental Engineering & Disaster Management) much of it is reflected or absorbed by the material that make up the cell. Because of this, a typical commercial solar cell has an efficiency of 15% only about one-sixth of the sunlight striking the cell generates electricity. Low efficiencies mean that larger arrays are needed and higher investment costs. The first solar cells, built in the 1950s, had efficiencies of less than 4%.

 Solar Water Pumps: In solar water pumping system, the pump is driven by motor run by solar electricity instead of conventional electricity drawn from utility grid. A SPV water pumping system consists of a photovoltaic array mounted on a stand and a motor-pump set compatible with the photovoltaic array. It converts the solar energy into electricity, which is used for running the motorpump set. The pumping system draws water from the open well, bore well, stream, pond, canal etc.

 Wind Energy

 Basically the conversion of kinetic energy of the wind into electrical energy. When solar radiation enters the earth's atmosphere, different regions of the atmosphere are heated to different degrees because of earth curvature. This heating is higher at the equator and lowest at the poles. Since air tends to flow from warmer to cooler regions, this causes what we call winds, and it is these airflows that are harnessed in windmills and wind turbines to produce power.

Wind power is not a new development as this power, in the form of traditional windmills for grinding corn, pumping water, sailing ships - have been used for centuries. Now wind power is harnessed to generate electricity in a larger scale with better technology.

 

Fig. 3 : Wind Turbine Configuration

 

Wind Energy Technology: The basic example of energy conversion device is the wind turbine. Although various designs and configurations exist, these turbines are generally grouped intotwo types:

(1)    Vertical-axis wind turbines, in which the axis of rotation is vertical with respect to the ground (and roughly perpendicular to the wind stream).

(2)    Horizontal-axis turbines, in which the axis of rotation is horizontal with respect to theground (and roughly parallel to the wind stream.)

 Illustrates the two types of turbines and typical subsystems for an electricity generation application. The subsystems include a blade or rotor, which converts the energy to the wind to rotational shaft energy, a drive train, usually including a gearbox and a generator, a lower that supports the rotor and drive train, and other equipment, including controls, electrical cables, ground support equipment and interconnection equipment.

Wind Energy in India

 India has been considered as one of the most promising countries for wind power development,with an estimated potential of 20,000 MW. Total installed capacity of wind electric generators in theworld as on Sept. 2001 is 23270 MW, and India-1426 MW top the list of countries. Thus, India ranksfifth in the world in wind power generation.

There are 39 wind potential stations in Tamil Nadu, 36 in Gujarat, 30 in Andhra Pradesh, 27 in Maharshtra, 26 in Karnataka, 16 in Kerala, 8 in Lakshadweep, 8 in Rajasthan, 7 in Madhya Pradesh, 7 in Orissa, 2 in West Bengal, 1 in Andaman Nicobar and 1 in Uttar Pradesh. Out of 208 suitable stations 7 stations have shown wind power density more than 500 Watts/m²

Applications of Wind Energy

·       Utility interconnected wind turbines generate power which is synchronous with the grid and are used to reduce utility bills by displacing the utility power used in the household and by selling the excess power back to the electric company. Wind turbines for remote homes (off the grid) generate DC current for battery charging.

·       Wind turbines for remote water pumping generate 3 phase AC current suitable for driving an electrical submersible pump directly. Wind turbines suitable for residential or village scale wind power range from 500 Watts to 50 kilowatts.

Merits of Wind Energy

(i)               Non-polluting and environment friendly source of energy

(ii)            Renewable and sustainable source of energy, available free of cost.

(iii)          Power generation is cheaper as there is no shortage of input cost and recursion expenses are almost nil,

Limitations of Wind Energy

(i) It has low energy density.

(ii) It is generally favorable in geographic locations which are away from cities.

(iii) It is variables unsteady, irregular, intermittent, erotic and sometimes dangerous.

(iv) The appearance of windmills on the landscape and their continual whirling and whistlingcan be irritating.

Bio Energy

The main and important source of bio energy is biomass. Biomass is a renewable energy resource derived from the carbonaceous waste of various human and natural activities. It is derived from numerous sources, including the by-products from the wood industry, agricultural crops, raw material from the forests, household wastes etc.

Biomass does not add carbon dioxide to the atmosphere as it absorbs the same amount of carbon in growing as it releases when consumed as a fuel. Its advantage is that it can be used to generate electricity with the same equipment that is now being used for burning fossil fuels. Biomass is an important source of energy and the most important fuel worldwide after coal, oil and natural gas. Bio-energy, in the form of biogas, which is derived from biomass, is expected to become one of the key energy resources for global sustainable development. Biomass offers higher energy efficiency through form of biogas than by direct burning (See chart).

 

Applications of Bio Energy

Bio energy is being used for cooking, mechanical applications, pumping, power generation etc.

Some of the devices used are Biogas plant/ gasifier/burner, gasifier engine pump sets, Stirling engine pump sets, producer gas/ biogas based engine generator sets etc.

Biogas Plants: Biogas is a clean and efficient fuel, generated from cow-dung, human waste or any kind of biological materials derived through anaerobic fermentation process. The biogas consists of 60% methane with rest mainly carbon dioxide. Biogas is a safe fuel for cooking and lighting. By product is usable as high-grade manure.

Atypical biogas plant has the following components:

1.A digester: In which the slurry (dung mixed with water) is fermented.

2. Inlet tank: For mixing the feed and letting it into the digester.

3.Gas holder: It is a dome shape collector in which the generated gas is collected. 4. Outlet tank: To remove spent slurry.

5.Distribution pipelines: To transport the gas into the kitchen.

6. Manure pit: To store the spent slurry.

 Biomass fuels account for about one-third of the total fuel used in the country. It is the most important fuel used in over 90% of the rural households and about 15% of the urban households. Using only local resources, namely cattle waste and other organic wastes, energy and manure are derived. Thus the biogas plants are the cheap sources of energy in rural areas. The types of biogas plant designs popular are: floating drum type, fixed dome-type and bag-type portable digester.

 

Biomass Briquetting: Biomass Briquetting is the process in which the loose agro-waste densifying into a solidified biomass of high density, which can be conveniently used as a fuel. Briquette is also termed as "Bio-coal". It is pollution free and eco-friendly. Some of the agricultural and forestry residues can be briquetted after suitable pre-treatment. A list of commonly used biomass materials that can be briquetted are given below:

ComCob, JuteStick, Sawdust, PineNeedle, Bagasse, CoffeeSpent, Tamarind, CoffeeHuskAlmondShell, Groundnutshells, CoirPith, BagascePith, Barleystraw, Tobaccodust, RiceHusk, DeoiledBran.

 

Advantages of Biomass Briquetting

Some of advantages of biomass briquetting are high calorific value with low ash content, absence of polluting gases like sulphur, phosphorus fumes and fly ash- which eliminate the need for pollution control equipment, complete combustion, ease of handling, transportation and storage - because of uniform size and convenient lengths.

 

Applications of Biomass Briquetting

Biomass briquettes can replace almost all conventional fuels like coal, firewood and lignite inalmost all general applications like heating, steam generation etc. It can be used directly as fuel tead of coal in the traditional chulhas and furnaces or in the gasifier. Gasifier converts solid fuel into a more convenient to use gaseous form of fuel called producer gas.

 

Biomass Gasifiers

Biomass gasifiers are the devices which can convert the solid biomass such as wood waste, agricultural residues etc. into a combustible gas mixture which normally called as producer gas. The conversion efficiency of the gasification process is in the range of 60%-70%. The producer gas consists of mainly carbon-monoxide, hydrogen, nitrogen gas and methane, and has a lower calorific value (1000-1200 kcal/Nm'),

Gasification of biomass and using it in place of conventional direct burning devices will result savings of atleast 50% in fuel consumption. The gas has been found suitable for combustion in the internal combustion engines for the production of power.

 

Applications

Water Pumping and Electricity Generation: Using biomass gas, it is possible to operate a diesel engine on dual fuel mode-part diesel and part biomass gas. Diesel substitution of the order of 75 to 80% can be obtained at nominal loads. The mechanical energy thus derived can be used either for energizing a water pump set for irrigational purpose or for coupling with an alternator for electricalpower generation-3.5 KW-10 MW

Heat generation: A few of the devices, to which gasifier could be retrofitted, are dryers-for drying tea, flower, spices, kilns for baking tiles or potteries, furnaces for melting non-ferrous metals,boilers for process steam, etc.

Direct combustion of biomass has been recognized as an importantroute for generation of power by utilization of vast amounts of agricultural residues, agro-industrial residues and forest wastes. Gasifiers can be used for power generation and available upto a capacity 500 kW. The Government of India through MNES and IREDA is implementing power-generating system based on biomass combustion as well as biomass gasification.

High Efficiency Wood Burning Stoves: These stoves save more than 50% fuel woodconsumption. They reduce drudgery of women saving time in cooking and fuel collection andconsequent health hazards. They also help in saving firewood leading to conservation of forestsThey also create employment opportunities for people in the rural areas.

Bio fuels: Unlike other renewable energy sources, biomass can be converted directly into liquid fuels biofuels-for our transportation needs (cars, trucks, buses, aeroplanes, and trains). The two most common types of biofuels are ethanol and biodiesel.

Ethanol is an alcohol, similar to that used in beer and wine. It is made by fermenting any biomass high in carbohydrates (starches, sugars, or cellulases) through a process similar to brewing beer. Ethanol is mostly used as a fuel additive to cut down a vehicle's carbon monoxide and other smog causing emissions. Flexible-fuel vehicles, which run on mixtures of gasoline and up to 85% ethanol, are now available:

Biodiesel, produced by plants such as rapeseed (canola), sunflowers and soybeans, can be extracted and refined into fuel, which can be burned in diesel engines and buses. Biodiesel can also made by combining alcohol with vegetable oil, or recycled cooking greases. It can be used as an additive to reduce vehicle emissions (typically 20%) or in its pure form as a renewable alternative fuel for diesel engines.

Biopower: Biopower, or biomass power, is the use of biomass to generate electricity. There mare six major types of biopower systems: direct-fired, coffering, gasification, anaerobic digestion,pyrolysis, and small-modular.

Basics of Environment

Most of the biopower plants in the world use direct-fired systems. They burn bioenergy feedstocks directly in boiler to produce steam. This steam drives the turbo-generator. In some industries, the steam is also used in manufacturing processes or to heat buildings. These are known as combined heat and power facilities. For example, wood waste is often used to produce both electricity and steam at paper mills. Many coal-fired power plants use coffering systems to significantly reduce emissions, especially sulphur dioxide emissions. Coffering involves using bio energy feedstock as a supplementary fuelsource in high efficiency boilers.

Gasification systems use high temperatures and an oxygen-starved environment to convert biomass into a gas (a mixture of hydrogen, carbon monoxide, and methane). The gas fuels a gas turbine, which runs on an electric generator for producing power.

The decay of biomass produces methane gas, which can be used as an energy source. Methane can be produced from biomass through a process called anaerobic digestion. Anaerobic digestion involves using bacteria to decompose organic matter in the absence of oxygen. In landfills-scientific waste disposal site - wells can be drilled to release the methane from the decaying organic matter. The pipes from each well carry the gas to a central point where it is filtered and cleaned before burning. Methane can be used as an energy source in many ways. Most facilities burn it in a boiler to produce steam for electricity generation or for industrial processes. Two new ways include the use of microturbines and fuel cells. Microturbines have outputs of 25 to 500 kilowatts. About the size of a refrigerator, they can be used where there are space limitations for power production. Methane can also be used as the "fuel" in a fuel cell. Fuel cells work much like batteries, but never need recharging, producing electricity as long as there is fuel.

In addition to gas, liquid fuels can be produced from biomass through a process called pyrolysis. Pyrolysis occurs when biomass is heated in the absence of oxygen. The biomass then turns into liquid called pyrolysis oil, which can be burned like petroleum to generate electricity. A biopower system that uses pyrolysis oil is being commercialized.

Several biopower technologies can be used in small, modular systems. A small, modular system generates electricity at a capacity of 5 megawatts or less. This system is designed for use at the small town level or even at the consumer level. For example, some farmers use the waste from their livestock to provide their farms with electricity. Not only do these systems provide renewable energy, they also help farmers meet environmental regulations.

 

Biomass Cogeneration: Cogeneration improves viability and profitability of sugar industries. Indian sugar mills are rapidly turning to bagasse, the leftover of cane after it is crushed and its juice extracted, to generate electricity. This is mainly being done to clean up the environment, cut down power costs and earn additional revenue. According to current estimates, about 3500 MW of power be generated from bagasse in the existing 430 sugar mills in the country. Around 270 MW of power has already been commissioned and more is under construction.

 

Hydro Energy

 

The potential energy of falling water, captured and converted to mechanical energy by waterwheels, powered the start of the industrial revolution. Wherever sufficient head, or change in elevation, could be found, rivers and streams were dammed and mills were built. Water under pressure flows through a turbine causing it to spin. The turbine is connected to a generator, which produces electricity. In order to produce enough electricity, a hydroelectric system requires a location with the following features:

Change in elevation or head: 20 feet @ 100 gal/min=200 Watts. 100 feet head @ 20 gal/min gives the same output.

In India the potential of small hydro power is estimated about 10,000 MW. A total of 183.45 MW small Hydro project have been installed in India by the end of March 1999. Small Hydro Power projects of 3 MW capacity have been also installed individually and 148 MW project is under construction.

Small Hydro Power: Small Hydro Power is a reliable, mature and proven technology. It is non-polluting, and does not involve setting up of large dams or problems of deforestation, submergence and rehabilitation. India has an estimated potential of 10,000 MW.

Hilly regions of India, particularly the Himalayan belts, are endowed with rich hydel resources with tremendous potential. The MNES has launched a promotional scheme for portable micro hydel sets for these areas. These sets are small, compact and light weight. They have almost zero maintenance cost and can provide electricity/power to small cluster of villages. They are ideal substitutes for diesel sets run in those areas at high generation cost.

Micro (upto 100kW) mini hydro (101-1000 kW) schemes can provide power for farms, hotels,schools and rural communities, and help create local industry.

 

Geothermal Energy

 

It is heat of the earth and is defined as naturally occurring thermal energy found within rock formations and the fluids held within those formations. Geothermal energy can be exploited only in those particular areas (hot spots) where geological formation lead to high temperature gradient. Such high temperature regions found in volcanic eruptions, geysers and bubbling mud holes. Geothermal energy taken from natural steam, hot water or dry rocks may be used for electric power generation. space heating, ground water heat pumps, recreational or health spas, agricultural growth enhancement, agricultural drying and industrial drying.

 

Merits of Geothermal Energy

 

(i)              Most versatile and least polluting renewable energy resource.

(ii)            It is relatively inexpensive.

(iii)          Power generation level is higher than solar and wind.

(iv)           Geothermal power plants could be brought online more quickly than most other energy sources in case of and extended national emergency.

 

Limitations of Geothermal Energy

 

(i)              Geothermal hot spots are sparsely distributed and usually some distance away from the area needing energy.

(ii)            The overall efficiency for power production is quite low (15% compared to 35-40% of fossil fuel).

(iii)          Air pollution results in case of release of gases like HS, NH, CO, present in the steam and hot water carrying out of the geothermal fields.

(iv)           Noise pollution results from the drilling operations in geothermal fields.

 

Tidal and Ocean Energy

 

Tidal Energy: Tidal electricity generation involves the construction of a barrage across an estuary to block the incoming and outgoing tide. The head of water is then used to drive turbines to generate electricity from the elevated water in the basin as in hydroelectric dams.

Barrages (dams) can be designed to generate electricity on the ebb side, or flood side, or both.Tidal range may vary over a wide range (4.5-12.4 m) from site to site. A tidal range of at least 7 m is required for economical operation and for sufficient head of water for the turbines.

 

Ocean Energy: Oceans cover more than 70% of Earth's surface, making them the world's largest solar collectors. Ocean energy draws on the energy of ocean waves, tides, or on the thermalenergy (heat) stored in the ocean. The sun warms the surface water a lot more than the deep oceanwater, and this temperature difference stores thermal energy.

The ocean contains two types of energy: thermal energy from the sun's heat and mechanical energy from the tides and waves.

Ocean thermal energy is used for many applications, including electricity generation. There are three types of electricity conversion systems: closed-cycle, open-cycle, and hybrid. Closed cycle systems use the ocean's warm surface water to vaporize a working fluid, which has a low boiling point, such as ammonia. The vapor expands and turns a turbine. The turbine then activates a generator to produce electricity. Open-cycle systems actually boil the seawater by operating at low pressures. This produces steam that passes through a turbine/generator. The hybrid systems combine both closed-cycle and open-cycle systems.

Ocean mechanical energy is quite different from ocean thermal energy, Even though the sun affects all ocean activity, tides are driven primarily by the gravitational pull of the moon and waves Ocean mechanical energy is quite different from ocean thermal energy. Even though the sun are driven primarily by the winds. A barrage is typically used to convert tidal energy into electricity by forcing the water through turbines, activating a generator.

 

India has the World's largest programs for renewable energy. Several renewable energy technologies have been developed and employed in villages and cities of India. A Ministry of NonConventional Energy Sources (MNES) created in 1992 for all matters relating to Non-Conventional Renewable Energy. Government of India also created Renewable Energy Development Agency Limited (IREDA) to assist and Bureau of Energy Efficiency 15912. Application of Non-Conventional and Renewable Energy Sources provide financial assistance in the form of subsidy and low interest loan for renewable energy projects.

IREDA covers a wide spectrum of financing activities including those that are connected to energy conservation and energy efficiency. At present, IREDA's lending is mainly in the following areas:

 

·       Solar energy technologies, utilization of solar thermal and solar photovoltaic systems

 

·       Wind energy setting up grid connected wind farm projects

 

·       Small hydro setting up small, mini and micro hydel projects

 

·       Bio-energy technologies, biomass based co-generation projects, biomass gasification, energy from waste and briquetting projects

 

·       Hybrid systems

 

·       Energy efficiency and conservation