Renewable Energy Technology 3(2+1)

Lesson 1. Introduction of renewable energy technologies

Estimates of technical potential for renewable energy technologies

Source/System	Approximate potential
Biogas plants (no.s)	12 million
Improved cook stoves (no.s)	120 million
Biomass energy	17000 MW
Solar energy	20 MW/km2
Wind energy	45000 MW
Small hydropower	15000 MW
Ocean energy	50000 MW

Source : MNRE

The applications of various renewable energy technologies are discussed below.

Solar Energy

Our country is blessed with abundant supply of solar radiation.  By adopting suitable gadgets solar energy can be used not only in agricultural sector but also for domestic and industrial applications. 

Solar dryers, solar water heaters, solar cookers etc are some of the solar based thermal appliances.  Solar water heating systems have two major applications: domestic and industrial.  In the industrial sector, solar thermal energy is utilized for preheating boiler feed water and also for supplying direct process heat.  These techniques are helpful in agricultural related industries like, food processing industries, agro based industries etc.  According to an estimate, the potential for the deployment of solar water heaters is around 30 million square meters of collector area, of which around 7 million square meters has already been installed.    

Semiconductors based solar cells provides one of the most environmentally friendly routes for power production.  Solar cells are connected together into a module as per the requirement of the appliance.  Module becomes the basic building block of a PV power system and required numbers of modules are suitably interconnected in a series and parallel combination to form a PV panel or an array.  About 1700 MW of power production has been achieved through solar photovoltaic systems.

Solar street lights, solar lantern, solar water pumps etc are some of the solar electrical appliances, which have been successfully developed.  In agriculture, photovoltaic systems are widely used in water pumping for irrigation and in rural domestic households for lighting.  These systems have higher installation cost with added advantages of environmental friendly and lesser operation and maintenance cost.

Cooking with solar energy appears to be a viable option in the domestic sector.  Of the different types of solar cookers like concentrating type solar cookers, indirect heating type solar cookers and hybrid type solar cookers, the box type solar cookers have reached the commercialization stage.   

 Wind Energy

Wind energy has a potential of 45000 MW in India.  Wind mills are commercially used for power generation, which is technically and economically viable and is a suitable alternate for fossil fuel power generation.  Out of the potential energy sources about 40 – 45 per cent has already been installed ie. India has about 19000 MW of wind mill installations.  Apart from power generation, water pumping is one of the applications of wind mills, which helps for irrigating water from shallow deep water sources. 

Biomass Energy

Biomass energy resources are organic matter available on a renewable basis for energy generation.  Forest thinning, agricultural crop residues, wood and wood wastes, animal wastes, aquatic plants, municipal waste etc. are all various available biomass.  Biomass, as a fuel, has been in use from ancient times and is produced locally everywhere.  They are generally available in sufficient quantities and have lesser economic value due to improper utilization.  Some of the benefits include CO₂ neutrality, lesser release of pollutants like So_x and No_x, water and soil quality improvement, biodiversity, landscape, job creation, rural rehabilitation etc. emphasis the development of newer technologies for effective utilization of biomaterials. 

Biomass provides the possibility of conversion in to liquid, solid or gaseous fuels through various conversion routes which provides more opportunities for its use in different applications.  Biomass could become a central part of future sustainable energy supply, due to its economic and technical feasibility. 

Biomass power generation potential is vast in a predominantly agricultural country like India.  With an annual biomass availability of about 500 million tonnes, the power generation potential is in the order of 17,000 MW.  With the available biomass conversion technologies, the installed power generation is about 500 MW.

Varieties of technologies are available for the conversion of biomaterials to useful energy forms.  The major classification is thermochemical and biochemical conversion technologies.  In biochemical conversion processes, microorganisms play major role in energy generation.   Where as in thermochemical conversion processes, heat will be introduced during the process.      

Thermo Chemical Conversion          

Thermochemical conversion can be classified into three major processes based on the supply of air viz. combustion, gasification and pyrolysis. 

Direct combustion in excess air  (incineration) is the best understood and most widely used energy conversion process today.  However, direct combustion in excess air has several problems, especially for general large-scale use.  There is also a serious air pollution problem associated with direct burning in excess of air, since large quantities of particulates are produced.  Combustion in a controlled atmosphere (gasification) is the conversion of solid or liquid to a gas.  The capabilities of this process were shown during World War II in Europe and Japan where gasifiers were used to operate tractors, automobiles and buses because petroleum was scarce.  Heating in the absence of air (pyrolysis) is the transformation of materials into another form by heating in the absence of oxygen.  This approach appears to offer a number of advantages over incineration.  Generally pyrolysis and gasification can be considered as very efficient means of increasing the options available for utilizing waste materials.

Gasification is the process in which restricted amount of air will be supplied.  Due to lesser air supply, the raw materials will be converted into an intermediate chemical gaseous product called producer gas.  Gasifiers are used for generating producer gas from biomaterials.  This gas can be used for burning, drying and also running engines.  This technology was used during World War II itself.  Due to the dominance of petroleum products during mid 20^th century, this technology got lesser importance.  Now, due to the dwindling nature of coal and petroleum products, gasification technology is re-energized and popularised.         

Pyrolysis is the process, through which organic materials are converted into secondary fuels and chemical products in the absence of oxygen.  The products are gases, condensed vapours as liquids, tars and oils and charcoal (solid).    

Among thermochemical methods, combustion and gasification are now widely in use for energy generation, and also for rural and industrial applications. 

Biochemical Conversion

These processes utilize microorganisms for the conversion of biomaterial into different end products such as biogas, ethanol, compost etc.  In standardizing and optimization of these processes, biochemical engineering concepts such as reaction rates, kinetics, design of reactors, transport phenomenon etc. play a major role.  Based on physiological conditions of the process, biochemical conversion processes are classified into aerobic and anaerobic. 

Biogas production through anaerobic fermentation of biomass offers a very prominent route for gaseous fuel generation besides fertiliser generation.  Biomethanation of industrial waste, garbage, domestic waste etc. is also being perfected and implemented by many institutions/agencies.  These raw materials are digested by anaerobic organisms (survive in the absence of oxygen) such as acetogenic and methanogenic bacteria and biogas will be released.  In addition to biogas, the nutrient rich organic manure (digested effluent) is also released.  The predominant types of bioreactors for generating biogas high rate reactors such as Upflow anaerobic slugde blanket, hybrid reactors and various biogas plants like floating drum, Janatha, Deenbandhu etc.  

Fermentation of suitable biomaterials leads to the production of alcoholic products.  Bioethanol can be produced from various sugar, cellulose and starch based biomaterials.  Sugar materials can be easily fermented and ethanol can be generated.  Whereas, starch and cellulosic based complex materials have to be subjected to different pretreatments and converted into simple sugars before fermentation.  Using microorganisms, biomaterials can be converted into compost, which has higher nutritive value and supplies nutrients to soil. 

Biodiesel

Biodiesel is a chemical process, by which vegetable oils can be converted into biodiesel.  This is the best alternative to diesel and can be used in engines and automobiles.  The raw vegetable oils are subjected into chemical and thermal processes and by removing the by product (glycerol), biodiesel is segregated.  The suitable crops for the production of biodiesel are oil bearing seeds producing trees such as Jatropha, Pungam etc. 

Thus, various forms of energy like chemical, mechanical, electrical and thermal can be generated efficiently and effectively from biomaterials, which is otherwise unutilized or underutilized.  The selection of process for various biomaterials is the key factor in efficient biomass energy conversion.  These end use forms of biomass based energy can be substituted well in various industrial and domestic applications, in the place of conventional energy sources.  This not only provides energy conservation but also safe, clean and greener environment to the mankind.           

Our country is well endowed with renewable sources of energy.  But, the exploitable potential depends upon the availability of resources, the status of technology, and the end-use patterns.  The application of these technologies is dependent on the degree of R&D, development of consumer satisfied appropriate products, as well as their commerialisation.  Widespread information dissemination and awareness campaigns need to be launched to apprise people of the benefits of renewable energy technologies and their advantages over other technologies.