eChapters

Soil sample collection is the first and most important step for soil quality analysis. A soil sample collected with due care and proper procedure is essential for getting reliable result of the analysis. The sample should represent the field and for practical purposes, an area of about 0.5 hectare is considered as one sampling unit. In case of conspicuous variation observed in the field in terms of texture, colour, slope etc, separate samples should be collected from areas differing in these attributes. In other words, sample should be collected from an area in the field with similar characteristics as seen through normal visual observation. Sampling should thus be avoided from areas like near trees, permanent vegetations, manure pits, manure piles or recently fertilized fields.

Soil Sampling procedure

1. For a particular field unit, one composite soil sample is prepared out of the samples collected from 7-8 spots distributed across the field unit. The entire field is covered by moving in a zig-zag manner from each sampling spot.
2. For each sampling point or spot, scrapping off the surface litter such as grasses or crop residues is done. Then, a “V” shaped pit of 15-20 cm length and of equal width is made. Depth of sampling depends upon the requirement and on the type of crop. For field crops like paddy, wheat etc, samples are collected from 15 cm depth. From the “V” shaped pits, take outslice of ½ inch thickness from both sides of the exposed pit surfaces from top to bottom.
3. The soil samples so collected from the 7-8 points are mixed thoroughly by hand and then is reduced to about 500 g by quartering process. The quartering process consists of a procedure in which the entire soil mass is divided into four quarters; the two opposite ones are discarded and the remaining two are remixed. This process is repeated till about 500g soil is obtained.

Soil pH is the measure of hydronium ion (H₃O⁺) or more commonly hydrogen ion (H⁺) activity in the soil suspension. Soil pH can be measured in soil-water suspension, saturation extract or in 0.01 M CaCl₂ solution. Saturation extract is used to identify specific soil problems such as salinity or sodicity. Measurement of pH using 0.01 M CaCl₂ solution gives more reproducible results than measured through soil-water suspension. It also provides a good approximation of field conditions as the electrolytic composition of 0.01 M CaCl₂ is considered similar to that of soil solution. However, among the three methods, soil-water suspension is most commonly used in research laboratories as well as for fertilizer recommendation as it is simpler and more convenient.

Electrical conductivity (EC) is a useful indicator of soil salinity. Relationships have been developed between EC and salinity classes for a 1:1 soil: water suspension. With increase in salt content in a soil, the EC increases. Thus, for salt affected soils, measurement of EC is vital as accumulation of salts in the root zone is detrimental to plant growth. EC is a measure of the ability of a soil solution to conduct electrical current.

Equipment and Reagents

1. Digital Conductivity meter
2. 0.01 M potassium chloride (KCl) solution: Dissolve 0.7456 g dry KCl in distilled water and make up the volume to 1.0 litre. This solution has an electrical conductivity of 1.413 dS m_-1 at 25ºC.

Ion exchange is a reversible process by which a cation or anion held on the solid phase is exchanged with another cation or anion in the liquid phase. Soil mineral and organic colloidal particles have negative valence charges that hold dissociable cations. The power to retain cations at the surface of soil colloids is referred to as the cation exchange capacity (CEC). Cation exchange is a reversible reaction in soil solution, dependent upon negative charges of soil components arising from permanently charged or pH-dependent sites on organic matter and mineral colloid surfaces. The CEC is the sum of cations held by a kilogram of soil and is expressed in Cmol (p₊)/kg soil. In most agricultural soils, the cation-exchange capacity (CEC) is generally higher than the anion exchange capacity (AEC).

Exchanges sodium (Na+) is animportantparameter forsalt affected soils. This is estimated by extraction with ammonium acetate and then measuring the extract inflamephotometer.

Reagents

1. Neutral normal ammonium acetate solution (1 N CH₃COONH₄ of pH 7): Dissolve 77.09 g of ammonium acetate in distilled water and make up the volume to one litre. Adjust the pH of the solution to 7 with ammonia solution or acetic acid.
2. Standard solution of Na (500 mg/L Na): Dissolve 1.271 g of NaCl in distilled water and make up the volume to one litre.
3. Working standard solution of Na (100 mg/L): Dilute 200 ml of 500 mg/L stock solution to 1000 ml.

Soil texture refers to the relative distribution of sand, silt and clay on a sample of <2 mm size. It is an intrinsic soil property and basically refers to the particle size distribution in a soil. A number of physical characteristics and chemical properties of a soil are influenced by texture or particle size distribution. To estimate the content of sand, silt and clay particles, the soil samples are first brought into a dispersed state by mechanical and chemical treatments so that different binding agents are removed. In the dispersed soil samples, the soil particles settle down at a differential settling rate according to their size. In laboratory, the common methods for analysis for particle size distribution are : Buyoucos hydrometer method and International pipette method. In this chapter, the procedure of Buyoucos hydrometer method is described.

Principle

This method is based on the principle of variable rate of settling of particles as per their size and as described by Stokes’Law. Large particles shall settle fast. The measurement of density of the suspension is done at different times using a hydrometer (ASTM 152H-Type hydrometer is preferred). The measurement in this hydrometer is based on a standard temperature of 20 _oC and a particle density of 2.65 Mg m_-3 and the units are expressed in grams of soil per liter.The principal source of error in this procedure is the incomplete dispersion of soil clays as the clay particles are cemented by agents such as organic matter, CaCO and iron oxides. Incomplete dispersion results in low values for clay and high values for silt and sand. Thus, soils with higher organic matter (>1.0%) should be first treated with 6% hydrogen peroxide (H₂O₂) for removal of organic carbon. The rate of sedimentation is also affected by temperature and the density of the dispersing solution.

Soil bulk density (BD) or apparent density is determined in -situ by core method. Stainless steel or metallic cores of cylindrical shape with known height and diameter are inserted into the soil till the rim of the core. The soil core is then excavated and the soil sample is oven dried to get the dry weight. The ratio of the oven dry weight to the total volume of the core gives the bulk density of the soil.

Aggregation is a direct indicator of soil structure. Ahealthy soil is considered to have well aggregated structure. Though not routinely followed during soil testing and chemical analysis, aggregation is one of the major indicators of soil physical health. Wet sieve method (Yoder, 1936) is usually followed for soil aggregate analysis. This involves gently raising and lowering a nest of sieves in water to assess the stability of aggregates to rapid wetting. However, the Yoder’s wet sieving method has been modified to make it simpler and currently, the method of Kemper and Rosenau, 1986 is being commonly used in research laboratories. One of the pre-requisites in these methods is the availability of wet sieving apparatus and further, these methods are laborious and time consuming. On the other hand, the method described by Cambardella and Elliott (1993) is considered very ideal because of its simplicity and is being widely used for aggregate bound soil carbon fraction study. The soil sample is wet sieved with a series of three sieves (2000, 250 and 53 micron size).

Aggregation is one of the basic physical characteristics of soil. Under natural conditions, primary soil particles, particularly clays, tend to join together to form secondary units called aggregates. Size distribution of soil aggregates is important because the size of the aggregates determines their susceptibility to water and wind erosion. Also, their size is important in determining the pore size distribution and regulating pore space in cultivated soils.

There are a variety of procedures being in use to test the stability of aggregates and aggregate size distribution. However, choice of the method for analysis of aggregate size distribution is determined by the purpose of analysis. The developed measures are relative and purpose specific. This chapter discusses dry aggregate analysis.

Thisprocedure estimates aggregatestabilitytoimpact ofraindropsand water erosion. Wet sieving procedure was originally proposed by Yoder, 1936. Later, the procedure was modified byKemper and Rosenau, 1986.

Equipment

1. Yoder type sieve shaking electrically operated machine (3/4 inch stroke at 30 strokes per minute)
2. Concentric sieves of various sizes of pores to fit properly into the machine.
3. Weighing balance

Wet sieving procedure separates soil into different size aggregates. However, for comparing the aggregate size distribution among management treatments and soil types, it is convenient to use indices. Mean weight diameter (MWD) and water stable aggregate percentage are some of the common indices used in aggregate stability studies.

Mean Weight Diameter (MWD)

This index was proposed by Van Bavel (1949) and is being used widely. The entire soil sample is passed through an 8 mm sieve prior to analysis and is subjected to wet sieving procedure as described before. The parameter which Van Bavel (1949) called the MWD is equal to the sum of the product of (a) the mean diameter (d ) of each size fraction and (b) the proportion of the total sample weight (w ) occurring in the corresponding size fraction. The summation is carried out over all ‘n’ size fraction including the one that passes through the finest sieve.

In dry combustion technique, the combustion of soil sample (about 250 mg and mm sieved) is carried out at high temperature (about 1000 ºC) through feeding in an inert boat in the electric furnace. The CO₂ produced from the oxidation of carbon present in the soil sample at high temperature is carried towards non dispersive infrared detector (NDIR) by a carrier gas where it is quantified and total carbon content is determined.

This is one of the commonly used method to estimate organic carbon content in soil. In this wet digestion method, soil organic matter is oxidised with a mixture of K₂Cr₂O₇ and concentrated H₂SO₄ utilizing the heat of dilution of H₂SO₄. The unused K₂Cr₂O₇ is back titrated with ferrous sulphate or ferrous ammonium sulphate.

Labile fractions of soil carbon (C) refer to the fraction of soil carbon that are easily altered by microbial activities. These fractions serve as sensitive indicators to changes in management induced soil quality and are grouped under active soil C pool. The method described by Weil et al. (2003)estimates changes in biologically active soil C using a dilute KMnO . This is an improvement over the method used by Blair et al (1995), where a very high concentration (0.333 M) of KMnO₄ was used.

Organic carbon present in soil can be very labile, labile or non-labile. This procedure measures the extent of lability of soil organic carbon through relative degree of oxidation by K₂Cr₂O₇.

Particulate soil organic matter (POM) is one of the important soil organic matter (SOM) pools and matches the characteristics of a slow, decomposable or stabilized SOM pool. The POM fraction is considered as one of the indicators to changes in management and thus has been used in soil quality assessment studies.

Soil respiration is a good estimator of overall biological activity and thus is often used for describing soil quality. Soil respiration is estimated as the flux of CO₂ emitted from the soil surface. It represents the sum of CO₂ produced by root respiration and by heterotrophic decomposition. This procedure is a laboratory method where soil is incubated for a given period of days and the released CO is trapped by sodiumhydroxide (NaoH). This is also known as alkali trap method.

This is a distillation method proposed by Subbiah and Asija (1956), where the soil is distilled with alkaline KMnO solution. The ammonia liberated is trapped in boric acid and then determined by titration against a standard acid. This procedure estimates the easily mineralizable nitrogen in soil.

Estimation of plant available phosphorus content in soil has been attempted using several extractants. However, Bray’s reagent and Olsen’s reagent are the two common extractants used in India. Bray’s reagent (0.03 N NH₄F and N HCl) is used for acid soils, where, the fluoride ion complexes with Fe and Al in soil and thus releases the bound P. The Olsen’s reagent (0.5 M NaHCO₃) is used for neutral-alkaline soils.

In soil system, potassium (K) exists as water soluble, exchangeable, non- exchangeable and lattice K. The plant available K refers to the sum of water soluble and exchangeable K. Estimation of available K is usually done using neutral normal ammonium acetate as the extractant.

In this method, plant available sulphur (S) is extracted with 0.15% CaCl₂ and the soluble sulphate is estimated on a colorimeter.

The hot water soluble method is the most common method to estimate available B content in soil

Reagents

1. Azomethine-H: Dissolve 0.45 g azomethine-H and 1.0 g L-ascorbic acid in about 100 ml de-ionized or redistilled water. If solution is not clear, it should be heated gently on water bath at about 30ºC till it dissolves. A fresh solution should be prepared every week and kept in a refrigerator.
2. Buffer solution: Dissolve 250 g ammonium acetate in 500 ml de-ionized or redistilled water. Adjust the pH to about 5.5 by slowly adding approximately 100 ml glacial acetic acid, with constant stirring.
3. EDTA reagent (0.025 M): Dissolve 9.3 g EDTA in de-ionized or redistilled water and makes the volume up to 1 litre.
4. Standard Boron solution: Dissolve 0.571 g boric acid (H₃BO₃) AR grade in a small volume of deionized water and make volume to 1000 ml to obtain a stock solution of 100 mg B/L.

This procedure uses Diethylene Tri-amine Penta Acetic acid (DTPA) as the chelating agent, which combines with free metal ions in soil solution and forms soluble complexes.

Analytical methods for study of soil microbes

The analytical techniques for study of soil microbes are grouped under the following heads :

• Determination of form and arrangement of microorganisms in soil
• Isolation and characterization of soil microorganisms
• Detection of microbial activity in soil
• Determination of microbial biomass.

For the above, the different analytical methods used are described below.

Enumeration of microbial flora present in soil is done by dilution plating technique. The technique is based on the fact of diluting the source inoculums to the extent that after plating the known volume of inoculums on appropriate media, the colonies will appear in countable range and each colony will be assumed to have been derived from a single cell/colony forming unit. Three numerically dominant groups of soil microbes are bacteria, actinobacteria and fungi. The most commonly used culture media for their enumeration include

Nutrient Agar-for heterotrophic bacteria,

Actinomycetes isolation Agar or Kenknight and Munaier’s agar for actinobacteria

Martin’s Rose Bengal Agar for fungi.

Biological activity or index of a soil is the function of number of organisms present in soil and their physiological efficiency. The rate of respiration can be used as an index of the biological activity of soil as it reflects the physiological efficiency of the organisms. Monitoring of dehydrogenase, which are respiratory enzymes and integral part of all soil organisms, will give a measure of biological activity of soil at a given time.

During respiration biological oxidation of reduced compounds occur which is catalyzed by dehydrogenase. In the process TTC gets reduced to a pink coloured compound Triphenyl formazan (TPF) which can be quantitatively extracted by methanol and measured colorimeterically. The soil dehydrogenase activity in the current experiment was measured as per the methods of Cassida, (1977).

Fluorescein diacetate (3’ 6’-diacetyl-fluorescein) is a fluorescein conjugated to two acetate radicals. This colourless compound is hydrolysed by both free (exoenzymes) and membrane bound enzymes, releasing a coloured end product, fluorescein. This end product absorbs strongly in the visible wavelength (490 nm) and can be measured by spectrophotometry. The enzymes responsible for FDA hydrolysis are plentiful in the soil environment. Non-specific esterases, proteases and lipases, have been shown to hydrolyse FDA. The hydrolysis of FDA by soil enzymes can be estimated by methods of Adam and Duncan (2001).

Principle

β-Glucosidase (BG) plays a major role in the degradation of soil organic matter and plant residues. It catalyzes the hydrolysis of β-d-glucopyranosides, the final, rate-limiting step in the degradation of cellulose, the most abundant polysaccharide providing simple sugars for the soil microbial population. BG has been shown to be sensitive to changes in soil and residue management as well as an early indicator of changes in SOC before these changes are reflected in total or organic C analyses. The method is based on colorimetric determination of the p-nirtrophenol released by β-glucosidase when soil is incubated with buffered PNG solution and toluene.

Acid and alkaline phosphatase enzymes are among the extensively studied phosphatases and classified so because of their optimum activities in acid and alkaline pH ranges, respectively. Acid phosphatase is predominant in acid soil while alkaline phosphatase is dominant in alkaline soils. The colorimetric assay of phosphatase is based on release of p-nitrophenol from hydrolysis of p-nitrophenyl phosphate byaction of phosphatase enzyme in buffered soil solution (buffer pH 6.5 for acid and 11 for alkaline phosphatase assay).

Principle

Different ions migrate at different speed dictated by their size and by the amount of charges they carry. As a result, different ions can be separated from each other by electrophoresis. The magnitude of the electric force F exerted on the charged particle when subjected to electrophoresis is product of the charge q of the particle and the electric field E generated between the two electrodes.

Mole

A mole is defined as the amount of chemical substance containing exactly 6.022 140 76 × 10₂₃ numbers of constitutive particles such as atoms, ions and molecules. This number is a fundamental constant named Avogadro’s number in honor of Italian scientist Amedeo Avogadro. This constant is properly reported with an explicit unit of “per mole,” and rounded version being 6.022 × 10₂₃/mol.

This definition has been adopted since November, 2018 revising the old definition based on the number of atoms in a sample of pure ₁₂C weighing exactly 12 g. Thus, as per the definition, 1 mole of any element contains the same number of atoms as 1 mole of any other element. However, the mass of 1 mole of a particular element is different from that of another element.

Molar mass

Molar mass of an element (or compound) is the mass in grams of 1 mole of that substance, a property expressed in units of grams per mole (g/mol).

Introduction

In order to keep pace with the development there is rise in energy use but it has adverse effects on climate due to greenhouse gas emissions from burning of fast depleting fossil fuels. In this context, we need to harness and use more and more renewable forms of energy, especially solar energy that is plentiful on most part of India. Also, at several locations harnessing wind power and utilizing biomass could be effective alternatives. Solar based devices may also work in an integrated manner with small wind turbines as hybrid devices. At present, about 20% of the country’s installed electricity generation capacity is contributed by renewable sources e.g. wind, solar, bioenergy, hydro etc., which is about 71.325 Giga Watt (GW) as on 30^th June, 2018. In agricultural sector, energy is directly used for pumping irrigation water, operating different mechanized farm implements/tools and processing of foods. Share of agricultural sector in total energy consumption is about 7-8% and further increase in energy use from its present value of 1.6 kW ha^-1 to 2.5 kW ha^-1 is expected to meet the production target of next 20 years.

Introduction

The development of any region is reflected in its quantum of energy consumption. With a view to keeping the pace we have to grow our energy resources at a rate that commensurate to sustainable development. There is already shortage of electricity, reflected in power cuts notwithstanding enhancement of electricity production of several folds in the country. The problem is more severe in context with rural areas in India where some 70% of population live and have agriculture as the main occupation. Although statistically few thousand villages are yet to be electrified, the availability of regular supply in far off places has been a problem and the farmers are unable to derive benefits of electricity. The fast depleting kerosene is used for lighting and diesel oil for running agricultural machinery including pumps. In addition people burn firewood, agricultural waste and cow dung cake for cooking food causing irreparable damage to the ecosystem. According to Lester Brown there will be plenty of food to eat but no fuel to cook. The burning of cow dung deprives farmers the use of potential source of organic manure. Further, due to shortage of energy resources, farmers are unable to process the agricultural products to enable them to accrue more benefits. The situation is still worse in arid region where bio mass is scarce and there is no hydro electricity. In addition, farmers are unable to generate additional income due to lack of energy resources to run appropriate device in cottage industries. In this context, solar energy utilization has a tremendous potential for providing needful energy to the farmers for domestic, agricultural and allied applications leading to a sustainable development.

Introduction

In Indian Thar desert regions, excessive heat is the major problem that causes human and animal thermal discomfort. Space cooling is, therefore, the most desirable factor for the inhabitants. Various examples of dwellings responsive to climatic constraints are found in vernacular architecture throughout the world. Compact cellular layout with minimum external surface exposure to the sun, whitewashed surfaces to reduce absorptivity, blind external facades, courtyards, vegetation to provide humidity and shade, and heavy buildings constructed from high thermal capacity materials are common passive features in most of the arid regions. Wind towers for cooling ventilation are well known in Iranian and Middle East architecture, which along with cooling of the air by earth and water evaporation keep the building comfortable in hot periods. Building underground to take advantage of the large thermal storage capacity of the earth is also used in Tunisia and central Turkey.

Introduction

The age-old necessities of life are food, clothing and shelter. The 20^th century had dramatized a fourth-energy. Energy starvation of the technological complex that maintains modern society may soon be as crucial a problem as feeding the hungry. Indeed, energy starvation could well precipitate more wide spread food starvation. Solutions for the energy crisis are strongly dependent on the technology of how energy is produced and used. To make a physical change in the world it is necessary to use four resources: energy, matter, space and time. How well a task has been performed can be measured in terms of amount of fuel consumed, the mass of material used, the space occupied, the hours of labour to accomplish it, and the ingenuity with which these resources are utilized. Squandering of irreplaceable energy resources, waste of materials, or large expenditure of space and time cannot be tolerated if the necessities of life are to be provided for all. Energy is intricately linked to development of a country. Growing demand on account of industrialization, urbanization, transportation and also increase consumption in rural areas is putting added pressure on energy supply network. Electricity generation has been increased from 1,400 MW in the year 1947 to 303,118 MW up to August 31, 2016 in India but still there is 10-15% shortage of power in peak hours and all villages are not electrified. Even many electrified villages receive 6 to 8 hours of electricity per day in India. To overcome this shortage there is a need to utilise new and renewable sources of energy. Fortunately, India is blessed with abundant solar energy. The arid parts of India receives much more radiation as compared to the rest of country i.e. maximum solar radiation i.e. 7600-8000 MJm^-2 (2111-2222 kWhm^-2) per annum, followed by semi-arid parts, 7200-7600 MJm^-2 (2000-2111 kWhm^-2), per annum and least on hilly areas where solar radiation is still appreciable i.e. 6000 MJm^-2 (1667 kWhm^-2) per annum (IMD 1985). In this chapter review of different solar thermal technologies in Indian perspective has been carried out.

For electromagnetic radiation, there are four “laws” that describe the type and amount of energy being emitted by an object. In the following sections, these four laws of radiation e.g. Planck’s law, Wien’s displacement law, Steffan-Boltzman law and Kirchhoff’s law are described briefly.

Planck’s Law

Planck’s law describes the spectral density of electromagnetic radiation emitted by a black body in thermal equilibrium at a given temperature T. The spectral radiance of a body, B_í, describes the amount of energy it gives off as radiation of different frequencies. It is measured in terms of the power emitted per unit area of the body, per unit solid angle that the radiation is measured over, per unit frequency. Planck showed that the spectral radiance of a body at absolute temperature T is given by

Introduction

Cooking accounts for a major share of energy consumption in developing countries. Fifty per cent of the total energy consumed in India is for cooking (Fritz 1981). Most of the cooking energy requirement is met by non-commercial fuels such as firewood (75%), agricultural waste and cow dung cake (25%) in rural areas. The fuel wood requirement is 0.4 tons per person per year in India. In rural areas firewood crisis is far graver than that caused by a rise in oil prices. Marginal villagers have to forage 8 to 10 hours a day in search of firewood as compared to 1 to 2 hours ten years ago. One third of India’s fertilizer consumption can be met if cow dung is not burnt for cooking and instead is used as manure. The cutting of firewood causes deforestation that leads to desertification. Fortunately, India is blessed with abundant solar radiation (IMD, 1985). The arid parts of India receive maximum radiation i.e. 7600-8000 MJ m^-2 per annum, followed by semi-arid parts, 7200-7600 MJm^-2, per annum and least on hilly areas where solar radiation is still appreciable i.e. 6000 MJm^-2 per annum. Therefore, solar cookers seem to be a good substitute for cooking with firewood.

Principle of cooking

The different methods of cooking of food are boiling, frying, roasting, and baking. For boiling of rice, lentils etc. the temperature of food being cooked is about 100° C while for other methods, high temperatures are required. Heat is supplied at the bottom of the vessel for frying and boiling purposes in conventional cooking. Roasting and baking is generally performed on open fire or in ovens, wherein food is surrounded by hot surfaces and heat is transferred to the food by radiation and convection.

Introduction

Flat plate collector is the heart of a solar heat collection system designed for delivery of heated fluid in the low to medium temperature range (5o70oC above ambient temperature) for applications, such as water heating, space heating, drying and similar industrial applications. The flat plate collectors absorb both beam and diffuse radiation. The absorbed radiation is converted into heat which is transferred to water or air flowing through the collector tubes or duct, respectively. Such collectors do not require tracking of the sun and little maintenance is required.

The conventional flat plate solar air heater, shown in Fig. 7.1, consists of a flat blackened absorber plate, a transparent cover (such as a glass cover) at the top and insulation at the bottom and on the sides. The air to be heated flows through the rectangular duct below the absorber plate. The glass cover transmits a major part of solar radiation incident upon it to the absorber plate where it is converted into heat. The glass is, however, opaque to longwavelength radiation and thus it does not allow the infrared radiation from the heated absorber plate to escape.

Karwa et al. (2002) have presented the following deductions of heat collection rate and pumping power equations for the flat plate solar air heater.

Introduction

We are blessed with solar energy in abundance at no cost. The solar radiation incident on the surface of the earth can be conveniently utilized for the benefit of human society. Solar energy can be used as thermal energy for water heating, cooking, drying, distillation, space heating, cooling and power generation or it can be converted to electricity through photovoltaic cells, commonly known as solar cells. One of the popular devices that harness the solar energy is solar hot water system (SHWS). Flat plate collectors are used for low temperature applications (below 100^oC) while concentrators are preferred for higher temperatures. The most efficient application of flat plate collector is for getting hot water. Hot water in winter is an essential requirement for domestic uses such as bathing, cleaning of utensils and washing of clothes. In rural areas hot water is also required for softening of animal feed. Generally it is obtained by using firewood and cow dung cake in rural areas or using kerosene, liquid petroleum gas, coal or electricity in urban areas. Therefore, the use of solar water heaters will conserve lot of commercial and non-commercial fuels which are being wasted in merely getting hot water. A solar water heating system (SWHS) is made of several important elements: one or more solar collectors, a pump, a heat exchanger, a storage tank (or multiple tanks) and a back-up storage tank. The Solar heating system can be classified as passive or active. For water heating purposes, the general practice is to use flat plate solar energy collectors (FPC). The evacuated tube collectors (ETC) and evacuated tube heat pipe collectors (ETHP) are more efficient, though, the initial cost is comparatively higher. There are three type of water heaters extensively studied by various workers viz. natural circulation, collector-cum-storage and forced circulation in all over the world.

Introduction

Solar refrigeration technology engages a system where solar power is used for cooling purposes. It offers a wide variety of cooling techniques powered by solar collector-based thermally driven cycles and photovoltaic (PV)-based electrical cooling systems. Cooling can be achieved through four basic methods: solar PV cooling, solar thermal cooling, solar thermo-electrical cooling and solar thermo-mechanical cooling. The first is a PV-based solar energy system, where solar energy is converted into electrical energy and used for refrigeration much like conventional methods. The second method utilizes a solar thermal refrigeration system, where a solar collector directly heats the refrigerant through collector tubes instead of using solar electric power. The third one produce cool by thermoelectric processes. The fourth method converts the thermal energy to mechanical energy, which is utilized to produce the refrigeration effect.

The performance of solar refrigeration systems is determined based on energy indicators of these systems. The COP (coefficient of performance) can be calculated as follows:

Introduction

Solar air heating is the conversion of solar radiation to thermal heat. The thermal heat is absorbed and carried by air which is delivered to a living or working space. The transparent property of air means that it does not directly absorb effective amounts of solar radiation, so an intermediate process is required to make this energy transfer possible and deliver the heated air into a living space (Fig.10.1). The technologies designed to facilitate this process are known as solar air heaters. Solar air heating technologies use only free, renewable and clean energy and can help defray the rising cost of conventional energy.

Introduction

The sun is an abundant source of solar energy (average value on horizontal surface 6 kW m^-2 day^-1), which is freely available. This huge source of energy is non-polluting and inexhaustible in nature. It has the potential of supplementing the conventional energy sources to a great extent. There is acute shortage of conventional energy sources, which affects the overall development. Work on the utilization of such a huge, non-polluting and everlasting energy source has been carried out at CAZRI, Jodhpur for various domestic, industrial and agricultural applications in order to supplement the energy demand. This includes the development of a lot of solar thermal devices, such as, solar still, solar dryer, solar cooker, animal feed solar cooker, solar candle device and cool chamber. The details of some of these devices are given as following.

Introduction

A solar collector, the special energy exchanger, converts solar irradiation energy either to the thermal energy of the working fluid in solar thermal applications, or to the electric energy directly in Photovoltaic (PV) applications. For solar thermal applications, solar irradiation is absorbed by a solar collector as heat which is then transferred to its working fluid (air, water or oil). The heat carried by the working fluid can be used to either provide domestic hot water/heating, or to charge a thermal energy storage tank from which the heat can be drawn for use later (at night or cloudy days). Solar collectors are usually classified into two categories according to concentration ratios: non-concentrating collectors and concentrating collectors. A non-concentrating collector has the same intercepting area as its absorbing area, whilst a sun-tracking concentrating solar collector usually has concave reflecting surfaces to intercept and focus the solar irradiation to a much smaller receiving area, resulting in an increased heat flux so that the thermodynamic cycle can achieve higher Carnot efficiency when working under higher temperatures.

Introduction

Water is the primary source of life for mankind and one of the most basic necessities for crop production. The demand for water to irrigate the crops is increasing. For sustainable production from agricultural farms, irrigating the crops at right stages is highly important. Even in rainfed situation, lifesaving irrigation during long dry spell has also been found beneficial for crop survival and to obtain the targeted yield. Considering the depletion of groundwater below the critical zone in most part of the country, energy intensive pumping for irrigation is not a viable option. Therefore utilization of available runoff water through surface storage systems followed by pumping may be a potential solution to achieve the set goal of ‘crop per drop’ mission. In this connection, micro-irrigation system including drippers and sprinklers is of great importance. However, ensured power supply is essential to operate the micro-irrigation system even in remote areas. Reliable solar photovoltaic (PV) pumps are now emerging in the market and are rapidly becoming more attractive than the traditional power sources. These technologies, powered by renewable energy sources, are especially useful in remote locations where a steady fuel supply or electricity supply is problematic. About 16 million electric pumps and 7 million diesel pumps are in operations in the country for irrigation purpose; however they are highly energy intensive. Moreover, diesel operated and electrified pumps directly or indirectly emit large amount of CO₂ gas in atmosphere and hence are not environment friendly. To meet the energy demand for irrigation, solar PV pumps have been introduced under the off-grid power generation category of National Solar Mission (NSM) with a target of 1000 MW by the end of phase II (2013-2017). The target has been revised in 2015 to a total grid connected solar power generation of 1,00,000 MW comprising 40,000 MW roof top generation and 60,000 MW grid connected solar power plants (Resolution of MNRE, Govt of India, No. 30/80/2014-15/ NSM dated 1^st July 2015).

PV clad structures and hybrid devices for rural and agricultural applications have been developed after considering different design aspects, climatic parameters, solar radiation availability on different planes, heat transfer coefficients, performance of PV in arid region and inter phasing of different components while keeping in view, practicality, application and ease of operation. Performance of the developed systems was studied, mathematical model developed and energy savings worked out for techno-economic considerations. The chronology and details of the developed PV structures and hybrid devices are as follows:

Green structure for environmental control

First of all a Quonset type environment control structure having a length of 5.3 m and width 4 m was fabricated with angle iron and iron rods and it was covered by agro-net (75%) having surface area of about 55 m². The structure having a volume of 33 m³ was fixed with long side along east west direction and had provisions for incorporation of misting unit on west side and a door on east.

Introduction

Agriculture has been the back bone of Indian economy and culture and it will be continued to remain as such for a long time in future. Parallel to this, energy security of a country is also very important and efforts have been given on renewable energy utilization since the fossil fuel based energy is depleting at a very fast rate. In agricultural fields, considerable amount of energy is used to do different field activities e.g. ploughing, irrigation through pumps, intercultural operations, spraying of agricultural chemicals for plant protection, harvesting, post-harvest processing etc. Therefore, there is also need to replace the conventional energy source with renewable sources to operate above mentioned agricultural activities.

Approximately, 35% of the crop production is damaged if pest and diseases are not controlled at right time. Uniform spraying of liquid formulations throughout the crop field is very important for effective control of pest and diseases. Using sprayer, liquid pesticide formulations are generally broken down to minute droplets of effective size for uniform distribution over a large surface area. Different types of sprayers are used in agricultural field based on different requirements.

Introduction

For optimum use of harvested rain water in surface reservoir like farm ponds or tankas, small sized solar PV pumping systems with 1 hp AC and DC motor were experimentally tested at research farms of ICAR-Central Arid Zone Research Institute, Jodhpur (Fig. 16.1). Total suction head in both pumps was about 5 m. Among two installed pumps, the system with AC pump consisted of 1400 Wp (200 Wp × 7) whereas the DC pump consisted of PV array of 920 Wp (230Wp × 4). Each PV panel of AC solar pump was connected in series, which was further connected with an inverter to generate AC output of about 220-240 volt and 4-4.2 ampere. In case of DC solar pump, panels are connected in parallel to generate DC output of 40-50 volt and 15-20 ampere.

Introduction

Agricultural produce are being sun dried since ages as the first step to preserve the product for future consumption. It is still practised being most inexpensive over mechanical and other advanced drying systems. The most prevailing disadvantage of open sun drying is the quality losses due to insect infestation, enzymatic reactions, microorganism growth, and mycotoxin development. On the other side, sun drying is also a highly labor intensive and time consuming process prone to theft and damage by birds. It also suffers with the lack of process control and treatment uniformity (Bansal and Garg 1987, Bansal, 1987).

To overcome these disadvantages several types of solar dryers have been developed over the years (Ekechukwu and Norton 1999). These dryer may be identified into three group namely active, passive and hybrid. As regards their structural arrangement three generic subclasses were also identified: direct-modes (the solar-energy collection unit is an integral part of the entire drying system), indirect-modes (the solar collector and the drying chamber are separate units) and mixed-modes solar dryers. Natural convection solar dryers have become more suitable for rural sector and remote areas, as they work on single energy option and do not require any other external energy source (Pangavhane et al. 2002).

Introduction

Cultivation of crops in greenhouse or protected structure has been increased tremendously in recent times and also has been spread from temperate regions to the warmer regions of tropics and subtropics. Plentiful technologies have been developed for heating the inside environment of greenhouse for optimum plant growth (Sethi et al. 2013). However, in hot arid areas, cultivation in greenhouse is very difficult as the temperature reaches to a very high level to sustain plant growth (Pek and Hayles 2004, Saran et al. 2010). Under such situation requirement for cooling the greenhouse microclimate environment is the necessity, but is very energy and water intensive. Hence, in such regions, reduction of air temperature inside the greenhouse or the regulation of temperature closer to the ambient temperature during summer is necessary for successful crop production. A typical diurnal variation of temperature and global solar radiation during late winter months inside a shade net structure has been plotted in Fig. 18.1. It has been found that global solar radiation has been decreased to almost 1/3 of the radiation received outside by using 75% shade net cover. The temperature inside structure during morning time has also been found higher than outside temperature and in summer such increase is expected to be much higher.

Therefore, cooling is considered as the basic necessity for greenhouse crop production in tropical and subtropical regions to overcome the problems of high temperatures during summer months. Development of suitable cooling system that provides congenial microclimate for crop growth is a difficult task as the design is closely related to the local environmental conditions. Different cooling techniques for greenhouse crop cultivation may be found in Kumar et al. (2009). Fan pad cooling system has been widely used for greenhouse cultivation however, requires large amount of water during evaporation based cooling. Since water resources are becoming scarce in future such fan-pad cooling system may not be viable in future specifically in hot arid region.

Life cycle cost analysis

Economics of solar energy devices can be calculated through life cycle cost (LCC) analysis. Total life cycle cost of a device is comprised of capital cost, maintenance cost, replacement costs for damagaed components and operational cost. Before adding these above costs, all future costs (C) are converted to present worth considering the relative rate of inflation (i) and discount rate (d).

Where, PW is the present worth of any future cost, i is the relative rate of inflation and d is the discount rate per year and n is the time period in years. Relative rate of inflation accounts for the escalted increase or decrease in prices of a commodity in comparison to general inflation rate. For any commodity, if the price escalation is expected as per the general inflation rate then relative rate of inflation is considered zero. In general case, relative rate of inflation is considered zero. Discount rate accounts the real value of money in future and in most of the economies of the world it is about 8-12%, and therefore 10% is considered in most analyis. The discount rate also refers to the interest rate used in discounted cash flow (DCF) analysis to determine the present value of future cash flows. The discount rate in DCF analysis takes into account not just the time value of money, but also the risk or uncertainty of future cash flows; the greater the uncertainty of future cash flows, the higher the discount rate. A discount rate of 10 % per year would mean that in real terms it makes no difference to a farmer whether he has ? 100 now or ? 110 in one year’s time. Conversely, a cost of ? 110 one year from now has a present worth of ? 100. For a future single cost in n^th year, the present worth of that cost is calculated using Eq (1). However, for future multiple payments, costs are to be converted to present worth for each year and then needs to be cumulated. For calculation of annualized life cycle cost (ALCC) of solar devices, annuity factor (AF) needs to be calculated for a period of life cycle of the device as follows: