eChapters

2.1 INTRODUCTION

With increasing population, urbanization and continuous depletion of natural resources, there has to be a paradigm shift in farmer’s perception from production to productivity and to profitability. In the present scenario, the major challenges arising are shrinking land and depleting water and other related resources in agriculture. There is need for promoting farmer friendly location specific production system management technologies in a concerted manner to achieve a vertical growth in horticulture production duly ensuring quality of produce and better remuneration per unit of area with judicious use of natural resources. In this endeavour, precision farming aims to have efficient utilization of resources per unit of time and area for achieving targeted production of horticultural produce. With the revolution in information technology, now it has become possible to focus on the positioning of agricultural tools with high degree of accuracy and sophistication for maximizing returns. The combination of information technology and use of hi-tech equipments made it possible for the introduction of precision farming. It is a comprehensive system designed to optimize agriculture production through the application of crop information, advanced technology and management practices. With recent advances in geographic information systems, it has become possible to focus on site specific crop production technologies so as to harness the potential of horticulture through innovative technologies in a sustainable manner.

1.1 INTRODUCTION

The share of agriculture in GDP is sharp declining. Its share which was 55.1 per cent in 1950-51 came down to 21.6 per cent in 2003-04 and it further reduced down standing barely at 14.6 per cent in 2009-10. Horticulture acconts for 29 per cent share in gross GDP obtained from agriculture sector from about 13.08 per cent area put forth under horticultural plantations (Anon., 2010). To achieve the targetted growth rate of 4 per cent in agriculture, horticulture has to grow at the accelerated growth rate above 7 per cent. As a result of R&D initiatives made, there has been considerable increase in horticultural produce which is acclaimed as golden revoution. Horticulture sector has emerged as the frontier area in dealing with the situation of livelihood security and the employment generation. However, looking to the pressure arising from rising population and erratic climatic variation, more attention is required towards the development of technology driven horticulture. Precision farming is being viewed as a promise in this regard.

Precision farming is the process by which exact or accurate results of farming can be obtained. It is a management strategy that relies upon detailed, site specific information to precisely manage production inputs.

Maximisation of quality yield by managing site variable specific management practices is the basic of precision farming. More emphasis needs to be given to make the farming sustainable. In order to make precision farming a reality the following area needs due consideration.

Postharvest losses of fruits and vegetables are even higher and are estimated to be 40-50%. Postharvest fruit rotting are a major cause of those losses and are chiefly caused by fungal pathogens after fruit ripening. In a manner similar to foliar diseases that occur in the field, several factors as fungal pathogenicity, host response and environment determine the outcome of host resistance or susceptibility. However, in postharvest diseases fruit ripening is another major component that will determine fruit resistance. The molecular trigger induces the germ tube to differentiate an appressorium. It has been shown that excess nutrients over ride it and protein synthesis is not required once germination has occurred. Protein synthesis during conidium germination and appressorium formation on cellulose membranes were observed (Pathak, 1997). A specific polypeptide (95 kDa) was synthesized only when appressoria matured (a period lasting from 12-24 h after germination). This molecule is involved in the synthesis of the melanin precursor, Scytalone.

Appressoria grown in the presence of cyclohexamide do not mature nor they subsequently differentiate a penetration peg. Appressorium maturation involves the formation of melanin. It has been shown that melanization of appressoria is necessary for formation of a successful penetration peg. The melanin appears to give the appressorium mechanical strength, but pigmentation is only one factor required for penetration competent appressoria. At restrictive temperatures, pigmentation of conidia of C. lagenarium mutants could be restored with dihydroxyphenylalanine without restoration of appressorial competence. Non-pathogenic mutants have been used to determine factors important for pathogenicity. Cutinase production was essential for penetration of papaya fruits. The cutinase produced during infection of papaya fruit by C. gloeosporioides has been purified and characterized as a glycoprotein of 24 kDa. Polyclonal antibodies raised against this enzyme do not cross react with cutinase from Fusarium so/ani, and lesions do not develop when papaya fruits are inoculated with spore suspensions containing the antibody preparation.

Postharvest food loss has been considered an unavoidable affliction since food storage first began. These losses are much more painful and costlier in terms of money and man-hours. Such losses due to plant parasitic nematodes, in particular, is severe in tropical regions especially in developing countries like India, where proper storage, transmit and marketing facilities are inadequate. In tropical agriculture, increase in production rate is generally low and, by itself, unable to keep pace with the requirements of the increasing population. Hence, such food shortage demands the need to reduce postharvest loss due to nematodes. Postharvest food losses also constitute a vast complex of physical and biological changes, which makes it very difficult to represent in a single figure. As suggested by different sources, an overall loss of at least 10 per cent occurs in the developing countries. However, the magnitude may range from negligible to cent percent in particular nematode species and crop.

In addition to causing direct losses individually, phytonematodes also favour the establishment of secondary, passive micro- organisms like fungi, bacteria, viruses etc. Nematodes cause mechanical wounds, which serve as avenue for the entry of secondary microorganisms (Ravichandra, 2008). This complex association results in severe damage to planting material.

Postharvest diseases due to nematodes can be managed through restricting the movement of infected planting material to uninfected areas; use of uninfected, healthy planting materials; use of treated planting materials; improvements in the cultural practices at the growing site; timely and careful harvesting; use of nematicides both at pre- and postharvest stages; employment of some physical means like heat, radiation etc; improved storage techniques and integration of these methods. By maintaining hygienic conditions during harvest, transportation, storage and packing most of the postharvest damage due to nematodes can be minimized. Of all the methods, however, regulatory measures like quarantine is more practical and effective in restricting the movement of nematode infected plant materials and contaminated soil into a state or country. Contaminated plant material should be treated (hot water or nematicides) to kill the plant parasitic nematodes before planting to prevent the further postharvest damage. These various measures are primarily aimed at either reduction or wiping out of stages of nematode from the site or protection of host from infection or creation of unfavorable host and/or environmental conditions for the nematodes.

A wide variety of fungal and bacterial pathogens cause postharvest disease in fruits and vegetables. Some of these infect produce before harvest and then remain quiescent until conditions are more favourable for disease development after harvest. Other pathogens infect produce during and after harvest through surface injuries. In the development of strategies for postharvest disease control, it is imperative to take a step back and consider the production and postharvest handling systems in their entirety. Traditionally fungicides have played a central role in postharvest disease control. However, trends towards reduced chemical usage in horticulture are forcing the development of new strategies. Controlling or reducing disease relies on integrated crop and postharvest management, with attention to fungicide application, crop hygiene and nutrition, and the management of ripening, to optimise advantages conferred by the plant’s natural resistance factors that prevent and delay disease development. Agricultural production and food distribution systems have evolved over many years to a complex system which allows for nearly year-round supply of most fresh commodities through longterm storage and long distance shipments to consumers. The expectation of year round supplies has resulted in increased challenges for postharvest handling systems. The availability of fungicides for disease management likely played a major role in the evolution of our current system of food distribution (Mitcham, 1999). With the recent loss of registration of many postharvestfungicides and more expected under the Food Quality Protection Act (FQPA), as well as consumer pressure to reduce the amount of chemicals used on food, the challenge to maintain our current system of food distribution increases.

The potential for significant economic losses from decay caused by postharvest pathogens is greater than is often realized. Harvesting and handling, and the attendant costs for labor and postharvest chemical treatments, can increase the cost of fresh fruits and vegetables several fold from the field to the consumer. Therefore, any produce lost in storage is worth more economically than an equivalent amount lost in the field. Considering economics and the problem of world hunger, it is imperative to understand the importance of postharvest disease and to continually strive to reduce postharvest losses from pathogens. In recent years, many international organizations have identified the necessity of reducing postharvest food losses as an important worldwide goal. While postharvest losses vary from season to season, an average loss of 10% to 30% after harvest is an average estimate. Significantly higher losses are not uncommon in developing countries. The extent of these losses justifies increased research efforts in postharvest pathology (Carl E. Sams, 1994). Chemical treatments and irradiation have effectively reduced the number of microorganisms on various commodities. However, consumer fears associated with chemical residues and the effects of ionizing radiation on fresh produce are forcing the development of alternative protection methods. Also, many pathogens have developed resistance to several commonly used chemicals, while other decaycausing microorganisms currently cannot be controlled by chemicals. Therefore it is better to seek control strategies that will supplement or replace current disease control methods.

Mycotoxins are naturally occurring toxins produced by certain molds and can be found in food. The molds grow on a variety of different crops and foodstuffs including cereals, nuts, spices, dried fruits, apples and coffee beans, often under warm and humid conditions. Mycotoxins can cause a variety of adverse health effects and pose a serious health threat to both humans and livestock. The adverse health effects of mycotoxins range from acute poisoning to long-term effects such as immune deficiency and cancer. A scientific expert committee jointly convened by WHO and the Food and Agriculture Organization of the United Nations (FAO), called JECFA, is the international body responsible for evaluating the health risk from natural toxins including mycotoxins. International standards and codes of practice to limit exposure to mycotoxins from certain foods are established by the Codex Alimentarius Commission based on JECFA assessments.

Mycotoxins are toxic compounds that are naturally produced by certain types of molds (fungi). Molds that can produce mycotoxins grow on numerous foodstuffs such as cereals, dried fruits, nuts and spices. Mold growth can occur either before harvest or after harvest, during storage, on/in the food itself often under warm, damp and humid conditions. Most mycotoxins are chemically stable and survive food processing. Several hundred different mycotoxins have been identified, but the most commonly observed mycotoxins that present a concern to human health and livestock include aflatoxins, ochratoxin A, patulin, fumonisins, zearalenone and nivalenol/deoxynivalenol. Mycotoxins appear in the food chain as a result of mold infection of crops both before and after harvest. Exposure to mycotoxins can happen either directly by eating infected food or indirectly from animals that are fed contaminated feed, in particular from milk.

In managing diseases of horticultural crops, pathogen quiescence has important implications in timing prophylaxis, the reduction of stresses that trigger the transition of quiescence to aggression, and managing the harvested crop to prolong quiescence to the point at which yield is no longer affected. The inception of pathogen quiescence and its maintenance on or within the host implies a dynamic equilibrium between the host, the pathogen, and their environment. Physiological and physical changes in the host, its environment, or both trigger changes in that equilibrium to permit the pathogen to resume aggression. Microorganisms lying on the host surface constitute a potential latent infection; as can be the case with Botrytis cinerea conidia that are prevented from germinating by antagonistic bacteria on leaf surfaces (William R. Jarvis, 1994). Quiescence can run the spectrum from the ungerminated spore; through symptomless, internal infections; to visible but nonexpanding lesions, such as ghost spot of tomato (Lycopersicon esculentum) to expanding lesions on banana caused by Colletotrichum musae and on avocado caused by C. gloeosporioides.

A latent, dormant, or quiescent parasitic relationship is a condition in which the pathogen spends long periods during the host’s life in a quiescent stage until, under specific circumstances, it becomes active. Epidemiologists might refer to the period from spore landing until the parasitized tissue produces new spores as a latent period (Dov Prusky, 1996). The term “period of quiescence” is referred to differentiate the quiescent parasitic relationship from the latent period. Quiescence can be enforced during the various processes of fungal attack, which suggests that quiescence may or could occur during any of the processes leading from fungal germination to colonization.

Postharvest handling is the stage of crop production immediately following harvest, including cooling, cleaning, sorting and packing. The instant a crop is removed from the ground, or separated from its parent plant, it begins to deteriorate. Postharvest activities include harvesting, handling, storage, processing, packaging, transportation and marketing. Losses of horticultural produce are a major problem in the postharvest chain. The diseases which develop on harvested parts of the plants like seeds, fruits and also on vegetables are the postharvested diseases. The amount or extent of damage depends mainly on the pathogen(s) involved, on the condition of the products and the condition of storage. Major tips to avoid postharvest losses include Tips to avoid postharvest losses include assessing maturity, to check your water quality, to check water temperature, avoid injury, keep the produce cool and proper storage.

“Storage” means the phase of the postharvest system during which the products are kept in such a way as to guarantee food security other than during periods of agricultural production at the marketing level, to balance the supply and demand of agricultural products, thereby stabilizing market prices. Grain, which includes dry kitchen ingredients such as flour, rice, millet, couscous, cornmeal, and so on, can be stored in rigid sealed containers to prevent moisture contamination or insect or rodent infestation. For kitchen use, glass containers are the most traditional method. Maturity indices are the sign or indication the readiness of the commodity for harvest. It is the basis for determining harvest date. Postharvest losses occur between harvest and the moment of human consumption. They include on-farm losses, such as when grain is threshed, winnowed, and dried, as well as losses along the chain during transportation, storage, and processing.

Postharvest loss of fruits and vegetables is defined as “that weight of wholesome edible product (exclusive of moisture content) that is normally consumed by human and that has been separated from the medium and sites of its immediate growth and production by deliberate human action with the intention of using it for human feeding but which for any reasons fails to be consumed by human.” Not only quantity and quality but even the appearance of fruits and vegetables are affected, and their market value is reduced. Most ‘skin deep’ injuries such as ‘fly speck’ in apples do not affect the edible part. Some infections are not harmful as they occur on inedible parts and can be trimmed off before consumption ego Colletotrichum spots on the outer leaves of cabbage]. Fresh fruits and vegetables are perishable and highly prone to these losses because they are composed of living tissues. These tissues must be kept alive and health throughout the process of marketing. These are composed of thousands of living cells which require care and maintenance (Alao, 2000). The pathological rots are the most serious which is followed by mechanical injury. Pathological rots in combination with mechanical damage cause serious damage to the perishables. Environmental factors such as temperature, relative humidity and oxygen balance most especially during storage are also greatly responsible for damage also environmental conditions such as temperature and humidity are responsible for rendering fruits and vegetables susceptible for pathological attacks (Yahaya and Mardiyya, 2019). Fungi and bacteria are the major pathogens, which cause postharvest diseases in crops leading to about 30 % loss. Normally diseases will be more at improper temperature and relative humidity. Apart from causing disease, pathogens are also involved in ethylene production, which hastens the deterioration of the product.

Fruits, nuts and vegetables play a significant role in human nutrition, especially as sources of vitamins, minerals, dietary fibre, and antioxidants. Increased consumption of a variety of fruits and vegetables on a daily basis is highly recommended because of associated health benefits, which include reduced risk of some forms of cancer, heart disease, stroke, and other chronic diseases. Both quantitative and qualitative losses occur in horticultural commodities between harvest and consumption. Qualitative losses, such as loss in edibility, nutritional quality, caloric value, and consumer acceptability of fresh produce, are much more difficult to assess than are quantitative losses. Quality standards, consumer preferences and purchasing power vary greatly across countries and cultures and these differences influence marketability and the magnitude of postharvest losses. Postharvest losses vary greatly across commodity types, with production areas and the season of production. Losses of fresh fruits and vegetables in developed countries are estimated to range from 2 percent for potatoes to 23 percent for strawberries, with an overall average of 12 percent losses between production and consumption sites. In contrast, the range of produce losses in developing countries varies widely. Losses at the retail, food-service, and consumer levels are estimated at approximately 20 percent in developed countries and about 10 percent in developing countries (Adel A. Kader and Rosa S. Rolle, 2004 ). Overall, about one third of horticultural crops produced are never consumed by humans. Reduction of postharvest losses can increase food availability to the growing world population, decrease the area needed for production, and conserve natural resources. Strategies for loss prevention include use of genotypes that have longer postharvest-life, use of integrated crop management systems and good agricultural practices that result in good keeping quality of the commodity and use of proper postharvest handling practices in order to maintain the quality and safety of fresh produce.

Food waste and loss is an enormous issue worldwide. The FAO states that ‘Hunger is still one of the most urgent development challenges, yet the world is producing more than enough food’, but a vast amount of what is produced gets lost on its way from the field to the consumer. According to the FAO, about 30% of cereals, 20% of dairy products, 35% of fish and seafood, 45% of fruits and vegetables, 20% of meat, 20% of oilseed and pulses and 45% of roots and tubers are lost or wasted. Postharvest food loss is defined as measurable qualitative and quantitative food loss along the supply chain, starting at the time of harvest till its consumption or other end uses. Food losses can either be the result of a direct quantitative loss, for example, during the process of harvest or transport or arise indirectly due to losses in crop quality such as undesired sprouting or water loss. Postharvest food loss consists of many factors, which have not changed much in the last 40 years and so postharvest food loss in general has not changed much. Figure 1 illustrates the main reasons for food loss along the supply chain and is based on ‘The food pipeline’ published by Bourne in 1977. Food loss is highest during storage due to pathogens (insects, bacteria and moulds), environmental conditions (e.g. rain, humidity, heat and frost), sprouting and quality loss (rancidity, water loss and saccharification) or animals (rodents and birds). Recently published data for Switzerland have shown that about 53%-55% of the initial fresh potato production and 41%-46% of the initial processing potato production are lost mostly due to pathogen infection, saccharification, water loss of tubers and early sprouting during storage (Buchholz et al, 2018).

10.1 INTRODUCTION

‘Tissue culture’ is commonly used as a blanket term to describe all types of plant cultures, viz., callus, cell, protoplast, anther, meristem, embryo and organ cultures (George, 1993). It relies on the phenomenon of cell totipotency. The different techniques of culturing plant tissues may offer certain advantages over traditional methods of propagation.

Growing plants in vitro in a controlled environment, with in-depth knowledge of the culture conditions and the nature of the plant material, ensures effective clonal propagation of genetically superior genotypes of economically important plants. Micropropagation has become an important part of the commercial propagation of many plants (George and Sherrington, 1983; and Zimmerman et al., 1986) because of its advantages as a multiplication system (Pierik, 1997 and Razdan, 2003). Several techniques for in vitro plant propagation have been devised, including the induction of axillary and adventitious shoots, the culture of isolated meristems and plant regeneration by organogenesis and/or somatic embryogenesis (Williams and Maheswaran, 1986; and Gautheret, 1985).

Tissue Culture is becoming as an alternative means to vegetative propagation of plants. In vitro growing plants are usually free from bacterial and fungal diseases. Virus eradication and maintenance of plants in virus free stage can also be rapidly achieved in cultures (Sharma, 2016).

9.1 INTRODUCTION

When a new individual arises from a somatic cell without formation of a seed, it is called vegetative propagation. Vegetative propagation occurs naturally (i.e., natural vegetative propagation) in many crops, and profitably exploited in horticulture using either conventional or biotechnological artificial techniques. We shall discuss conventional artificial vegetative propagation in this chapter including cuttings, grafting, budding, layering, suckering, etc. They have been widely used for commercial propagation of fruit trees and ornamental shrubs.

8.1 INTRODUCTION

Natural methods of vegetative propagation include strategies that the plants have developed for self-multiplication or perpetuation. Natural vegetative propagation is mostly a process found in herbaceous and woody perennial plants, and typically involves structural modifications of the stem, although any horizontal, underground part of a plant (whether stem, leaf, or root) can contribute to vegetative reproduction of a plant. In crops like ginger, turmeric, onion, garlic, gladioli, and dahlia etc. they continue to grow from buds that are present on the surface of the stem. In some plants, like sweet potato adventitious roots can give rise to new plants. In Bryophyllum and Kalanchoe, the leaves have small buds on their margins. On detachment from the plant, they are able to grow into independent plants and they may also start growing into free plants if their leaves were made to grow in the soil. In nature, vegetative reproduction occurs through underground stems, sub-aerial stems, bulbils, leaves and even roots.

7.1 INTRODUCTION

Grafting and budding are horticultural techniques used to join parts from two or more plants so that they appear to grow as a single plant. In grafting, the upper part (scion) of one plant grows on the root system (rootstock) of another plant. In the budding process, a bud is taken from one plant and grown on another. The practice of grafting can be traced back 4,000 years to ancient China and Mesopotamia. As early as 2,000 years ago, people recognized the incompatibility problems that may occur when grafting olives and other fruiting trees.

7.2 ROOT STOCK

The part of the graft that provides root system to the grafted plant is known as rootstock. It is, normally, raised by seeds in the seedbed and then, transplanted in the nursery bed for budding and grafting. Rootstocks are also raised in pots and polythene bags.

6.1 INTRODUCTION

The ultimate success of an orchard enterprise largely depends upon the quality and genuineness of planting materials as nursery plants are the foundation of the orchard. Fruit crops, mostly being perennial in nature, call for utmost care in selection of cultivar, quality planting material and adoption of right technology for mass multiplication of planting material. Mistakes committed during the initial establishment of orchards cannot be corrected and will cause serious damage to production and productivity. The variation of scion-wood and rootstock has great bearing on the productivity of an orchard. Thus, it is of immense importance having all plants carefully labelled or otherwise marked. Cuttings taken from the mother plant will grow to have the same genetic qualities as the original plant. This is why the plants resulting from these cuttings are called “clones”. When a stem cutting is taken from a mother plant, the piece of stem will produce new roots if it is properly hydrated. Additionally, some plants can be grown from leaf pieces, or leaf cuttings and these will produce both stems and roots.

Thus, the progeny trees are the basic component for the multiplication of fruit plants and ultimately deciding the quality and productivity of the fruit crops. Hence, it is necessary to stock the true to type and best quality progeny trees.

In asexual methods of plant propagation, plant parts are being used as propagating materials. The plant from which the plant parts are collected is known as mother plant. There is every possibility of transmission of disease or pest which is present in the mother plant to the progeny. The mother plants have to be maintained properly to obtain disease free planting materials so that multiplication of disease/pest can be prevented. Thus, there is a need for the establishment of mother plant block/scion banks.

5.1 APOMIXIS

Apomixis is derived from two Greek words “Apo” (away from) and “mixis” (the act of mixing or mingling). It refers to the occurrence of an asexual reproductive process in the place of normal sexual processes involving reduction division and fertilization. During sexual reproduction, developmental steps occurring inside the ovule produce the female gametophyte (embryo sac) and following a double fertilization event give rise to embryo and endosperm structures. Apomixis can be best described as the reference to the asexual process. In some species, embryo sac is produced not as a result of meiosis and fertilization but by certain asexual processes. The occurrence of such asexual reproductive process in the place of normal seed reproductive processes of reduction division and fertilization is known as Apomixis. Such seedling plants produced in this manner is known as apomicts. ’’Apomixis’’ is used synonymously with ’’agamospermy’’ (Stebbins 1950), referring to the asexual production of seed.

Apomixis (asexual seed formation) is a phenomenon in which a plant bypasses the most fundamental aspects of sexual reproduction—meiosis and fertilization—to form a viable seed. Plants can form seeds without fertilization, and the seed genotype is consistent with the female parent. The development of apomictic technology would be revolutionary for agriculture and for food production as it would reduce costs and breeding times and also avoid many complications typical of sexual reproduction (e.g., incompatibility barriers) and of vegetative propagation (e.g., viral transfer). The application of apomictic reproductive technology has the potential to revolutionize crop breeding. Apomixis is widely distributed among higher plants. More than 300 species belonging to 35 families are apomictic. It is most common in Gramineae, Compositae, Rosaceae and Rutaceae. Among the major cereals maize, wheat and pearl millet have apomictic relatives. Apomixis is reproduction where only one parent passes genes to the offspring (King, 2006). Apomictically produced offspring are genetically identical to the parent (clones).The method is mostly seen in plants, especially flowering plants. Apomixis was defined by Hans Winkler (2008) as the replacement of the normal sexual reproduction by asexual reproduction, without fertilization. Propagation from cuttings or leaves, is not apomixis. Natural replacement of the seed by an asexual method is apomixis.

4.1 INTRODUCTION

The method of propagation in plants may be sexual or asexual. In sexual method of propagation, specialized reproductive cells called gametes are formed by the process of gametogenesis. Fusion of the male and female gametes leads to the development of an embryo and eventually the seed.

4.2 GAMETOGENESIS

The production of male and female gametes is known as gametogenesis. It occurs within microspores and megaspores. It involves only mitosis. It is of two types: (1) microgametogenesis and (2) megagametogenesis.

3.1 INTRODUCTION

A nursery is a place, where seedlings, saplings, trees, shrubs and other plant materials are grown under intensive care and maintained until they are ready for final transplanting in the main field. The importance of the best quality planting material as an initial investment is a well-realized factor for persons engaged in horticulture field. So, nurseries have great demand for the production of plants, bulbs, rhizomes, suckers and grafts. But in general, good quality and assured planting material at reasonable price is not available in most of the cases. Nursery is the basic need of horticulture. Plant propagation techniques and practices is the core of horticulture nurseries. The planting materials for horticultural plantations are raised from seeds and vegetative parts. The difficulty of procuring seeds and their rising cost makes it necessary to find means to increase seedling survival and growth.

2.1 INTRODUCTION

Several propagation structures are helpful in propagation of horticultural crops. These structures are helpful for seed germination, rooting of cuttings, layering, grafting etc. and other hardening operations. The structures which facilitate propagation of plants are called propagation structures. Propagation structures are required for propagating plants by seed, cuttings and grafting.2.2

GREENHOUSE

Greenhouse is a structure covered with glass or polythene for protection against adverse climatic conditions as well as to provide optimum environment for growth of the plants. Greenhouse has been used long back by horticulturists as a means of forcing rapid growth of plants and extending the growing season particularly in colder areas. Plants are grown or cuttings are rooted in a greenhouse when the atmospheric condition does not permit for raising them in outdoor conditions. Modern greenhouses are equipped with regulatory mechanisms for controlling temperature, light intensity, air, humidity etc. Plants in green house are grown in the ground bed or bench type raised beds. The size of the greenhouses and dimensions of beds vary according to the need of propagators. Glass covered greenhouses are expensive but they have long life. However, for short-term benefits, plastic covered greenhouses can also be made. Plastic covered greenhouses are lighter than glass covered ones but there is increase in humidity is such houses, especially in winters, which results in undesirable water drops on the plants. It can however be overcome by making adequate ventilation. Polyvinyl chloride (PVC) has also been used in construction of greenhouses but it tends to darken pre-maturely in sunlight. In India, construction of temporarily low-cost poly houses is in fashion for raising nursery of fruit plant in off-season. Such low-cost greenhouses are constructed either on wood or metal framework and are covered with polyethylene sheet of 0.10 to 0.15mm thickness, which is resistant to ultra-violet rays. These houses are equipped with thermostat, cooler or an air conditioner or humidifier etc for rigid control on temperature and humidity. Greenhouses made from fibre glass sheet are more durable than the polythene houses, but are quite expensive. In greenhouses, two types of beds are used for raising seedlings. In greenhouses, the beds may either be prepared on ground itself or raised beds or bench type beds are used. Greenhouse structures vary from elementary home constructed to elaborate commercial installations.

1.1 WHAT IS PLANT PROPAGATION?

Propagation of plant is defined as multiplication and perpetuation of new individuals from a selected plant having all the characters of the original one. It is the process of increasing the number of plants of a particular species or cultivar. It refers to the multiplication of an individual plant or group of plants, which have specific value to mankind. New plants or new individuals are required for establishing new plantings/new gardens/new orchards.

Ornamental plants that are adapted to an aquatic environment are commonly grown in water gardens and pools. They include those that are entirely submerged or floaters that are free living in the surface water or having roots anchored firmly in the ground beneath and marginal plants that thrive along the edges of water bodies and in shallow water. Spectacular flowering plants like the lotuses and water lilies to plants like the tape grass that are entirely submerged and grass like are grown in natural or structured fresh water habitats throughout the world. Many of these are also inhabitants of aquaria.

Some of the popularly grown water garden plants are listed below:

Acorus calamus

Araceae

Sweet Flag, Vayambu

Plants are rhizomatous herbs adapted to low lying and wet situations. The leaves are closely spaced, distichously arranged and resembling a fan, leathery, dark green, smooth and shiny. The inflorescence is a spadix that emerges from the middle of the terminal leaf. Plants are valued medicinally for their aromatic rhizomes and are also commonly grown as marginals of water gardens.

Grasses, bamboos, sedges and rushes are plants that are being used increasingly in xeri-scaping and in marsh gardens for getting the benefits of their unusual foliage textures and colours. Their hardiness, stature and canopy frame make them more suited for specimen planting in gardens and landscapes.

GRASSES

Grasses are the most successful of monocots belonging to the family Poaceae that are found the world over. Low growing perennial grasses are used to make attractive lawns in gardens and to provide a desirable turf cover for various situations. A number of species belonging to various genera differing in leaf colour, shape and growth pattern are used for this purpose. Mixtures of different varieties of grasses are also used for making turf having desirable blends of textures and hardiness. Tall bushy grasses having a mound-like or fountain–like habit and fine to velvety surfaces are grown for their textural and architectural features in landscaping. Many are grown as specimen plants for their display value at flowering. In selecting grasses for gardens, their potentially invasive nature is to be taken into account and seed dispersal controlled by timely cutting.

Grass species that thrive in the hot and humid tropics are called warm-season grasses and include Bermuda grass, Carpet grass and St. Augustine grass. Cool season grasses that are adapted to temperate regions and thrive at temperatures of 10 to 20^oC include Blue grass, Fescues and Zoysia.

Pteridophytes such as ferns belonging to several families, selaginellas popularly called ‘club mosses’ belonging to Selaginellaceae and the Lycopods which resemble both these, belonging to Lycopodiaceae are shade loving plants adapted to cool and moist or hot and humid ecosystems of tropical to temperate climates. They are mostly epiphytic or lithophytic and are grown as foliage ornamentals in a fernery or in shaded areas in gardens. Many are favoured indoor plants.

Popularly grown ferns, lycopods and selaginellas of gardens are listed below:

Adiantum capillus-veneris

Adiantaceae

Common Maidenhair fern

Plants are shade loving bushy lithophytes and have delicate looking thin black stems carrying light green oblique-ovate fronds. They are pot grown as ornamental foliage plants.

Adiantum decorum

Syn. Adiantum raddianum

Adiantaceae

Maidenhair fern

Terrestrial or epiphytic members of the family Bromeliaceae that are grown in gardens for their unusually coloured and patterned leaves or showy inflorescences and fruits are referred to as ornamental ‘Bromeliads’. Being low growing, they are ideally displayed in containers or as epiphytes. They are sun loving, suckering in habit and have xerophytic adaptations. The leaves are tough and fibrous often with spiny margins and sheathing leaf bases that hold water. A grayish-white waxy or powdery coating often covers the lamina. Certain bromeliads have a water collecting depression at the center. Inflorescences are sunken, erect or reclining, with condensed or long and much branched stalks carrying colourful bracts and usually, less showy flowers. In many, the terminal leaves become brightly coloured at flowering. These and the floral bracts remain showy even after the flowers are shed.

Ornamental bromeliads popularly grown in gardens include the following:

Aechmea blanchetiana

Copper leaf bromeliad

Plants have strap like leaves that develop streaks of coppery red colour on the upper surface in bright sunlight.

Aechmea burle-marxii

Burle-Marx bromeliad

These are a broad group of plants that have evolved in situations characterized by very high day temperatures and low night temperatures with very low available moisture in the growing medium. Their plant body is modified to conserve moisture with physiological adaptations that help to reduce moisture loss considerably and to survive in hot desert situations or drought conditions. Stems, leaves and roots of these plants are fleshy and rich in watery mucus. The unusual morphological features that these plants have developed to enable them to survive in their harsh native habitats, set them apart from other plants and have given them rarity value when grown as ornamentals. They are hence displayed individually or grown in a rockery where a landscape of rocks and stones highlight their features and at the same time provide desirable contrast with other garden plants. Many members of Cactaceae, Crassulaceae, Aizoaceae, Euphorbiaceae, Asphodelaceae and Agavaceae belong to this group and are commonly referred to as rock garden plants.

Among garden plants, herbaceous perennials that produce perennating structures like bulbs, corms, tubers, rhizomes or fascicled tuberous roots are called bulbous plants. They belong to various plant families such as Amaryllidaceae, Cannaceae, Heliconiaceae, Iridaceae, Liliaeceae, Musaceae, Ranunculaeceae and Zingiberaceae. The possession of perennating structures that are modifications of plant parts- mostly stems- is common to these plants. These modifications aid in their vegetative propagation as the dormant buds associated with them regenerate when conditions are favourable to result in new plants. In both tropical and temperate climate zones, bulbous plants have evolved and naturalized in several ecological ‘niches’. Many of these have been domesticated centuries ago and are familiar garden plants. Generally, bulbous plats are adapted to grow vegetatively putting forth shoots carrying a limited number of leaves. When further vegetative growth has ceased these shoots produce terminal or basal inflorescences. Bulbous plants are grown and displayed in clumps.

Based on the requirement of relatively low or high temperatures for sprouting and flowering they are classified into warm- season bulbous plants and cool-season bulbous plants. These groupings are not exclusive and many plants have evolved varieties that thrive in both seasonal conditions.

Pants that tend to climb vertically on to supports are called climbers. reepers are plants that tend to creep or ramble over the ground or other surfaces spreading horizontally. These have showy flowers or decorative foliage. Climbers are conventionally used in gardens to cover fences, bare walls and tree trunks. They are used to provide ornamentation in a vertical aspect. Creepers on the other hand are used as ground covers and function as decorative elements in a horizontal aspect.

CLASSIFICATION OF CLIMBERS AND CREEPERS

Depending upon their habit, vigour, duration, nature of flowering, adaptations for climbing and shade tolerance, they can be classified as follows:

H erbs include non-woody or succulent-stemmed plants that are relatively shorter in stature when compared to shrubs. Based on their ornamental nature they can be broadly grouped as Flowering Herbs and Foliage Herbs. Flowering Herbs can be further classified based on their duration into Annual Flowering Herbs and Perennial Flowering Herbs. Foliage herbs of a perennial nature are further differentiated into monocotyledonous and dicotyledonous foliage herbs.

ANNUAL FLOWERING HERBS

Annual herbs are grown in gardens for their spectacular beauty when they are in flower. They are seasonal in habit and have duration of up to four months. Most of them have a short vegetative phase, which is followed by continuous flowering for several weeks. They are used in gardens for obtaining various colour effects. Varieties of annuals having analogous or similar flower colours can be grouped in flowerbeds and flower borders for monochromatic effects. For contrasting colour effects, varieties having complementary or contrasting colours like violet and yellow or blue and orange as well as green and red can be used. For colour blending effects, flowers having different shades of the same colour can be grown.

Shrubs are the most diverse groups of ornamentals grown in tropical gardens. In habit they are hardy perennials having low spreading woody branches. They vary widely in stature and include dwarf bushes to those attaining the stature of small trees.

IMPORTANCE AND USES OF SHRUBS

Shrubs are quick growing and many of them flower continuously in the humid tropics. Their variability in flower colours and foliage characteristics and their easiness in propagation by vegetative means make them garden favourites. The various uses to which shrubs are put to in gardens are detailed below: -

In A Shrubbery : Grouping of shrubs in a shrubbery is done to display the attractiveness of their flowers and foliage. In temperate situations shrubs grown in shrubberies include Rhododendron, Peony, Fuchsia, Buddleia, and Camellia while in the tropics and subtropics, the range of shrubs available for planting are very wide.

As Focal Point Plants : Shrubs that are ever flowering like Hamelia and Hibiscus or those that have spectacular flowers such as Mussaenda, Neerium and Ixora are grown as focal point plants in small gardens. They are also grouped for mass effect in large gardens.

Trees are the largest plant components of gardens and landscapes. However much architectural features dwarf them, for human beings, they are the largest living entities in the environment. Profoundly influencing our habits, styles of habitation, culture and daily life, trees have been revered, sanctified and given symbolic importance and above all, depended upon as means of livelihood by entire communities through the ages. Through folklore, traditional knowledge and rituals, the usefulness of trees has been handed down from generation to generation-in societies all over the world. In India, cave paintings and carvings in addition to ancient literary works document the aesthetic and medicinal knowledge of our forefathers about trees found in the sub-continent.

Trees differ in stature, branching habit, girth of trunk and branches, canopy structure, outline and crown shape. The colour of the foliage, its texture, glaze, shape and size, foliage colour, floral features and season of flowering also differ among trees. These characteristics in addition to giving distinctiveness, also determine their ornamental use in gardens and landscapes. In tropical gardens evergreen dicotyledons and palms dominate among the trees, whereas in temperate situations evergreen conifers are selected over the deciduous dicots for tree planting. Palms among trees are universally grown as avenue trees or as clumps in areas where they can be easily grown while the other trees are grown as such or pruned and trained into various forms or as bonsai in gardens.

Introduction

Considering the accountable post-harvest losses which is approximately 30-35 percent, food processing becomes an extremely important sector for preventing the losses and feeding the growing population. The Indian food industry is poised for huge growth, as currently valued at US$ 1.3 billion with compound annual growth rate of 20 per cent per year, increasing its contribution to world food trade every year. In India, the food sector has emerged as a high-growth and high-profit sector due to its immense potential for value addition, particularly within the food processing industry. Increasing population of the country and high cost of fuels have also created a demand for new alternate sources of energies for post-harvest processing of foods. Solar food processing technologies may become a viable option that provides good quality foods at low or no additional fuel costs. The energy policy of the developing countries now focuses on the clean renewable energy to create a further reduction of the petroleum import and to alter the utilization of petroleum energy toward the utilization of solar energy. It is an interesting fact that most of the developing countries fall in the climatic zone where the insolation is considerably higher than the world average of 3.82 kWh m-2 (Majumdar 2015). The daily horizontal insolation of India is approximately 5.80 kWh m-2 (Visavale 2009, Visavale et al. 2011). Solar dyers are an alternative to traditional drying technique and a contribution towards the solution of the problems of the open sun drying from perspective of renewable and clean energy. The International Energy Agency (IEA) declared in its 2011 solar energy perspectives executive summary (SEP 2011): “Solar energy offers a clean, climate-friendly, very abundant and inexhaustible energy resource to mankind, relatively wellspread over the globe. Its availability is greater in warm and sunny countries that will experience most of the world’s population and economic growth over the next decades.

Introduction

The thermal performance of a building refers to the process of modeling the energy transfer between a building and its surroundings. For a conditioned building, it estimates the heating and cooling load and hence, the sizing and selection of HVAC equipment can be correctly made. For a non-conditioned building, it calculates temperature variation inside the building over a specified time and helps one to estimate the duration of uncomfortable periods. These quantifications enable one to determine the effectiveness of the design of a building and help in evolving improved designs for realizing energy efficient buildings with comfortable indoor conditions. The lack of proper quantification is one of the reasons why passive solar architecture is not popular among architects. Clients would like to know how much energy might be saved, or the temperature reduced to justify any additional expense or design change. Architects too need to know the relative performance of buildings to choose a suitable alternative. Thus, knowledge of the methods of estimating the performance of buildings is essential to the design of passive solar buildings.

Introduction

As the most of the conventional resources are depleting and can last only for about a few 30 to 50 years. Scientists worldwide are looking for alternative energy resources and they have come to an agreement that solar energy can provide much of our energy needs in the future. The major challenge before them is to store this energy. The radiation falling on the earth surface can be tapped and stored in no of ways. However, the most efficient way is done through the latent heat storage through PCM. The PCM has many added advantages i.e. high energy density, isothermal behavior, non-polluting and low cost. Nowadays, it gaining popularity worldwide and now seen as the most efficient way of thermal energy storage. There is a large number of PCM at use i.e. organic, inorganic, eutectic and salt hydrates. Their utilization depends on the user’s requirement technological constraints. They also serve the purpose of energy availability at night beside the uninterrupted supply during the day. They are seen as the materials for ensuring the environmental sustainability

Introduction

Solar energy could be converted to electricity both through thermal route and photovoltaic cells but the latter is more advantageous as it has no moving part, it doesn’t require water, a rare commodity specifically in arid regions. Moreover, the maintenance of PV systems is easy, it can be installed right at the place of utility, the system is modular and these are reliable having life more than twenty years and of course eco-friendly.

In photovoltaic cells, generally known as solar cells, charge carriers are generated by the incoming irradiance (energy greater than band gap) and these are separated and swept away by an internal electric field, which is created by either making metal semiconductors contact (Schottky barrier) or p-n junction or MIS (Metal Insulator Semiconductor) or SIS (Semiconductor Insulator Semiconductor) devices. The height of potential barrier at the junction determines the voltage and the flowing charge carriers contribute to the current when connected externally. The choice of material depends on its band gap, absorption coefficient, diffusion length, mobility of charge carriers, ease in contact formation, type of junction with thermal and electronic compatibility, availability of material, toxicity and several other fabricational opto-electronic and practical aspects. PV cells based on single crystal and polycrystalline silicon, amorphous silicon, CdS, CdTe, CuInGaSe, InP, GaAs etc. have been much studied. PV modules of efficiency above 16% on silicon and 10% on CdTe, CuInGaSe and 8-9 % on amorphous silicon are commercially available. Dye sensitized TiO₂ devices have also been receiving more attention with coloured panels for windows. Organic semiconductors are explored and more recently perovskite solar cell has been studied. Flexible solar cell panels based on thin film devices are in use. The applications have gone from solar lighting to operation of pumps, small and medium size equipment, stand alone and grid connected solar power plants, roof top and building integrated PV and now even energizing cars and aero planes. With technological advancement and enhanced production (233 GW in 2015) the cost of commercially available PV modules, which used to be high at one time has been brought down from 30 $/Wp in seventies to about $0.5/Wp at present.

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:

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.

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

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

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.

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

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).

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

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

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

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

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

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

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.