M Ramakrishna Rao, DJ Rao and SL Kumar discuss the role of solar energy for food processing and its applications for Indian food processors The growing energy demands and excessive exploitation of non-renewable energy resources have created some serious issues worldwide. Along with the associated costs and environmental implications of fossil fuels, their depletion is a major threat for mankind. In this scenario, the emergent technologies need to be built around renewable energy resources. In this context, solar food processing technology is important for the socioeconomic development of the country, especially for the rural population. It has become an interdisciplinary technology with a multiphase characteristic in the rural setup.
In this system, solar air dryers can be employed to provide a substantial boost to the food processing technology in India. The factors that have hindered the growth of the Indian food processing industry include paucity of capital inflow and energy scalability. To scale the constraints, a cabinet solar dryer, which uses solar photovoltaic to capture solar thermal energy, is an apt solution in the food processing context. Along with it being a renewable energy driven device, cabinet solar dryer has a diverse range of applications for food processing in particular. These include dehydration of fruits, vegetables, forest produce and medicinal herbs.  The device operates at zero energy cost, which is very cost-effective for small-scale food processing. Since the dryer has a modular structure and design, the capacity of the drying systems can be adjusted as per the market demand for products and the investment capacity. The technology also satisfies international standards of cleanliness and hygiene. Solar dryer technology is based on an inexhaustible and clean energy resource, protecting the environment from greenhouse gas emissions. Besides its role in promoting the food processing industry, a larger section of society can also get employment opportunities from this technology. This article discusses some of these groundbreaking innovations in solar dryer technology and its application for solar food processing. The principle of solar drying
In a solar dryer, solar radiations pass through a transparent glass window located on the top of the cabinet, which is oriented with a tilt equal to the latitude to collect maximum solar radiation. The cabinet is made of anticorrosive material (aluminium and stainless steel) and is designed in a modular fashion to meet varying size requirements and processing capabilities. During the drying process, the ambient air enters from the bottom of the cabinet and its three sides, and is heated with the solar radiation incident from the top window. Meanwhile, the heat energy is trapped in the cabinet and heats the trapped air. As a result the wavelength of solar radiation shifts to the infrared region, causing the greenhouse effect to come into action. This hot air then passes through the trays and thus carries the moisture from the product to the space above the trays and below the glass. Here, it is exhausted by three solar photo voltaic (SPV) fans arranged on the top of the cabinet. During this process, forced circulation of this air is achieved using these solar fans. Moreover, electrical heaters are also provided as standby source to meet any exigencies on cloudy days. A solar air dryer, in general, has the capacity to evaporate around 15 kg of water per day from food. The loading capacity for the device is 50 kg at the maximum for wet products. The loading capacities for solar dryers range from small-scale to commercial-scale, depending on the size and the number of dryers used. Salient features of the cabinet solar dryer
Some of the salient features of cabinet solar dryers are listed below. • Moderate temperatures in the range of 35–70°C can be achieved using the cabinet on clear sunny days. • Temperature differences ranging from 15–30°C between the ambient air and the air inside the cabinet can be achieved using the dryer on bright sunny days. • SPV fans are also provided with the device for forced circulation of air. • Temperature control can be exercised in the desired temperature range with the use of the solar-electrical mode built in the device. • A special glass filter is also provided with the device to cut off the UV radiations and solar intensity needed in special drying applications such as shade drying. • Products processed using the device are hygienic and meet the cleanliness specifications of the American Spice Trade Association (ASTA) of USA. • These dryers have modular design, are portable and can be configured according to the availability of space. • The device is fully scalable as per specific demand due to its modular design. • Available in sizes from small size to commercial production. • These dryers are multi-purpose, applicable to multi-crops and work for more than 300 days in a year. • These are small systems that are easily manageable and need minimal maintenance. The drying chambers can be arranged together in series or parallel rows according to the availability of space. • They are suitable for small group activity and are often independently operated and maintained by women entrepreneurs and youth in hilly areas. • It does not require conventional electricity for blowers and fans and it runs on solar photovoltaic fans with variable voltage. • They have high-efficiency as the solar radiation directly enters and heats the air entering into the drying chambers, unlike the air collector, which heats the air indirectly. They conserve photovoltaic electrical energy as well, as the moisture evolution from the product is the function of solar radiation, and the same radiation induces variable voltage and speed, unlike the air collector system which depends partially on electricity. The instrument measuring system indicates cabinet and ambient temperatures on a digital display or liquid thermometer. Along with the advantages of solar dryer, solar drying process itself has many inherent benefits. Some of these are listed below. • Solar drying has zero energy cost and uses pollution-free energy. • The process results in clean and uncontaminated food products. • Solar drying is an internationally compliant process in terms of cleanliness. • It is highly effective as a moisture-control process. • The technology has great potential to become a source of employment for rural population. Solar Food Processing Technology—Applications Solar food processing is a technology for dehydration of various types of food products—fruits, vegetables, forest produce, spices and sea-food—which can be solar dried till the permissible moisture content is attained. Thus, the technology helps in improving the preservation and shelf life of a wide range of food products in compliance with international cleanliness standards. Moreover, with a cabinet solar dryer, the process can be performed with zero energy cost, unlike electrical drying where energy and environmental pollution are the major issues. Also, with solar drying, most of the vital nutrients remain preserved in the processed food. The following case study discusses the implementation of a cabinet solar dryer by the Society for Energy, Environment and Development (SEED) for processing natural food products. It discusses the significance of solar food processing technology and cabinet solar dryers in the contemporary food industry. Solar Food Processing—A Case Study SEED was in search of an energy-efficient technology that could be used to process natural food products in compliance with international standards. Another major requirement was to employ a technology that was clean, efficient and cost-effective, especially from the perspective of rural applications for the Indian population. Along these lines, SEED opted for a cabinet solar dryer to dry a wide variety of food products. The organisation used the device to dehydrate a variety of food products—vegetables, herbs, medicinal plants and forest produce—on a pilot plant scale. The technical know-how of the dehydration process was released for solar dryer entrepreneurs in the training programmes. To prove the value addition and commercial viability of the dryers, field tests for mango bar processing were carried out for six years for test market development and the cost economic analysis of mango bar production. Starting from 10 kg of production per month, SEED scaled up the production to one tonne of mango bars and fruit bars per month in a short period. On recognising the successful implementation of solar dryer technology, the Ministry of New and Renewable Energy (MNRE) sanctioned a 50 per cent subsidy on the cost of solar dryer system during October 2008. This augmented the widespread adoption of solar food processing technology among the micro-enterprises, allowing entrepreneurs to start a food processing unit with 10 dryers as a unit of operation. The new solar micro-enterprises expanded their product ranges from green leafy vegetables to marine food.  Results Using the food dryer, SEED obtained hygienically dried and nutritionally preserved food products. Moreover, the whole process levied zero energy costs on the user and was absolutely clean and environment friendly. A wide variety of fruit bars were also processed using the cabinet solar drier. With the experience gained in processing mango bars, it became feasible to process and develop fruit bars such as guava, sapota, mixed fruits and amla supari. Among these products, mango bar (aampapad), prepared in a clean and hygienic environment with a special recipe, has been acclaimed as one of the best-quality products in the country. In the SEED Food Laboratory, senior scientists and technologists and qualified project assistants managed the applications laboratory where the dehydration process was carried out. Later, based on the results of the project, SEED imparted workers with training pertaining to solar food processing, exclusively based on the outcome of R&D, thus rectifying the procedures needed to obtain high-quality processed food products. Moreover, with the methodology, SEED gave rural workers the confidence to take up a big project which could become national programme in many states. The organisation succeeded in developing a good market for the device after the successful accomplishment of the project. The mango bar obtained using solar drying has been introduced in the US, the Middle East and African countries. Many other superior quality products processed in solar dryers have also been exported to these countries through cooperatives and sales networks. Repeat orders for exports have continued since the first consignment of mango bars was dispatched. The solar processed products have gained an edge over products which are processed by utilising conventional electricity. The solar dryer has helped the organisation to achieve global competence. Latest developments from the Indian perspective
The cost economics of solar micro-enterprises have been worked out for fruits and vegetables with an investment of Rs 10 lakh for one unit of 10 dryers. It can transact 10 tonne of fruits or fruit bars in dehydrated form. The value addition is two to two-and-half times the raw material and the profit is Rs 0.45 million per annum. This is an excellent profitable venture for rural India. The cost benefit analysis as per the tests conducted by SEED indicate that a commercial venture of a project with 10 solar dryers will have a pay back period of 2–2.5 years with the 50 per cent subsidy from MNRE. The profitability of the technology in terms of employment potential and income generation is established and acceptability of the product in the market is evaluated from its growing market demand. The feasibility of the technology for rural employment has been largely recognised. The solar dryer is an innovative food processing device, which has great application potential for Indian conditions, especially for the rural part of the country. With its implementation, high-quality processed food can be obtained with zero energy costs and virtually no pollution. The technology is also scalable in terms of its adaptability for various application needs. In the current scenario, when the rural population in India is largely unemployed, the technology is a huge source of permanent employment. Prof M Ramakrishna Rao is Founder and General Secretary, SEED DJ Rao is Treasurer, SEED Dr SL Kumar is Project Director, SEED |
