Abstract

The present crisis of fossil fuel shortages for producing thermal energy is creating increasing emphasis on the use of solar energy. Solar energy is freely available and is abundant in India for most of the year It is non-polluting and inexhaustible. This paper describes different solar energy systems developed in India with their technical and economical feasibility criteria for the post-harvest technology of cereal crops. These include drying, storage, processing, and household cooking in order to save costly fuels now used for these operations.

Post-harvest technology is a multidisciplinary field and includes various treatments and operations carried out on harvested crops for the purpose of preservation or enhancement of quality for marketing and consumption. In these operations, a considerable amount of produce is lost that needs to be minimized. The factors responsible for these losses include inefficient harvesting, threshing, handling, drying, processing, and cooking.

Solar equipment costs are generally high, relative to fossil fuel equipment costs, but operating costs are much lower. The variability of solar energy also limits its usefulness. However, as fossil fuel supplies dwindle and costs continue to rise, solar energy should become economically feasible for many applications in agriculture.

With the introduction of high-yielding varieties, fertilizer and better land and water management practices, crop yields have increased substantially (from 52 mill. t. in 1951/52 to 130 mill. t. in 1979/80) in India. However, the benefits of increased crop production are lost if management is lacking to handle this increased production with minimum grain losses during the post-harvest period.

Post-harvest technology is a multidisciplinary field and includes various treatments and operations carried out on harvested crops for the purpose of preservation or enhancement of quality for marketing and consumption. The major operations are threshing, drying, storage, processing, packaging, transport, and cooking. In these operations, a considerable amount of produce (about 10 to 15 per cent for cereal grains and 30 to 40 per cent for pulses) is lost, which needs minimization (Ojha 1976). The factors responsible for the above losses of food grains include inefficient harvesting and threshing, handling, drying methods, poor processing techniques, and inadequate cooking methods.

Solar energy can be used in many of the above post-harvest operations to save costly fossil fuel now in use. Some of these are crop conditioning, hot water production, and steam generation for crop processing and household cooking. Solar-powered cold storage is also technically feasible (Pandya et. al. 1980).

Solar energy is free, non-polluting, and inexhaustible. Based on the data available with the Indian Meteorological Department, the average solar radiation for India is about 420 cal/cm2-day ranging from 323 cal/cm2-day at Gulmarg to 511 cal/cm2-day at Jodhpur. The total energy received in India is estimated to be 60 X 10(16) kwh/year (Bhide 1975).

Although solar energy is free, the equipment required to collect and use it is not. Solar energy utilization devices and processes in general follow one of three pathways; (a) utilizing heat from the sun (thermal devices), (b) converting solar energy directly into electrical energy (photovoltaic), and (c) using photosynthetic and biological processes (biological). Major operations in post-harvest technology use heat from the sun at low temperatures (40° C-90° C). These devices have been developed to a stage at which they can be used on a large scale immediately.

Most of the devices depend upon collection of heat by either a flat plate collector or through concentrating systems and utilize thermal energy to heat a working substance (air, water or some other fluid) to do a desired function. The majority of these thermal devices use flat plate collectors that are simple and stationary. Concentrating systems, although capable of giving higher temperatures, are costly and complicated as they have to track the sun. A well-designed flat plate collector system is capable of attaining temperatures of 80-90° C at 70 per cent collection efficiency.

The development of suitable solar energy systems is a potential means of utilizing solar energy most effectively if based on least-cost criteria designs. Solar equipment costs, relative to fossil fuel equipment costs, have slowed solar development. But as fossil fuel supplies dwindle and fuel costs continue to rise, solar energy collection should be economically feasible for many applications in agriculture. Solar energy can reduce our dependence on fossil fuel, but at the present level of technology its availability is too variable and too limited to completely replace fossil fuel.

This paper describes different solar energy systems developed in India with their technical and economical feasibility criteria for the post-harvest technology of cereal crops. These include drying, storage, crop conditioning, processing, and household cooking.