Harnessing Solar energy, Options for India

2. Solar Drying
Annually in India, about 35% of all agricultural produce worth roughly `500,000 million goes to
waste during the post-harvest period. 10 The loss is anywhere from 10% for durables (cereals and
pulses) to about 40% for perishables (fruits and vegetables). 11 Proper drying techniques for grains,
cereals and pulses can ensure effective storage and reduce losses. Grains are traditionally dried in
the open under the sun, but may be susceptible to moisture in case of a flash rain. Quality may also
be compromised since there is no control over temperature and external pollutants. Strengthening
the centralised food storage systems that currently suffers from poor quality control would be ideal.
However, food storage at the farm level will help increase the farmer’s income and security, as food
prices flatten out at the end of the crop season.
Fossil-fuel-fired dryers (commonly used in the food processing industry) can also be used to dry
large quantities of produce in a short period of time. However, this entails a significant initial
investment and ongoing fuel costs, as well as considerable damage to the environment. Solar
agricultural drying has received increased attention in recent years as it is more economical than
fossil-fuel-based drying and the equipment can be easily assembled with low-cost materials.
The Ministry of Food Processing Industries has framed a vision for the year 2015 to increase the
processing of perishables from 6 to 20%. 12 This can viewed as an opportunity for solar dryers or air
heating systems to penetrate the food processing industry. Hence, the twin objectives of solar
agricultural drying are to reduce agricultural wastage through remote independent solar drying
(with innovative financial mechanisms and institutional structure) and to reduce the energy
consumption through solar air heating systems.
2.1. Types of Solar Dryers
One of the more common dryers uses an FPC-based solar air heating system to absorb solar energy.
The temperature achieved through solar air heating/drying ranges from 50°C to 80°C. This
technology can act as a Partial Energy Delivery (PED) or a Full Energy Delivery (FED) unit. The PED
unit requires a back-up energy system and is used when the temperature requirement is high, while
an FED system can be used when the temperature is lower. A hybrid system of biomass and solar
energy can also be considered. Depending on the drying process, required temperature,
microclimate and site conditions, solar drying technology has the potential of saving considerable
amounts of conventional energy in a variety of industrial establishments.
Drying or process heat is crucial in any food processing industry. For example, solar dried tomatoes,
bananas, peaches and mango pulp have great potential in a global market. As solar drying is fairly
new in this segment, energy savings figures as compared to the use of fossil fuels are not readily
available. However, there are several installations of solar driers in industries such as fish drying,
leather tanneries, spice drying, drying of fruit pulp and paint shops (automobiles, motorcycles or
bicycles). Figure 19 depicts two such installations in India.
Solar Thermal Applications CSTEP | Page 93