Up and Coming

Solar bubble dryer for agricultural crops

Recently, the International Rice Research Institute (IRRI), Philippines, demonstrated a crop drying technology in Odisha. The solar bubble dryer (SBD) technology, jointly developed by GrainPro, a leading post-harvest solution providing company, IRRI and the University of Hohenheim, Germany, has been showcased for the first time in India.

Krishi Vigyan Kendra-Khordha, affiliated to the Indian Council of Agricultural Research-Central Institute of Freshwater Aquaculture, held a demonstration of the technology, which, it claims, dries up crop at a minimal cost. According to Dr Martin Gummert, an IRRI scientist, “The quantitative loss in the traditional sun-drying method is estimated to be in the range of 15-30 per cent between harvesting and milling. Due to quality loss, farmers do not get a proper price for their produce.” He further said, “After harvesting, the moisture content in paddy is found to be about 20-24 per cent and it needs to be brought down to below 14 per cent in order to protect the stock from insect attack and fungus formation.

The dryer uses solar energy in two ways. First, the drying tunnel serves as a solar collector to convert the energy drawn from the sun’s rays entering its transparent top to heat, which increases the temperature of the drying air for faster drying. Second, it is equipped with a photovoltaic (PV) system consisting of a solar panel, a deep cycle rechargeable battery and a controller to generate electricity that drives a small blower to move air through the drying tunnel, inflate the tunnel and remove the water evaporated from grains placed inside it. A simple roller dragged on ropes attached to the ends underneath the tunnel is used for mixing the grains without the need to open the tunnel. A rake for internal mixing is also available.

The SBD improves the traditional sun-drying process, in which farmers dry the paddy in the open under the sun, by protecting it from animals, insects, contamination and rain. The drying tunnel also provides a buffer for the temperature and protects grains from overheating, as it is common during the sun-drying at noon. Depending on the weather, the drying rate during daytime is 0.5-1 per cent per hour. Drying time depends on the weather and the initial moisture content of the grains. The manufacturers of the dryer claim that skin-dry grains can be dried to 14 per cent moisture content within a sunny day. During cloudy days and for wet grains, the drying might take two days. During rain and at night when the relative humidity of the air is high, the drying process stops, but by keeping the tunnel inflated, the grains can be safely kept inside the SBD, while they need to be collected into bags in the traditional sun-drying.

The first version of SBD was commercialised in September 2014. The SBD is in use in almost all Southeast Asian countries since 2016. The technology has been developed in such a way that farmers can dismantle the machinery and reassemble it on their own. It can be powered both from solar energy sources and traditional electricity. Products such as SBD will surely prove profitable for the agricultural sector in India, given that the country receives abundant sunlight and the farming sector is highly dependent on mechanical dryers, which have a higher capex as well as opex.


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