The Solar Bubble Dryer (SBD) is one of the low-cost drying technologies that aim to provide a simple and flexible alternative to sun drying. The construction of SBD is very simple, it can be easily transported to any places and completely independent of fuel and is therefore very cheap to operate. It comes in different sizes, with current models having either 0.5 or 1-ton batch capacity.
The SBD improves qualitatively and quantitatively the traditional sun-drying process and eliminates all losses due to spillage, animals, weather and vehicles running over the grains. During sunny days, the drying time is comparable to that of sun drying. Usually, a batch can be dried within a day.
During cloudy days or when it rains, drying time might take up to two days. The typical average drying rate is 0.5% moisture reduction per hour.
The main purpose of the Solar Bubble Drier is to protect grains from rain, transform solar energy into heat, and lead the drying air over the grains.
The Solar Bubble Dryer uses solar energy from the sun in two ways. First, the drying tunnel serves as a solar collector to convert energy from the sun’s rays (entering through the transparent top of the drying tunnel) to heat, therefore increasing the temperature of the air for faster drying.
Second, the SBD is equipped with a photovoltaic system that consists of solar panels for generating electricity - a rechargeable deep cycle battery for use at night and a blower to inflate the drying tunnel and move air through it. The air also removes water evaporating from the grains inside the tunnel. A simple roller with ropes attached to both of its ends is periodically dragged underneath to mix the grains without the need to open the tunnel. A rake for internal mixing is also available.
Author - Suryakanta Khandai* Caling Balingbing, Martin Gummert
*Senior Specialist, Post harvest & Rice Value Chain, IRRI India
