The Solar Bubble Dryer
The Solar Bubble Dryer (SBD) is the latest low-cost drying technology developed by IRRI, Hohenheim University and GrainPro. The SBD is mobile and is completely independent from fuel or the power grid, and therefore has very low operating cost. It comes in different sizes, with current models having 0.5 and 1t batch capacity.
Fact sheet: Solar Bubble Dryer
How does it work?
The SBD uses energy from the sun in two ways. First the drying tunnel serves as a solar collector to convert the energy contained in the sun rays entering the transparent top of the drying tunnel to heat, which increased the temperature of the drying air for faster drying. Second it is equipped with a photovoltaic 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 the grains placed inside the tunnel. 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.
How does it compare to other dryers?
The SBD improves the traditional sun drying process, in which farmers spread 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 the grains from overheating, as it is common during sun drying at noon.
The SBD completely eliminates the re-wetting of grains during rain and losses due to animals, spillage and cars running over the grains if they are spread on roads.
Depending on the weather the drying rate during daytime is 0.5-1%/h. Drying time depends on the weather and the initial moisture content of the grains. Skin-dry grains can be dried to 14% moisture content within a sunny day. Wetter grains and during cloudy days 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 and bagged in the traditional sun drying.
Compared to a mechanical dryer the SBD is more flexible, requires lower investment and does not need fuel for heating the air or running the blower.
How to use?
The SBD can be used on any reasonably plane surface like a pavement, on a lawn or even in a harvested rice field with short stubbles. The SBD should be exposed to the sun throughout the day, so it needs to be set-up clear of buildings, trees or other structures that might provide shade at some time during the day. For best results:
Where to get a SBD?
The first version of the Solar Bubble Dryer was commercialized in September 2014. Units with 1t and 0.5t capacity can be bought from GrainPro.
GrainPro Philippines Inc.
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