In the rural town of Bogale, Myanmar, 9 women and 16 men from the Myanmar Department of Agriculture, partner NGOs, and IRRI trained on how to operate and set up a newly designed dryer that could protect rice grains from sudden rain, pests and intense heat.
The name comes from the unique characteristics in its design: "solar" due to ambient conditions that provide heat from the air that flows inside the dryer and “bubble” for the dome-like shape of the cover or roof when it is set up.
“We tried several designs when we started, not one of them was the bubble design,” explained Engr. Ana Salvatierra, a researcher and postgraduate student from the University of Hohenheim, who works on the project.
“In the early designs, we included a chimney, but it was not very efficient to move air through the drying tunnel. And when there was a typhoon, the chimney fell. So, we reworked the design using small ventilators to move air. That’s when we also came up with the bubble concept,” she said.
The small ventilator inflates the bubble and circulates air. The airflow then removes water from inside the drying tunnel, where the grains are, and prevents overheating. To make sure that the grains dry evenly, they are stirred from time to time using a metal roller underneath the dryer.
“Based on our grain quality results in the lab, its drying performance is quite satisfactory,” said Engr. Salvatierra.
It can dry rice grains to a moisture content level of 10–13%, depending on whether the weather is dry or wet.
"For laboratory experiments that assess grain quality, our ideal moisture content is 14%," she said. "But, most of the time, the moisture content would depend on the milling facility, and if the grains will be used for consumption or for seed production.
"For example, if the grains will be used for seed production then it is advisable to dry to less than 12% to maintain good germination rates in storage over an extended period," she explained.
“The dryer is still a work-in-progress, but it has numerous advantages over a mechanical dryer for small farmers. It is affordable, easy to use, and is ideal for rural areas without a power grid or source of electricity,” explained Engr. Martin Gummert, head of the IRRI Postharvest Unit.
“Unlike most dryers that require higher amounts of paddy to dry, the solar bubble dryer has a capacity of 1 ton, which it can dry in 1-2 days depending if it’s sunny or rainy,” he added.
A typical recirculating batch dryer, for example, requires at least 10 tons of rice in just one drying operation. Because it needs electricity to run the dryer and fuel for the air heater at the same time, the investment and operating cost for such a dryer is higher.
“An additional benefit of the solar bubble dryer comes from its photovoltaic solar panels that provide power to the battery of the ventilators,” said Engr. Gummert.
“For example, in Myanmar, many farming villages do not have access to electricity. The solar panels and the battery can also be used for other purposes, such as lighting the house when the dryer is not used,” he explained.
Currently, the solar bubble dryer is being tested in Cambodia, Myanmar, the Philippines, Vietnam, and Africa.
“We need to test it in different countries to optimize its design, its management, adapt it to local conditions, and minimize investment cost,” said Engr. Gummert.