#401Solar dryers
401⸱AConcept
- Reduces drying time
- Protects coffee cherries
- Improves coffee quality
Solar dryers are used to dry coffee more efficiently during coffee processing, making use of solar energy. They consist of a cabinet of transparent polyethylene wrapped around a dryer frame with trays of synthetic mesh on which the coffee is spread for drying. Compared to conventional drying methods, solar dryers offer a more consistent drying time regardless of weather conditions, protect the coffee from external influences, increase the product quality by obtaining cleaner grain without stains, and maintain the bean size, flavor, and aroma of the coffee.
Usually, coffee is dried uncovered and in the open sun on cemented floors, tarpaulins, raised tables, or wire mesh. It is thereby exposed to rain and contamination by dust and debris, animal droppings, or insects. This increases the risk of molds, yeasts, bacteria, and toxin development, reduces coffee quality, and leads to losses. Climate change impacts such as unseasonal rainfalls, hailstorms, and winds even worsen the situation.
In solar dryers, the coffee is spread inside the cabin on the trays of synthetic mesh. The top and sides of the cabinet are closed through a transparent, foldable polyethylene tarp that lets solar radiation pass through.
The basic operating principle is to heat the indoor air using the sun's rays, thus reducing its relative humidity. Upon contact with moist coffee, the air tends to absorb water, thereby drying the grain. Due to the temperature differences between the indoor and outdoor air, the air circulates through the phenomenon of natural convection. In this way, the coffee gradually loses moisture. This allows for natural ventilation through air movement. The polyethylene tarp provides for higher drying temperatures and allows for consistency and relatively quick drying with less interruption of weather conditions. The fruit is prevented from absorbing moisture again during the night by closing the ventilation windows.
401⸱BTo be considered
The use of solar dryers is a good option for farmers, especially in regions with rainfall during the harvest period. For small-scale farmers (up to 1.5 hectares / 3 acres), the conventional use of tarpaulins with coffee turning and thin layer spread during drying is still a good and recommended method. However, with increasing rainfall uncertainties, to achieve consistency in drying time and quality of coffee, solar dryers can be recommended for all farmers.
The useful life of the entire structure is approximately 8 years, except for the polyethylene film, which has a useful life of between 2 to 3 years and which will have to be changed when it is very deteriorated.
Timing: Reduction of up to 30-40 % in drying time.
401⸱CImplementation
Materials
For dome-type solar dryers of the established dimensions: 3 to 3.4 m wide by 10 m long and a height of 2.25 m, with a processing capacity of 360 to 440 kg per solar dryer:
401⸱1Preparation
Solar dryer
401⸱2Procedure
Drying bed
If the grain is not drained before spreading it on the drying bed, all the water it contains drops on the floor of the dryer. When it evaporates, it will circulate inside the dryer and will not allow rapid and uniform drying. This can cause a prolongation of drying up to 7 or 8 days.
401⸱3
If temperatures are getting too high, always fold up the sides of the UV polyethylene tarp for aeration.
401⸱4
If the outside temperatures are high, the moving should be done as quickly as possible to avoid body dehydration due to the more extreme temperatures that can be reached inside the solar dryer.
401⸱5
Coffee bag
Great care must be taken at the drying point, since if the coffee is not removed at the correct time, over drying may occur. There must be a way to get the coffee out of the solar dryer as quickly as possible, it can be with baskets or small sacks depending on the space on the street in the middle of the drying bed.
Storage
Fill the dried coffee into gunny bags or polyester bags used exclusively for coffee.
Put the bag or storage container on a raised platform like pallets.
The storage place should be free of agro-inputs or other odor substances as coffee will absorb the odors.
Storage space should be well-ventilated to reduce dumbness.
If coffee is stored for more than a month, it should be checked and if dumbness is noticed, it should be redried.
Coffee must be processed after 30 days of storage, if possible.
401⸱DEconomic benefits
Better coffee quality
The effects of this tool can lead to a better coffee quality and therefore a higher income.
Lower labor costs
This tool might cause some extra workload and material costs in the beginning. However, its advantages ultimately result in lower labor requirements and therefore lower costs.
401⸱EGreen benefits
Energy saving
This tool doesn’t require electric energy or burning fuel. This saves resources and helps to reduce CO₂ levels in the atmosphere.