Solar collector for Drying Cocoa: Prototype testing


Project Background

The department of Nariño, in Colombia, is famous for being one of the regions where the highest quality cocoa is produced. Its production is largely carried out by farmer families of African origin with very limited resources. In 2022, Social Solver launched a challenge for its community of engineers to propose innovative and sustainable solutions to improve the cocoa drying process in this region.

The challenge was to develop a drying system to reduce the moisture levels of the cocoa bean below 7% (quality required for export) using renewable energy or biofuels available in the area.

In the end, 30 participants from different countries such as Spain, Iran, Venezuela, Australia, France, Argentina, Switzerland, Indonesia, Portugal or Serbia joined the challenge. Finally, 14 different solutions were received.

Some proposed the use of commercial solutions and others, although less widespread, were being used in other countries to generate energy through agricultural waste.

The most suitable solution, and therefore the winner of this challenge, was the one developed by the French engineer Olivier Loidi. The design he presented is a completely new and innovative solution for the application of solar energy.

Olivier's idea consisted of a drying solar collector. It used the technology of high-performance flat solar collectors, similar to those used to heat water or oil in high-performance processes.

Due to the novelty of the design, it was necessary to manufacture prototypes and carry out field tests to demonstrate its feasibility.

Original design of the cocoa drying solar collector

Olivier Loidi's solution received and evaluated by Social Solver had the following characteristics, parts, and operation:

●  A double glass (replaced by plastic to make it lighter and cheaper) where the sun shines. Having a double glass makes its insulating properties better.

●  A double rack where a layer of cocoa beans is introduced.

●  A double glass like the first one to collect the radiation that bounces off the white stone floor or similar.

Design of the solar collector designed by Olivier Loidi.

Between each layer, there is a space of about 2 cm where the air circulates through small holes made in the base and in the upper part. This allows aeration in the cocoa fermentation stage, in addition to allowing moisture to escape.

In this way, instead of heating water or oil which later will heat the air to dry the beans, we directly heat the cocoa beans, achieving a higher temperature and faster drying. This way, the heating can be done even on cloudy days, due to the efficiency of the panel and to the high radiation available in the area.

Construction of solar collector prototype

However, during the construction of the prototype, certain changes were made to the original design due to the difficult access to materials and their cost. For example, the plastic cover was replaced by polycarbonate sheets and a thermo-hygrometer was installed both inside the prototype and outside. Both drying prototypes were manufactured by Andrés Daniel Ortega, a professional in electronics and automation.

Once the prototype was built, the cost of which was 183 euros, ambient temperature and relative humidity tests were run both within and outside the panel, as well as grain moisture index tests and cutting tests.

The installation of the first solar panel for cocoa drying was carried out in Tumaco - San Luis Robles, where there is an approximate ambient temperature of 30°C and a relative humidity of 82%. Likewise, a second prototype was installed in Policarpa - La Vega, with a temperature of 32 °C to 35 °C and a relative humidity of approximately 70%. In both cases, it was located at an approximate tilt angle of 20°.

The data for Tumaco were provided by Albeiro, from Asociación Corpoteva, and the data for Policarpa, in the Vega area, were taken by field technician Edison Yair Jaramillo Villota.

Prototype testing phase and results

After 12 days of cocoa drying, different but similar results were obtained in both locations where both prototypes were installed. Although a grain moisture of 7% was obtained in both Tumaco and Policarpa, it was possible to reach 60ºC inside the panel in Tumaco, while 62ºC was reached in Policarpa. The ambient temperature was 40ºC in both places.

With traditional methods, the approximate drying time of cocoa in a canopy is 16 days to achieve a moisture content of 7% in the grain. With the new panels, it was reduced by 4 days with this new sustainable technology.

About 9 panels are needed to dry the production of one hectare at peak harvest time.

The Corpoteva Association has participated in the Tumaco tests and, in the Policarpa area, both the producer of the Valdez Lopez farm Ermis Arcadio and the field technician Edison Yair Jaramillo Villota have participated.

Next steps to improve the prototype

With the aim of optimising this drying technology and going from 12 to 8 days of drying time, some conclusions have been drawn from the tests carried out and the results obtained, which suggest improvements and next steps:

  1. The proposed design tilt angle of 45° would not be possible as the cocoa beans roll to the bottom. However, testing has shown that an angle of approximately 20° is feasible. As far as possible, an attempt will be made to increase the degree of inclination.
  2. The temperature inside the panel reached approximately 60°C with an ambient temperature of 40°C, which would give an approximate temperature gain of 50%. Nevertheless, improving the construction details and the tightness of the panel, it is expected to exceed this temperature.
  3. It is necessary to be able to control the airflow inside so that the humidity leaves the panel.
  4. The tests were carried out on sunny days. Therefore, to make the operation more reliable, it is necessary to carry out more field tests to obtain more accurate results regarding ambient temperature, internal temperature of the panel, ambient relative humidity, and relative humidity of the panel on rainy days too to see how it affects the results.
  5. The results were favorable in terms of drying time, although it is necessary to perform sensory analysis of the grain (tasting) and cutting tests to establish the quality obtained.
  6. Modifications to the drying panel are required to improve functionality and versatility so that one person can feed the cocoa in, turn it over, and remove it.

Did you like the cocoa drying solar collector project

If you are interested in this solution or want to make a donation, please contact Social Solver.