The international demand for organic dried fruit is increasing. High quality dried fruit offers an excellent and healthy alternative to sugary sweets. The predominant energy source for fruit drying in Africa is fossil fuel (mainly gas) and, due to the rising costs of fossil fuel, the interest in renewable energy sources is self-evident. While in industrialised countries high quality dried fruit is produced using high-tech and often patented methods such as vacuum and microwave drying, small agricultural cooperatives in rural areas in developing countries have great difficulty in delivering the required quality and quantity to the international market using acceptable energy efficient technologies. In fact, no feasible drying technologies based on renewable energy sources and suitable for developing countries were available on the market at the time that this project was implemented.
Products from typical low-tech dryers, which have direct contact with combustion gases, are banned from the European market. Therefore, it was considered necessary to introduce better drying technologies in developing countries to replace the existing low-tech dryers to meet the requirements of the fruit importing nations.
In general, professional drying involves a long chain of operations covering growing/organising the raw material, storing the fruit before drying, peeling the fruit under hygienic conditions, dealing with the fruit waste, drying the fruit, packing the dried fruit, storing the fruit before shipping and selling the product.
In this project, implemented by Oekozentrum Langenbruck, an east-west exchange of know-how was foreseen, permitting Eritrea (with its lack of drying structures) to benefit from an exchange with Burkina Faso (with its established drying industry). In 2007 Eritrea had no tradition in professional fruit drying and did not export dried products, while Burkina Faso has an established drying industry and produced about 810 kg dried mangoes and pineapples per day (March - August) for the export market in 2005.
Different concepts for using the sun for drying purposes were studied. The aim was to design a feasible, technologically simple and robust system that could be replicated by local craftsmen in Africa using mainly local materials.
Technology, Operation and Maintenance
At the beginning different existing drying technologies were tested in relation to their technical and economic aspects. Based on these results, the basic design of the systems in Eritrea and Burkina Faso was determined to be the same: a big surface of solar air collectors and an efficient fan. Experiments in the laboratory showed that, with high air velocity, thin slices of fruit and temperatures of 50 - 65 °C, it would be possible to dry the fruit within a day. High air velocity produced by low energy consumption was made possible by a centrifugal ventilator, which was the only piece of imported machinery. Energy efficiency could be further improved by recirculating the air in the dryer. To compensate for the humid and cloudy season, the surface of the solar air collector had to be bigger for use in Burkina Faso compared to that in Eritrea.
In terms of technological innovation, the project developed a lightweight solar air collector covered with a durable transparent foil and a dryer concept that facilitated low cost drying using mainly solar heating energy.
Financial Issues and Management
At the beginning of the project a market survey was carried out in cooperation with Gebana AB in Switzerland to determine whether dried tomatoes from Eritrea would be acceptable to the European market. A group of small-scale customers gave positive feedback on the quality of the tomatoes, whereas the majority of the big customers found the quality unsatisfactory.
In order to ensure quality standards the intention was, therefore, to acquire biological certification for the dried products. Unfortunately the Eritrean Ministry of Agriculture wanted to define a self-made bio-label and would not accept the international certification process.
Environmental Issues
Solar drying can result in CO
2 savings if gas or other non-renewable energy sources are replaced by solar power. The project aimed to reimburse the dryer-owners by certifying the emission reductions and selling CERs on the voluntary carbon market. However, it was not possible to validate the CO
2 reduction levels and the planned reimbursement scheme before the end of the project as units have to be in operation for several months before certification can be considered. On average one dryer could save about 5000 kg CO
2 per year if it replaces a comparable gas dryer.
Results & Impact
A dryer designed to operate on 100 % solar heating energy was constructed in Eritrea. Based on outline designs from Oekozentrum, the partner Tesinma Sh. was able to carry out the assembly. Testing the dryer showed that the fruit quality fulfilled the requirements for the European market.
Early in 2007 the gas heater in one of the 2 chambers of a CEAS dryer (this is the traditional model used in Burkina Faso) was replaced by a 20 m
2 solar air collector. Tests showed positive results outside the rainy season with a reduced processing time (16 - 20 hours), excellent fruit quality and little need for replacing the grids during the drying. However, although drying is possible in the rainy season, it took much longer (up to 48 hours) and the quality of the fruit was much lower.
Replicability
This type of project requires a great deal of coordination and logistical cooperation between the funding organisation, the implementing organisation and the organisations on the ground and lessons were learned that should be taken into account when implementing such a project. However, despite the challenges, there is nevertheless significant potential for solar dryer technology in countries with high levels of natural sunlight and local fruit and vegetable production.
Lessons Learned
The lack of local materials and transport issues made the planning and implementation difficult. Materials were lost during transportation from Europe to Burkina Faso and although these could be replaced with local parts, this was not easy.
It was also a challenge to develop components for Burkina Faso, with its different environment, market and mentality. To take the heavy dust and rain into account a long testing period was planned in order to test the stability and performance of the construction. One of the biggest constraints was the weakness of roofs in Burkina, which could not support heavy constructions such as glass covered collectors. Using plastic foil as an alternative made the construction lighter, but introduced uncertainty concerning long-term stability.
As well as the logistical and technical problems another major influencing factor was the political situation in Eritrea. In 2007 Eritrea declared that it wished to become independent from import and foreign aid, which restricted the import of materials necessary for the production of the solar dryers. Ultimately this meant that the project in Eritrea could not proceed.
