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Cycle 9 (2020 Deadline)
Solar dryer integrated with energy storage system: An energy efficient and environmentally friendly technology for drying biomaterials in Tanzania
PI: Thomas Kivevele (thomas.kivevele@nm-aist.ac.tz), Nelson Mandela African Institution of Science and Technology (NM-AIST)
U.S. Partner: Sunghwan Lee, Purdue University
Project Dates: July 2021 - July 2023
Project Overview:
Over 40% of agricultural produce in developing countries is wasted, not only due to lack of storage and processing facilities, but also due to limited knowledge of processing technologies. Biomaterials, which are traditionally sun-dried, are often of poor quality due to the complexity in controlling drying parameters. Presently, most farmers in Tanzania use biomass and natural sun for drying their farming products, but biomass is becoming increasingly scarce and farmers, especially woman, have to walk long distances to fetch firewood (Mwema and Gheewalaa, 2011). Tanzania receives abundant solar radiation that can be used for drying agricultural produce. Solar dryers have the potential to exploit this renewable resource, and the technology is attractive because of its ability to rapidly, uniformly, and hygienically meet drying standards with zero energy costs. Despite development of solar drying technology in sub-Saharan Africa, most countries like Tanzania have seen limited market penetration because of a need for further research. Many solar dryers are only useful on sunny days and useless at night or during cloudy days. To facilitate drying in the absence of sunlight, dryers must have the capacity to collect and store heat for later use (e.g., overnight drying). This project is intended to develop an inexpensive, effective, and reliable solar dryer integrated with a thermal energy-storage system made of locally abundant and affordable materials (rocks) with favorable thermal and mechanical properties. The dryer prototype will include a solar collector and bed storage made of carbonate (dolomite and limestone) and granitic rocks. The project will further theoretically and experimentally investigate in-situ performance and economic feasibility of the developed dryer. Successful execution of the project will decrease wood-burning for drying purposes, thereby protecting the environment and reduce postharvest loss. The U.S. Government-supported partner is expected to use his expertise in solar energy conversion to provide guidance in the research design, data analysis, and review of manuscripts and patents resulting from this project. Also, he will facilitate access to lab equipment at Purdue University to characterize energy storage materials.
The Tanzanian government is promoting industrialization with the goal of achieving middle income by 2025. It is therefore important for institutions like the Nelson Mandela African Institution of Science and Technology to support these initiatives, especially with regard to developing technologies that will assist in reducing postharvest loss, which is one of the outstanding problems in the country. Agriculture is the backbone of the national economy of Tanzania in terms of food production, employment, production of raw materials for industries, and generation of foreign-exchange earnings. The national objective is to enhance production of quality products to improve market competitiveness of agricultural produce. This project is aligned with this policy for increasing productivity and reducing postharvest loss through drying. The proposed drying technology uses solar energy, which decreases deforestation problems resulting from using fuelwood for drying purposes in line with the Tanzania National Forest Policy of 2008 and the National Climate Change Strategy of 2012. This research will contribute to increased high-quality dried products such as fruits and vegetables, which are market-competitive and hence improve farmers’ livelihoods and national income in general. The project will also engage three graduate students (two MS and one PhD) and take into consideration the gender equality aspects at various stages of project implementation. The proposed technology will have a significant impact on the drying activities of fruits and vegetables, which mostly involve women. The project will also train women how to use the drying technology thereby promoting adoption and acceptability of the technology during and after the planned training workshops.
Final Summary of Project Activities
The primary objective of this project was to develop inexpensive, effective, reliable, and environmentally benign drying technology for small-scale farmers in Tanzania, the team managed to complete all the proposed activities. Before designing solar dryer integrated with natural rocks as energy storage material as proposed in this project, the team studied challenges of existing solar dryers that were developed in Tanzania by the Centre for Agricultural Mechanization and Rural Technology (CAMARTEC) based in Arusha-Tanzania. The team found that CAMARTEC were constructing passive solar dryers which become useless in the absence of sunlight thus the dehydration process is interrupted at low or at night when solar radiation is unavailable, resulting in a bad quality of the dried products. In addition, since temperature control in drying using this type of dryer is difficult, at high temperature a product can be dried too quickly resulting in surface hardening which increases resistance to the moisture diffusivity. Formation of a hard layer on the outer surface of a drying product increases drying time because of impervious to the water evaporation. Heat sensitive agricultural produce are therefore recommended to be dried using appropriately lower temperatures to lessen or avoid case hardening of the product.
The team in this project managed to design and construct a prototype of solar dryer integrated with natural rocks as energy storage materials to prolong the drying process when the sunlight is unavailable. The project supported two and analyzed the selected rock samples (soapstone and granite) to be used as energy-storage materials in the proposed dryer and in the concentrated solar power generation. Caton soapstone performed the best as a thermal energy storage material, effectively absorbing, storing, and transmitting heat while maintaining good chemical stability and mechanical strength, a sign that soapstone is a strong contender for energy storage in drying applications and concentrated solar power generation.
The developed dryer is installed at a Tanzania Horticultural Association (TAHA) training center where tests were carried-out and groups of small-scale farmers involved in drying agricultural produce have being granted access to use it. According to the results, the drying temperature within the drying chamber ranges between 45 and 65 °C, soapstone as energy storage material in solar dryers recorded the temperature inside the drying chamber over 35 °C up until 22h00. The team patented the developed dryer with Business Registration and Licensing Agency (BRELA) in Tanzania.
The quality analysis tests of dried vegetable (carrots) and fruit (pineapples) were done at Sokoine University of Agriculture based in Morogoro, Tanzania. The fresh and dried carrot and pineapple were grounded into fine paste and powder form by using an electric blender. The fine paste/powder was then used in the analysis. Proximate and micronutrients analyses were carried-out on the samples to determine the presence of moisture, protein, ash, carbohydrate, vitamins and minerals (Ca, K, Mg, Na, P) using standard analytical methods as described by the Official Methods of Association of Official Analytical Chemists (AOAC). Dried products retained micronutrients (vitamins and minerals), and had concentrated proteins and carbohydrates as compared to fresh products and the ones dried using traditional open sun as detailed in the second published paper.
The first project awareness workshop was conducted on 10th December 2021 which helped to enhance the knowledge of stakeholders on solar drying technologies due presentations made by the project principal investigator and students. The workshop was attended by 29 stakeholders (12 females and 17 males) from government institutions, nongovernmental organizations, and community groups. The participants were informed on the importance and expected impacts of this project especially on reducing post-harvest loss through drying and environmental friendliness of the technology. The second workshop to demonstrate the developed dryer prototype was held on October 21, 2022 where staff from USAID and NASEM also attended to oversee progress of the project.
A mentorship program on STEM was organized to assist secondary and primary schools in developing drying and biofuels innovations. The team visited these schools for mentorship programs, which included raising awareness about clean energy technologies and their projected contribution to greenhouse gas reduction. Five primary and five secondary schools within Arusha region were engaged in this program. The purpose of the program is to mentor and motivate the young science students to come up with innovations in the area of clean energy technologies. One technical research presentation was made at the World Science Forum held in Cape town, South Africa from 6 - 9 December 2022 under Thematic Session IV/e: Challenges of Urbanization: Food Security in Africa. The presentation by the principal investigator (Prof. Thomas Kivevele) was based on "The role of solar dryers on Food Security in Africa", key findings from this project were presented to create awareness to participants on the importance of clean drying technologies. US Government supported partner (Prof. Sunghwan Lee) and Prof. Richard M. Voyles from Purdue University visited NM-AIST from 18 – 27.06.2023. The purpose of the visit was to discuss project progress and develop further collaborations beyond life time of this project, visit a prototype of the developed dryer, and present a seminar to NM-AIST scientists. A number of stakeholders from NM-AIST, Tanzania Horticultural Association (TAHA), Arusha Technical College (ATC), Centre for Agricultural Mechanization and Rural Technology (CAMARTEC), Tanzania Commission for Science and Technology (COSTECH), invited groups of small-scale farmers who are drying agricultural products for business purposes attended the meetings where key findings from the project were presented by the principal investigator of the project and the students supported by the project.
The techno-economic assessment and life cycle analysis indicate that the payback period for the dryer for drying pineapple is 1.5 years whereas for carrots is 1.6 years which is a short period as compared to the estimated lifespan of the dryer of 20 years. The dryer is environmentally friendly with negligible emissions. Based on thermal and economic performance assessment results, the developed solar dryer is technically and economically viable and is currently being piloted by two groups of women engaged in drying agricultural products for business (Mwambesi in Arusha and Efeso from Moshi-Kilimanjaro).
Publications
Kakoko, L.D., Jande, Y.A.C., kivevele, T. 2023. Experimental investigation of soapstone and granite rocks as energy-storage materials for concentrated solar power generation and solar drying technology, ACS OMEGA. https://doi.org/10.1021/acsomega.3c00314.
Rulazi, E. L., Marwa, J., Kichonge, B., Kivevele, T. 2023. Development and performance evaluation of a novel solar dryer integrated with thermal energy storage system for drying of agricultural products, ACS OMEGA, https://doi.org/10.1021/acsomega.3c07314.
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