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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 (, 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.

Summary of Recent Activities:

In this last quarter of 2022, the team continued to collect data from the developed solar dryer integrated with energy-storage materials. The team also made additional modifications to the developed dryer to improve the performance (reducing heat loss at the solar collectors). The developed dryer is installed at Tanzania Horticultural Association (TAHA) training Centre which is located at Tengeru area, Arusha where tests are being carried-out before moving it to the group of small-scale farmers involved in drying and processing of vegetables and fruits for piloting. The team completed analysis of selected rock samples used as energy-storage materials in the developed dryer and it can also be used in concentrated solar power generation. Among the samples tested, soapstone samples performed better when it was heated-up at various temperatures. Granite rock fractured and disintegrated at the temperature of 1000 ℃ while soapstone had no visible cracks at that temperature, an indication that soapstone is an ideal candidate for energy storage in the developed dryer and concentrated solar power generation. The manuscript on “Experimental investigation of soapstone and granite natural rocks as energy-storage materials for concentrated solar power generation and solar drying technology” was submitted to the Journal of ACS Applied Energy Materials.

The second workshop of technical stakeholders to demonstrate the constructed dryer was organized on October 21, 2022. Staff from USAID and NASEM also attended the workshop and participants visited the site where the dryer is installed. The comments that were provided including engaging farmers in the project were well-noted for implementation. The team is also simultaneously collecting data for cost of materials used in the construction of a dryer, wasted materials etc. to be used in techno-economic and life cycle analysis.

Analysis of the dryer's performance involves measuring solar irradiance, drying parameters (temperature, relative humidity, and airflow), moisture extraction rate/ drying rate, while analysis of the energy-storage materials' performance involved measuring the materials' charging and discharging times. According to preliminary findings, the drying temperature within the drying chamber ranges between 40 and 60 °C. Due to the integration of energy-storage materials, the temperature inside the chamber was recorded over 30 °C. The quality analysis tests of dried carrots and pineapple were done at Sokoine University of Agriculture based in Morogoro, Tanzania. Proximate and micronutrients analyses were carried-out on samples to determine the presence of moisture, protein, ash, carbohydrate, vitamins and minerals 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 open sun.

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