INVESTIGATION OF SOLAR WATER HEATING SYSTEMS FOR INDUSTRIAL APPLICATIONS IN NORTHERN ETHIOPIA

摘要

Low temperature water heating for industrial process is one of the ideal applications for solar energy. The paper looks at an investigation of the feasibility of solar water heating systems for industrial applications in Northern Ethiopia. The study was conducted at four factories, namely, a tannery, a particleboard factory, a textile factory and an edible oil factory. The factories use hot water for different processes for the production of their products. The daily hot water consumption is high but most of the processes in the factories require low temperature hot water (<80°C). The current source of energy for water heating at the factories is mainly furnace oil. The first part of the study was to conduct measurements on the hourly hot water demand in each factory. The processes demanding hot water, the temperature and volume needed were studied to establish the heat load in each factory. In summary the hot water demand for each factory was: a) Tannery, 141 m~3/day, 35 - 65 °C, b) Textile, 49 m~3/day, 60 - 80 °C, c) Edible oil, 24 m~3/day ,70-90 °C, d) Particleboard, 7 m~3/day ,40-55 °C. The hourly hot water demand was found to be mainly during the day time having peak demand around noon. The second part is on study of the solar energy availability. Ethiopia is one of the countries endowed with plenty of sunshine. However, long term solar radiation data is scarce. Hence, study on solar radiation estimation models was conducted. Data from solar radiation instrumentation recently installed at Mekelle University was used to compare with results of the estimation models. Measurement data were available for one year (July 2010 - June 2011). The comparison indicates that the estimated monthly average solar radiation is close to the measured data for the months of January to April and September to December. For the rainy months of June until August the estimation was higher than the measured data. The third part is the overall system design and sizing based on the hot water demand of part one and the solar radiation data of part two. Flat plate solar collector with unit collector area of 2 m~2, aluminum absorber, eight copper tubes, single 4 mm thick glass and mineral wood insulation was selected as it is appropriate for such industrial applications. The system sizing results for each factory are: a) Tannery, number of collectors 960 and overall space requirement 3200 m~2 b) Textile, number of collectors 384 and overall space requirement 1500 m~2 c) Edible oil, number of collectors 240 and overall space requirement 800 m~2 d) Particleboard, number of collectors 48 and overall space requirement 300 m~2. All factories have plenty of space to accommodate the solar collector systems. Finally economic analysis for the implementation of the solar water heating systems was conducted. The current furnace oil cost is estimated at 9 USD cents per kWh. The analysis results on solar water heating indicate that it will cost the factories about 5 USD cents per kWh and the payback period will be 6 - 7 years. In addition to the advantage of using clean energy, the factories can save their energy cost up to 30% by implementing the solar water heating systems.