A review on solar thermal utilization for industrial heating and cooling processes : global and Ethiopian perspective

A substantial share of the total energy in various countries is consumed by industries and manufacturing sectors. Most of the energy is used for low and medium temperature process heating (up to 300 degrees C) as well as low and medium cooling capacity (up to 350kW). To meet the demand, the industrial sector consumes most of its energy in either thermal (heat) or electrical energy forms. The use of fossil fuels accounts for about half of the overall share. This resulted in a necessity to commercialize local and clean renewable energy sources efficiently considering the reduction of economic dependence on fossil fuels and greenhouse gases emission. As such, solar energy has proven potential and resulted in considerable development and deployment of solar heating industrial processes (SHIP) and solar cooling systems in recent times. Thus, an attempt to present a review of the available literature on overall energy intensiveness, process temperature levels, solar technology match, and solar thermal system performance and cost have been made in this paper. The review also includes identifying the potential and relevance of involving solar thermal for industrial heating and cooling demand. As a result, at least 624 SHIP including promising large-scale plants and 1350 solar cooling systems most of them in small and medium capacities in operation are identified. Though limited data is available for solar cooling potential and installation, investigations projected the global SHIP potential to 5.6 EJ for 2050. Consequently, given the presence of many low and medium temperature heating processes and cooling capacities in industries with immense solar energy potential, developing counties such as Ethiopia can take experience and pay attention to the development of sustainable industrial systems

Performance Enhancement of Natural Convection Indirect Solar Dryer by Integrating Reflectors

Natural convection indirect type solar dryer integrated with reflectors that can be used for drying fruits and vegetables was designed, constructed, and evaluated. The study mainly tried to improve the performance of a prototype natural convection indirect solar dryer. The solar dryer was integrated with reflectors and its thermal performance was experimentally analyzed and results were compared with the same dryer without reflectors. The experiments conducted included a no-load test to determine the stagnation temperature that can be reached and drying tests using tomato slices. During the drying test, moisture content at the initial and final stages was measured using a moisture balance instrument. The mass of the tomato slices was measured every two hours to find the drying efficiency. Temperatures were measured using thermocouples located at the absorber plate and at the trays inside the drying cabinet. Solar radiation was also measured using a pyranometer located near the dryer. During no load experiments, the maximum temperature reached the collector was around 98oC for the dryer without reflectors. The maximum temperature was improved to around 154oC during the test with reflectors. Similar temperature improvement was obtained during the drying tests as well. Due to the improvement in the temperature in the collector, the drying rate was also improved by 8% for 10 kg and 14% for 5 kg load. The experimental results indicate that the dryer performance was improved when the reflectors were added

Energy consumption performance analysis of electrical mitad at Mekelle City

The Injera baking electrical mitad is the most energy-consuming device in every household in Ethiopia. This research presents a detail engineering study on the energy-consumption performance of existing electrical mitad in Mekelle city. The research work considered thirty-one electrical mitad from different workshops in Mekelle. Depending on the number of clay used, there are three types of electrical mitad; the single clay, the double clay and the rotating type mitad. In this research, it was found out that the average power consumption of existing mitad is in the range of 3.5 KW to 3.9 KW. The specific average baking energy is 0.82, 0.73 and 0.54 kWh/kg of injera for double clay, single clay and rotating type mitad respectively while the thermal efficiency by considering baking of 6kg of Injera on each mitad is 38%, 47% and 61% respectively. In all designs, the baking temperature is in the range of 130-140 0C. Although the rotating type mitad is more energy efficient, it has technical limitations. Due to that, the single and the double clay mitad are widely used by households hence share all the market penetration of injera baking electrical mitad. These commonly used electrical mitad have an energy loss from 50-60% of the input energy.Keywords: Electrical mitad, Injera baking energy, Thermal efficiency, Baking temperature, Ethioopi

Design and Manufacture of 1kW Wind Turbine Blades

To meet sustainable development goals and address concerns on climate change, much of the world's energy demand is expected to be delivered from clean alternative energy sources. Small-scale wind turbines have proven to be applicable for off-grid electrification. The objective of this study is to present the details on the design and manufacture of a 1 kW wind turbine blade for specified conditions. Blade element moment theory is adopted in the design of the geometry of the blade. Accordingly, the aerodynamic analysis on NACA 64A410 airfoil resulted in a blade radius of 1.95m, an overall twist angle of 31°, and a gradually tapering chord length of 0.062m at the root and 0.247m at the tip of the blade. Then, the wind turbine blades are manufactured from fiberglass (mat350g), resin, catalyst, and gelcoat.  Experimental results reveal the wind turbine blades started producing power at a cut-in wind speed of 3m/s. The maximum power achieved during the testing process was 900W at a hub wind velocity of 9m/s. This is lower than the expected 1000W theoretical power output due to not perfect workmanship in the manufacture of the wind turbine blades. This study will help in building local manufacturing facilities and enhance rural electrification through off-grid technologies

Theoretical and Experimental Comparison of Box Solar Cookers with and without Internal Reflector

AbstractBox solar cookers are commonly built with internal sheet metal painted black as an absorber. In order to increase the performance, a design which incorporates internal reflection is proposed in this paper. The aim of this paper is to report comparisons made between box solar cookers with and without internal reflector. Theoretical modelling of the two types of cookers has been made by considering the radiation, convection and conduction heat transfer employing the thermal network method. The theoretical analysis made was based on steady state heat transfer analysis of the cookers. Experimental comparisons were also made on two cookers having the same aperture area and made from the same type of materials except the internal absorber. The tests were made as per the American Society of Agricultural Engineers (ASAE) procedure.The result of the theoretical analysis predicts that the performance will be higher in the cooker with internal reflector than the same cooker without reflector. The steady state analysis shows that for the cooker with reflection the temperature of the bottom absorber plate is higher than the cooker without reflector. Similarly, results of dry test and water boiling test show better performance by the cooker with reflector. The standard stagnation temperature and the cooking power were higher in the cooker with reflector as compared to the cooker without reflector. In conclusion, the performance of box solar cookers can be enhanced by making appropriate angle side walls of the absorber and providing internal reflection

Performance of Wind Pump Prototype

A wind pump prototype with 3.6 m rotor diameter, 19 m hub height above ground and 0.22 mm reciprocating pump stroke has been developed at the Department of Mechanical Engineering, Mekelle University. The prototype was designed and manufactured locally. Theoretical model based on combined efficiency of the rotor and the reciprocating pump was used to estimate the performance of the wind pump. One year wind speed data collected at 10 m height was extrapolated to the wind pump hub height using wind shear coefficient. The model assumed balanced rotor power and reciprocating pump, hence did not consider the effect of pump size. The theoretical model estimated the average daily discharge to be around 50 m3 and 30 m3 at 8 m and 12 m head, respectively. The prototype was tested with the same pump stroke but two different size pumps at two different heads. The pumps were with internal diameter of 55 and 70 mm and the test heads were at 8 and 12 m. Measurement of the flow rate, rotational speed and wind speed were made every 10 minutes during the test period. The data collected were analyzed to find the performance of the wind pump at the two test heads and two pump sizes. The flow rate data was plotted against binned wind speed data to determine the linear fit function. The linear fit function was then used to estimate the flow rate at any wind speed. With the 55 mm pump the measured average daily discharge was 20 and 19 m3 at 8 m and 12 m head, respectively. With the 70 mm pump the measured average daily discharge was 41 m3 and 30 m3 at 8 m and 12 m head, respectively.Keywords: Wind pump, Windmill, Performance testing, Pump efficiency, Pump discharge, Ethiopia

Excess Energy from PV-Battery System Installations: A Case of Rural Health Center in Tigray, Ethiopia

PV-Battery systems are commonly sized based on the lowest solar radiation of the site of implementation. This implies that during days of high solar radiation excess energy is available. This study investigated the potential of excess energy for thermal storage from PV systems for a case of a rural health center. The system components of a typical PV installation in a rural health center in Tigray, Ethiopia, were considered. The electricity load profile of the health center and solar radiation data available from Mekelle city were used as inputs to a TRNSYS model. Analysis of excess energy in the system at hourly and ten-minute time intervals was conducted. The analysis results indicate that during the months from September to May excess energy was available that could be thermally stored and utilized. During these months, the excess peak power ranged from 737 to 841 W and daily average excess energy ranged from 2070 to 2959 Wh. In contrast, in the months from June to August, no excess energy was available due to low solar radiation

Design and Development of Solar Thermal Injera Baking: Steam Based Direct Baking

AbstractEthiopia, the second most populated country in Africa, meets 96% of its energy need from bio-mass and majority of this energy goes entirely to Injera baking. Injera, a pan-cake like bread that is consumed by most of the population, demands a temperature of 180-220 oC to be well baked. Both traditional and newly developed biomass Injera stoves are energy inefficient; besides the kitchen environment is highly polluted with soot and smoke that affect the health of household inhabitants. This article introduces new technology that enables Injera baking using indirect solar stove. A parabolic dish with an aperture area of 2.54 m2, a well-insulated stainless steel pipe of 10mm, a coiled stainless steel heat exchanger, a pressure relief valve and three gate valves were equipped in the system and K-type thermocouples were used to record the temperature. The heat transfer process has been governed by the principle of natural circulation boiling-condensation between receiver and stove. A preset pressure relief valve is used to control the self-circulating working heat transfer fluid (steam at a temperature of 250 oC). The system was developed and tested for steam based direct baking in the same fashion as the traditional Injera stove. In this experiment, heat transport without significant loss from the receiver for baking at some distance is demonstrated. The challenge with manual tracking and direct steam based baking model indicates the performance of the technology can be improved. It can also win more acceptances if it is equipped with auto trackers and heat storage mechanism. In conclusion, unlike previous efforts, the experiment demonstrated that a high temperature indirect baking of Injera is possible