Automation, Software Development & Engineering, Vol.1 – ISSN 2415-6531
Design and Automation of a Hybrid System for Generating Electric Power Mosiori, Cliff Orori1,a and Maera, John2,a 1 — Department of Mathematics and Physics, Faculty of Pure and Healthy Sciences, Technical University of Mombasa, P. O. Box 90420 – 80100, Mombasa. 2 — Department of Mathematics and Physical Sciences, Maasai Mara University, Box 420, Narok, Kenya a —
[email protected]
Keywords: hybrid power generation system; wind turbines, wind -solar system. ABSTRACT. A novel system for generating electric power using a combined wind and solar energy is discussed and proposed for real implementation. It combines a compressed system for air transmission, storage, and a large solar reservoir integrated air heating collector. It employed a CAD/CAA tool which will help designers determine the optimal hybrid wind-solar power system for either autonomous applications. Linear programming techniques were used to the load requirements in a reliable manner. They design takes into account environmental factors both in the design and its operation phases. The essential subsystems include coupled to air compressors to wind turbines, high pressure large diameter pipeline, solar collectors, and a turbo-expander driven generator. This hybrid power generation system will be useful in electric systems with very large wind and solar energy potential areas. This hybrid wind -solar system is expected to be a more economical than independent construction of wind and solar plants. A controller that monitors the operation of the autonomous systems was designed from each of the system components and the environmental credit of the system.
1.0 Introduction The world is facing a major threat of fast depletion of the fossil fuel reserves [3] as well as air pollution. A small part of alternative energy is met by the renewable energy technologies that include the wind, the solar,[10] the biomass and the geothermal resources. As per the law of conservation of energy, “Energy can neither be created, nor be destroyed, but it can only be converted from one form to another” [6]. Current research is embarked on the development of reliable and robust systems to harness energy from nonconventional energy resources. Wind energy and solar power resources have undergone a rapid growth in the past few years confirming the assumptions that both resources are free sources of abundant power with high economic return rates. Solar energy is energy from the Sun [6] and it is renewable, inexhaustible, and environmental pollution free. Solar charged battery systems provide power supply for complete 24 hours a day irrespective of bad weather. Therefore if adopting solar energy technology for the Kenyan location in the world, we can extract a large amount of power from solar radiations that Kenya real needs especially during dry spells. Solar energy is seen to be the most promising alternate source of energy and therefore a search to outdo conventional fossil fuel is making progress in Kenya. Generators which were used as an alternative to power supply systems now run only during certain hours of the day in most parts of Kenya. Kenya is a wind prone country. Wind energy has kinetic energy associated with the movement of atmospheric air [4]. Though, it has been used for hundreds of years for many applications including, sailing, grinding grain and for irrigation, little innovation has been added to it. It has maintained its convention old technology for centuries. With modern technology, wind energy systems convert this kinetic energy to more useful forms of power. Windmills for water pumping have been installed in many countries particularly in the rural areas. Wind turbines transform the energy in the wind into mechanical power. They further convert to electric power to generate electricity [6]. There is a growing awareness that renewable energy such as photovoltaic system and Wind power in Kenya. Hybrid power systems have been designed in developed countries. They consist of a combination of renewable energy source such as wind generators and solar sources which then have charge storage batteries provide power on energy demand. In Kenya, these types of systems are not connected to the grid. Most of them are autonomous and therefore used in stand-alone applications [2] and operate independently. The best ASDE Journal. Open Access www.asdej.xyz
Automation, Software Development & Engineering, Vol.1 – ISSN 2415-6531
application for these type of systems are in remote places especially in Turkana, Bomet, Masai and some parts of Nandi hills. Hybrid systems have grown. They appear as a solution for a clean and distributed energy production. Such systems are growing also as the Kenyan government is encouraging a zero-emission generating systems during peak load periods. It was noted that neither wind alone nor solar energy alone can satisfy the Kenya’s energy capacity during peak periods that is in late afternoon and early in the morning. This design hence seeks design wind and solar hybrid system that is capable of energy storage capacity. It will consist of a compressed air, thermal storage device for solar generated energy and electrochemical systems [3] using a system of batteries and electrolysis with fuel cells inclusive. It will be more economical to integrate wind, solar-thermal, and their energy storage media in a single system, than to separately design and construct wind and solar plants. 1.1 Overview for design of system Solar - wind hybrid system suits to Kenyan conditions where sunlight and wind has in most cases non-seasonal but experience shifts [3]. In the parts proposed in Kenya, wind does not blow throughout the day but the sun does shine for almost the entire day. Even throughout the year, over 78% of the day, there is strong sunlight suitable the choice of this system. Therefore, a hybrid arrangement of combining the power harnessed from both the wind and the sun and stored in a battery can be a much more reliable and realistic power source. The load can still be powered using the stored energy in the batteries even when there is no sun or wind. Hybrid systems are built for design of systems with maximum reliability [5]. Though, the high cost of solar PV cells makes it less competent for larger capacity designs, the wind turbine comes in a cheaper cost as compared to the PV cells. Battery systems are required to store solar and wind energy produced during the day time. During night time and even some day time, the presence of wind is an added advantage, which increases the reliability of the system. 1.2 Conceptual design 1.2.1 Photovoltaic solar power Solar panels of medium size were used to convert solar energy into the electrical energy. Solar panels can convert the energy directly or heat the water with the induced energy. Photo-voltaic cells used are those made up from semiconductor structures as in the computer technologies [6,7]. Sun rays are absorbed with this material and electrons are emitted from the atoms .This release activates a current. Photovoltaic is known as the process between radiation absorbed and the electricity induced. Solar power is converted into the electric power by a common principle called photo electric effect. The solar cell array or panel consists of an appropriate number of solar cell modules connected in series or parallel based on the required current and voltage. 1.2.2 Batteries The batteries used in this hybrid system were providing to store the electricity that is generated from the wind or the solar power. Any required capacity can be obtained by serial or parallel connections of the batteries. The battery that provided the most advantageous operation in the solar and wind power systems are maintenance free dry type and utilizes the special electrolytes. 1.2.3 Inverter Energy stored in the battery was drawn by electrical loads through the inverter, which converted DC power into AC power using the in-built protection for Short-Circuit [4, 6], Reverse Polarity, Low Battery Voltage and Over Load. 1.2.4 Microcontroller A microcontroller was used to compare the input of both Power system and give the signal to the particular relay and charges the DC Battery. The DC voltage was to convert AC Supply by Inverter Circuit. The MOSFET (IRF 540) [4] was used and it was s connected to the Secondary of the centre tapped transformer. By triggering of MOSFET alternatively, the current flow in the Primary winding was alternative in nature and hence gave the AC supply in the primary winding of the transformer. 1.2.5 Wind Turbines. ASDE Journal. Open Access www.asdej.xyz
Automation, Software Development & Engineering, Vol.1 – ISSN 2415-6531
To estimate the number and rating of the wind turbines, it was necessary to compress 11.2 million kg of air per day. Directly coupling smaller air compressors to the shafts of these wind turbines would probably result in the same number of wind turbines.
Fig.1 Schematic Diagram of Concept and utilization system under investigation. 2.0 Implementation of the Hybrid System The subsystems includes: wind turbines directly coupled to air compressors [5], or conventional wind turbines used to power a central air compressor on the ground; a collector system consisting of high pressure pipes to collect compressed air from several turbines, high pressure (100 bar) large diameter pipeline to transport the compressed air from the wind turbines to the solar site which will also contain the expander-generator, possibly a compressed air storage cavern, which could be sited either near the wind turbines, along the transmission pipeline [6], or at the solar collector site, solar thermal collectors [8] with integral thermal storage for heating the compressed air to as high as 1000° C, and a uniquely designed turbo-expander-driven generator. Figure 1 show a sketch on how its implementation can be carried out. 2.1 Analysis of the System Analysis was performed for the months of January, February and March 2016 at Technical University of Mombasa, found in Judah, Mombasa by assuming a six (6) hour storage system. The value of the scheduled generation from storage was found to be higher than 80 % than the value of the conventional wind plant for that period located two (2) kilometers at a person generating home in Mikindani, Mombasa. It was also realized that a third benefit was obtained through the addition of energy storage with an ability to enable renewable energy to effectively substitute for generating capacity. This was then described as “dispatchability” capacity. 3.0 Results and Discussions In this work, three categories of data in the utility-scale energy storage technology was investigated. This was done when the compressed air was assumed to be far below the one causing charge from wind to cause current to flow into batteries. In a compressed air energy storage system [11], offpeak electricity was assumed to be used to power motor-driven air compressors and the compressed air is stored in underground cavern. In the generation mode, the pressurized air was withdrawn from the cavern, preheated using a combustible fuel and then expanded through a hot air turbine which drives a generator. [12] Figures 3 and figure 4 illustrate the obtained data during the peak hours at Technical University of Mombasa. Though in some days, solar radiations could falls to as low as zero at the time of day, our design could still record load of about at 90% of the peak.
ASDE Journal. Open Access www.asdej.xyz
Automation, Software Development & Engineering, Vol.1 – ISSN 2415-6531
Fig 2: Combined percentage performance of the hybrid system
Fig. 3 Wind Plant Output and ERCOT Load and energy storage As from the results, figure 4 show a significant decrease in power generated. This was attributed to the amount of air required per unit of energy produced by the expander. This avoided clogging the air turbine with moist during rainy and cloud days since expansion of highly compressed air has a cryogenic cooling effect. In recently proposed designs in USA and Canada [8], the compressed air would be heated using the exhaust of a conventional gas turbine or an industrial waste heat source. The essence of the Hybrid Wind / Solar Power Plant is substituting solar-heated thermal storage for natural gas for the pressurized air preheating [9]. However, these energy sources are based on the weather condition and possess inherited intermittent nature, which hinders stable power supply.
ASDE Journal. Open Access www.asdej.xyz
Automation, Software Development & Engineering, Vol.1 – ISSN 2415-6531
Fig. 4 Peak Day Load and Solar Generation Profile Combining multiple renewable energy resources can be a possible solution to overcome defects [3], which not only provides reliable power but also leads to reduction in required storage capacity. Although an oversized hybrid system satisfies the load demand, it can be unnecessarily expensive. An undersized hybrid system is economical, but may not be able to meet the load demand. The optimal sizing of the renewable energy power system depends on the mathematical model of system components. Because of the nonlinear power characteristics, wind and PV system require special techniques to extract maximum power. Hybrid system has complex control system due to integration of two (or more) different power sources. The complexity of system [1,2] increases with maximum power point tracking (MPPT) techniques employed in their subsystems. However, optimization to determine the best inlet temperature for the hot air expander was not carried out. It’s believed that higher temperatures will increase the output per kg of pressurized air though they may require more complex solar collector systems similar to the famous sun-tracking systems for concentrating solar. It’s also proposed that an analysis of power variation under various combinations of air temperature and flow rate entering the expander be performed in order to quantify the seasonal variation in power output capability of the system designed. This will require a selection of the most suitable thermal storage media which theoretically estimated to be optimal for the inlet temperature. Finally it is proposed that a cost estimation and benefit analyses be carried out to demonstrate the advantages of this design over conventional wind and solar power development. Conclusion Initial theoretical tests and analysis show that this proposed hybrid system may have several advantages over separate wind and solar generating facilities in the following ways: Though, a single prime mover needs a generator and substation, it does not need for electric transmission connection to the wind farm. It needs an expander-generator. In addition, a wind turbine gear box only needs to be greatly simplified since the torque characteristics of a wind turbine rotor are better matched to an air compressor than a generator in this system. Therefore, if this system is implemented, there is no need for natural gas or an industrial waste heat source, and no need for cooling water through solar thermal plants. However, wind energy production may tends to be higher in certain times and while solar irradiance highest at certain different times, seasonal fluctuations in energy supply may tend to even out when the two sources are combined in an integrated system. This may be a challenge to consider during implementation. ASDE Journal. Open Access www.asdej.xyz
Automation, Software Development & Engineering, Vol.1 – ISSN 2415-6531
References [1] Dornfeld, D., 2014. “Moving Towards Green and Sustainable Manufacturing,” Int. J. Precis. Eng. Manuf.-Green Tech., Vol. 1, No. 1, pp. 63–66, [2] Nema, P., Nema, R. K., and Rangnekar, S., 2009. “A Current and Future State of Art Development of Hybrid Energy System using Wind and PV-solar: A Review,” Renewable and Sustainable Energy Reviews, Vol. 13, No. 8, pp. 2096–2103, [3] Stroe, D., Stan, A., Visa, I., and Stroe, I., 2011. “Modeling and Control of Variable Speed Wind Turbine Equipped with PMSG,” [4] Ahn, S. -H., 2014. “An Evaluation of Green Manufacturing Technologies Based on Research Databases,” Int. J. Precis. Eng. Manuf.-Green Tech., Vol. 1, No. 1, pp. 5–9, [5] Kalantar, M. and Mousavi G, S. M., 2010. “Dynamic Behavior of a Stand-Alone Hybrid Power Generation System of Wind Turbine, Microturbine, Solar Array and Battery Storage,” Applied Energy, Vol. 87, No. 10, pp. 3051–3064, [6] Soetedjo, A., Lomi, A., and Mulayanto, W. P., 2011. “Modeling of Wind Energy System with MPPT Control,” International Conference on Electrical Engineering and Informatics (ICEEI), pp. 1–6, [7] Adzic, E., Ivanovic, Z., Adzic, M., and Katic, V., 2009. “Maximum Power Search in Wind Turbine Based on Fuzzy Logic Control,” Acta Polytechnica Hungarica, Vol. 6, No. 1, pp. 131–149, [8] Ahn, S. H., Lee, K. T., Bhandari, B., Lee, G. Y., Lee, C. S., and Song, C. K., 2012 “Formation Strategy of Renewable Energy Sources for High Mountain Off-grid System Consideting Sustainability,” J. Korean Soc. Precis. Eng., Vol. 29, No. 9, pp. 958–963, [9] Bekele, G. and Palm, B., 2010. “Feasibility Study for a Standalone Solar-Wind-Based Hybrid Energy System for Application in Ethiopia,” Applied Energy, Vol. 87, No. 2, pp. 487–495, [10] Dali, M., Belhadj, J., and Roboam, X., 2010. “Hybrid solar-Wind System with Battery Storage Operating in Grid-Connected and Standalone Mode: Control and Energy Management — Experimental Investigation,” Energy, Vol. 35, No. 6, pp. 2587–2595, [11] Ram Prabhakar, J. and Ragavan, K., 2013. “Power Management Based Current Control Technique for Photovoltaic-Battery Assisted Wind-Hydro Hybrid System,” International Journal of Emerging Electric Power Systems, Vol. 14, No. 4, pp. 351–362, [12] Jeon, Y. -J., Kim, D. -S., and Shin, Y -E., 2014. “Study of Characteristics of Solar Cells through Thermal Shock and High-Temperature and High-Humidity Testing,” Int. J. Precis. Eng. Manuf., Vol. 15, No. 2, pp. 355–360, Bibliography [1] Cliff Orori Mosiori is a lecturer in Electronics & Instrumentation and a researcher at the Technical University of Mombasa [2] John Maera is a senior lecturer and researcher in renewable energy and solid state physics at the Masai Mara University.
ASDE Journal. Open Access www.asdej.xyz
