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1.1       Introduction

The progress and growth of any nation depends on its socio-economic development and to achieve that it needs to have reliable electric supply systems. The rise in the cost of conventional fossil fuels and the increasing negative impact of using non-renewable energy in the environment is posing several challenges. The increasing demand for electricity and global warming has influenced many nations to opt for environment-friendly type of energy solutions to preserve the natural resources for future generations (Moriarty & Honnery, 2012). There are various renewable energies, which are acting as good source of electricity, which includes hydro power, and other sources such as wind and photovoltaic energy. Renewable energy is gaining significance as it is a critical part of reducing global carbon emissions (Boyle, 2012). Fossil fuels, gas and other non-renewable energy alternatives together pose a threat to the environment and the society, which is the end user of this form of energy (Thorogood & Thorogood, 2012). Since non-renewable energy sources are experiencing depletion in the reserves, there is a need for the nations to generate more and more energy from renewable sources (Sangster, 2014). Generation of energy using renewable sources such as solar and wind had remained cost ineffective till recently (Thorogood & Thorogood, 2012).


Research on Hybrid System for Water Pumping


However, the costs of renewable energy production are continually decreasing making it affordable even for private use (Khattab et al., 2016). Wind energy and Solar Energy are some of the renewable energies, which are used to produce electricity, pump water and hot water heating (Sangster, 2014). Single source renewable energy solutions work effectively only when the resource is available to be harnessed such as for solar energy the area should receive adequate direct sunlight and for wind energy there should be adequate wind for turning the turbines, which then generate energy (Khattab et al., 2016). To maximize the potential of available resource and to provide consistent and stable energy generation there is a need of mixed technologies, which can be achieved by fully integrating hybrid energy solution.


1.2       Purpose of the Research

Oman like the other Middle Eastern nations depends on oil and gas for producing electricity. But these resources are not expected to last forever (Shere, 2013). The gas production is not very stable and the oil is expected to run in the next few decades, which has led the government to develop Omani Vision of 2020 to reduce its dependency on oil and diversify the economy and source of electricity whose demand is increasing with growing population (Price, 2017). The volatile prices of gas and oil is also influencing government and institutions to promote researches and approaches to find energy resources, which are sustainable, have less environmental impact, are stable and cost less (Ramu & Rambabu, 2014). Oman has hence been focusing on utilizing the renewable sources for electricity generation. The nation has increased potential for producing renewable energy as the level of solar energy density in Oman is among the highest across the globe and there is increased scope for developing solar energy resources through the region (Price, 2017). Wind energy potential is also found to be high in Oman mainly in the coastal areas in Southern part of Oman, which has enabled the nation to take advantage of the opportunities and use these sources for electricity generation (Price, 2017). These renewable energy sources though are abundant in Oman they are available intermittently, which reduces reliability of power output and can restrict the usage of the output power (Hatmi & Tan, 2013). The intermittent nature of these sources can lead to component over-sizing and increased complexity in the operations and increase lifecycle cost (Hatmi & Tan, 2013). To address such challenges hybrid systems are used wherein the solar and wind sources are used in combination to improve load factors and save maintenance and replacement costs as their components complement each other (Khattab et al., 2016). Using renewable energy for water pumping is considered to be clean and effective method as such locations have easy availability of sun radiation and wind (Khattab et al., 2016). Water pumping system require consistent supply of electricity to provide the required output and hence depending on any one of the sources cannot be reliable. Thus, hybrid wind/solar source for getting the required supply electricity will enable the pump to work effectively and the dependency on one so urce will reduce. This research aims at designing hybrid wind/solar energy system for pumping water for use in small agricultural farm.


1.3       Research Objectives


  • To understand the importance of renewable energy sources such as solar and wind to aid agricultural farming

  • To study feasibility of solar/wind hybrid renewable energy for water pumping

  • To design solar/wind hybrid system for pumping water for use in a small agricultural farm


1.4       Research Limitations

This research aims at designing hybrid wind/solar energy providing system specifically for small agricultural farm and hence the efficiency of the system might be good as the system is small. This cannot be generalized to bigger systems as there are various factors, which might influence the efficiency of the system.


2        Literature Review

Energy is the basis for modern industrial economy and is an essential component for all the human activities. It is used for various purposes such as lighting, production, transportation, space/water heating, mineral extraction and many other activities (Energy Information Administration, 2016). There are many factors, which influence energy supply and the main factors are availability, accessibility and price.



Above figure shows the different sources from where the energy is produced as of 2015 and it can be seen that the dependency on the non-renewable sources such as natural gas, oil and coal constitute a greater part of energy generation. Non-renewable energy sources drain the fossil reserves, which is deposited since centuries and it has led to increased negative impact on environment (Boyle, 2012).  Coal is one of the widely used fossil fuel across the globe as it is found in abundant but when it is burnt to generate energy it produces increased carbon dioxide, which has led to global warming (Energy Information Administration, 2016). The reserves are depleting at a faster pace due to increasing global demand for energy. The other non-renewable energy, which is widely used, mainly in the Middle Eastern countries such as Oman is oil, which has resulted in massive air pollution (International Energy Agency, 2016). Non-renewable energy sources have contributed to a great extent in the growth of industries and the excess use of non-renewable energy has led to several environmental issues such as land pollution, air pollution, which has affected the eco-system to a great extent (Shere, 2013). To address these challenges the use of renewable energies is advancing rapidly to close the energy access gap and to reduce the impact of the energy sources on the environment and humans. Renewable energy supply is continuously increasing across the globe. Many nations have been investing significantly from past few years and the rapid advancement in the technology has enabled nations to produce renewable energy at a cost-effective price (Thorogood & Thorogood, 2012).


2.1       Types of Renewable Energy


The main types of renewable energy widely used across the globe are biomass, solar power and wind power.



Biomass is one of the renewable energy, which refers to use of organic materials and converting them into different forms of energy, which can be used (Shere, 2013). Biofuel is produced through biological processes, which include agriculture and anaerobic digestion (Sangster, 2014). Some other fuels are produced by fermenting carbohydrates derived from sugar or starch crops.


Solar power

Solar power is the most popular and fast growing source of renewable energy. The solar power system involves solar cells, which rely on photovoltaic effect absorb photons and convert them to electrons (Sangster, 2014). The solar cells present on the large solar panels absorb light from the sun and convert it to electricity (Shere, 2013). Solar power can be generated in areas where abundant sunlight it available. Solar power is widely used in grid-connected processes as an approach to feed low-carbon energy into grid (Shere, 2013). According to International Energy Agency, by 2050 solar power will constitute over 25% of the market and will become world’s largest source of electricity (Moriarty & Honnery, 2012).


Wind Power


Wind power is being used for various purposes from thousands of years, which include powering windmills or generating pressure for water pumps (Shere, 2013). Wind power is generated based on operation of wind turbines, which turn when wind blows (Sangster, 2014). The turbines are connected to a rotor, which connected to main shaft that spins a generator and electricity is produced. According to the Global Wind Energy Council and Greenpeace International, by 2050 the wind power produced worldwide would be as much as 25 to 30% (Moriarty & Honnery, 2012).


2.2       Oman’s Potential for Renewable Energy and Sources 

Sultanate of Oman’s peak power demand is expected to increase substantially by 10% annually from 4455MW in 2013 to 9133MW in 2020 due to growing population, increasing disposable income, continuing government investment in infrastructure projects and hence the electricity and water demand is expected to rise significantly (Price, 2017). One of the main sources for electricity generation in Oman was oil and gas and with increasing impact on the oil industry due to price fluctuation and difficulty in accessing the oil field (Moriarty & Honnery, 2012). Oman has to invest significantly to exploit the oil reserves and they are expected to run dry in next 40 years (Price, 2017). Also, the country’s growing population and driving demand for residencies and increased living standard has been placing increased pressure on the national power grid and leading to frequent blackouts (Price, 2017).

In regional and rural areas blackouts occur more regularly and force them to rely on diesel generators, which account for around 2.5 % of fuel used for generation of electricity (Shere, 2013). There is a need for the country to meet the expected demand more effectively (Price, 2017). This led the nation to consider the researchers to identify the most effective source of electricity generation and the study by Oman’s Authority for Electricity Regulation identified that solar and wind power offer greatest potential as renewable sources for generation of electricity in Oman (Thorogood & Thorogood, 2012).  Oman has some of the best solar potential in the world as it is best positioned in the location where high levels of solar irradiation can be captured. The country received on average of 18 to 20 percent more solar Kilowatt/hour per square meter as compared to other parts of Middle East. Oman’s ration of sky clearness is very high and is at 342 days per year along with high irradiation and hence the country receives highest solar energy densities in the world (Price, 2017).

Oman’s wind energy potential is also very strong as good wind resource exists in southern and eastern areas of the nation, which recorded good wind speeds as compared to the wind speeds of European sits having commercial wind power projects operating effectively (Price, 2017). The country has average wind speed slightly over 5 m/s and estimated hours of full load power per year is 2,463 hours, which makes wind power economically viable form (Thorogood & Thorogood, 2012). As per the studies carried out by researchers, the four main locations where abundant wind power is available include Masirah, Thumrait, Sur and Qayoon Hyriti. Oman already has constructed wind power plants at Thumrait and Qayoon Hyriti of the capacity of 375MW each and the electricity production is 2.3 TWh a year both sites included. The only disadvantage of wind power in Oman is that wind is more seasonal (Hatmi & Tan, 2013). Studies have shown that wind speed is higher in summer months of June to August and is lower during the months of October and November (Price, 2017). The wind power speeds are higher when the Oman’s power supply demand is peak so wind power electricity generation is found to be feasible for the country though it might not be feasible to be used throughout the year (Hatmi & Tan, 2013). The intermittent availability of wind and solar can lead to discontinuity in power generation, which might not enable effective generation of electricity to the desired level and hence use of these renewable sources independently for different processes is not feasible as the return on investment would be less (Hatmi & Tan, 2013). The lack of continuity in the supply due to the intermittent nature will not allow the effective usage of produced electricity and hence hybrid wind/solar system has been studied across Oman to ensure that the utilization of each of the renewable sources is done effectively.


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2.3       Hybrid Wind and Solar Systems

Hybrid system refers to a system developed by combining more than one element. In generating energy more than one source such as wind, solar, biomass and other can be used (Yahyaoui, 2016). To generate hybrid energy there are different modules such as wind-solar hybrid, solar-diesel hybrid, wind-hydro hyrbrid system and wind-diesel hybrid system (Arjun et al., 2013).  Wind-solar hybrid system is one of the widely used hybrid system across the globe. Hybrid design is found to be very useful and sustainable approach for generating energy due to intermittent availability of solar power and wind energy in many areas (Shirsath et al., 2016). Hybrid systems are mostly stand-alone systems and operate off-grid and not connected to electricity distribution system. Most of the hybrid systems include batteries where the generated electricity is stored and/or is connected to generator powered by conventional fuels and is used when batteries run low. The engine generator is used to provide power and recharge batteries.  


The hybrid wind/solar system combines two individual system as solar system and wind system. Solar system will generate electricity from the sun and convert it into electrical energy, which is collected and stored as DC energy (Yahyaoui, 2016).  Wind system includes generating wind energy using the wind turbines having large blades, which are connected to rotor of generator, which leads to production of electrical energy depending on the movement of blades due to wind flow (Zhou et al., 2010). Wind turbine is a mechanical system and the amount of energy generated depends on the speed of the wind (Shirsath et al., 2016). The hybrid system includes batteries, which is essential for storing the electrical energy produced by both the systems. Electrical batteries are used as it is low cost, and provides maximum efficient storage for storing electrical energy. Inverter is an electronic system, which is used to convert direct current (DC) into alternating current (AC). The stored electrical energy in the batteries is direct current and cannot be utilized for different types of loads (Yahyaoui, 2016). To provide AC supply to the load, inverter is used, which is then connected to the load and the hybrid power can thus, be consumed continuously without any interruption as the source of energy is from wind as well as solar (Zhou et al., 2010). The various applications of wind/solar hybrid system include street lighting, traffic signals, pump irrigation systems, various monitoring systems and for many domestic purposes.


2.4       Wind Turbine/Solar PV Water Pumping Systems

Wind/Solar hybrid energy is widely used in water pumping and irrigation as a standalone system. In many parts of the world many water pump users are switching to solar/wind hybrid energy for small systems and large systems stull run on diesel generations (Yahyaoui, 2016). Researches have highlighted that wind turbine/hybrid photovoltaic has improved water pumping reliability and also increases daily volume of pumped water as compared to mechanical wind mills and solar PV systems along (Negi & Mathew, 2014). Brian et al. has carried out research in analyzing the effectiveness of use of solar system and wind power system independently and in combination for pumping water (Hodge, 2017). His research highlighted that hybrid systems delivered more energy than using the systems independently by around 28% (Hodge, 2017). The research study used boost converter as a controller to improve hybrid PV/WT water pumping system (Zhou et al., 2010). Gopal et al studied various research developments in the field and reviewed several articles based on water pumping system and studied different systems used to power water pumping system and investigates five different configurations using different types of energy such as thermal, biomass, solar and wind (Maheshwari & Gupta, 2014). The research concluded that use of renewable energy such as solar, wind or both together highly reduces the dependency on conventional energy and has positive impact on the environment. It also reduces the cost of energy and provides efficient option to generate clean energy for operating water pump (Maheshwari & Gupta, 2014). Zhou et al. (2010) state that the effectiveness of WT/PV array systems have been studied in many locations and these systems with batter backup is found to be reliable as compared to using WT or solar PV alone. The only maintenance item in such hybrid systems included replacing the batter every two years.


The research included designing standalone hybrid power system to generate power for running a water pump system for agricultural activities in a farm. Figure 3 shows the block diagram of the hybrid system.

The power generated is required to operate a 0.5hp water pump.

Power required to run the pump = 0.5 X 0.746 = 376 Watts


3.1       Wind Power System

The power in the wind is directly proportional to area of the wind turbine swept by wind and to the cube of velocity of wind. The expression for power generated from wind is given by

Where  density of air and is considered as 1.225 kg/m3

A is area of wind turbine swept by wind

V= velocity of wind

In this research, the wind power generated will be 1kW. The wind turbine selected to generate the power would be having 3 blades and the wheel diameter will be 2.8 m. The start-up wind turbine speed will be 3m/s and survival wind speed will be 45 m/s.


3.2       Solar Power System

Solar energy is produced by sun by a process of thermonuclear fusion. The sun’s heat is instrumental in maintaining the thermonuclear reaction and the electromagnetic radiation created by heat is streamed out in all directions and some energy is lost in the process due to scattering, cloud cover, absorption, reflection and the climate (Negi & Mathew, 2014). The solar PV installations are static and does not produce any noise or vibrations like the wind turbine. In the solar system considered for this research solar panel of PV cells will be included which would collect radiation that falls on it and convert it into form of energy, which is then stored in a battery (Zhou et al., 2008). The storage battery will hold the energy produced by the solar cell sin the day time.

The solar energy power supply components in this research included

 To generate solar power of 400W

  Operation hours = 10 hours

   Total Watt-Hour = 373 X 10 = 3730w-hour

    Exposure of Solar panel= 8 hours

    Solar panel of 400 W will be required for the design of system

    Number of Panels= 3730W/400 W = 10 panels


3.3       Batteries

The power generated from both the sources will be stored in the batter, which is then connected to inverter to power AC loads (Zhou et al., 2008). The recommended batteries for renewable energy systems are deep cycle batteries. The battery bank size has to be chosen effectively to ensure adequate reserve capacity. The battery storage capacity is decided based on Watt hours of electricity usage per day, number of days of autonomy, ambient temperature of battery bank and depth of discharge limit (Arjun et al., 2013).

The connected load will be of 373 W to run the 0.5 hp water pump. The water pump will be operational for ten hours and hence total power requires will be 3730 Wh. The days of autonomy refers to number of days of backup required by the system. The system should be able to draw power even if due to some reason the battery has not been charged. The days of autonomy considered for this research was 2 days. The typical temperature compensation value considered in this project was 1.1.  Depth of discharge is another factor, which has to be considered while deciding on battery bank. It is expressed as percent of total capacity. The faster the battery is discharged fewer cycles the battery could complete and it will then shorten the battery life. The system voltage is usually 12 V, 24V or 48 V. The choice of battery bank voltage for this research is 48V as it reduces losses. The battery bank consumption in Ah would be

Ahc = Er/Battery bank voltage = 3730/48 = 77.70Ah

The capacity of the battery bank would be

Aha = Ahc X Temperature Control X Days of Autonomy/ Depth of Discharge = 77.70 X 1.1 X 2/ 0.5 = 341.91 Ah

The battery size considered in this research is 12 V 200 Ah, connected in series to get 48 V and two of them connected in parallel to get total current of 400 Ah. The inverter uses will have power factor .8 and inverter efficiency of 90% approximately was chosen and the capacity was 5KVA


4        Results and Discussion

The design of the wind/solar hybrid system presented in this research has the capacity to operate 0.5hp water pump, which requires 378 Watts power every hour. The Wind power system is designed to draw 1kW power every hour, which is stored in the battery. The solar power system is aimed at drawing 3.73 kW for 10 hours, which would also be stored in the battery. The final set-up involved integration of both the systems to draw the power required to run the water pump and store the rest of the generated power in storage battery.  The solar system has the capacity to generate 373 watts per hour by operating the 10 panels, which is adequate to run the water pump. The wind power if generated at the same time would be stored in the battery and the battery will be charged. This hybrid system will enable the water pump to operate throughout the required 10 hours as the intermittent availability of either solar power or wind power will not affect the operation of the water pump.

If the solar radiation is reduced on someday the wind power would be able to draw the required current, which would operate the water pump and in case of absence of wind power the solar power will run the water pump. If both the resources are scarce on someday the part of the day when its availability is high the battery will store the generated energy from each source and the pump would still operate effectively on the battery, which has the capacity to store the required amount of power required for the water pump to run for 10 hours in a day. The hybrid design provides an efficient way to generate required power to run the water pump and the storage capacity of battery would be monitored periodically to ensure its efficiency. The designed wind/solar hybrid system provides the desired power of 3.4kW for 10 hours and ensures that the battery provides the adequate current to drive the water pump for 10 hours as per the requirement. The hybrid system is found to be more efficient as in spite of the variation in the wind and solar power on daily basis the water pump runs without any interruption. The research design has ensured that the battery capacity is adequate to store the energy in case there is no availability of both the resources for a day. The backup power will enable the water pump to operate for 10 hours in the absence of both the energies.


5        Conclusion and Recommendations

Use of renewable energies is gaining increased importance across the globe and is used for various applications. Renewable energies provide clean energy and enable the users to make lesser impact on the environment. The demand for renewable energy is increasing in Oman as the nation has increased resources to generate renewable energies due to the abundant natural resources available in the nation. Oman receives the highest irradiation as compared to other nations in the world. The nation gets increased sunlight for most part of the year, which provides an advantage to the nation to use the most popular renewable source, which is solar energy.  The government is encouraging the use of solar power as the demand for power is increasing due to growing population. In rural areas, there are frequent blackouts and diesel generators are used to keep the power up and running. Oman has increased capacity to generate power through solar energy and through wind energy.

The intermittent nature of both the resources makes them inefficient to be used independently and hence wind/solar hybrid system is being considered in the nation to increase the efficiency of the power generated by the two systems. Wind/solar hybrid system provides more reliability and reduces power loss and hence is a more effective solution to get uninterrupted power supply. The design of the hybrid system in this research operated a 0.5 hp water pump, which is used for irrigation purpose in a farm. The operating hours was 10 hours and use of hybrid system enabled to generate the required power on daily basis. The power generated by the wind power system and solar power system was stored in battery, which can be used for more than one day even if both the resources do not produce adequate energy in one day. The power generated by using the solar system was 3.7 kW for 10 hours and 10kW was generated by the wind power, which is adequate to run the water pump, which requires 373 watts, hour to operate. The battery storage enables storage of the energy and invertor is used to convert the power to AC. The current system can be further improvised by increasing efficiency of solar panels by exposing them for longer period and using new technologies in solar power to increase power generation from solar panels. The hybrid system provides more consistency in power generation as compared to using the solar power and wind power being used independently. The hybrid system has increased scope of being used for larger system as they overcome the drawback of the intermittent nature of the renewable power supplies.  Hybrid wind/solar system design helped in understanding the effectiveness of solar and wind power systems used in combination and can be considered as most efficient way to generate power from the renewable sources.

It is recommended that the solar system should be further enhanced by using solar tracking systems, which would help in orienting the solar panel or concentrating solar reflector or lens towards the sun. This will help in increasing the efficiency of the solar systems and it can be further used for pumping water without the need for a high capacity battery. It is recommended that fixed-tilt solar panels should be used to maximize the exposure of the panels to the sun. The solar power generation can be further enhanced by using ground installation which would provide increased efficiency. It is recommended that the wind power efficiency can be increased by using weight reduction in blades and maintaining the stiffness of blades, which will help in turning the blades more effectively and generate more power. It is recommended that the wind turbine and solar PV system should be further analyzed and effectively integrate to reduce power loss in the process. There is further scope for research on eliminating the use of battery and using the power generated form the hybrid system directly, which will help reduce the power loss and will require almost no maintenance as currently the battery has to be replaced in few years. The design of the hybrid system should be further analyzed to identify if the system can produce more energy to carry out more activities for irrigation activities. There is scope for identifying new storage technologies, which have increased life cycle.



6        References


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