Nowadays, renewable energy resources are considered as the most suitable option as they are environmentfriendly, sustainable, and inexhaustible. It is a well-known fact that the standard of living in any society improves with the provision of resources to that society. Besides being abundant, renewable energy resources have the limitations of intermittency. In addition, these resources are site-specific, that is, different sites have different availability in terms of resources as well as their quantum. These limitations of renewable energy resources can either be overcome by creating a renewable based energy generation facility or by the development of Integrated Renewable Energy Systems (IRES) [5]. This option has opened new avenues to provide electricity to remote rural areas in a decentralized mode.

India has got very high potential in the renewable energy sector, but still, the total contribution of renewable power as compared to electricity generation is very low contributing to around 6 to 8% of the total production. Hence it is necessary to utilize these resources in an optimum manner so as to achieve overall development of society.

In order to meet sustained load demands of Sri Venkateswara College of Engineering and Technology, Chittoor during varying natural conditions, different energy sources and converters need to be integrated with each other for extensive usage of alternative energy sources such as wind-solar Hybrid Energy System for SVCET, Chittoor. The use of the stand-alone solar-wind with diesel and battery backup system for the power supply of remote areas may give an economically attractive alternative for grid source in near future.

Even with such developments going all around the globe, a big percentage of the world's population residing in the remote rural areas is still not getting the advantages of such developments. Such areas are geographically located in such a manner that the access to these areas is very difficult. These areas are very sparsely populated. In such scenario, connecting these areas to the utility grid is a tedious and uneconomical task. This sparsity is the prime impediment to the development of a country. Electrical energy is considered as the most convenient and clean energy and is, therefore, considered as the most viable option for the development of a nation.

Deepak Kumar Lal et al. [7] presented a hybrid system containing PV, Wind, Micro-hydro and Diesel Generator for Sundargarh district of Orissa in India. Two simulations have been done in this study with the HOMER software; the first arrangement consists of the Wind, PV and Diesel Generator, whereas the second arrangement consists of Wind, PV, small hydro and Diesel Generator. The author suggests that wind power fluctuation and demand variation are the constraints of the system.

J.B. Fulzele and Dutt [2] presented a hybrid system for Yavatmal district in Maharastra, India. The hybrid system consists of PV Panel, Wind Turbine, Generator, Inverter, and Storage Batteries. These systems are optimized by the HOMER software.

Abbas Babaei et al. [1] presented a techno- economic analysis for powering residential building, Sari city in Iran. The hybrid system is optimized using HOMER software using PV system, Generator, Inverter, and Batteries.

The hybrid energy system is an outstanding solution for the energy problems in the rural areas where grid extension is difficult and not feasible. It does not depend on a single type of energy. It is a combination of two or more different types of energy system which comes together to give the optimum output by utilizing the available natural resources. But the design of such system is a very difficult task as the integration and control of renewable energy sources, energy storage and loads are very complicated. Hence optimum planning of such a system is very indispensable before its construction [4] [14].

The hybrid system is able to overcome intermittent nature of non-conventional energy resources. But hybrid system increases complexity in the system hence optimization of the hybrid system is required. Several studies have been done on the optimization of hybrid energy resources in India, considering different configuration and conditions.

HOMER performs a comparative economic analysis on a distributed generating power systems. Inputs to HOMER will perform an hourly simulation of every possible combination of components entered and rank the systems according to user defined criteria, such as the cost of energy (COE, US$/kWh) or capital costs. Furthermore, HOMER can perform “sensitivity analyses” in which the values of certain parameters (e.g., solar radiation or wind speed) are varied to establish their impact on the system configuration [9].

This paper gives the design idea of the wind, solar photovoltaic, diesel generator along with the battery backup hybrid energy system. Based on the energy consumption of SVCET, Chittoor and the availability of renewable energy sources, it was decided to implement an innovative stand-alone Hybrid Energy System combining small wind turbine-generator, solar photovoltaic panels, battery storage, advanced power electronic equipment, and existing diesel generators.

In this paper, different possible renewable energy resources combinations have been presented and the best combination based on minimum Cost of Energy (COE) and Total Net Present Cost (TNPC) criteria has been suggested.

The availability of renewable energy resources at SVCET, Chittoor is an important factor to develop a hybrid energy system. Many parts of the India, wind and solar energy is abundantly available. The energy sources are irregular and naturally available; due to this factor, their first choice to power the SVCET, Chittoor will be renewable energy sources such as the wind and solar.

Weather data are an important factor for the pre-viability study of renewable hybrid energy system for any particular site. In South India, wind speed is an average and sun brightness is strong. Before the system sizing, load profile and available radiation should be evaluated. Therefore they are presented in the following sections.

1.1 Location of Study Area

The site selected for hybrid renewable energy system is located in Chittoor district, R.V.S Nagar in Andhra Pradesh, India having Latitude 13^o16.3'N and Longitude 79^o7.1'E as shown in Figure 1.

Figure 1. Map of Study Area

1.2 Solar Radiation and Wind Speed Data

In the present work, solar insolation and wind speed data represents the average of the period 10 years from July 1983-June 1993 and collected the data from the real case near Chittoor (South, India, 13°16.3' N, 79°7.1' E) as in Table 1 [8]. This data has been analyzed to assess utilization of hybrid PV/WG/DG/battery power systems to meet the load requirements of an SVCET College with annual energy demand average of 1200 (kWh/d).

Table 1. Solar and Wind Data of SVCET Chittoor

The annual average solar radiation for this area is 5.52 kWh/m²/d. Figure 2 shows the solar radiation profile over a one-year period.

Figure 2. Solar Radiation Available at Chittoor

Monthly average wind data sets for Chittoor were collected from environment Chittoor climate. This is an average of last ten years and the annual average wind speed is shown in Figure 3. From the above-given data, wind speed probability function and average hourly wind speed throughout the year is shown in Figure 3.

Figure 3. Wind Speed Available at Chittoor

Average wind speed in the summer season is slightly higher than the winter season. The annual average wind speed for the location is 4.07 m/s with the anemometer height at 50 meters. Figures 4 and 5 show the wind speed profile and wind turbine power curve, respectively at the study site.

Figure 4. Wind Speed Profile at Chittoor

Figure 5. Wind Turbine Power Curve

1.3 Load Profile

An important consideration of any power generating system is load. As a case study and as a representation of SVCET College which can access to the utility grid, the measured annual average energy consumption has been considered to scale the load to 1200 (kWh/d) in the present study. The daily average load profile, seasonal profile and yearly profile are shown in Figures 6, 7, and 8, respectively. The peak requirements of the load dictate the system size. In this study, 250 (kW) has been considered to scale peak load.

Figure 6. Daily Average Load Profile at the Site

Figure 7. Monthly Average Load Profile at the Site

Figure 8. Yearly Average Load Profile at the Site

In the present work, the selection and sizing of components of hybrid power system have been done using NREL's HOMER software. HOMER is general purpose hybrid system design software that facilitates the design of electric power systems for stand-alone applications [9] . Input information to be provided to HOMER includes electrical loads (one year of load data), renewable resources, component technical details and costs, constraints, controls, type of dispatch strategy, etc. HOMER designs an optimal power system to serve the desired loads.

HOMER is a simplified optimization model, which performs hundreds or thousands of hourly simulations over and over (to ensure best possible matching between supply and demand) in order to design the optimum system. It uses life cycle cost to rank order these systems [9].

The model developed using HOMER, consists of a PV, WG(s), Diesel Generator, and a Battery. The schematic of this hybrid power system is shown in Figure 9. In order to verify the system performance under a different situation, simulation studies have been carried out using real weather data (solar irradiance and wind speed). The goal of the optimization process is to determine the optimal value of each decision variable that is available in the interest of the designer. A decision variable is a variable over which the system designer has control and for which HOMER can consider multiple possible values in its optimization process. In this study, decision variables in HOMER, include:

• The size of the PV array.
• The number of WG.
• The number of DG.
• The capacity of batteries.
• The size of the DC/AC converter.

Figure 9. Proposed System Configuration in HOMER

2.1 Power Management Strategy

The dispatch strategy is load following type and interaction between different components is as follows: In normal operation, PV and WG feed the load demand. The excess energy from PV and WG is stored in the battery until full capacity of the battery is reached. The main purpose of introducing battery storage is to import/export energy depending upon the situation. The DG is brought into the line when PV and WG fail to satisfy the load and the battery storage is depleted (i.e. when the battery's SOC is minimum) [3, 8, 11].

2.2 Photovoltaic Panels

After surveying different products focusing on the cost provided, the following panel was chosen. The reason for choosing the product from the stated company is due to its low cost as long as efficiency is not a big concern here. The installation cost of PV may vary from (132 to 264/ W). Considering a more optimistic case, a 200 kW solar energy system's installation and replacement costs are taken as (1,98,000), (see Table 2). The different sizes are considered, which are 0, 50, 100, 150 and 200 kW from Su-Kam Company. The selected panel was polycrystalline silicon made with an efficiency of 14 to 15% [12 & 13]. The lifetime of PV arrays are taken as 25 years and no tracking system is included in the PV system. The following parameters have been considered like; the derating factor was taken as 80%, the ground reflectance was also considered as 20%, slope 26.98 (latitude of the location), and azimuth 0 (south orientation).

Table 2. The Input Window of Hybrid System Components

2.3 Wind Turbine

Availability of energy from the wind turbines shown in Figure 3 depends greatly on wind variations. Therefore, wind turbine rating is much lower compared to the average electrical load. In this analysis, Generic 10 kW model with hub height (50 m) is considered. It has a rated capacity of 100 kW and provides (AC) voltage as an output. The cost of system is considered to be (33,00,000) while replacement, operation, and maintenance costs are taken as (19,80,000) and (6,600/year) (see Table 2). To allow the simulation program, find an optimum solution, provision for using 0 (no turbine), 5, 10 and15 units is given. A lifetime of a turbine is taken to be (20 years).

2.4 Diesel Generator

Diesel generators do not allow running at less than the minimum load ratio of 30%. In this study, after surveying of various diesel generator suppliers, the selected one is from Cummins, supplied by POWERICA Silent Diesel Generator. Generator size is among the input sizes to consider working with the wind and solar PV to meet the load requirement in the case of no wind flows and no sunshine times. Power rating is 250 kW of selected diesel generator. The cost of diesel generators available in the market is about 17,82,858 [10]. Lifetime operation of generation is about 50,000 hours.

2.5 Grid

The proposed system is a grid-connected system in which the Grid acts as a backup power component. The grid is activated and supplies electricity when there is not enough renewable energy power to meet the load.

2.6 Battery

Batteries are considered as a major cost factor in smallscale stand-alone power systems. A battery bank of commercially available units, Trojan IND17-6 V model (6 V, 7.61 kwh) was considered in this simulation. The estimated lifetime is (15 years) and the cost of one battery is (33,000) with a replacement cost of (26,400) while the maintenance cost is expected at (660/year). The battery to be considered in this simulation ranges from 10 to 50 units. The battery cost, its replacement, and O&M costs as used for simulation are shown in Table 2.

2.7 Converter

A converter needs to maintain flow of energy between AC and DC power system components. A power electronics converter is needed to maintain flow energy between the (AC) and (DC) components. As shown in (Table 2), (20 kW) system the installation and replacement cost are taken as (19,800). The different sizes of the converter (5 kW, 10 kW and 20 kW) are taken in the model. A lifetime of a unit is considered to be (15 years) with an efficiency of 90%.

The proposed hybrid system supplies the power to the Sri Venkateswara College of Engineering and Technology, Chittoor (AP) continuously throughout the year. An optimal system is defined as a solution for hybrid system configuration that is capable of meeting the load demand of this SVCET College, Chittoor.

A total of 720 simulations with 27 sensitivities were performed by the HOMER software. From the simulation result, the installation of wind solar hybrid system configuration for various locations are most suitable power solutions for Grid transformer station network in Indian sites. The present cost analysis of a PV/Wind hybrid system is suitable for stand-alone loads around Chittoor. From the optimization results, the best optimal combination of energy system components is Ten number of Generic 10 kW WGs, 200 kW PV-Array and 250 kW diesel Generator, 30 kW Convertor, and (6 V, 7.61kWh) Trojan IND17-6 V battery. Total Net Present Cost (NPC), Capital Cost, and Cost of Energy (COE) for such a system are 5,51,34,611, 29,88,699.78, and 9.8472 /kWh, respectively for one year. The detailed optimization results are shown in Table 3. The net project cost is 5,51,34,611 and the expenditure of conventional existing grid system is 4080000 per year.

Table 3. Optimization Results of SVCET College, Chittoor

Thus the simple payback period is the ratio of net project cost to the expenditure of conventional existing grid system cost per year so pay back year is 10 years.

Several simulations have been made by considering different PV capacities and the number of WG. The PV capacity has been allowed to vary from 0 to 200 (kW), and the number of WG has been allowed to vary from 0 to 10. The battery storage size (kWh) considered include 0-6 load-hours autonomy (equivalent to 0-6 hours of average load). Also, the DG power has been considered to change from 50 to 250 (kW). The simulation results for 5.52 2 (kWh/m /day) solar radiations and 4.07 (m/s) wind speed (equivalent to a monthly average of Chittoor weather data) are presented in Table 3. The first column shows the presence of PV modules, WG(s), DG and Battery in a hybrid system. It can be noticed from these results that the first system consist of PV/WG/DG/Battery /Converter is the most commercial but in this paper, the result of the fourth configuration has been considered because the presence of all components are feasible.

The aim of this study is to achieve a stand-alone hybrid generation system, which should be appropriately designed interms of economic, reliability, and environmental measures subject to physical and operational constraints/strategies [6, 15].

The system cost is defined as the sum of PV cost (C_PV ), WG cost (C_WG ), battery cost (C_BAT ), diesel generator cost (C_DG ), and converter cost (C_COW ).

[1]

The cost for each element should be deducted:

[2]

where, i = PV, WG, Battery, DG, Converter,

N_i is the number/size of the system component, C_costi is the capital cost, R_costi is the replacement cost, K_i is the number of replacement, and O&M_costi is operation and maintenance cost through the system operation.

The cost cash flow summary diagrams at different NPCs of the system elements can be shown in Figures 10, 11, 12, and 13.

Figure 10. Cash Flow Summary at Option-I

Figure 11. Cash Flow Summary at Option-II

Figure 12. Cash Flow Summary at Option-III

Figure 13. Cash Flow Summary at Option-IV

HOMER software was used to determine the optimum hybrid configuration of Sri Venkateswara College of Engineering and Technology, Chittoor (Latitude 13^o16.3'N and Longitude 79^o7.1'E). As a result of which the Option IV, is proposed for the site. The system architecture, includes PV System 200 KW, ten numbers of Wind Generators (Generic 10 kW), Diesel Generator 250 KW, Battery Trojan IND17-6 V model (6 V, 7.61kwh) and Converter 30 KW. The Net Project cost is 5,51,34,611 and the payback period of the proposed hybrid renewable energy system is 10 years. The system is designed for 25 years. Thus it is concluded that after 10 years we can enjoy the profits with green energy resources for next 15 years, which is sustainable and environment friendly. The proposed system is a very good choice in the remote and village areas also. The integration of renewable energy technologies into electric power distribution systems enhances the benefits associated with fuel savings and avoidance of emissions penalties. Renewable energy technologies, such as photovoltaic and wind turbine power are environmentally beneficial sources of electric power generation. It should reduce approximately 70%-80% running cost over conventional grid system and also it had reduced the emission of CO₂ and other harmful gasses in the environment.