Integrated Alternative Source of Energy System with Grid Substation

This paper discusses the modeling, simulation and optimization of integrated alternative source of energy system with grid substation. When there is a lack of energy in grid substation to meet the demand of customer load then alternative source of energy compensates energy deficiency and after that if there is excess energy available then remaining energy is stored in battery bank or sells to grid according to need. In another case when required energy is not generated by alternative sources then remaining energy is purchased from the grid and if the grid substation hasn't available these remaining energy to meet the customer load demand during the peak load then stored battery energy is also active. The size of integrated alternative source of energy system may vary from few hundred watts to ten or hundreds of MW. The possible sources of alternative energy like solar, wind and biomass are considered under this paper. Study location, Muzaffarpur district of Bihar (India), is taken because there is good potential of energy generation from alternative source of energy and still there is no any wind and solar energy power plant. The modeling and simulation of the system is done by using HOMER software and the software solve the optimization problem to minimize the total cost of system and maximum utilization of alternative source of energy.


Introduction
India's significant and sustained economic growth is placing enormous demand on its energy resources. However, there is a pervasive demand-supply imbalance that necessitates serious efforts by the government of India to augment energy supplies. The country imports about 80 percent of its oil. With the threat of a further increase in oil prices, serious problems with regard to energy security is anticipated. India also runs the substantial risk of lesser thermal capacity being installed. While dependence on imported coal is increasing, supply of indigenous coal is likely to decrease in the coming years because of production and logistic constraints [1]. Economic growth, increasing prosperity and urbanization, rise in per capita consumption, and spread of energy access are the key factors that would be responsible for substantially increasing the total demand for electricity. Thus there is an emerging energy supply-demand imbalance. According to a Central Electricity Authority report, the anticipated energy and peaking shortage in the country is estimated to be 10.3 percent and 12.9 percent, respectively, in 2011 and 2012.
Muzaffarpur district of Bihar state, India as the study area there is still a wide demandsupply gap that needs to be bridged, one glaring proof of the same is the fact that Bihar's power system has a peak of about 1500 MW under the constrained demand scenario and the availability is about 950 MW. Only 52.8 % of villages and 6 % of households of the state are electrified, leaving about 85 % of the population with no access to electricity [2]. The Bihar state government still totally dependent on thermal and hydro power plant to overcome this energy shortage but there is a good potential to generate power from alternate source of energy like solar and biomass because there is good annual average solar radiation (5.27kWh/m^2/d) and abundant in biomass residue respectively. As per C-WET'S India wind atlas, Bihar lies in low wind zone and no wind power density is observed at more than 200 watts per square meter at 50 meter hub height which is minimum requirement for installation of large wind power plant. As  [3]. Muzaffarpur is suitable for small wind power generation. Integration of alternative source of energy with grid substation is best to overcome this energy deficiency. Hence it is necessary to integrate alternative source of energy and alternative units can chosen so that they satisfy the customer load demand in remote area at minimum cost all the time and maximum utilization of alternative sources.
The integrated power systems which utilize renewable energy generators can be classified into two basic configurations: Series hybrid system and Parallel hybrid system [4]. Both the systems have their own characteristics. The proposed scheme is based on parallel hybrid system a shown in Figure 1. Many hybrid systems have been proposed in the past for electrification of remote areas or grid connected sites. Many tools are also available for sizing and simulation of a hybrid system. But fewer include biomass resources. The performance of integrated power system is dependent on climate condition and availability of biomass resources.
In designed system biomass power plant is largest supplier of energy and it is active in all possible condition which we have got in simulation model. In our simulation model primary load is variable and average demand is 2.3 MWh/d and peak demand is 225kW. Data of annual wind speed and solar radiation of Muzaffarpur is taken from [5] [6]. Wind speed vary seasonally from (3.1 -4.3) m/s. All Analysis is doing by using HOMER software means hybrid optimization model for electrical renewable [7] [8]. Our propose model shows how much percentage contribution of alternative sources in total power generation and how it make us partially independent on conventional energy sources. In case of PV/biomass integrated system we have got 65% renewable fraction means 65% of total energy generated by alternative sources but in case of PV/wind/biomass integrated system we have got 70% renewable fraction but NPC of this system is 13% more than the PV/biomass integrated system. But for optimum utilization of alternative sources NPC doesn't matter so much; if we consider conventional sources are no longer uses because of its limited amount. We have also study how energy purchasing and selling from the grid vary month by month. Since in cloudy day sun light effect has become lesser so we have not got sun light properly. So that in the month of July, August and September net energy purchasing is more as compare to other months and at the same time it is depends on the availability of biomass resources and wind speed

Integrated Power System (IPS) Configuration
The configuration of hybrid system depends on three factors: resource (renewable sources), load, and cost (initial capital and operating cost) [9]. The major problem faced by power generation using the integrated system is the variation in load and alternative resources (solar radiation, wind speed and biomass production). Therefore, the major concern in the design of an electrical power system that utilizes alternative energy resources is the accurate selection of system components that can economically satisfied the load demand.
In the above optimization problem, integrated power system sizing is done with the aim of maximizing renewable fraction. The purpose of this paper is to explore the possibility of integrated power system with grid substation through design and optimization of PV/Wind/Biomass integrated system using a computer based design optimization. To demonstrate the potential of alternative source of energies to less dependent on grid substation as a source of energy for customer load. This study will provide energy system solution that can reduce customer load dependency on grid substation and maximum utilization of alternative sources which are environmental friendly.

Homer
HOMER (hybrid optimization model for electrical renewable) simulation simulates the operation of a system by making energy balance calculation for each of the 8,760 hours in a year. For each hour HOMER compare the electrical and thermal load in the hour to the energy that the system can supply in that hour. For system that includes batteries, HOMER decides for each hour how to operate the generators and whether to charge or discharge the batteries. If the system meets the loads for the entire year, HOMER estimates the life cycle cost of the system, accounting for the capital, replacement, operation and maintenance, fuel and interest cost [10].

Study Location
Muzaffarpur (Latitude 26 04 , Longitude 85 36 ) city of Bihar, India has taken for study. The district occupies an area of 3173 km² and has a population of 3,743,836 (as of 2001).

Load Profile
A typical daily and annual electrical load profile are shown in Figure 2 and Figure 3 respectively. Muzaffarpur district has been considered for load analysis. For a particular area we consider home, shops, street, schools and other some load.

Solar Photovoltaic (PV) System
Solar energy is the most promising of the renewable energy sources in view of its apparent unlimited potential. The sun radiates its energy at the rate of about 3.8 x 1023 kW per second. Most of this energy is transmitted radially as electromagnetic radiation which comes to about 1.5kW/ at the boundary of the atmosphere. After traversing the atmosphere, a square meter of the earth's surface can receive as much as 1kW of solar power, averaging to about 0.5 over all hours of daylight. Solar radiation details of study area is taken from [5] is given in Figure 4.

Wind Energy System
The energy available in the wind depends on the density and air velocity. The density, as any other gas, changes with the temperature and pressure which varies with the high level of the sea. The energy of a mass of air which is displaced is determined by the Kinetic Energy (K.E) flux [11]. The hub height of the wind turbine system is 20m and altitude (m above the sea level) of Muzaffarpur is 46. Wind speed details of study area are taken from the website [6] which is given in Figure 5.

Biomass Energy System
Biomass energy system converts biomass energy into electrical energy. The energy availability is depends on the type and the quantity of biomass residue. The main biomass residue in this region is rice husk, rice straw, paddy straw, maize cobs and municipal solid waste. The annual production of biomass residue of Muzaffarpur district is given in terms of M.T./year is taken from [11]. Therefore annual average biomass production is 176 tones/day. Annual biomass production profile is shown in Figure 6.

Battery Storage System
Battery bank is a conventional approach to store electrical energy with high efficiency. Its discharging level cannot exceed a minimum limit defined as depth of discharge. The capacity of the battery is so designed so as to supply the primary load during the non-wind and non-solar hours.

System Constraint
The constraints which are given in Figure 7 are conditions that system meet to be feasible. Infeasibility systems do not include operating in the sensitivity and optimization analysis [12].

HOMER Simulation and System Architecture
HOMER helps determine how different conventional, renewable, and hybrid systems interact with primary load demand. Based on availability and potential of alternative sources in the study area, an integrated power system is modeled consists of a photovoltaic, wind power system, and biomass plant. Battery is used for back-up and storage system. The project life time is estimated at 25 years. The Figure 8 shows an integrated alternative source of energy system with grid substation.  Table 1. System architecture of integrated energy system

Result and Analysis
Homer simulates system configuration with all of the possible combinations of components that are specified in the component input. Homer performs hundreds or thousands of hourly simulations (to ensure best possible matching of supply and demand) and offers a list of possible schemes ranked on the basis of NPC(net present cost). The system is design in such a way that the power generated from this integrated system to meet the load demand. The integrated alternative source of energy system with grid substation evaluated to determine the feasibility of the system. The system is also simulated in order to evaluate its operational characteristics, renewable fraction, grid sold and purchased energy table, namely annual electrical energy production, annual electric load served, capacity shortage, and unmet electric load as shown in Figure 9 to Figure 15.
In the month of July, August and September due to cloudy day the generation of power through PV system is less so that energy purchased from grid in this month is high as compared to other months. In the month of May total energy purchased is very less because solar radiation is maximum (7.070 kWh/ /h) as compare to other months. The maximum energy generation from wind plant in the month of April, May and June due to good wind speed. The maximum energy generation from biomass power plant of an average 79.9 kW. In this paper we are mainly focus energy optimization so that renewable fraction should be high and net energy purchases is low then our system would be most effective.  Table 2. Annual grid energy purchased and sold data table

Conclusion
The proposed integrated system is designed and optimized using HOMER software to supply energy to primary load and in case of base load excess energy generated by alternative sources sold to the grid substation. The monthly variation of net purchased energy is given in Table 2. Which shows that how climatic condition change the energy generation by alternative sources. our main focus is not a NPC (net present cost) of the system but maximum utilization of alternative sources which is environmental friendly and we can easily see in Figure 7 how second row system (PV/wind/biomass integrated energy system) maximize the energy utilization by 70% through alternative sources as compare to other two sources and net purchased energy (kWh/yr) from grid substation is also low as compare to other two systems in which either PV or wind is not included. Battery storage system is also important which stored energy in case of low demand and excess generation of electricity and it gives to supply in case of peak load demand. The total energy IN and OUT from the battery is given in Figure 12, where energy IN mean excess generation and energy OUT means stored energy supplied to load in case of peak load demand or low power generation. Thus battery utilize 20,152 kWh/yr energy which may be loss during the excess generation of electricity.