Implementation of microgrid with integration of hybrid renewable sources using different backup techniques

Background/Aim: This research aims to design and compare four Hybrid Microgrid Systems involving different backup techniques for a remote village in Sindh, Pakistan and finds the most optimal hybrid system based on Net Present Cost (NPC) and Cost of Electricity (COE).Methods/Statistical analysis: In order to make a suitable hybrid system, firstly, a proper literature review was done to get the information about the recent work done on this system after that four hybrid systems were designed with two common primary sources: Solar and Wind and different backup sources including Batteries, Fuel Cell, Diesel Generator and Gird. HOMER performed optimization on all four hybrid system cases based on NPC and COE to find the most optimal hybrid system for each case. Findings: The comparison of all four optimal hybrid cases shows that Solar/Wind/Grid Hybrid Microgrid System is themost optimal system for that location with NPC PKR 21M and COE PKR 12.84. The payback period of this system is 3 years. This research is based on real-time data and involves the comparison of four different hybrid systems to find an optimal hybrid system. Novelty/Applications: The world is greatly moving towards renewables keeping in view their enormous benefits and the current global warming issue. Pakistan is one of those countries who are blessed with an abundant renewable resource, which if utilized properly then it can fulfil the whole country’s energy demand, and this will also reduce the use of fossil fuels in the energy sector of the country.


Introduction
Electricity has become a basic need for living in today's world, from home to every small or large business today depends on electricity. Electricity has a vital role in the https://www.indjst.org/ country's development and economy. This electricity demand is increasing globally with an annual average growth rate of 2.3% due to the increase in the population worldwide (1) . The use of fossil fuels to generate this electricity is becoming a major issue due to diminishing resources, expensive fuel prices and environmental concerns. These issues are the major reasons behind the growing popularity of renewable energy sources. The world is moving rapidly towards renewables because of their enormous benefits like they are environment-friendly, have least fuel cost and electricity is also cheaper than that of fossil fuels. The main drawback of renewable sources is they are intermittent by nature but with the advancement of new technologies, these sources can now be integrated to make a hybrid system (2) .
The two most common renewables sources being used worldwide are Solar and Wind but they both lack in producing continuous power as they both depend on nature that is why their combination makes a suitable and reliable hybrid system and some means must be provided for storing the generated electricity from these sources like batteries, fuel cell or a grid can be integrated with these sources for backup supply. Pakistan is one of those countries who are blessed with enough renewable energy potential, with 300+ sunny days, tremendous wind speed in some areas especially coastal areas of Sindh and many other resources are also available which can be utilized to meet country's energy demand (2) . Despite having enough renewable potential, Pakistan is generating 62% of its electricity from fossil fuels as can be seen in Figure 1 (3) . Pakistan being a developing country is facing energy crisis for the last 20 years and the supply and demand gap is increasing since that. This causes the load shedding especially on rural areas to meet the demand of urban areas. This load shedding has been increased up to 10h in summer and 6h in winter. This daily power outage is one of the main reasons for the country's lower GDP (4) . Pakistan's energy mix scenario chart (3) HOMER Software has been used by many researchers to design different microgrid models and to perform different tasks like finding feasibility or doing cost analysis etc. A feasibility study was carried out of a hybrid microgrid system containing WTG, Diesel Generator (DG) and battery on the basis of technical and economical parameters. The system was tested with different types of batteries like Lead Acid, Lithium Ion, Zinc Bromine (ZB) etc. to find the optimal system for a residential community with 280 houses, located in Gansu, China. The results indicate that hybrid system containing DG and ZB Batteries is the most optimal system with 1460kW DG, 500 ZB Batteries and a 400kW Converter. This optimal hybrid system has NPC of $ 7,735646 and COE of $ 0.47/kWh (5) .
A standalone system was designed using single renewable energy source Solar PV with battery storage for a typical rural house in Punjab, Pakistan. The average daily consumption of that rural house was calculated to be 10 kWh/day. HOMER Software was used to find the optimal solution for that house (4) . Another feasibility study was carried out on a standalone Solar PV-Biogas hybrid system for a small village of a Cholistan Community. The village had more than 80 houses. Two load profiles were considered one for local consumption other for agriculture need and according to that a model was developed and HOMER Software was used to find the optimal solution for that village (6) . https://www.indjst.org/ 2 Methodology

Study area
A village named as Saeedpur Takkar near Mulaqatiar Road Tando Muhammad Khan, Sindh is selected for the case study as shown in Figure 2. This village is located at the latitude 25.1326'N and longitude 68.4539'E (7) . It consists around 85 houses, some shops and a secondary school. The houses in rural areas, unlike urban areas, are scattered. This location is chosen because it is rich in renewable resources like solar and wind.

Solar data
The horizontal global solar irradiation for the selected location is obtained from NASA Surface Meteorology and Solar Energy Database (8) . The maximum average solar irradiation obtained for the selected location is 6.86kWh/m2/day in the month of May and the annual average solar irradiation is 5.38kWh/m2/day as can be seen in Figure 3. Monthly solar irradiation data (8) https://www.indjst.org/

Wind data
The wind speed data for the selected location is obtained from NASA Surface Meteorology and Solar Energy Database (8) . The maximum average wind speed obtained for the selected location is 9.6m/s in the month of June and the annual average wind speed is 5.86m/s as can be seen in Figure 4. In our study turbine height is considered 25m to 30m, HOMER will convert these values from 50m anemometer height to 25m turbine height.

Load assessment
The load survey was conducted on the selected village and the data was collected from each consumer. The total average daily consumption of the whole village was calculated very carefully keeping in view the total operating hours and seasonal load growth and reduction. As shown in Table 1, the average daily consumptions of a household, shop and school were found to be 4.73kWh/day, 3.67kWh/day and 4.2kWh/day respectively. The average daily consumption of whole village was calculated to be 367kWh/day with peak load of 37.6kW.
In Figure 5, the hourly load profile for 24 hours is shown. The daily peak load is 13kW that usually occurs for 2 hours (i.e. from 10am to 11am and from 2pm to 3am). https://www.indjst.org/ To make a suitable Hybrid System we have assumed WTG sizes as 20kW, 30kW, 40kW, 50kW and 60kW. HOMER will choose the optimum size from these values. The converter of 90% efficiency and 15 years of life cycle is used in this study.
The cost of Solar PV, WTG, Battery, Converter and Diesel Generator are obtained from the local Solar and Wind Turbine installation companies of Pakistan whereas the cost and specifications of Hydrogen FC, Electrolyzer and Hydrogen Tank are taken from (9) . This system is designed for 25 years life span. All cost values are taken in Pakistani Rupees (PKR) and all the calculations are done in Pakistani Rupees (PKR) for accuracy purpose.  Figure 6, Solar PV and Wind Turbine are the primary sources in all models and the backup sources includes a battery, hydrogen fuel cell, diesel generator and grid supply. These backup techniques are integrated one by one with primary sources to investigate all four hybrid cases and to find the most optimum hybrid system configuration for each case.

Case A. PV/Wind/Battery Hybrid System
This hybrid system consists of two renewable sources Solar PV, Wind Turbine Generator and a battery for storage purpose as shown in Figure 7. A 12V, 83Ah lead-acid battery with maximum 3 years of life cycle is selected in this system. Case B. PV/Wind/Hydrogen fuel cell hybrid system In this hybrid system, Hydrogen FC is integrated with Solar PV and WTG sources for storage purpose a scan be seen in Figure 8. For the low power application (i.e. less than 100kW) the most preferred technology to generate Hydrogen is Proton Exchange Membrane (PEM) (9) . It has three components, Electrolyzer to generate hydrogen from water, Hydrogen Tank to store that hydrogen in a compressed form and a Fuel Cell to generate electricity from that hydrogen when required. The sizes of Hydrogen Tank are assumed as (30kg, 40kg, 50kg and 60kg), for Hydrogen FC as (10kW, 20kW, 30kW and 40kW) and for Electrolyzer as (40kW, 50kW, 60kW and 70kW). HOMER will choose the optimum size for each component.

Case C. PV/Wind/Diesel generator hybrid system
This hybrid system involves a diesel generator as a backup source with Solar PV and WTG sources as shown in Figure 9. Diesel Generator sizes are assumed as (10kW, 20kW, 30kW and 40kW), HOMER will choose the optimum size from these values. The sensitivity analysis is performed on this system due to the variation in diesel fuel prices every year. The sensitivity values in terms of diesel fuel prices are taken as PKR 124/liter and PKR 128/liter.

Fig 9. PV/Wind/DG Based Hybrid Microgrid System
Case D. PV/Wind/Grid hybrid system This hybrid system contains Solar PV and WTG along with a Grid connection for backup power supply as can be seen in Figure 10. The Grid supplies power when the demand exceeds the supply coming from renewable sources. The sensitivity analysis is performed on this system due to variation in the unit cost over the units consumption. The sensitivity values in terms of Grid unit prices are taken as PKR 17/kWh and PKR 25/kWh.

Results and Discussion
HOMER performed the optimization during the simulation period on all four hybrid systems based on the given inputs and showed the number of possible system configurations on the basis of NPC and COE.

Simulation Results
Case A. PV/Wind/Battery hybrid system HOMER performed optimization on this hybrid model and provide the optimal results based on given inputs ( Table 2). The simulation results for this hybrid system show that the optimal design contains 276kW Solar PV, 40kW WTG, 512 Batteries and 37.3kW Converter. The NPC of this optimal hybrid system for 25 years is PKR 50.3M and COE is PKR 34.74. This hybrid system is completely renewable with 100% Renewable Fraction. The replacement cost of batteries in this system is high as compared to other components.

Case B. PV/Wind/Hydrogen fuel cell hybrid system
The optimization is performed by the HOMER on this hybrid model based on given inputs and then optimal results are provided ( Table 3). The simulation results for this hybrid system show that the optimal design consists of 224kW Solar PV, 60kW WTG, 36kW Converter, 30kW Hydrogen FC, 60kW Electrolyzer and 60kg Hydrogen Tank. The NPC of this system is PKR 79.1M and COE PKR 54.56. This system has 100% Renewable Fraction Case C. PV/Wind/Diesel generator hybrid system In this hybrid system, HOMER performed optimization method on two models with different sensitivity values for diesel fuel prices (i.e. PKR 124/L and PKR 128/L) and provided two optimized results based on those sensitivity values ( Table 4).
https://www.indjst.org/ Case D. PV/Wind/Grid hybrid system In this hybrid system, the optimization is performed on two models with different sensitivity values for Grid unit prices (i.e PKR 17/kWh and 25/kWh). As shown in Table 5.

Conclusion
In this study, four hybrid systems involving two common primary sources Solar and Wind along with different backup sources which have been designed and optimized with the help of HOMER. Then, a comparative analysis is carried out on all the possible system configurations obtained from HOMER based on NPC and COE to find the most optimal hybrid system with minimum NPC and COE. After the comparison of all optimum hybrid cases as shown in Figure 11, it is found that the most optimal and least cost hybrid system is Case D. PV/Wind/Grid hybrid system with NPC PKR 21M and COE PKR 12.84. The payback period of this hybrid system is 4.25 years. The 2nd optimal but little expensive system is Case A. PV/Wind/Battery Hybrid System with NPC PKR 50.3M and COE PKR 34.74. This hybrid system is 100% renewable and has payback period of 2.96 years. The Case B. PV/Wind/Hydrogen FC Hybrid System and Case C. PV/Wind/DG Hybrid System are the most expensive and unfeasible hybrid systems due to the high capital cost and operating cost of Hydrogen Fuel Cell Components and Diesel Generator Respectively. Moreover, the surplus energy produced from the Grid connected optimal Hybrid System can be sold back to the National Grid at a specific price and this may further reduce the NPC and COE of the system.