Exploitation of Biogas Resources for Electric Vehicle Charging Station in Bangladesh

The abrupt increase of the electric vehicles in Bangladesh needs huge amount of power. As a result, alternative energy sources are emphasized due to limited fossil fuels in order to develop a sustainable energy sector with environment friendly resources. Bangladesh has an enormous potential in the field of renewable resources like biogas and biomass. This paper presents 20 kW electric vehicle charging station (EVCS) utilizing biogas resources where maximum energy requirement is 100 kWh. In this paper, the biogas based EVCS is designed using MATLAB Simulink and HOMER software. Daily 15-20 electric vehicles can be recharged their batteries using the proposed charging station. The proposed system offers lower cost of energy compared to the grid electricity. Moreover, the proposed charging station shows 68.75% reduction in CO2 emission than grid based charging station. In addition, the proposed EVCS will save monthly $ 16.25 and $ 27.50 respectively for easy bike and auto rickshaw type electric vehicles in Bangladesh.


Introduction
Bangladesh is an energy-starved country where natural gas and petroleum products are the main sources of energy [1].Transportation sector consumes 46.46% of the total petroleum consumption and 6% of the total natural gas consumption.In addition, only 8% of the total demand of petroleum is reserved in Bangladesh and every year about 1.2 million tons of crude oil and 2.6 million tons of refined petroleum products need to import [2,3].So, the government has to pay a high amount of budget to import it from abroad.Besides this scenario, greenhouse gas (GHG) emissions due to the transport sector increases significantly [4].Growing concern about the GHG emissions to the environment encourage to use electric vehicles (EV) that is the cheapest mode of transportation.In Bangladesh due to rapid industrialization and increasing income level, peoples are using electric vehicles that have the several key benefits including reduction of sound pollution, fumes and GHG emission.However, the steady increase in the number of EVs in Bangladesh needs 500 MW power daily from the national grid.This huge demand creates a burden on the grid and affects the stability & power quality of the grid [5].Moreover, almost all of the EVs are charged their batteries from the residential connection which is illegal.The EV owner pays the bill as residential consumer that leads the failure of the power sector to reach the profitability margin.Bangladesh has an enormous potential for renewable energy resources like solar, biogas/biomass, wind, hydro etc. [6].These renewable resources can be used to charge the EVs that can help to reduce pollution [7].Different institutions are working jointly with the Government of Bangladesh to utilize renewable resources.Although, solar charging stations are establishing in different cities of Bangladesh.
These are not sufficient and therefore a lot of charging stations is required to work with the EV charging by renewables.In addition, solar-based charging station can only work when solar energy is available.İn this case, biogas resources can increase the effective operational hours for charging EVs [8].To the best of the authors knowledge, no initiative up to date has been taken place to determine the feasibility of biogas/biomass incorporation in EV charging stations in Bangladesh.Therefore, this study carried out to open a new door for connecting biogas in EV charging.The main contributions of this paper are given as follows: a) To analyse the potential of biogas/biomass resources available in Bangladesh; b) To design the proposed EVCS by MATLAB Simulink; c) To analyse the cost and environmental benefits of the proposed EVCS by HOMER software and d) To illustrate the social benefits of the proposed EVCS.
In this paper, the prospects and potentials of biogas/biomass resources are analysed.Based on the potentiality of biogas resources, a novel model for EV charging scheme in Bangladesh is proposed in this research.Mathematical modelling and analysis are performed with the help of MATLAB Simulink.Environmental impacts and benefits are also demonstrated in this research using HOMER software.Social benefits of the EV adaptation involving biogas energy are illustrated in the paper.

Literature Review
Growing popularity of EVs in Bangladesh, encourage researcher to do research with the establishment of EVCS and utilize the renewable energy like biogas and biomass.
The literature survey is divided into three parts.These include the assessment of the biogas/ biomass potential in Bangladesh, existence of the charging stations by renewable energy and the charging stations using biogas/biomass.The electricity and transportation sector requires a major portion of the total fossil fuel demand in Bangladesh.However, the fossil fuels are limited in stock and have to pay large budget to import it from abroad.Thus it is high time to use renewable energy resources instead of petroleum resources for sustainable development in Bangladesh [9].Renewable energy resources are very much eco-friendly and emit less amount of GHGs [10].To promote development in urban areas as well as rural areas it is necessary to fulfil the electricity demand.In rural areas where grid electricity is unavailable, electricity demand can meet using renewable resources like solar, biogas, wind etc. Solar energy is available in all over the country to generate electricity effectively for 5-6 hours with solar irradiation of 4 to 6.5 kWh/m 2 -day [11].Necessary wind speed in Bangladesh is limited to only coastal and off-shore areas [12].Moreover, the biogas resources are available throughout the country.Thus, the proper use of biogas/biomass resources for electricity generation increase the effective operation hours.
Bangladesh has an abundant resource of biogas/biomass for power generation.M. S. Shah et al. estimated the 7.6775 billion m 3 biogas potential in the fiscal year of 2012-13 which can be used as bio-CNG of 5.088 billion m 3 [13].As an agricultural country, biomass energy has a great potential to strengthen the industrial and manufacturing sectors in Bangladesh [14].In a study, the biomass potential is explored in Bangladesh through gasification technology and concludes that agriculture residue, rice husk, bagasse, wheat straw, jute stalks, maize residues, coconut shells, forest residue and municipal solid waste (MSW) are the main biomass resources [15].According to waste statistics from Sustainable and Renewable Energy Development Authority (SREDA) and Waste Concern, Bangladesh, it is found that cow dung, poultry waste, MSW can be a potential source of electricity generation in Bangladesh [16,17].With increasing population, the volume of solid waste is increasing enormously which may become a good source of energy as well as a part of solid waste management.Controlling temperature and P H of the waste are the main factors of biogas production [18].Potentiality of biogas resource facilitates the sustainable development which is analysed in a legal framework and future market situations [19].A study shows that, approximately 4 million biogas plants can be established in Bangladesh which can meet the 20% of the total household demand [20].
A small-scale biogas plant of 3.2 m 3 in Bangladesh is capable of mitigating GHG emission compared to the conventional power station.In addition, the environmental impacts are determined by evaluating biogas, methane, construction materials and feedstock demand [21].In South Africa, a biogas plant was found economically viable which generates 166.6 kW power and 277.7 kW heat from cattle manures of 58330 kg/day [22].Co-digestion may increase the biogas production efficiency and efficient use of biogas resources [23].Anaerobic co-digestion of cow dung with kitchen waste, rice husk, water hyacinth is analyzed to get the maximum possible benefits of biogas resources and found the efficiency of biogas production increases up to 150% [24].Biogas can be used as bio-CNG (bio-methane), combined heat and power generation.Only 35% of biogas is converted into electricity, 50% is converted into heat and 15% is into losses [25].Transport vehicle (CNG driven) can be run by using bio-CNG whereas electric vehicle from electricity generation from bioenergy.The heat produced from biogas plant can be used for heating applications like the gas stove for cooking.Bi-product of biogas plant can be used as fertilizer/fish feed which consists of nitrogen, phosphorous, carbon etc. [26,27].Different studies and research are carried out in the context of Bangladesh to design, development and performance analysis of biogas plants using the locally available waste material in a costeffective manner [28][29][30][31][32][33][34].Various factors such as biogas potential of feedstock, design of digester, inoculum, nature of substrate, pH, temperature, loading rate, hydraulic retention time (HRT), C: N ratio, volatile fatty acids (VFA), etc. influence the biogas production [35,36] C that is very close to the optimum requirement [37].Renewable energy resource based electricity generation helps to meet up present energy crisis to charge the EVs.EVs charged by renewable based charging station offers less GHG emission than grid-based charging station [38].The electric vehicle can be used as a load or distributed energy source in bidirectional power flow method popularly known as vehicle to grid technology.V2G offers reactive power compensation, active power regulation, load balancing which are capable of increasing efficiency and grid reliability [39].In a research, the real time simulation for vehicle to grid, grid to vehicle and vehicle to vehicle technology are implemented and described charging & discharging requirements.Also the energy management system is needed for dynamic price model of multiple EV charging station [40].Feasibility analysis of solar-based electric vehicle charging station and their design consideration is assessed in different research where the method was found economically and environmentally acceptable [41,42].Design of EVCS using solar and biogas resources can make the system cost-effective and reduces the environment pollution significantly [43].However in case of solar, the effective hours are very low.As EVs need the power to charge at any time of the day, it is important to use biogas resources for EV charging to increase the effective hour and management of wastes in a proper way [44].Single EV can draw less amount of power where the aggregate effect of EVs can be a threat to the normal electric power system infrastructure and its operation.Also the charging load profile can be designed using the time of use to recharge the battery [45].
A study in the context of Denmark shows that biogas used for EV charging reduces the fuel consumption and GHG emission [46].Biogas can be converted into bio-CNG which is further used for transportation vehicles.Biogas applications for EV charging are seen in different areas of the world with the emphasis on renewable energy and reduce the use of fossil fuel & GHG emission from transport sector [47][48][49][50][51][52].Fuzzy logic based feed stock selection for biogas production according to C/N ratio of the waste was performed in a research [53].A MIMO fuzzy logic based system was developed for prediction of biogas and methane production rates in a pilot -scale mesospheric USAB reactor treating molasses waste water [54].Although the huge potentiality of biogas/biomass in Bangladesh, there is very few research performed to use it in the transportation vehicle i.e.Electric Vehicle charging.The eco-friendly, cheapest and effective waste management facilities grow up our interest to perform this research on the use of biogas resources.

Electric vehicle in Bangladesh
Electric vehicles are now running almost all corners of the Bangladesh.There are three types of electric vehicles used in Bangladesh-such as-Easy bike carries 5 passengers.Auto-rickshaw carries 2 passengers and Electric motorcycle carries 2 passengers.These EV can travel for distances ranges from 70-120 km and energy requires per day is about 8-11 kWh.All of these vehicles are charged from the utility grid as a residential consumer.However, the EV charging rate declared by government is higher than residential consumer and EV owner treated as a business consumer.Thus, the government is facing difficulties with earning profit from power sector.It is well known that, unavailability of the charging stations and load shedding affects the EV charging.Although, the government has taken initiatives by establishing solar charging station (SCS) in different points of Bangladesh.The government needs a massive plan to establish new charging stations in all over the country and reduction of the pressure on the grid performance.An EV charged from the grid-based charging station requires 120-150 BDT. per day for full charging.For a km run, it needs approximately 0.11 kWh and costs BDT.1.078.Specifications of the EVs used in Bangladesh are given in Table [1].

Potentials of Biogas Resources in Bangladesh
Biogas is a source of energy which can be used for the purpose of electricity generation, cooking and other heating applications.Typically, it is a mixture of methane and carbondi-oxide, produced by the breakdown of the organic wastes without oxygen.Biomass is also a resource of bio-energy which consists of wood, crop residues, foods, garbage and landfill gas etc.In Bangladesh, huge potential of biodegradable resources like animal waste, food substrate, wood & paper, garbage, municipal solid wastes are treated as the main sources of biogas.The chemical composition of biogas is shown on the Table [2].The commonly used fuels with their calorific value and thermal efficiency are shown in Table [3].
Table [2]: Chemical composition of Biogas [52] Chemical parameter % Content Near about 4200 tons of MSW generates in Dhaka city in every day.The improper management of MSW creates a negative environmental impact and it appears to be a growing concern now a days.The proper management of these wastes can be a tremendous source of energy generation.The government and other stakeholders are thinking about this matter.Recently GIZ, German development agency has performed a detailed feasibility study with the collaboration with Sustainable and Renewable Energy Development Authority (SREDA), Bangladesh to identify the prospects and potentials of MSW to electricity generation in Keraniganj, Dhaka.The experts recommended dry fermentation technology for the waste to energy project (WTE), Keraniganj.Depending on the suitable waste management, the expert advices to establish 4-5 MW power plant based on organic waste and industrial waste.Bangladesh Power Development Board (BPDB) has assigned to establish 1 MW combined heat and power unit by the government.

System Components selection and design
To develop the EV charging station based on biogas resources requires energy demand, biogas/biomass potential, size of the biogas plant, available space for plant, initial cost, O& M cost per year and finally the daily output from the plant.The design and development phases of the proposed EVCS are given below.

Energy required for EVs:
In this research, 20 EVs are considered for charging by biogas resources daily.It is assumed that, the proposed charging station can continue the operation for 24 hours daily.EV comes at charging station to charge their batteries according to the SOC.The load curve is shown in Figure 2 which describes the variation of EV load with time.Figure 2 shows that at the evening period load gradually increases and at morning hour load is relatively lower than other time.

Fig. 2: Daily load curve of the proposed EVCS
Fig. 2 shows that at the evening period load gradually increases and at morning hour load is relatively lower than other time.

Waste required for the power generation:
Total waste requires for the electricity generation for the EV charging is the important parameter for designing biogas based charging station.In this research, a charging station is designed where the maximum energy requirement is approximately 100 kWh and load curve is plotted in Fig. 2. Use of poultry waste, cow dung and MSW are considered for power generation.However, the energy output will not be same for different types of wastes.Therefore, calculation of electricity from different wastes are need to evaluate first.

Possible amount of electricity generation,
where W, BW and BkW stands for total waste in kg, biogas production per kg of waste and biogas required for 1 kW electricity generation, respectively.It is assumed that for It is also assumed that biogas required for 1 kW electricity generation is 0.71 m 3 .Table [6] shows that, different waste requirement for biogas production.It is worth mentioning that outputs of a biogas plant are in the forms of heat and biogas.Only 35% of the biogas is used for generating electricity but 65% of output energy is utilized for mechanical losses and heat.The heat produced from this plant can be a good source for cooking.Fig. 3 shows the monthly collection of biomass from the nearby cattle farm, poultry farm and urban areas of Bangladesh.
Collected biomass is firstly processed and stored into a tank for further anaerobic digestion in the digester.According to the weight of the processed biomass, biogas generator generates electricity.
Fig. 3 shows the monthly collection of biomass from the nearby cattle farm, poultry farm and urban areas of Bangladesh.Collected biomass is firstly processed and stored into a tank for further anaerobic digestion in the digester.According to the weight of the processed biomass, biogas generator generates electricity.

Digester design:
Anaerobic digester is the main component of a biogas plant in which biogas is produced after breakdown of organic waste in the absence of oxygen.
The produced biogas can be used for driving transport vehicle and generating electricity.The volume of the digester is the product of the daily substrate input and the retention time which is expressed as equation ( 2) [57].As in this research, the size of the digester is found 40 m 3 to produce 100 kWh of electricity per day.Therefore, a special design of 40 m 3 digester is required for this EVCS.Otherwise, 4.8 m 3 digester of 8 nos.and a 3.2 m 3 digester can fulfil the demand of 40 m 3 .

Gasholder:
The gasholder is used in biogas plant to hold the biogas produced by the digester.The design considerations are rate of biogas generation and the rate of consumption.It should be designed such a way so that it can hold maximum amount of biogas during zero consumption period.

Biogas generator:
The power generated from the biogas generator depends on the torque and speed of the generator.The biogas is converted into rotating force or torque by an engine which is directly proportional to the power generated.Assuming the mechanical losses and copper losses, the output electrical power is obtained.This is approximately 35% of the total biogas energy.

5252
For a 4-pole generator and frequency of 50 Hz, speed, N=1500 rpm.A 4 kW generator can run with the output of 4.8 m 3 digester at 8-10 hours effectively.

Rectifier:
It is used to convert the AC voltage into DC for charging EVs.It is assumed that rectifier has 90% efficiency.The rectifier is connected to the charging assemblies where EV is charged.

AC P DC P
  

Battery:
The battery is used to store the excess energy when the EV is unavailable to charge.Therefore, it should be designed very carefully to handle the emergency situation.It is assumed that, the battery bank is designed to store the energy of 50 kWh.The battery capacity is expressed as So for 30 kWh energy and terminal voltage of 12 V, there are a total number of batteries required= 25 of 100 Ah.
The charging profile of an EV depends upon the following factors-i.e.EVs arrival time, charging level and time required to recharge the battery.The energy required to charge the battery can be determined by following equation [61].
) 1 ( arg Where E K is the total energy required to charge the battery (kWh), SOC k is the percentage of remaining charge in the vehicle battery, C k is the battery capacity and η k charger is the efficiency of the vehicle battery charger assumed as 90%.

Design of the proposed EVCS
Conceptual design of the biogas based EVCS is shown in Fig. 4. Animal wastes and other wastes are collected and processed to recover the energy content.Mixer is used to mix up the slurry which is made by a combination of processed waste and water.Then, anaerobic digestion occurs at a temperature of 35 o C at digester and biogas is produced.The biogas is stored into a gasholder.In Bangladesh, fixed dome type digester is often used.The size of the digester is determined by the retention time and daily feedstock/substrate input.Gasholder stores the biogas produced by digester at low consumption period.The produced biogas is warm and it contains large amount of water vapour.When cooled, most of the water will condense out and it can be supplied back to make slurry.Gas purification plant mainly removes the H2S content, because it is corrosive with the CO2 and water.Digestate slurry can be used to land and ponds as fertilizer and fish feed.Biogas generator unit consists of an engine and a generator.An engine converts the chemical energy into mechanical energy which is further used to run a generator to generate electricity.The proposed EVCS is designed for generating electricity and further charging EVs according to the battery SOC.The monthly optimum power generation from the proposed EVCS is shown in Fig. 6 where the maximum generation is in the month of July and the minimum in February.It depends upon the biomass collection.The processed biomass is ready for anaerobic digestion in the fixed dome type or floating dome type digester.In accordance with the calorific value of the waste materials, the biogas produces and thus electricity is generated.In a biogas plant, the production of biogas is not only the output parameter but digestate produces from the anaerobic digestion is also carries importance.Digestate can be formed as a good fertilizer and selling this bi-product at a minimum rate to the farmers, developer can minimize the running cost of the plant.In the proposed EVCS, monthly digestate production from the biogas plant is plotted in Fig. 7.In a biogas plant, the production of biogas is not only the output parameter but digestate produces from the anaerobic digestion is also carries importance.Digestate can be formed as a good fertilizer and selling this bi-product at a minimum rate to the farmers, developer can minimize the running cost of the plant.In the proposed EVCS, monthly digestate production from the biogas plant is plotted in Fig. 7. Fig. 7: Month wise digestate production from the proposed EVCS.

Cost Analysis:
The economic parameters related to the proposed EVCS consist of initial capital cost, O&M cost, replacement cost, cost of energy, payback period.These parameters play a vital role for accomplishment and desired success of the project.

Cost of energy:
The EVCS delivers power to the consumer on the basis of power demand and power availability.The cost of charging EVs per kWh is called the cost of energy (COE).In case of the proposed EVCS, the charging cost can be determined by the following equation [62].
The CBase is the base or minimum value of the EV charging cost and Cvariable is the variable cost of charging depending of the time.It may vary according to the peak and off-peak periods and thus the charging cost also varies.In this proposed research, the COE per kWh for EV charging is found BDT.5.70.
In this research, the total life time is assumed 10 years and the effective payback period is found as 5.81 years.The payback period is less than the life time.Thus, the system would be profitable.

Profitability index:
It is defined as the ratio of future cash in-flow and cash out flow.This index determines that, the project would be profitable or not.If the project is profitable, the profitability index would be greater than unity.In this research, the profitability index is obtained using equation (10) that is greater than unity.It means that the system would be profitable.The Fig. 8 shows the profitable period and payback period of the proposed EVCS.

Ton
Months from January to December 6.0 Environmental aspects of the proposed EVCS Electric Vehicles are becoming popular day by day due to their eco-friendly nature.The GHG emission and other pollutants which are noxious to the environment is reduced by using EV.In Bangladesh, the CO2 emission for per unit of electricity generation is approximately equal to 640 g [63].The main sources of electricity generation in Bangladesh are natural gas and coal.These two resources are limited and producing large amount of CO2 emission.As compared to these resources, renewable resources like biogas/ biomass has the greater advantages of reducing CO2 penetration from electricity generation purposes.In this proposed charging station, biogas and biomass is used for the purpose of generating electricity which will further charge the EVs.Thus the CO2 emission is reduced significantly by using biogas resources.Fig. 9 shows the comparison of the CO2 emission from the grid based EVCS and biogas based EVCS.In the proposed EVCS, yearly CO2 emission is about 5,840 kg whereas for the same demand grid based charging station produces 18,688 kg of CO2.Thus, the CO2 emission is reduced to 68.75% from the grid based charging station.The waste material pollutes environment and scatters acrid bad smell to the atmosphere.Utilization of these wastes relief the environment from pollution and bad smell.Another advantage is that, there is a lot of slurry produces which can be used as fertilizer and it makes the atmosphere fresh & clean.The application of slurry improves the physical, chemical, and biological characters of the soil.

Social benefits of the Proposed EVCS
Electric vehicle charging infrastructure opens a new lucrative area of research and application in Bangladesh.
Growing popularity of electric vehicles gives few benefits.Environmental and socio-economic factors are working behind the popularity of electric vehicles.Electric vehicles such as Easy Bikes, Auto-rickshaws and Electric rickshaw vans have high potential of reducing emissions, improving air quality in both urban and rural areas and increasing the income level of the lower class people.An Easy Bike driver in Bangladesh can easily earn approximately $18-$25 where the energy consumption cost of this car is only $1-$1.25 daily.Due to electric vehicle adaptation the living standard is improved.It cuts the physical labor and saves transportation time.Charging cost of an Easy Bike is around $53 per month.It will be lower than the present cost if the EVs are charged by the proposed charging station.Table [9] shows the summary of the charging cost in a grid-based system and the proposed EVCS-based system.The monthly savings and monthly income by using this EVCS for an EV driver are given in

Conclusion
In Bangladesh, almost all the electric vehicle charging infrastructure are operated by grid electricity.Increased demand of electricity requires more generation.Thus it is necessary to incorporate available renewable energy resources like biogas to increase the generation to charge the electric vehicles.The concept of using biogas/biomass resources for charging battery driven electric vehicles opens a promising area of research and application in Bangladesh.
In this paper, the proposed EVCS is found economically feasible and the investment will be returned after 5.80 years.
The proposed EVCS saves $16-$28 per month than grid based EVCS.In the case of environmental aspect, the proposed EVCS can reduce GHG emissions remarkably.Efficient use of locally available wastes in the proposed EVCS ensures continuous power supply, stability, and reliability of the charging infrastructure.To strengthen the national grid by reducing extra burden like electric vehicle charging by biogas resources can make the energy sector more reliable and, improves power quality towards sustainable development.

Conflicts of Interest:
The authors declare no conflicts of interest
poultry waste & MSW biogas production per kg of waste is 0.074 m 3 and for cow dung biogas produced per kg is 0.034 m 3 .

PreprintsFig. 6 :
Fig.6: Electricity generation scenario of the proposed EVCS In a biogas plant, the production of biogas is not only the output parameter but digestate produces from the anaerobic digestion is also carries importance.Digestate can be formed as a good fertilizer and selling this bi-product at a minimum rate to the farmers, developer can minimize the running cost of the plant.In the proposed EVCS, monthly digestate production from the biogas plant is plotted in Fig.7.

5. 2
Payback period: It is expressed in years after which the investment is equal to its total cash in-flow.It indicates the project will be profitable at the end of the payback period.

Fig. 8 :
Fig.8: Lifetime and payback period of the proposed EVCS

Table [ 1
]: specifications of Electric Vehicles in Bangladesh

Table [ 3
[53]ommonly used fuels in Bangladesh[53] [54]Animal waste:Animal wastes can be used as potential biomass resource.In Bangladesh, there are 150,000 poultry farms of chicken and duck.According to the statistics obtained for the fiscal year 2016-17, waste generation per day from different livestock (i.e.Cattle, buffalo, chicken and duck etc.) is shown in Table[4].The wastes produced from these livestock can be utilized to generate power.Table[4]: Waste generation from livestock[54]vegetables. Bangladesh is a major rice producing country.Rice straw and rice husk are the main residues of rice.Depending on the residue collection period, the crop residues can be categorized as-field residues and processed residues.The rice straw and rice husk residue recoverable rate is 35% and 100% respectively.Sugarcane residue is one of the Preprints (www.

preprints.org) | NOT PEER-REVIEWED | Posted: 31 July 2018 doi:10.20944/preprints201807.0625.v1 powerful
[58]urce of biomass.In Bangladesh, the volume of sugarcane cultivation reached about 4,434,070 metric tons.The tops & leaves, bagasse residues are utilized as biomass energy where residue recoverable rate for processed bagasse is 73.42%.Jute is another biomass source in which the recoverable rate is 37.12%.All of these agriculture residues can be a good source of biomass for power generation and also effective in heating applications[58].