Modeling and Analysis of Solar Photovoltaic Assisted Electrolyzer-Polymer Electrolyte Membrane Fuel Cell for Running a Hospital in Remote Area in Kolkata, India

The present work consists of the modeling and analysis of solar photovoltaic panels integrated with electrolyzer bank and Polymer Electrolyte Membrane (PEM) fuel cell stacks for running different appliances of a hospital located in Kolkata for different climatic conditions. Electric power is generated by an array of solar photovoltaic modules. Excess energy after meeting the requirements of the hospital during peak sunshine hours is supplied to an electrolyzer bank to generate hydrogen gas, which is consumed by the PEM fuel cell stack to support the power requirement during the energy deficit hours. The study reveals that 875 solar photovoltaic modules in parallel each having 2 modules in series of Central Electronics Limited Make PM 150 with a 178.537 kW electrolyzer and 27 PEM fuel cell stacks, each of 382.372 W, can support the energy requirement of a 200 lights (100 W each), 4 pumps (2 kW each), 120 fans(65 W each) and 5 refrigerators (2 kW each)system operated for 16 hours, 2 hours,15 hours and 24 hours respectively. 123 solar photovoltaic modules in parallel each having 2 modules in series of Central Electronics Limited Make PM 150 is needed to run the gas compressor for storing hydrogen in the cylinder during sunshine hours. Article History: Received Feb 5th 2017; Received in revised form June 2nd 2017; Accepted June 28th 2017; Available onlineHow to Cite This Article: Talukdar, K. (2017). Modeling and Analysis of Solar Photovoltaic Assisted Electrolyzer-Polymer Electrolyte Membrane Fuel Cell For Running a Hospital in Remote Area in Kolkata,India. International Journal of Renewable Energy Development, 6(2), 181-191.https://dx.doi.org/10.14710/ijred.6.2.181-191


Introduction
Demand for electricity and the standard of living are increasing day by day. However, power in the form of electricity is not available in plenty of remote areas like villages. Many people have worked for providing power and useful technology to remote areas and areas where power is not easily available. Chow et al (2006) developed hybrid PVT (photovoltaic-thermal) technology using water as the coolant in order to improve the energy performance of the photovoltaic system in residential areas. Nfah et al (2008) simulated off-grid generation options for remote villages in Cameroon using a load of 110 kWh/day and 12 kWp. Chaurey & Kandpal (2010) used solar home systems for providing basic electricity services to rural households that are not connected to electricity grid. Elhadidy (2002) analysed hourly wind-speed and solar radiation measurements made at the solar radiation and meteorological monitoring station, Dhahran (26°32'N, 50°13'E), Saudi Arabia, to investigate the feasibility of using hybrid (wind+solar+diesel) energy conversion systems at Dhahran in order to meet the energy needs of 22-bedroom houses. Similarly authors in reference (Nfah et al. 2007;Wies et al. 2005;Al Suleimani &Nairb 2000;Manolakos et al. 2001;Zhai et al. 2009;Beck 2007;Saheb-Koussa et al. 2009;Nfah & Ngundam 2008) used different technologies and powering of appliances in different remote areas.
Hospital is very important for people since many villages do not have hospital. If the village has, it is not having proper facilities like electricity. So if somehow electricity can be supplied to hospital in remote villages, village people could be cured without going to town or city. New technologies can be used for assisting the functioning of hospitals. Yoshida et al (2007) used rational method to determine the system structure and operational strategies for the energy supply system for a hospital based on the optimization approach. Paksoy et al (2000) designed a system using solar energy in combination with Aquifer Thermal Energy Storage (ATES) that conserved a major part of the oil and electricity used for heating or cooling the Cukurova University, Balcali Hospital in Adana, Turkey. Similarly, authors in references (Bizzarri & Morini 2004;Bizzarri & Morini 2006;Al-Karaghouli & Kazmerski 2010) used different technologies for running and assisting hospitals.
The present work in this paper deals with the use of solar photovoltaic system assisted PEM electrolyzer fuel cell for powering a hospital. Many works on fuel cell application and solar hydrogen systems had been done. Wu et al (2005) presented an integrated system framework for fuel cell-based distributed energy applications. Veziroglu & Macario (2011) highlighted some of the research and developmental work, which had occurred in the past five years on fuel cell vehicle technology, with a focus on economic and environmental concerns. Similarly, authors in references (Kelly et al 2011;Solis et al 2010;Dorer et al 2005;Hawkes et al 2006;El-Shatter et al 2002;Shapiro et al 2005;Galli & Stefanoni 1997;Uzunoglu et al 2009;Barbir 2005;Kelly et al 2008;Zervas et al 2008) used different technologies based on fuel cells for useful and beneficial purposes.
From the mentioned reviews a considerable work of powering remote areas, powering health clinics and on fuel cell has been done,yet no work on powering health clinic by using solar photovoltaic integrated with electrolyzer PEM fuel cell has been done. The system configuration consists of solar photovoltaic modules, charge controller, PEM electrolyzer, gas storage cylinder, PEM fuel cell stacks and two inverters as shown in Fig.1. When enough sunlight is available, sun rays fall on solar photovoltaic modules and generate current IPV. Some amount of current required for hospital (IH) goes through an inverter to operate various appliances of the hospital. The excess current (IPV-IH) after meeting the requirements of the hospital goes to PEM electrolyzer. In electrolyzer water is present which gets dissociated into hydrogen and oxygen. The hydrogen gas generated in electrolyzer is stored in gas compressor. For pressurization of the hydrogen gas owing to low mass density, which requires a very large storage tank, the compressor derives its electrical energy (IG) from solar photovoltaic modules and operates only when electrolyzer is in operation.
When enough sunshine is not available i.e. deficient current (IH-IPV) comes from the PEM fuel cell stack. The hydrogen required for running the fuel cell is obtained from gas storage cylinder which gets stored during sufficient solar radiation from the electrolyzer.

Modeling of solar photovoltaic system
The electrical energy was generated by harnessing solar energy using photovoltaic modules. In the present work Central Electronics Limited Make PM-150 (Solar photovoltaic modules pm 150 2011) solar photovoltaic module has been used. The single cell terminal current is given by (Chenni et al 2007): Where L i is the light current generated by a solar cell as a function of solar radiation (G) and D i is the diode current.
The light current generated from a photovoltaic module at any given intensity of solar radiation and temperature is given by (Chenni et al 2007): Where G, Gref is the solar radiation at actual (Tiwari 2004)   The diode current in equation (1) is a function of reverse saturation current and given by (Chenni et al.2007): Where sat i -reverse saturation current(A), q -electron charge(1.6 x 10 -19 C), V -terminal voltage(V), S Rseries resistance,  -shape factor, k -Boltzamann constant(1.38 x 10 -23 J/K). Shape factor ) ( which is a measure of cell imperfection is given by Chenni et al (2007): Where , A NCS , S N is completion factor, number of cells connected in series in a single module (specified by manufacturer of the module) and number of modules connected in series of the entire photovoltaic array respectively.
Where system V is the system voltage of the photovoltaic array (considered 48 V in present study) and ule V mod is the voltage obtained from single module. Table 1 shows the specification of various equipment used in the hospital. The total daily electrical load (Ah)( o i )due to operation of equipments mentioned in table 1 is given by: Where io-electrical load of an equipment, Po-power rating of an equipment, t-operating hours of an equipment and n-number of items, PF-power factor (considered 0.85). The total daily electrical load(Ah)( total i ) consisting of lights, pumps, fans and refrigerator can be given as: Where inverter  -inverter efficiency (0.85) The design current required from photovoltaic array( spv i ) is given by (Ganguly et al. 2010 Where imp is the maximum current available from single module under peak power condition(Solar photovoltaic modules pm 150 2011) Net current from solar PV array is: Table 2 shows the input parameters used for modelling fuel cell.  (Hayre et al.2006) Charge transfer coefficient of reaction 0.5 (Hayre et al.2006) Cell effective area 100 cm 2 (Pal 2004) Operating current density 0.1 A/cm 2 (Pal 2004) The net voltage ( fc V ) of a PEM fuel cell is given by (Ganguly et al. 2010):

Modelling of PEM fuel cell
© IJRED -ISSN: 2252-4940, 15 th July 2017, All rights reserved Nerst potential ( nerst V ) of PEM fuel cell is given by Ganguly et al (2010): is the reference reversible potential, T is fuel cell operating temperature (60 o C in the present study), F is Faraday constant (96500 C/mole), p is the partial pressure of the gases(Pa), Activation voltage( activation V ) is given by Tafel equation (Hayre et al. 2006): Where  is the charge transfer coefficient of the reaction (Hayre et al. 2006 ) is given by Ganguly et al. (2010): Where l j is limiting current density of fuel cell and given by (Ganguly et al. 2010): Where D is the effective reactant diffusivity within catalyst layer having typical value 10 -2 cm 2 /s (Hayre et al. 2006),  is the electrode(diffusion layer) thickness whose value ranges from 100-300µm (Hayre et al. 2006).
CB is the bulk (flow channel) concentration of the reactant given by (Bhagat & Dhoble 2007): Where 2 H m is the mass of hydrogen.
Peak hourly current requirement from fuel cell stack ( fuelcell i ) is given by: In Equation 24 peak load current means the maximum current requirement at any hour during non sunshine hours i.e from 1:00 am to 5:00 am and 7:00pm to 1:00 am.
Number of PEM fuel cell stacks in parallel ( fcparallel N ) can be obtained as shown: Where cell i is the current generated by single fuel cell, which can be obtained from effective area of each cell, and fuel cell operating current density. fcseries N is the number of fuel cell connected in series and is given by The hourly hydrogen consumption of a fuel cell stack ( fc m ) at design load is given by (Ganguly et al 2010): Where fuel  -fuel utilization factor in fuel cell (considered 0.9)

Modeling of PEM electrolyzer
In electrolyzer excess current after meeting the requirements of the hospital is used for dissociating water into hydrogen and oxygen gas. Table 3 shows the various input parameters used for modeling electrolyzer. The voltage efficiency is assumed to be 74 % (Li et al. 2009). Amount of hydrogen produced (in gm mol) in electrolyzer with Nelec (number of cell in series) in one hour is given by (Li et al. 2009

Modelling of gas compressor
Hydrogen gas produced in electrolyzer needs to be compressed. For compressing the hydrogen gas energy i.e current is obtained from solar photovoltaic modules integrated with inverter as shown in fig.1. Table 4 shows the various input parameters used for modeling gas compressor.
The power required to run the gas compressor is given by (Li et al. 2009): The design current required from photovoltaic array (ispv) given by:

Results and Discussion
A numerical code in C was developed for simulating the required combination of solar photovoltaic assisted electrolyzer PEM fuel cell for running a hospital. Table 5 shows different appliances operated at different hours of a day for all the months i.e. March, May, September and December. The ratings of different power system components are given in Table 6. In Table 6 it is seen that number of photovoltaic modules in parallel is 875 which is obtained from equation 2 where ispv total is 4198.033 and imp is 4.8 A. Number of modules in series is given by equation 8 where Vsystem is 48V and Vmodule is the maximum voltage from a given module being 34 V. Electrolyzer input at 48 V is 178.537 kW which is taken at 12:00 hours (maximum radiation in a day) for the month of May because month May has the highest solar radiation and electrolyzer input will be maximum due to greater production of hydrogen by electrolyzer, hence electrolyzer which works well in May will work well throughout the year. The number of fuel cells in a stack in series is 47 is given by equation no.26 where Vfc is given by equation no.14 is 1.028 V. The number of fuel cell in stacks in parallel is given by equation no.24 and 25.In equation no.24 peak load current during non-sunshine hours is 228.984 A which is between 17:00 hours to 22:00 hours. icell is the current obtained from parameters given in Table no. 2.
The maximum output of each fuel cells stack in series is 7.966 A and power of each fuel cell stack is given by product of 48 V and 7.966 A which is 382.372 W. Gas compressor rating at 48V (14.234kW) is given by equation 31 and is taken from the month of May at 12:00 hours because at this time the hydrogen production is maximum (1189.084 gm.mol) and consumption of power by gas compressor to compress large hydrogen generated by electrolyzer is maximum, Hence gas compressor if it works well in this time and it can work well also throughout the year. The number of photovoltaic modules in parallel for operating the gas compressor is given by equation 35. The total ispv current for the gas compressor is 588.235 Ah and number of photovoltaic modules in parallel needed is obtained by dividing 588.235 Ah by imp. Current ispv for the gas compressor is taken for the month of May due to the fact that month May has highest solar radiation, hence it will need a more current and more number of photovoltaic modules for generating current to compress a large amount of hydrogen generated by electrolyzer in the month of May. The number of modules in series is obtained by the same method as equation 8. Fig. 2, 4, 6, 8 shows the hourly current consumption (load current Ah) throughout the day for running the appliances of the hospital by using equation 11. In all the figures it is seen that current consumed in Ah from 10 PM to 7 AM is 181.733 Ah per hour. Similarly, current consumed from 7 AM to 9AM is 277.446 Ah per hour, 9 AM to 5 PM is 107.828 Ah per hour, 5 PM to10 PM is 228.984 Ah per hour. The current consumption will be same for all the months due to the operation of the same number of equipments for the same number of hours shown in Table 5 for all the different months i.e. March, May, September, and December. Solar photovoltaic (SPV) current generated during sunshine hours (6:00hours to18:00hours) in Figures  2,4,6,and 8 from the photovoltaic array for the months i.e. March, May, September, and December is obtained from equation 13. It was observed that the trend of SPV current generated increases from 6:00 hours to 12:00 hours and again decreases to 18:00 hours because solar radiation increases from 6:00 hours to 12:00 hours and again decreases to 18:00 hours. Based on the analysis of Figures 2, 4, 6, and 8 it is seen that months March and September have the same pattern of SPV power generation due to the same amount of solar radiation values from 6:00 hours to 18:00 hours. Month May has highest SPV power generation due to the availability of maximum solar radiation in a year. Month December has lowest SPV power generation due to the availability of lowest solar radiation in a year. The SPV power generated is almost same at 6:00 hours and 18:00 hours in figures 2, 4, 6, and 8 due to the same value of solar radiation at 6:00 hours and 18:00 hours. The solar radiation data is taken from Tiwari (2004). In Figs. 3, 5, 7, 9 shows hydrogen consumption (gm mole/hour) by fuel cell stacks which are dependent on the types of equipment operated in given hours shown in Table 5. Hydrogen consumption(gm mole/hour) is same for all the months due to the reason mentioned earlier by fuel cell stacks during non-sunshine hours using equation no. 27 i.e. from 22:00hours-5:00hours is 413.423 gm mole/hour and 19:00hours-22:00hours is 520.913 gm mole/hour. Figs. 3, 5, 7, 9 also shows hydrogen production (gm mole/hour) using equation no. 30 by electrolyzer from the current generated by photovoltaic modules during sunshine hours(i.e. from 6:00 hours to 18:00 hours).It is seen that hydrogen production increases from 6:00 hours to 12:00 hours and decreases to 18:00 hours. It is due to the fact that solar radiation increases from 6:00 hours to 12:00 hours and again decreases to 18:00 hours. Thus more solar radiation means more amount of current being generated by utilizing to produce more hydrogen by given electrolyzer after meeting the hospital's current requirements.  Based on the analysis of figures3, 5,7, and 9 it is seen that months March and September have the same pattern of hydrogen generation due to the same reason mentioned earlier in Figs. 2,4,6,and 8 for SPV power generation. Month May has highest hydrogen generation and month December has lowest hydrogen generation due to the same reason mentioned in Figs.

Fig.2 Electrical load variation for the month of March
2, 4, 6 and 8 for SPV power generation. It is also seen that hydrogen production is less at 18:00 hours compared to 6:00 hours due to the greater amount of current consumed from 17:00 hours to 22:00 hours which is 228.984 Ah per hour by the hospital as discussed earlier, hence less amount of current is available to electrolyzer for hydrogen production. The cumulative daylong hydrogen generation in electrolyzer is summation of hydrogen generated from 6:00 hours to 18:00 hours and cumulative consumption of hydrogen in fuel cell stacks is the summation of hydrogen consumption during nonsunshine hours from 19:00 hours to 5:00 hours for different months representing different seasons of a year is shown in Table 7. It can be seen that cumulative day long hydrogen consumption is same for all the four months due to operation of same number of equipments for same definite hours throughout the year.

Conclusion
In the present work appliances of a hospital located in a remote area in Kolkata is operated with the integrated system of solar photovoltaic and electrolyzer-polymer electrolyte membrane fuel cell. It is seen that cumulative hydrogen generation in electrolyzer is more than hydrogen consumption in PEM fuel cell stack of four different months of a year.
A total of 875 solar photovoltaic modules in parallel, 2 modules in series of Central Electronics Limited Make PM 150 with a 178.537 kW electrolyzer and 27 PEM fuel cell stacks, each of 382.372 W can support the energy requirement of a 200 lights (100 W each), 4 pumps (2 kW each), 120 fans (65 W each) and 5 refrigerators(2 kW each)system operated for 16 hours, 2 hours, 15 hours and 24 hours respectively. 123 solar photovoltaic modules in parallel each having 2 modules in series of Central Electronics Limited Make PM 150 is needed to run the gas compressor for storing hydrogen in the cylinder during sunshine hours. If the number of types of equipment and operating hours change, then the configuration of integrated solar photovoltaic and electrolyzer-PEM fuel cell will change References AlKaraghouli,A.,&Kazmerski,L.L.(2010)Optimization and life-cycle cost of health clinic PV system for a rural area in southern Iraq using HOMER software. Solar Energy,84,[710][711][712][713][714]