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Proceeding Paper

Characterization of PEM Fuel Cell in the Context of Smart Microgrids Involving Renewable Energies †

by
David Calderón
,
Francisco Javier Folgado
*,
Isaías González
and
Antonio José Calderón
Department of Electrical Engineering, Electronics and Automation, Universidad de Extremadura, Avenida de Elvas, s/n, 06006 Badajoz, Spain
*
Author to whom correspondence should be addressed.
Presented at the 2nd International Electronic Conference on Processes: Process Engineering—Current State and Future Trends (ECP 2023), 17–31 May 2023; Available online: https://ecp2023.sciforum.net/.
Eng. Proc. 2023, 37(1), 55; https://doi.org/10.3390/ECP2023-14634
Published: 17 May 2023

Abstract

:
Fuel Cells (FCs) constitute an enabling technology for the integration of renewable energies and for the deployment of the next generation of power grids, the so-called Smart Grids/Microgrids. These devices perform the process of converting hydrogen into electricity without emitting pollutant emissions. Characteristic curves, mainly polarization curves, are a paramount resource to study the performance of FCs and to determine accurate models that fit their behavior. This paper presents the characterization of a commercial Polymer Electrolyte Membrane (PEM) FC consisting of 24 cells in series with a nominal output of 500 W, used to supply electricity in a Smart Microgrid involving renewable energies and hydrogen. The process evolution takes place under different laboratory conditions, so voltage, current, and hydrogen flow are measured and plotted to build the polarization curves. The equipment and components involved in the operation of the FC are described, as well as their technical features. Namely, a metal-hydride bottle is used to store the hydrogen that feeds the FC, an electronic programmable load establishes different charge conditions, and a precision multimeter collects the measurements provided by a set of sensors physically coupled to the FC. The characterization conducted in this research is envisioned to be used to build a digital twin of the FC. The developed experimentation and achieved results are described. The obtained results show a proper match between the experimental data and the curves reported in the literature and in the FC datasheet.

1. Introduction

Hydrogen is an energy carrier expected to solve the long-term energy storage issue for power grids based on renewable energy sources [1]. Even, the term “Hydrogen economy” has been gaining strength in recent years [2]. In this context, the so-called Smart Grids are intelligent power networks with enhanced capabilities in terms of performance and stability due to the massive introduction of sensing, automation, and monitoring technologies [3]. Small-scale Smart Grids are known as Smart Microgrids which can be connected to the main distributed grid or operate in a stand-alone model. Smart Grids and Smart Microgrids integrating renewable energies can reduce greenhouse gases and help meet the incessantly rising energy demand [4].
Decentralized generation and consumption are features of these modern grids, so a lot of energy conversion equipment is required. For instance, electrolysers can be used to generate hydrogen from local renewable energy sources, whereas Fuel Cells (FCs) can be used to produce electricity from stored hydrogen in an environmentally friendly system. In fact, FCs receive important research efforts, from constructive aspects [5] to monitoring systems [6], passing through modeling of their behavior. In this latter regard, existing literature reports a large number of papers about different models of FCs, including theoretical and empirical models centered on the whole FC, while others are focused on different FC components (electrodes, membrane, etc.) [7].
In particular, the polarization curve is a useful tool to analyze the behavior of Polymer Electrolyte Membrane (PEM) FCs [8,9,10]. Some examples are devoted to studying aged PEM FCs [8], long-term operations [9], or diagnostic methods [10].
In an ongoing R&D project, a Smart Microgrid hybridizing photovoltaic generation and hydrogen is being deployed. The goal of this project is to develop digital models of the actors in such microgrids to replicate their behaviors, performances, and interactions. This paper presents the characterization of a PEM FC used to supply electricity in the aforementioned Smart Microgrid. The characterization conducted in this research is envisioned to be used to build a digital replica of the FC.
The structure of the rest of the paper is as follows: Section 2 deals with the mathematical modeling of FCs. Materials and methods are described in the third section. Section 4 reports the experimental setup and results. Finally, the main conclusions of the research are addressed.

2. Mathematical Modeling of FC

A PEM FC is an electrochemical device that produces electricity from hydrogen and oxygen. Besides the energy released as electricity, water and heat are also generated [11]. Figure 1 illustrates this process.
The amount of energy produced in the electrochemical process that takes place in a fuel cell can be calculated from changes in Gibbs free energy, that is, the difference between the Gibbs free energy of products and reactants. Gibbs free energy represents the energy available for external work and depends on the temperatures and pressures of the reactants. If the electrochemical processes that take place in the cell were reversible, all Gibbs free energy could be converted into electrical energy. Thus, the “reversible” voltage of a PEM cell would be expressed as:
E = g f 2 F = g f 0 2 F + R T f c 2 F l n P H 2 P O 2 1 2 P H 2 O
where gf is the Gibbs free energy, R is the universal constant for ideal gases, PH2 is the hydrogen partial pressure, PO2 is the oxygen partial pressure, PH2O is the water vapor partial pressure, and Δg of the change in the process gf at a standard working pressure (1 bar), which in turn changes with the temperature of the FC (Tfc).
The expression (1) is the so-called Nernst voltage of a PEM FC. Applying standard thermodynamic relationships with respect to entropy changes, Equation (1) can be written as:
E = 1.229 0.85 10 3 T f c 298 + 4.3 10 3 T f c ln P H 2 + 1 2 ln ( P O 2 )
The model expressed in Equation (2) aims to reflect the theoretical performance of a generic FC. Additionally, the cell voltage varies with electric load conditions. This is due to electric losses, which can be classified as activation (Vact), ohmic (Vohm), and concentration or diffusion losses (Vconc) [11]. Therefore, considering all the losses, the cell voltage can be written as:
V f c = E V a c t V o h m V c o n c
Substituting the terms associated with the stated losses, the output voltage of the FC can be written as:
V f c = E R T 2 α F ln i i 0 R 0 R 1 λ m i m e n i + b l n P O 2 a
where α, i0, R0, R1, m, n, b, and a are empirical parameters that take into account the different polarization effects and are adjusted for a specific FC stack.
Several scientific works are focused on obtaining an extended model for different stack types. In a practical case, the parameters included in each model must be adjusted to fit the semi-empirical model to the real behavior of the stack [12]. Therefore, before adjusting these parameters of the model to our particular case, it is convenient to verify that the behavior of the FC under study corresponds to what the manufacturer provides in its datasheet.

3. Materials and Methods

In this section, the involved devices are described, e.g., the FC and the instrumentation equipment. Their most relevant features are given, as are their physical aspects.

3.1. H-500 FC Stack

The FC that was used for the development of this work is the H-500 model of the manufacturer Horizon [13]. Figure 2 depicts the aspects of this model of the FC. The main features of this device are summarized in Table 1. In addition, a control unit is required to manage the operation of the FC.

3.2. Flow Meter Bronkhorst

To measure the hydrogen flow consumed by the FC, a flow meter from the manufacturer Bronkhorst [14] is mounted. This sensor is shown in Figure 3. The most relevant characteristics of this device are listed in Table 2.

3.3. Current and Voltage Sensors

In order to sense the electrical magnitudes of the FC, two sensors are dedicated to measuring the voltage and the current supplied. Namely, a voltage divider based on a precision potentiometer is used to measure the voltage output. On the other hand, a current sensor based on the Hall effect is chosen. In particular, the model LA 25-NP of the company LEM is used [15]. Table 3 contains the signal ranges managed by this sensor.

3.4. Hydrogen Storage

To enable the operation of the FC, a hydrogen storage device is necessary. In the present case, this issue has been solved through a metal-hydride bottle model HBond-1500 L from the manufacturer Labtech [16]. It has a charging pressure of 15 bar and a storage capacity of 1500 N liters. The appearance of this storage bottle is shown in Figure 4.

3.5. Ancillary Components

A set of ancillary components is required to complete the experimental arrangement. Specifically, electro-valves, pressure sensors, pressure regulators, and power supplies for electronics. Furthermore, a programmable load and a precision multimeter have been employed for the polarization process.

4. Experimental Setup and Results

The aforementioned equipment has been assembled in a laboratory to perform a set of experiments and measurements. Figure 5 portrays the appearance of the system.
The manufacturer of the fuel cell provides a series of theoretical polarization curves on its data sheet. As previously said, the aim of this work is to experimentally obtain the operating curves of the FC. The final purpose consists of obtaining a mathematical model of such a system. The adjustment of the coefficients (parameters) of the chosen model will be carried out with the set of data obtained for characterizing the FC.
Firstly, the polarization curve corresponding to the relationship between the voltage and the current produced by the FC is given in Figure 6a. Regarding the power generated by the FC with respect to the delivered current, Figure 6b shows the experimental data. Figure 6c depicts the curve obtained for the relationship between the hydrogen fed to the FC and the generated power.
The trend of the curves corresponds with those reported both in the datasheet and in FC-related literature. Hence, the behavior of the FC is adequate.
A noteworthy remark is that the curves provided by the manufacturer are illustrative for all the cells of the same model and for determined operating conditions. We have developed the described tests, taking into account the particular FC and the conditions of pressure and temperature during such tests. These conditions are required for the further adjustment of the parameters of the mathematical model.

5. Conclusions

This paper presents the experimental characterization of a PEM FC as a necessary stage before its usage within a Smart Microgrid that integrates renewable energies and hydrogen. The equipment used for characterizing the FC has been described, and the achieved results have been expounded. The obtained results show a proper match between the experimental data and the curves reported in the literature and in the datasheet.
Future works deal with the adjustment of the parameters in the mathematical model of the FC. Additionally, the integration of such FC in the Smart Microgrid will also be carried out. Indeed, further characterizations will be performed aimed at detecting degradations of the stack.

Author Contributions

Conceptualization, I.G. and A.J.C.; Methodology, I.G.; Software, F.J.F. and D.C.; Validation, A.J.C. and I.G.; Investigation, F.J.F., I.G. and A.J.C.; Data curation, F.J.F. and D.C.; Writing—original draft preparation, F.J.F. and I.G.; Writing—review and editing, I.G. and A.J.C.; Supervision, I.G. and A.J.C.; Project administration, A.J.C.; Funding acquisition; A.J.C. All authors have read and agreed to the published version of the manuscript.

Funding

This project was co-financed by the European Regional Development Funds FEDER and the Regional Government of Extremadura (IB18041).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data sharing not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. González, I.; Calderón, A.J.; Andújar, J.M. Novel remote monitoring platform for RES-hydrogen based smart microgrid. Energy Convers. Manag. 2017, 148, 489–505. [Google Scholar] [CrossRef]
  2. Barbir, F. Transition to renewable energy systems with hydrogen as an energy carrier. Energy 2009, 34, 308–312. [Google Scholar] [CrossRef]
  3. González, I.; Calderón, A.J. Integration of open source hardware Arduino platform in automation systems applied to Smart Grids/Micro-Grids. Sustain. Energy Technol. Assess. 2019, 36, 100557. [Google Scholar] [CrossRef]
  4. Faheem, M.; Shah, S.B.H.; Butt, R.A.; Raza, B.; Anwar, M.; Ashraf, M.W.; Ngadi, M.A.; Gungor, V.C. Smart grid communication and information technologies in the perspective of Industry 4.0: Opportunities and challenges. Comput. Sci. Rev. 2018, 30, 1–30. [Google Scholar] [CrossRef]
  5. Xue, B.; Zhou, S.; Yao, J.; Wang, F.; Zheng, J.; Li, S.; Zhang, S. Novel proton exchange membranes based on sulfonated-phosphonated poly (p-phenylene-co-aryl ether ketone) terpolymers with microblock structures for passive direct methanol fuel cells. J. Memb. Sci. 2020, 594, 117466. [Google Scholar] [CrossRef]
  6. Calderón, A.J.; González, I.; Calderón, M.; Segura, F.; Andújar, J.M. A new, scalable and low cost multi-channel monitoring system for polymer electrolyte fuel cells. Sensors 2016, 16, 349. [Google Scholar] [CrossRef] [PubMed]
  7. Martín, I.S.; Ursúa, A.; Sanchis, P. Modelling of PEM fuel cell performance: Steady-state and dynamic experimental validation. Energies 2014, 7, 670–700. [Google Scholar] [CrossRef]
  8. Kulikovsky, A. Polarization curve of a non-uniformly aged pem fuel cell. Energies 2014, 7, 351–364. [Google Scholar] [CrossRef]
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  13. Horizon H-500 FC. Available online: https://www.horizoneducational.com/h-500-pem-fuel-cell-500w/p1353 (accessed on 14 March 2023).
  14. Bronkhorst Flowmeters. Available online: https://www.bronkhorst.com/int/ (accessed on 14 March 2023).
  15. LEM Current Sensor. Available online: https://www.lem.com/en/product-list/la-25np (accessed on 14 March 2023).
  16. LabTech. Available online: https://www.labtechsrl.com/index.php/en (accessed on 14 March 2023).
Figure 1. Scheme of the FC system.
Figure 1. Scheme of the FC system.
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Figure 2. H-500 FC stack.
Figure 2. H-500 FC stack.
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Figure 3. Flow meter Bronkhorst.
Figure 3. Flow meter Bronkhorst.
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Figure 4. Metal-hydride bottle.
Figure 4. Metal-hydride bottle.
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Figure 5. Experimental setup.
Figure 5. Experimental setup.
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Figure 6. FC polarization curves. (a) Curve V-I. (b) Curve P-I. (c) Curve Flow-P.
Figure 6. FC polarization curves. (a) Curve V-I. (b) Curve P-I. (c) Curve Flow-P.
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Table 1. FC main features.
Table 1. FC main features.
Type of fuel cellPEM
Number of cells24
Performance14.4 V @35A
Rated power500 W
Max stack temperature65 °C
H2 Pressure0.45–0.55 bar
H2 purity≧99.995% dry H2
Flow rate at max output6.5 L/min
Table 2. Flow meter characteristics.
Table 2. Flow meter characteristics.
Pressure6 bar
Power supply24 V DC (15–24 V DC)
Temperature20 °C
Flow5000 mLn/min
Table 3. Current sensor signal ranges.
Table 3. Current sensor signal ranges.
Current range±25 A
Power supply±15 V DC
Temperature−40 to 85 °C
Output current range±25 mA
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MDPI and ACS Style

Calderón, D.; Folgado, F.J.; González, I.; Calderón, A.J. Characterization of PEM Fuel Cell in the Context of Smart Microgrids Involving Renewable Energies. Eng. Proc. 2023, 37, 55. https://doi.org/10.3390/ECP2023-14634

AMA Style

Calderón D, Folgado FJ, González I, Calderón AJ. Characterization of PEM Fuel Cell in the Context of Smart Microgrids Involving Renewable Energies. Engineering Proceedings. 2023; 37(1):55. https://doi.org/10.3390/ECP2023-14634

Chicago/Turabian Style

Calderón, David, Francisco Javier Folgado, Isaías González, and Antonio José Calderón. 2023. "Characterization of PEM Fuel Cell in the Context of Smart Microgrids Involving Renewable Energies" Engineering Proceedings 37, no. 1: 55. https://doi.org/10.3390/ECP2023-14634

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