ALLSHIFT/docs/04-simulations/pem-electrolyser-and-fuel-cell-models.md

PEM Electrolyser and Fuel Cell Models (MathWorks Simscape examples)

Markdown report of non-markdown source files.

Sources	Simulations/Ready Made PEM Electrolyzer/ · Simulations/Ready Made PEM fuel cell/ · duplicated in Simulations/Big Ugly Folder/
Origin	MathWorks Simscape shipped examples, obtained via openExample(...)
Licence	© 2020–2024 The MathWorks, Inc. — see Provenance
Status	Current — but still at vendor default parameters
Report generated	2026-07-25

Provenance and licensing

Warning

This is unmodified third-party code. Every .m and .ssc file in both folders carries a MathWorks copyright line; not one carries SHIFT attribution. Unlike the EST model — which ships its MIT LICENSE and upstream URL — this vendored code is marked nowhere in the repository.

Ready Made PEM Electrolyzer/Electrolyzer.ssc:9          % Copyright 2021-2024 The MathWorks, Inc.
Ready Made PEM Electrolyzer/PEMElectrolysisSystemExample.m:57    % Copyright 2021 The MathWorks, Inc.
Ready Made PEM Electrolyzer/PEMElectrolysisSystemParameters.m:6  % Copyright 2021 The MathWorks, Inc.
Ready Made PEM fuel cell/FuelCell.ssc:10                % Copyright 2020-2024 The MathWorks, Inc.
Ready Made PEM fuel cell/PEMFuelCellSystemExample.m:64  % Copyright 2020-2021 The MathWorks, Inc.
Ready Made PEM fuel cell/PEMFuelCellSystemParameters.m:6         % Copyright 2020 The MathWorks, Inc.
…and 8 more Plot*.m files, all MathWorks

How they were obtained is recorded only as a comment in Constants.m:

%openExample('simscape/PEMElectrolysisSystemExample')
%openExample('simscape/PEMFuelCellSystemExample')

Recommended: add a PROVENANCE.md to each folder stating that the contents are unmodified MathWorks Simscape examples retrieved via openExample, and that redistribution is governed by the MathWorks licence terms.

The unfinished sizing work

Constants.m records the requirement and the plan, verbatim:

%Ready made electrolyser - %Good news: it has a solar profile. %Bad news: random constants - we want it at 128m3 hydrogen production a day %I have attempted to find volume via the volumetric flow rate, however this %uses "standard conditions". THIS BRINGS IT TO 12.8m3, JUST ADJUST (power?) %SO ITS 10 TIMES BIGGER AND WE ARE GOOD!

%openExample('simscape/PEMFuelCellSystemExample') %This one is also PEM so it should work?

%To do: Check if PEM is ok, change parameters for electrolyzer so that %production is exactely 10times bigger, adjust fuel cell, create grid, %ensure its power output is appropriate

Important

That TODO has not been carried out. The parameter files are still at MathWorks demo defaults:

• The electrolyser's 24-hour solar_profile_power still peaks at exactly 100 kW — the vendor's round demo number, not a SHIFT-derived profile.
• The fuel cell still loads PEMFuelCellSystemDriveCycle.mat — an automotive drive cycle, wholly inappropriate for a hospital microgrid.

No SHIFT-specific hydrogen system parameterisation exists anywhere in this tree, despite Constants.m recording the requirement since the earliest revision. This is the single largest gap between the simulator specification and the models that are supposed to implement it.

Note also that the "just multiply by 10" approach to sizing is recorded as an unverified assumption ("This one is also PEM so it should work?"), and that scaling a Simscape electrolyser's hydrogen output by 10× is not achieved by scaling power alone — cell count, active area, and current density all enter.

Electrolyser parameters

PEMElectrolysisSystemParameters.m — 71 lines, 11,972 B, MD5 7871b9ab. Byte-identical in Ready Made PEM Electrolyzer/ and Big Ugly Folder/.

Environment

Parameter	Value	Unit
env_p	0.101325	MPa
env_T	20	°C

Solar profile (24 h)

Parameter	Value	Unit
solar_profile_time	(0:23)' * 3600	s
solar_profile_power	[0 0 0 0 0 0 0.572 13.1 44.9 74.5 96.4 100 97.5 89.5 65.8 34.0 7.61 0 0 0 0 0 0 0]'	kW

Stack

The comment header in the source says "Fuel cell stack" — a MathWorks copy-paste artefact in the electrolysis file.

Parameter	Value	Unit	Description
stack_num_cells	50	–	Number of cells
stack_area	280	cm²	Cell area
stack_t_membrane	125	µm	Membrane thickness
stack_t_gdl_A	25	µm	Anode gas diffusion layer thickness
stack_t_gdl_C	250	µm	Cathode gas diffusion layer thickness
stack_w_channels	1	cm	Gas channel width and height
stack_num_channels	8	–	Gas channels per cell
stack_io	1e-04	A/cm²	Exchange current density
stack_alpha	0.7	–	Charge transfer coefficient
stack_D_gdl_A	0.07	cm²/s	Water diffusivity in anode GDL
stack_D_gdl_C	0.07	cm²/s	Water diffusivity in cathode GDL
stack_membrane_rho	2000	kg/m³	Density of dry membrane
stack_membrane_MW	1.1	kg/mol	Equivalent weight of dry membrane
stack_mea_rho	1800	kg/s (sic)	Overall density of MEA — vendor unit typo, should be kg/m³
stack_mea_cp	870	J/(kg·K)	Overall specific heat of MEA

Piping and heat exchanger

Parameter	Value	Unit	Description
water_pipe_D	0.01	m	Water pipe diameter
gas_pipe_D	0.01	m	Gas pipe diameter
exchanger_L	1	m	Overall radiator length
exchanger_W	0.025	m	Overall radiator width
exchanger_H	0.5	m	Overall radiator height
exchanger_N_tubes	25	–	Number of coolant tubes
exchanger_tube_H	0.0015	m	Height of each coolant tube
exchanger_fin_spacing	0.002	–	Fin spacing
exchanger_eta_fin	0.7	–	Fin efficiency

Derived quantities computed in the script: exchanger_gap_H, exchanger_air_area_primary, exchanger_N_fins, exchanger_air_area_fins, exchanger_tube_Leq.

Fuel cell parameters

PEMFuelCellSystemParameters.m — 94 lines, 12,709 B, MD5 6eaf6bf3. Byte-identical in Ready Made PEM fuel cell/ and Big Ugly Folder/. Line 8 executes load PEMFuelCellSystemDriveCycle.mat (13,667 B).

Environment

Parameter	Value	Unit
env_p	0.101325	MPa
env_T	20	°C
env_RH	0.5	– (relative humidity)
env_yO2	0.21	– (oxygen mole fraction)

Fuel tank

Parameter	Value	Unit
tank_p	70	MPa
tank_yH2	1 − 3e-4	– (hydrogen mole fraction)
tank_V	120	L

tank_V = 120 L at 70 MPa is an automotive hydrogen tank. The project spec calls for up to 200 kg across two tanks — roughly three orders of magnitude larger. Another consequence of the untouched vendor defaults.

Stack

Parameter	Value	Unit	Description
stack_num_cells	400	–	Number of cells (vs. 50 in the electrolyser)
stack_area	280	cm²	Cell area
stack_t_membrane	125	µm	Membrane thickness
stack_t_gdl	250	µm	Gas diffusion layer thickness
stack_w_channels	1	cm	Gas channel width/height
stack_num_channels	8	–	Gas channels per cell
stack_io	1e-04	A/cm²	Exchange current density
stack_iL	1.4	A/cm²	Limiting current density
stack_alpha	0.7	–	Charge transfer coefficient
stack_D_gdl	0.07	cm²/s	Water diffusivity in GDL
stack_membrane_rho	2000	kg/m³	Density of dry membrane
stack_membrane_MW	1.1	kg/mol	Equivalent weight of dry membrane
stack_mea_rho	1800	kg/s (sic)	Vendor unit typo, should be kg/m³
stack_mea_cp	870	J/(kg·K)	Overall specific heat of MEA

Gas tubes and coolant

Parameter	Value	Unit	Description
anode_tube_D	0.01	m	Hydrogen tube diameter
cathode_tube_D	0.05	m	Air tube diameter
coolant_w_channels	1	cm	Coolant channel width/height
coolant_num_passes	12	–	Coolant channel passes per layer
coolant_num_layers	20	–	Coolant layers in stack
coolant_tube_D	0.05	m	Coolant tube diameter

Radiator

Parameter	Value	Unit	Description
radiator_L	1	m	Overall radiator length
radiator_W	0.025	m	Overall radiator width
radiator_H	0.5	m	Overall radiator height
radiator_N_tubes	25	–	Number of coolant tubes
radiator_tube_H	0.0015	m	Height of each coolant tube
radiator_fin_spacing	0.002	–	Fin spacing
radiator_eta_fin	0.7	–	Fin efficiency
radiator_t_wall	1e-4	m	Material thickness
radiator_rho	2700	kg/s (sic)	Vendor unit typo, should be kg/m³ (2700 = aluminium)
radiator_cp	910	J/(kg·K)	Radiator material specific heat

Compressor map

Parameter	Value	Unit
comp_p_ratio_TLU	[1; 1.25; 1.5; 1.75; 2]	– (pressure ratio)
comp_rpm_TLU	[0, 1800, 3600]	rpm

comp_mdot_corr_TLU = [
    0, 0.05,   0.1;
    0, 0.0375, 0.075;
    0, 0.025,  0.05;
    0, 0.0125, 0.025;
    0, 0,      0] * 4;   % [kg/s] Corrected mass flow rate table

Gas properties (shared by both files)

Gas	_R [J/(kg·K)]	_D [mm²/s]
H₂	4124.48151675695	74
O₂	259.836612622973	18
N₂	296.802103844292	—

Each gas also carries 52-element lookup vectors sharing the temperature grid _T = [-56.55, -50:10:-10, -5:1:5, 10:10:350] °C, with _h in kJ/kg (specific enthalpy), _mu in µPa·s (dynamic viscosity), and _k in mW/(m·K) (thermal conductivity).

What differs between the two models

The two parameter files share identical gas property tables and identical membrane/MEA parameters. The substantive differences:

Aspect	Electrolyser	Fuel cell
stack_num_cells	50	400
Limiting current density	—	stack_iL = 1.4 A/cm²
Gas diffusion layer	Split anode/cathode (_A 25 µm / _C 250 µm)	Single stack_t_gdl = 250 µm
Fuel storage	—	tank_* block, 120 L @ 70 MPa
Air handling	—	env_RH, env_yO2, compressor map
Cooling	Heat exchanger	Coolant channels + radiator
Drive input	24 h solar profile	Automotive drive cycle .mat

Supporting scripts

Both folders ship MathWorks' plotting and example scripts, all copyright MathWorks:

Electrolyser	Fuel cell
PEMElectrolysisSystemExample.m	PEMFuelCellSystemExample.m
PEMElectrolysisSystemPlot1IV.m	PEMFuelCellSystemPlot1IV.m
PEMElectrolysisSystemPlot2Power.m	PEMFuelCellSystemPlot2Power.m
PEMElectrolysisSystemPlot3Hydrogen.m	PEMFuelCellSystemPlot3Efficiency.m
	PEMFuelCellSystemPlot4T.m
	PEMFuelCellSystemPlot5Energy.m

The Plot*.m files carry polished vendor documentation citing textbook figures — for example "The theoretical maximum efficiency for a PEM fuel cell is 83%. However, actual efficiency is around 60% due to internal losses", which lines up with the 40% fuel-cell loss figure in AI Efficiency Improvements.

The .ssc component sources use the Simscape foundation.moist_air.moist_air and foundation.thermal_liquid.thermal_liquid domains.

Related

• Simulink Model Inventory — including the Constants.m staleness
• Simulator I/O Interface §1.1–1.3 — the parameters these should match
• UCSD Equipment Manual — real-world PEM electrolyser specifications
• AI Efficiency Improvements — the loss targets
• Existing EST Model — the other vendored subtree