NREL is a national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

Operated by the Alliance for Sustainable Energy, LLC

This report is available at no cost from the National Renewable Energy

Laboratory (NREL) at www.nrel.gov/publications.

Contract No. DE-AC36-08GO28308

Milestone Report

NREL/MP-5400-73571 

April 2019 

System Design, Analysis, and Modeling 

Activities Supporting the DOE 

Hydrogen Storage Engineering Center 

of Excellence (HSECoE)

Final Project Report

Matthew Thornton and Lin Simpson

National Renewable Energy Laboratory
NREL is a national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

Operated by the Alliance for Sustainable Energy, LLC

This report is available at no cost from the National Renewable Energy

Laboratory (NREL) at www.nrel.gov/publications.

Contract No. DE-AC36-08GO28308

Milestone Report

NREL/MP-5400-73571 

April 2019 

National Renewable Energy Laboratory

15013 Denver West Parkway

Golden, CO 80401

303-275-3000 • www.nrel.gov

System Design, Analysis, and Modeling 

Activities Supporting the DOE 

Hydrogen Storage Engineering Center 

of Excellence (HSECoE)

Final Project Report

Matthew Thornton and Lin Simpson

National Renewable Energy Laboratory

Suggested Citation

Thornton, Matthew and Lin Simpson. 2019. System Design, Analysis, and Modeling 

Activities Supporting the DOE Hydrogen Storage Engineering Center of Excellence 

(HSECoE): Final Project Report. Golden, CO: National Renewable Energy Laboratory. 

NREL/TP-5400-73571. https://www.nrel.gov/docs/fy19osti/73571.pdf.
NOTICE

This work was authored by the National Renewable Energy Laboratory, operated by Alliance for Sustainable 

Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding 

provided by U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Fuel Cell Technologies 

Office. The views expressed herein do not necessarily represent the views of the DOE or the U.S. Government.

This report is available at no cost from the National Renewable 

Energy Laboratory (NREL) at www.nrel.gov/publications. 

U.S. Department of Energy (DOE) reports produced after 1991 

and a growing number of pre-1991 documents are available 

free via www.OSTI.gov. 

Cover Photos by Dennis Schroeder: (clockwise, left to right) NREL 51934, NREL 45897, NREL 42160, NREL 45891, NREL 48097, 

NREL 46526.

NREL prints on paper that contains recycled content. 
iii

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

Final Report

Project Title

System Design, Analysis, and Modeling Activities Supporting the DOE Hydrogen Storage 

Engineering Center of Excellence (HSECoE) 

Project Period

October 1, 2009 to June 30, 2015 

Date of Report

March 5, 2019 

Recipient 

National Renewable Energy Laboratory (NREL) 

Working Partners

HSECoE team: Savannah River National Laboratory (SRNL), Los Alamos National Laboratory 

(LANL), Pacific Northwest National Laboratory (PNNL), NASA Jet Propulsion Laboratory 

(JPL), Ford, General Motors (GM), United Technologies Research Center (UTRC), HexagonLincoln, Universite Du Quebec A Trois-Rivieres (UQTR), BASF, University of Michigan, and 

Oregon State University 

Cost-Sharing Partners

None 

Contact

Matthew Thornton 

National Renewable Energy Laboratory 

303-275-4273

matthew.thornton@nrel.gov

DOE Manager

Ned Stetson, Hydrogen Storage Technology Manager 

DOE Fuel Cell Technologies Office 
iv

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

Table of Contents

Project Objective......................................................................................................................................... 1

Background ................................................................................................................................................. 1

Vehicle Simulation Modeling ..................................................................................................................... 1

Phase 1 System Results.......................................................................................................................... 5

Phase 2 System Results.......................................................................................................................... 7

Phase 3 System Results.......................................................................................................................... 8

Trade-Off Study Results......................................................................................................................... 9

Storage System Energy Analysis............................................................................................................ 11

References................................................................................................................................................. 14

List of Figures

Figure 1. HSECoE framework system model showing main blocks, inputs, outputs, and a sample of 

storage systems that were implemented................................................................................... 2

Figure 2. WTW GHG emissions breakdown .............................................................................................. 12

List of Tables

Table 1. Test Cases for Exercising the Storage Systems Using Various EPA Fuel Efficiency 

Drive Cycles............................................................................................................................. 4

Table 2. Adsorbent System Phase 1 System Results for Case 1 (UDDS/HWFET Cycles).......................... 6

Table 3. Adsorbent System Phase 2 System Results for Case 1 (UDDS/HWFET Cycles).......................... 8

Table 4. Adsorbent System Phase 3 System Results for Case 1 (UDDS/HWFET Cycles).......................... 8

Table 5. Adsorbent System Phase 3 Results for Case 2 (US66 Drive Cycle—Aggressive Driving) ........... 9

Table 6. Constant Volume Range Impact Study......................................................................................... 10

Table 7. Vehicle WTW Results for Adsorbent and CH Systems Compared to Compressed Gas and 

Liquid Hydrogen Systems...................................................................................................... 11

Table 8. Vehicle WTW GHG Breakdown for Adsorbent and CH Systems Compared to Compressed 

Gas and Liquid Hydrogen Systems........................................................................................ 12

Table 9. HSECoE Base Assumptions for HDSAM .................................................................................... 13

Table 10. Storage System Information Required for HDSAM Analysis.................................................... 13
1 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

Project Objective 

The objective of this project was to identify optimal pathways for successful hydrogen storage 

system technology through modeling, analysis, and testing support. The National Renewable 

Energy Laboratory’s (NREL’s) first objective was to perform vehicle simulations of various 

system configurations to support the overall systems engineering. The second objective was to 

lead the storage system energy analysis and provide the Hydrogen Storage Engineering Center of 

Excellence (HSECoE) with results that will help guide engineering design. Finally, the third 

objective was to compile and obtain media engineering properties for the HSECoE. 

Background 

The work described here is an integral component of the U.S. Department of Energy’s (DOE’s) 

HSECoE. As part of the National Hydrogen Storage Project it will help meet the overall goals of 

the Fuel Cell Technologies Office. DOE’s program also supports the Advanced Energy 

Initiative. NREL’s work supports DOE’s objectives and expected outcomes of the HSECoE. 

Vehicle Simulation Modeling 

In other efforts under the HSECoE, a number of detailed numerical models were described for 

different materials-based storage systems. However, those models are restricted to specific 

storage media and vessel geometries, which include placement and function of heat transfer 

elements. While useful for evaluating specific storage system designs, the analyses in the 

literature are not suitable for general systematic assessment of storage vessel/media 

configurations against a set of performance targets. The detailed models also require time to 

develop and run. As part of NREL’s HSECoE modeling effort, it was found useful to have 

simplified models that can quickly estimate optimal loading and discharge kinetics, effective 

hydrogen capacities, system dimensions, and heat removal requirements. Parameters obtained 

from these models can then be input into the detailed models to obtain an accurate assessment of 

system performance that includes more complete integration of the physical processes. The 

following paragraphs in this section (1) describe the methodology developed for conducting such 

system models across the HSECoE and the integration of those models with full vehicle models, 

and (2) present some of the performance results from studies using these system models to 

support and guide the design of materials-based systems for the HSECoE. 

To meet the objectives of the HSECoE, there was a need to quickly and efficiently evaluate 

various materials-based storage systems and to compare their performance against DOE 

hydrogen storage targets for light-duty vehicles. To accomplish this task, a modeling approach 

was created that enabled the exchange of one hydrogen storage system for another while keeping 

the vehicle and fuel cell systems constant [1]. Figure 1 shows a block diagram of the modeling 

“framework” that was used for system evaluation and comparison by the HSECoE. The 

framework was used to implement the integrated vehicle, the power plant, and the storage system 

models. This framework tool was used across the HSECoE to evaluate candidate storage system 

designs on a common vehicle platform with a consistent set of assumptions. 
2 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

Figure 1. HSECoE framework system model showing main blocks, inputs, outputs, and a sample 

of storage systems that were implemented

The framework shown in Figure 1 was implemented using a commercial software platform, 

Simulink. The vehicle-level model was developed by NREL based on its HSSIM (Hydrogen 

Storage SIMulator) software, which was originally developed to simulate a hydrogen fuel cell 

vehicle running on compressed gas tanks. The HSSIM vehicle model is designed to evaluate 

high-level attribute improvements. To accomplish this, the inputs, such as the glider and 

powertrain components, are also defined at a high level. The vehicle glider is defined with a 

specific frontal area, drag coefficient, mass, center of gravity, front axle weight fraction, and 

wheel base. The wheels are defined by inertia, a rolling resistance coefficient, coefficient of 

friction, and radius. The inputs for the motor are power, peak efficiency, mass per unit of power, 

cost per unit of power, and time to full power. The battery inputs include power, energy, mass 

per unit of energy, and round trip efficiency. Auxiliary loads are assumed to be a specified 

constant plus an amount required for the fuel cell and hydrogen storage systems. These inputs 

match DOE’s technical target units, such as battery kilograms per kilowatt hour, so that the 

impact of improvements can be evaluated over time as the targets change. For applications for 

this program, a standard mid-sized vehicle class was selected that included a 100 kW electric 

motor and a 20 kW/1 kWh battery to capture regenerative braking and provide minor propulsion 

assistance. The vehicle glider weight (excluding the hydrogen storage system) was 1,610 kg. The 

fuel cell system was developed by Ford and is based on an 80 kW net stack operating at 80°C. 

The fuel cell efficiency was consistent with the DOE fuel cell system targets for 50% efficiency 

at rated power and 60% at quarter power. The fuel cell model included only the essential 

elements to interface with the vehicle and the hydrogen storage blocks. These included a 

polarization curve to translate vehicle power to hydrogen required, parasitic power from the 

compressor, and stack temperature to provide waste heat. 
3 

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Examples of some of the different storage systems evaluated by the HSECoE in the framework 

model are shown in Figure 1. These included various metal hydride (MH), chemical hydride 

(CH), and adsorbent storage systems, in addition to compressed gas systems, which were 

included to benchmark the other systems. Most of the adsorbent storage systems involved metalorganic framework MOF-5 because of its existing material property data and previous modeling 

studies. The use of a common storage media also allowed for a good comparison of different 

engineering concepts and configurations on the systems’ performance. 

In addition to modeling the storage, fuel cell, and vehicle systems, the HSECoE team also 

developed a standard matrix of test cases to exercise the different hydrogen storage systems 

against the DOE performance targets. The test cases, which made use of five fuel economy drive 

cycles from the U.S. Environmental Protection Agency (EPA), are shown in Table 1. Cases 1 

through 4 are looped until the storage system can no longer provide the required hydrogen flow 

rate. Case 1 is used to determine if the storage system can provide its required 5.6 kg of usable 

hydrogen to the vehicle. It uses a 55%/45% weighting factor between city (urban dynamometer 

driving schedule, UDDS) versus highway (highway fuel economy test, HWFET) driving. Case 2 

uses the US06 (aggressive) drive cycle to confirm the storage system can deliver the DOE peak 

flow of 1.6 grams of hydrogen per second to the fuel cell. Case 3 (cold case) is used to evaluate 

the storage system’s performance for -20°C cold startup scenarios. Case 4 (hot case) runs the 

system at 35°C with SC03, the EPA air conditioning test conditions. Case 5 tests the storage 

system dormancy for cryogenic systems, but it was not used for this reported analysis in the 

framework.
4 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

Table 1. Test Cases for Exercising the Storage Systems Using Various EPA Fuel Efficiency Drive Cycles
5 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

The integrated system model was used to evaluate the performance of various materials-based 

hydrogen storage systems on a common basis. The test matrix (shown in Table 1) was structured 

to evaluate the performance of the storage systems against the technical targets under standard 

and realistic transient driving conditions. The matrix was also designed to exercise a given 

system from full to empty to provide an understanding of its performance over the entire range of 

fill conditions. Therefore, the test cases were designed to repeat a drive cycle or set of drive 

cycles until the storage system being evaluated was empty. Standard drive cycles are typically 

not long enough to achieve this and would not even deplete a buffer tank in some systems. The 

important point here is that when evaluating the complex dynamics of hydrogen storage systems, 

this approach of repeating drive cycles to create test cases is critical to gaining the feedback 

necessary to refine and improve the systems. As briefly described earlier and shown in Table 1, 

the test matrix includes five test cases. The first case combines repeats of the UDDS and 

HWFET cycles until the storage system is depleted. This is used to determine the vehicle-level 

fuel economy and, from that, to estimate the vehicle range. The fuel economy is calculated using 

the current EPA five-cycle procedure of adjusting and weighting the UDDS and HWFET figures 

to provide one fuel economy figure that represents real-world use—it is not the raw figures that 

come directly from running the cycles. Similarly, the range is then calculated from the adjusted 

and weighted UDDS and HWFET figure and not simply the cycles’ miles achieved until the 

storage system is empty. The test matrix was found to be a key means of evaluating the fuel 

economy, range, and other vehicle-level performance features of the storage systems on a 

common and comparable basis [1]. The following sections show the results for fuel economy, 

range, and onboard efficiency for the various materials-based storage systems compared with 

compressed gas systems for HSECoE Phases 1, 2, and 3. 

The model outputs from the framework were used to evaluate the status of materials-based 

systems from all phases of this program. The intent was (1) to use model outputs to evaluate and 

compare different storage systems and to guide engineering solutions to identify potential 

solutions to particular barriers; and (2) to develop a platform for evaluating the relative vehiclelevel performance of the various materials-based storage systems. 

For the following discussion of all simulation results, model applications and results reported are 

based on Case 1 of the framework exclusively (i.e., UDDS and HWFET combined test cycles). 

In addition, a mid-size car class was selected as the initial baseline simulation within the 

framework, as discussed previously. The intent was to be representative of a high-sales-volume 

mid-size car, such as the Ford Fusion, Chevrolet Malibu, or Toyota Camry. All of the following 

results are based on the mid-size vehicle configuration described above, but the model is capable 

of simulating both larger and smaller vehicle classes and configurations. All of the simulation 

results for range have been normalized to 5.6 kg nominal onboard usable hydrogen mass. 

Phase 1 System Results

Simulation results for the Phase 1 systems—an AX-21 system, two MOF-5 adsorbent systems, 

an ammonia borane (AB) system, and an alane slurry chemical hydride system—are shown in 

Table 2. In addition, 350-bar and 700-bar compressed gas systems are included for comparison 

to the materials-based systems.

As shown in Table 2, the fuel economy for materials-based systems ranged from 49 miles per 

gasoline gallon equivalent (mpgge) for the MOF-5 Press–FCHX system to 43 mpgge for the 
6 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

alane CH system. The alane CH system performed the worst in terms of fuel economy due to its 

requirement for high temperature conditions to release hydrogen from the material. As a result, 

the system burns hydrogen to create the needed temperatures for the storage system so that 

hydrogen can be released for use in the fuel cell. The use of hydrogen for system thermal 

management results in poor onboard efficiency and, subsequently, poor fuel economy. 

Alternatively, the AX-21 and MOF-5 Press–FCHX systems performed better due to their high 

gravimetric efficiency resulting in lower overall system and vehicle mass and therefore better 

fuel economy. As a result, the AX-21 and MOF-5 Press–FCHX systems also offer the best range 

results of 274 miles based on the above vehicle configuration and 5.6 kg nominal usable 

hydrogen storage capacity. All of the other systems in this example were near the 300-mile range 

target (ranging from 241 to 274 miles). The compressed gas systems demonstrated slightly better 

but comparable fuel economy and range relative to these example material-based systems. 

The MOF-5 Press–FCHX adsorbent system and the AB and alane slurry CH systems all had a 

gravimetric density of 4.6 weight percent (i.e., the percent of usable hydrogen mass stored to the 

overall storage system mass; the DOE 2020 technical target for gravimetric density is 5.5 weight 

percent). These were the best-performing materials-based systems and were comparable to the 

compressed gas systems, which had gravimetric densities of 4.7–4.8 weight percent. However, 

the AB and alane slurry systems outperformed the compressed gas systems and all of the other 

materials-based systems in terms of volumetric density with nearly 40 grams of hydrogen per 

liter of system. Note that DOE’s 2020 technical target for volumetric density is 40 g/L. Out of all 

the materials-based systems included in Phase 1, the MOF-5 Press–FCHX and AX-21 systems 

performed the best in terms of fuel economy, range, and gravimetric density, and were 

comparable to or better than the compressed gas systems. The AB and alane slurry systems 

performed best in terms of volumetric density; however, it is important to remember that the 

fluid AB system is an off-board regenerable system that is accompanied by unique refilling 

challenges, logistics, and costs that are not captured within these simulations (but are discussed 

later).

Table 2. Adsorbent System Phase 1 System Results for Case 1 (UDDS/HWFET Cycles)

Case 1 Adjusted Fuel

Economy 

(mpgge) 

Range

5.6 kg H2

(mi)

Onboard

Efficiency

(%)

Volumetric 

Density

(g/L) 

Gravimetric 

Density

(wt%)

AX21 Press–FCHX 49 274 97.0 25.2 4.3

MOF-5 Comp–FCHX 48 269 97.0 24.1 3.5

MOF-5 Press–FCHX 49 274 98.0 25.3 4.6

AB Slurry—Exothermic 45 252 96.0 38.9 4.6

Alane Slurry—Endothermic 43 241 88.0 38.9 4.6

350 bar Compressed Gas 50 280 100.0 17.0 4.8

700 bar Compressed Gas 50 280 100.0 25.0 4.7
7 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

Phase 2 System Results

For the Phase 2 adsorbent system, the focus was on improving the thermal management systems 

for the MOF-5 material. These systems were designed around the HexCell and MATI heat 

exchangers and the material density appropriate for each of these respective systems (i.e., MOF5 powered for the HexCell and compressed puck for the MATI). Concurrent with the Phase 2 

design changes for the adsorbent systems, improvements were also made to the CH slurry 

systems. 

For the Phase 2 systems shown in Table 3, the new designs did not result in any significant 

changes to the vehicle-level performance. This provided a reality check on these system designs, 

confirming that design changes that resulted in better system performance in terms of weight, 

volume, and cost did not result in any degradation in the vehicle-level performance. The fuel 

economy for Phase 2 materials-based systems ranged from 49/48 mpgge for the MOF-5 systems 

to 44 mpgge for the alane slurry system. As with the Phase 1 designs, the alane slurry system 

performed the worst in terms of fuel economy due its onboard endothermic nature. As mentioned 

above, the system burns hydrogen to create the needed temperatures for the storage system 

hydrogen release and storage system thermal management. The use of hydrogen for system 

thermal management results in poor onboard efficiency and, subsequently, poor fuel economy. 

Alternatively, the AB slurry and MOF-5 systems performed better in this example due to their 

high gravimetric efficiency, resulting in lower overall system and vehicle mass and therefore 

better fuel economy. As a result, the MOF-5 systems also showed the best range results of 

274/269 miles based on the above vehicle configuration and 5.6 kg nominal usable hydrogen 

storage capacity. The compressed gas systems demonstrated slightly better but comparable fuel 

economy and range relative to these example material-based systems. 

The AB slurry chemical hydrogen storage material system had a gravimetric density of 4.2 

weight percent (i.e., the percent of usable hydrogen mass to the overall storage system mass; the 

DOE 2020 technical target for gravimetric density is 5.5 weight percent). This was the best 

performing materials-based system and was comparable to the compressed gas system, which 

had a gravimetric density of 4.7 weight percent. As with the Phase 1 systems, the AB slurry 

system outperformed the compressed gas systems and all of the other materials-based systems in 

terms of volumetric density with nearly 37 grams of hydrogen per liter of system. DOE’s 2020 

technical target for volumetric density is 40 g/L. For all of the materials-based systems included 

in Phase 2, the HexCell powder MOF-5 system performed the best in terms of fuel economy and 

range, and was comparable to the compressed gas systems. As noted, the AB slurry system 

performed best in terms of volumetric density, but the AB slurry system is an off-board 

regenerable system that is accompanied by unique refilling challenges, logistics, and costs that 

are not captured in these simulations. 
8 

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Table 3. Adsorbent System Phase 2 System Results for Case 1 (UDDS/HWFET Cycles)

Case 1 Adjusted Fuel

Economy 

(mpgge) 

Range

5.6 kg H2

(mi)

Onboard

Efficiency

(%)

Volumetric 

Density

(g/L) 

Gravimetric 

Density

(wt%)

MOF-5 HexCell 49 274 92.0 17.5 3.5

MOF-5 MATI 48 269 97.0 20.7 3.4

AB Slurry—Exothermic 47 263 97.0 36.8 4.2

Alane Slurry—Endothermic 44 246 93.0 34.3 3.4

350 bar Compressed Gas 50 280 100.0 17.0 4.8

700 bar Compressed Gas 50 280 100.0 25.0 4.7

Phase 3 System Results

For the Phase 3 adsorbent systems, the focus was on final design refinements for the HexCell 

and MATI systems. The simulation results for these systems are shown in Table 4 and Table 5. 

In addition to changes made within the storage system models, the base vehicle model was also 

changed between Phase 2 and Phase 3 in order to improve the vehicle-level modeling based on 

new validation information. Specifically, changes were made to the vehicle model to include 

more aggressive controls for assist, more regen recapture, and higher efficiencies within the 

vehicle. As a result, the fuel economy and related range improved for all of the systems, but the 

relative performance across the Phase 3 systems remained constant with that of past phases. That 

is, the adsorbent systems showed marginal improvement over the CH systems and the physical 

storage systems performed best in terms of fuel economy and range. These enhancements were 

performed in order to improve the overall robustness of the framework model as it will be made 

available to the broader research community and become a research tool that will be used beyond 

the life of the HSECoE. The framework model, as well as many of the other models developed 

under the HSECoE, is available through NREL at the HSECoE website (www.hsecoe.org) [2].

Table 4. Adsorbent System Phase 3 System Results for Case 1 (UDDS/HWFET Cycles)

Case 1 Adjusted Fuel

Economy 

(mpgge) 

Range

5.6 kg H2

(mi)

Onboard

Efficiency

(%)

Volumetric 

Density

(g/L) 

Gravimetric 

Density

(wt%)

MOF-5 HexCell 54 302 97.0 20.5 4.1

MOF-5 MATI 53 297 96.1 23.2 3.5

AB Slurry—Exothermic 54 302 96.5 36.9 3.9

Alane Slurry—Endothermic 48 269 82.5 33.1 2.9

350 bar Compressed Gas 55 308 100.0 17.1 4.8

700 bar Compressed Gas 55 308 100.0 25.3 4.8
9 

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Table 5. Adsorbent System Phase 3 Results for Case 2 (US66 Drive Cycle—Aggressive Driving)

Case 2 Unadjusted 

Fuel 

Economy 

(mpgge) 

Range

5.6 kg H2

(mi)

Onboard

Efficiency

(%)

Volumetric 

Density

(g/L) 

Gravimetric 

Density

(wt%)

MOF-5 HexCell 57 319 97.1 20.8 4.2

MOF-5 MATI 56 314 96.2 23.1 3.5

AB Slurry—Exothermic 57 319 97.8 37.4 4.0

Alane Slurry—Endothermic 49 274 84.1 32.0 2.8

350 bar Compressed Gas 58 325 100.0 17.1 4.8

700 bar Compressed Gas 58 325 100.0 25.3 4.8

Trade-Off Study Results

In addition to providing high-level feedback on the performance and design of a given materialsbased system, trade-off studies quantifying the relative range impacts resulting from changes to 

the storage system capacity and volume were also performed. Table 6 shows results of the 

volume study based on the Phase 2 adsorbent storage systems. In this application, modelers 

worked with HSECoE system architects to provide high-level feedback on the performance and 

design of their given material systems. The focus of this activity was an example of a trade-off 

study quantifying the relative range impacts resulting from a fixed-volume study. 

In this fixed-volume study, four different adsorbent system designs were evaluated in 

conjunction with three different volume levels. The four adsorbent systems included powdered 

MOF-5 operating at 60 bar and 80 K full tank conditions with an assumed aluminum tank, 

powdered MOF-5 operating at 60 bar and 40 K full tank conditions with an assumed carbonfiber tank, compacted MOF-5 0.52 g/cc operating at 200 bar and 80 K full tank conditions with 

an assumed aluminum tank, and compacted MOF-5 0.52 g/cc MOF-5 operating at 200 bar and 

40 K full tank conditions with an assumed carbon-fiber tank. Each system was simulated in a 

mid-size passenger vehicle using the modeling framework for Case 1 to provide range and fuel 

economy for three volume assumptions: 140 L, 205 L, and 253 L. These three volume levels 

were based on assumptions from the DOE 2020 hydrogen storage technical targets and represent 

the high, medium, and low range of practical storage system volume for passenger vehicles. For 

comparison, the usable capacity in the 350 bar compressed gas storage system for the Ford Focus 

fuel cell vehicle was 4 kg with an external volume of about 230 L. 

This study shows that the volumetric target is much more sensitive to range than the gravimetric 

target is. That is, storage systems that had high mass but allowed for more onboard hydrogen 

storage through compaction or low-temperature operation had small fuel economy penalties but 

were accompanied by much higher ranges due to their ability to store more hydrogen onboard for 

a given volume. This information was used by the adsorbent system architects and modelers to 

help refine their system designs for Phase 3.
10 

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Table 6. Constant Volume Range Impact Study 

Hydrogen 

Storage System

Adjusted 

Fuel 

Economy 

(mpgge)

Usable 

H2 

(kg)

Range 

Usable H2 

(mi)

Gravimetric 

Capacity 

(wt%)

Volumetric 

Capacity 

(g/L)

Volume 

(L)

Powder MOF-5 

60 bar 80 K Al 51.11 2.00 102.20 2.80 12.86 140

Powder MOF-5 

60 bar 40 K CF 51.30 4.20 215.50 6.61 29.84 140

0.52 g/cc MOF-5 

200 bar 80 K Al 50.47 3.35 169.10 2.68 23.94 140

0.52 g/cc MOF-5 

200 bar 40 K CF 50.62 4.60 232.90 4.18 32.59 140

Powder MOF-5 

60 bar 80 K Al 50.95 2.80 142.70 3.15 13.67 205

Powder MOF-5 

60 bar 40 K CF 50.97 6.70 341.50 7.97 32.64 205

0.52 g/cc MOF-5 

200 bar 80 K Al 49.93 5.35 267.10 2.92 26.11 205

0.52 g/cc MOF-5 

200 bar 40 K CF 50.18 7.30 366.30 4.61 35.51 205

Powder MOF-5 

60 bar 80 K Al 50.73 3.60 182.60 3.39 14.18 253

Powder MOF-5 

60 bar 40 K CF 50.89 8.60 437.60 8.68 33.96 253

0.52 g/cc MOF-5 

200 bar 80 K Al 49.32 6.85 337.90 3.02 27.05 253

0.52 g/cc MOF-5 

200 bar 40 K CF 49.71 9.30 462.30 4.77 39.56 253

Al: aluminum tank

CF: carbon-fiber tank
11 

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Storage System Energy Analysis 

In support of the engineering and design of the materials-based systems under the HSECoE, 

energy analyses on the various storage system designs were performed to provide high-level 

estimates on the overall energy inputs required by a given system, including well-to-power-plant 

(WTPP) efficiency (%), hydrogen cost ($/kg), and greenhouse gas (GHG) emissions (carbon 

dioxide equivalent) on a gram per mile basis for future 2020 scenarios. Results of some of these 

analyses obtained from running the H2A Hydrogen Delivery Scenario Analysis Model 

(HDSAM) are shown in Table 7 and Table 8. The HDSAM model was run for several adsorbent 

systems (the HexCell powder MOF-5, the MATI compacted puck MOF-5 [0.32 g/cc], and a 60 

bar 80 K gas adsorbent) and for the AB slurry and alane slurry chemical hydrogen storage 

material systems to produce preliminary WTPP efficiency, GHG emissions, and hydrogen cost 

figures. In addition, model runs were performed on a 700-bar compressed gas system and a 

cryogenic-compressed liquid hydrogen system (CcH2 <200 K) for comparison to the materialsbased systems. The well-to-wheel (WTW) GHG emissions breakdowns by category for this 

analysis are shown in Figure 2. 

The AB system offers several onboard advantages over the alane system—being an exothermic 

onboard reaction leads to higher onboard efficiency (96% vs. 88%). The alane system has higher 

regeneration cycle costs, and higher energy inputs. Both chemical hydrogen materials systems 

showed a higher cost and lower efficiency than the adsorbent systems and the two physical 

storage systems. This indicates a need for advancements and cost reductions for chemical 

hydrogen storage material systems in general. This analysis supports the need for additional 

research focused on reducing the cost of chemical hydrogen storage material off-board 

regeneration cycles in order for these systems to be viable. The adsorbent systems performed 

better than the chemical hydrogen storage material systems in terms of cost, energy, and GHG 

emissions, but they were still higher in all of these areas than the physical storage systems were. 

The adsorbent systems also require additional advancements in order to compete with the 

incumbent systems. In general, the results from Table 7 and Table 8 shows that the adsorbent 

systems investigated do not outperform compressed gas systems. 

Table 7. Vehicle WTW Results for Adsorbent and CH Systems Compared to Compressed Gas and 

Liquid Hydrogen Systems

WTW H2

Cost 

($/kg-H2) 

WTW 

Energy 

Efficiency

WTW GHG 

Emissions 

(g/mile)

Volumetric 

Efficiency 

(g-H2/L)

2020 700 bar Gas—T520a $3.91 56.4% 230 25.6

2020 CcH2—Liquid Hydrogen Truck $4.49 46.5% 289 41.8

2020 Liquid AB $13.96 16.5% 915 41.4

2020 Liquid Alane $7.89 24.7% 642 32.2

2020 Adsorbent 1 60 bar 80 K Gas—T340b $5.92 40.4% 401 24.1

2020 Adsorbent HexCell 100 bar 80 K Gas—

T340b

$6.16 39.2% 412 17.5

2020 Adsorbent MATI 100 bar 80 K Gas—T340b $5.69 42.1% 391 20.7

a T520: 520 bar insulated tube truck; b T340: 340 bar insulated tube truck
12 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

Table 8. Vehicle WTW GHG Breakdown for Adsorbent and CH Systems Compared to Compressed 

Gas and Liquid Hydrogen Systems

WTW GHG Breakdown 

(g CO2 eq/mile)

700 bar Gas 

2020

CcH2 Liq. H2

2020

Liquid AB 

2020

Liquid 

Alane 2020

Adsorbent 

2020

Plant Gate 186 186 206 218 218

Regen 0 0 670 344 0 

Liquefaction 0 91 0 0 0 

Terminal 23 12 1 1 62

Transport (Trailer) 3 1 2 2 2 

Station 19 3 0 0 79

Vehicle Storage Parasitics 0 0 37 77 46

Total 230 292 915 643 407

Figure 2. WTW GHG emissions breakdown 

Use of HDSAM requires a specific hydrogen delivery scenario as well as specific information 

for each storage system. Table 9 and Table 10 show the specific delivery and storage system 

information used for these analyses. 
13 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

Table 9. HSECoE Base Assumptions for HDSAM

Base Assumptions

Production Steam methane reforming

Market: Sacramento Sacramento, 15% market penetration

Plant (and Regeneration) 62 miles (100 km) from city gate

Electricity U.S. grid

Large Scale Storage—Geologic Liquid hydrogen

Transport Plant to city gate terminal

Gaseous Hydrogen Pipeline

Liquid Hydrogen Liquid carrier—truck

Distribution City gate terminal to refueling stations—truck

Refueling Station Size 1,000 kg/day max. (may be limited by one delivery per day or 9% 

coverage)

Table 10. Storage System Information Required for HDSAM Analysis

System Information

System weight, wt%, density, and volume

Total and usable H2 (5.6 kg)

Venting rate and dormancy time

System temperature and pressure at full and 1⁄4 tank

Energy used to release H2

System cost

Cooling load at refueling station

Fill time

Fuel economy (from HSSIM)
14 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

References

1. M. Thornton, A. Brooker, J. Cosgrove, M. Veenstra, and J.M. Pasini, “Development of a 

Vehicle-Level Simulation Model for Evaluating the Trade-Off between Various Advanced 

On-Board Hydrogen Storage Technologies for Fuel Cell Vehicles,” SAE Technical Paper

2012-01-1227 (2012), doi:10.4271/2012-01-1227. 

2. U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Fuel Cell 

Technologies Office Hydrogen Storage Engineering Center of Excellence, 

http://hsecoe.org/models.html.