Hydrogen Storage in Wind 

Turbine Towers: Design 

Considerations

Preprint 

September 2003 • NREL/CP-500-34759 

R. Kottenstette 

Summer intern from Santa Clara University 

J. Cotrell 

National Renewable Energy Laboratory 

To be presented at WINDPOWER 2004 

Chicago, Illinois 

March 28-31, 2004 

National Renewable Energy Laboratory 

1617 Cole Boulevard 

Golden, Colorado 80401-3393 

NREL is a U.S. Department of Energy Laboratory 

Operated by Midwest Research Institute • Battelle • Bechtel 

Contract No. DE-AC36-99-GO10337 
NOTICE 

The submitted manuscript has been offered by an employee of the Midwest Research Institute (MRI), a 

contractor of the US Government under Contract No. DE-AC36-99GO10337. Accordingly, the US 

Government and MRI retain a nonexclusive royalty-free license to publish or reproduce the published 

form of this contribution, or allow others to do so, for US Government purposes. 

This report was prepared as an account of work sponsored by an agency of the United States 

government. Neither the United States government nor any agency thereof, nor any of their employees, 

makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, 

completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents 

that its use would not infringe privately owned rights. Reference herein to any specific commercial 

product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily 

constitute or imply its endorsement, recommendation, or favoring by the United States government or any 

agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect 

those of the United States government or any agency thereof. 

Available electronically at http://www.osti.gov/bridge

Available for a processing fee to U.S. Department of Energy 

and its contractors, in paper, from: 

U.S. Department of Energy 

Office of Scientific and Technical Information 

P.O. Box 62 

Oak Ridge, TN 37831-0062 

phone: 865.576.8401 

fax: 865.576.5728 

email: reports@adonis.osti.gov 

Available for sale to the public, in paper, from: 

U.S. Department of Commerce 

National Technical Information Service 

5285 Port Royal Road 

Springfield, VA 22161 

phone: 800.553.6847 

fax: 703.605.6900 

email: orders@ntis.fedworld.gov 

online ordering: http://www.ntis.gov/ordering.htm

Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste 
 1

Abstract 

The paramount considerations associated with a hydrogen tower are corrosion (in the 

form of hydrogen embrittlement) and structural failure (through bursting or fatigue life 

degradation). Although hydrogen embrittlement (HE) requires more research and 

experimentation, it does not appear to prohibit the use of turbine towers for hydrogen 

storage. Furthermore, the structural modifications required to store hydrogen in a tower 

are technically feasible. 

We discovered that hydrogen towers have a “crossover pressure” at which their critical 

mode of failure crosses over from fatigue to bursting. The crossover pressure for many 

turbine towers is between 10 and 15 atm. The cost of hydrogen storage per unit of 

storage capacity is lowest near the crossover pressure. Above the crossover pressure, 

however, storage costs rise quickly. 

Introduction 

Low-cost hydrogen storage is recognized as a cornerstone of a renewables-hydrogen 

economy. Modern utility-scale wind turbine towers are typically conical steel structures 

that, in addition to supporting the rotor, could be used to store hydrogen. During off-peak 

hours, electrolyzers could use energy from the wind turbines or the grid to generate 

hydrogen and store it in turbine towers. The stored hydrogen could later be used to 

generate power via a fuel cell during times of peak demand. This capacity for energy 

storage could significantly mitigate the drawbacks to wind’s intermittent nature and 

provide a cost-effective means of meeting peak demand. 

Hydrogen storage creates a number of additional considerations in turbine tower design. 

Under certain conditions hydrogen tends to react with steel, adversely affecting the 

mechanical properties such as ductility, yield strength, and fatigue life. Additionally, 

storing hydrogen at pressure significantly increases the stresses on the tower. These 

factors require a structural analysis to evaluate how internal pressure may affect the 

tower’s design life. 

Storing hydrogen in a turbine tower appears to have been first suggested by Lee Jay 

Fingersh at the National Renewable Energy Laboratory (NREL) (Fingersh 2003). As 

outlined above, this technology could play an important role in the hydrogen economy 

and is, therefore, worth exploring. The objective of this paper is to identify the 

paramount considerations associated with using a wind turbine tower for hydrogen 

storage. This paper summarizes work presented in an NREL technical report 

(Kottenstette and Cotrell 2003). 

Benchmarks and Assumptions 

We based our analysis on a 1.5-MW tubular steel tower designed to withstand peak and 

fatigue bending moments at the base and top. It has a linear taper of diameter and wall 

thickness, a constant tower diameter/wall thickness (d/t) ratio of 320, and the top 

diameter equal to 1⁄2 of the base diameter. We assume the construction material to be 
 2

structural steel with a yield strength of 350 MPa. The cost of the tower is estimated by 

multiplying the tower mass by $1.50/kg (Malcolm 2002). 

It should be mentioned that where the mass of pressurized hydrogen is computed, 

hydrogen is modeled as an ideal gas. 

Corrosion 

Both atmospheric corrosion and HE must be considered with regard to a hydrogen tower. 

Conventional turbine towers are adequately protected from atmospheric corrosion by a 

layer of paint. When a tower is used to store a pressurized gas, however, it becomes 

subject to the guidelines set forth in the American Society of Mechanical Engineers 

(ASME) Boiler and Pressure Vessel Code. The ASME code requires that paint not be 

considered an adequate form of protection for the interior of pressure vessels. Enough 

material must therefore be added to anticipate corrosion (ASME 2001). 

Fortunately, the interior of a hydrogen tower is a controlled environment. Hydrogen 

from a PEM electrolyzer does not contain contaminants that cause atmospheric corrosion 

(of primary concern are sulfur dioxide and chlorine). The product hydrogen (which 

would be fully saturated with water vapor) could be dried to below the critical humidity 

level (less than 80% relative humidity) at minimal cost. Under these conditions, 

corrosion would penetrate the steel’s surface at the negligible rate of less than 0.1 μm per 

year (Roberge 1999). 

Hydrogen Embrittlement 

HE is the primary form of corrosion that threatens the viability of hydrogen towers. HE 

is a process in which atomic hydrogen (H as opposed to H2) adsorbs to a metal surface 

and causes brittle failure far below the yield strength of an affected material. A 

component’s susceptibility to HE is determined by environmental effects, including 

temperature, pressure, and hydrogen purity, as well as material properties, including grain 

size, hardness, and strength. This section explores HE’s possible effect on a turbine 

tower. 

HE may be most severe at ambient temperatures, and its effects increase with the square 

root of hydrogen gas pressure (Gray 1974; Mohitpour, Golshan, and Murray 2000). This 

suggests that designing turbine towers for relatively low-pressure storage may help 

prevent HE. It is fortunate, therefore, that the storage pressures under consideration are 

only about 10% of hydrogen pipeline operating pressures. 

Hydrogen gas purity is another major environmental factor controlling HE. Experimental 

evidence has shown that crack propagation in a stressed specimen could be controlled by 

the introduction of oxygen into the hydrogen environment. Investigators demonstrated 

that a crack propagating in a pure hydrogen environment could be stopped with the 

introduction of as little as 200 ppm oxygen at atmospheric pressure (Gray 1974). 
 3

Because the method of H2 production under consideration is via an electrolyzer, O2 gas 

will be readily available. Although adding O2 to H2 can result in an explosive mixture, 

adding the necessary levels of O2 is expected to have little effect on safety. This is 

because the required oxygen concentration (approximately 200 ppm) is far above the 

upper combustible limit of hydrogen in oxygen (93.9% by volume). Two hundred ppm 

oxygen in hydrogen represents only 0.02% (by volume) of the oxygen required to create 

an explosive environment. 

Larger grains with precipitates heavily concentrated along grain boundaries can also 

expedite HE because they allow for easier diffusion of hydrogen through the metal’s 

lattice structure (Gray 1974). The Sourcebook for Hydrogen Applications lists proper 

control of grain size as a successful measure of HE prevention (Bain et al., 1998). Grain 

size is controlled in the steel forming and treatment process. Fortunately, selection of 

steel plate with the appropriate grain size is not anticipated to be difficult. 

Increased material hardness can also magnify the effects of hydrogen embrittlement. 

Typically, hardness is increased by causing residual tensile stresses in a material’s 

surface through treatments like forging, cold rolling, or welding. Additionally, it is 

theorized that when hydrogen adsorbs to a material’s surface, it decreases the energy 

required to form a surface crack (Mohitpour, Golshan, and Murray 2000). The 

combination of these two factors facilitates the formation of surface cracks. 

Tower welds are therefore particularly susceptible to HE because rapid cooling of the 

welds can cause “hard spots” where carbon and other impurities coalesce. However, as a 

general guideline, trouble-free welds can be obtained in low-alloy steels containing up to 

about 0.28% carbon and to a carbon equivalent (C+1/4Mn) of about 0.55% (Cox and 

Williamson 1977). 

Steels offering the strength assumed in this study (such as S355J0 as specified by British 

Standard EN 10025 and Grade 485 steel as specified by ASTM Specification A 516/A) 

have equivalent carbon contents of 0.65% and 0.60% respectively. These steels require 

preheating of the joint and the use of low-hydrogen electrodes to protect their welds from 

HE. Alternatively, the tower’s structural requirements could be met with thicker walls 

made of steels having lower carbon and manganese contents. Tower welds that are 

protected from hydrogen embrittlement can therefore be devised without difficulty. 

Material strength, a property related to both grain size and hardness, is perhaps the most 

predominant material property influencing hydrogen embrittlement. It has been generally 

observed that higher-strength steels exhibit greater loss of ductility, lower ultimate 

strengths, and greater propensity for delayed failure than their lower-strength 

counterparts when subjected to a hydrogen environment (Bain et al., 1998). It is for these 

reasons that many experts suggest use of lower-strength steels for hydrogen applications. 

Some experts have designated an ultimate strength of 700 MPa as a benchmark, below 

which steels are significantly less susceptible to HE (Mohitpour, Golshan, and Murray 

2000; Cox and Williamson 1977). Steels commonly used for tower construction fall well 
 4

short of this benchmark; towers are typically constructed of a low-strength, low-carbon 

structural steel with yield and ultimate properties at or below 350 and 630 MPa, 

respectively. 

Based on the considerations outlined above, the risk of HE does not exclude the use of 

turbine towers for hydrogen storage. It is, however, difficult to compare the use of a 

wind turbine tower as a pressure vessel to more traditional hydrogen applications 

because, unlike conventional pressure vessels, they are subjected to significant dynamic 

loads. The dynamic structural loads applied to a turbine tower would serve to repeatedly 

open microfissures, one mechanism by which HE is theorized to propagate. Due to the 

potential for catastrophic failure, HE requires more research and experimentation. 

Structural Analysis 

Pressurizing the interior of a wind turbine tower creates unique structural demands. A 

pressurized tower must not only withstand loads caused by normal operation of the wind 

turbine, but it must also fulfill the requirements of a pressure vessel. Tubular towers for 

modern utility-scale wind turbines are typically limited by the fatigue strength of the 

horizontal welds. One primary concern, therefore, is the effect of pressurizing the tower 

on the fatigue strength of these welds. In addition, the hydrogen pressure loads must not 

exceed allowable margins for pressure vessels. 

Loads and Stresses 

Wind turbines are subjected to widely varying aerodynamic loads. These loads induce 

large bending moments that, in turn, cause tensile and compressive stresses parallel to the 

axis of the tower (axial stresses). At the base of the tower, these stresses significantly 

exceed the compressive stresses caused by the weight of the turbine. Frequent, 

fluctuating aerodynamic loads seen during normal operation make fatigue the critical 

mode of failure for modern turbine towers. 

Subjecting a tower to internal pressure creates a different loading scenario. Because the 

pressure is uniform, it causes loads in the axial direction and in the plane normal to the 

tower’s axis. The axial stresses induced in cylindrical pressure vessels are half the 

magnitude of the stresses induced in the plane normal to the axis (hoop stresses). The 

loads to which pressure vessels are subjected make ultimate strength the limiting design 

constraint for most pressure vessels. 

Fatigue Failure 

One popular theory describes fatigue failure as crack propagation resulting from 

repetitive plastic deformation. In turbine towers, cracks primarily propagate when a 

tensile stress is applied perpendicular to the crack’s length. This suggests that, in turbine 

towers, the stress state in the hoop direction has little effect on fatigue in the axial 

direction. 

When a tower is pressurized, however, the large surface area over which this pressure 

acts results in significant axial tensile stresses even at low pressures. For the tower 

geometry considered in this study, the tensile stress induced by one atmosphere above 
 5

gauge pressure is nearly four times the magnitude of the compressive stress caused by the 

entire weight of the turbine. As a result, internal pressures work together with the 

aerodynamic loads on the tower to degrade its fatigue life. 

The Goodman equation accounts for the effect of mean stress on fatigue strength. One 

way to ensure an adequate tower life is to increase the tower wall thickness, thereby 

distributing the load and reducing the stresses. During this study, the Goodman equation 

was used to derive an expression for the increase in wall thickness required to maintain 

the tower’s designed fatigue life: 

2( ) 2 1Sut

pr t − t = ∆t = (1) 

where 

t2 = the thickness required of a pressurized tower 

t1 = the thickness required of an equivalent tower without internal pressure 

p = the gauge pressure 

r = the radius of the cross section being considered 

Sut = the ultimate tensile strength. 

This equation dictates the amount of wall reinforcement required to maintain the tower’s 

fatigue life. It is valid for all towers and tower sections that are critically limited by 

fatigue rather than peak loads or buckling constraints. See the appendix for a derivation 

of this equation. 

Crossover Pressure 

As the pressure rating of a hydrogen tower is increased, the primary mode of failure for 

the tower walls crosses over from fatigue to bursting. Once this “crossover” pressure is 

reached, the required wall thickness is determined by the maximum allowable hoop 

stress, rather than axial fatigue. From the ASME Pressure Vessel Code (ASME 2001), 

the maximum allowable stress in a pressure vessel equation is given as: 

3.5 max

Sut

σ ≤ (2) 

where 

σ max = the maximum allowable stress 

Sut = the ultimate tensile strength. 

Fig. 1 shows required thickness as a function of pressure for both the fatigue and burst 

conditions. 
 6

0

5

10

15

20

25

30

35

40

0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200

Pressure (kPa)

Thickness (mm)

Base Fatigue

Base Hoop Stress

Top Fatigue

Top Hoop Stress

Crossover Pressure

Figure 1: Wall thickness as a function of pressure for different failure modes. 

The solid set of lines describes thickness required at the base of the tower, and the dashed 

set of lines describes thickness required at the top of the tower. The crossover pressure 

for a given tower cross section is defined as the point where the line describing maximum 

stress requirements (the line with the steeper slope) overtakes the line describing fatigue 

requirements (the line which is almost horizontal). Below the crossover pressure, the 

required tower wall thickness is determined by the more gradual fatigue line. Above the 

crossover pressure, the required thickness is determined by the steeper line for the burst 

strength. 

Solving for the crossover pressure (the intersection of the two lines) at an arbitrary tower 

cross section results in the following equation: 





 





 − 

 



 =

7

7 1

4( )

1

E

t

d

E S

p ut

crossover (3) 

where 

E = the welded joint efficiency 

Sut = the Ultimate Tensile Strength 





 





t1

d = the diameter/thickness (d/t) ratio. 

This study assumes that the tower is fatigue constrained at every section and has a 

constant d/t ratio. For these assumptions, the crossover pressure is the same at all points 

in the tower. This can be seen in Fig. 1 by noticing that the solid lines and dashed lines 
 7

cross at the same pressure. Furthermore, this equation demonstrates that crossover 

pressure is dependent only on ultimate tensile strength, welded joint efficiency, and d/t 

ratio. For the assumptions in this study (Sut = 636 MPa and d/t = 320), the crossover 

pressure is 1.1 MPa (11 atm). Crossover pressures for most utility-scale turbines are 

expected to be between 1.0 and 1.5 MPa (10 and 15 atm). 

Tower Radius and Taper 

Below the crossover pressure, where fatigue is the limiting constraint, tower thickness 

requirements are sensitive to tower radius and subject to Eq. 1 given above (the thickness 

equation). This relationship is demonstrated by the following figure: 

0.00

5.00

10.00

15.00

20.00

25.00

0 200 400 600 800 1000 1200

Pressure (kPa)

Required Increase in Thickness (mm)

r =1.41m

r = 2.12m

r = 2.82m

Figure 2: Plot of the thickness equation for three tower radii. 

This figure suggests that towers with smaller radii are able to tolerate higher pressure 

with a smaller increase in thickness than their larger-radii counterparts. Larger radius 

towers, on the other hand, enclose a greater volume. These two factors must be weighed 

to determine the radius size that is most economical for hydrogen storage. 

The relative cost of a tower section is reflected by the ratio of the mass of wall 

reinforcement to the mass of H2 stored. For a fatigue-limited tower, this ratio is 

independent of both pressure and tower radius. This ratio is given by the following 

equation: 
 8















 =





















( )

2

RT

S

m

m ut

steel

H stored

ρ

 (4) 

where 

ρ = the density of steel 

Sut = the ultimate tensile strength of the steel 

R = the gas constant for molecular hydrogen 

T = the absolute temperature of the gas. 

This equation, together with the fact that end caps are more costly per kilogram than wall 

reinforcement, suggests that the ideal pressure vessel geometry is long and slender. It 

also implies that the methods described for determining costs associated with wall 

reinforcement apply to towers of any taper angle. 

Conclusions 

As a result of this study, we developed two significant conclusions regarding hydrogen 

towers. First, HE does not appear to be a major obstacle, but more research is needed in 

the area of long-term, low-pressure storage. Second, fatigue-driven towers have a 

crossover pressure at which they offer the most cost-effective storage capacity. For most 

utility-scale towers, this crossover pressure is expected to be between 1.0 and 1.5 MPa 

(10–15 atm). Finally, turbine towers may offer economical hydrogen storage because 

they approach the ideal pressure vessel geometry. 

Future Work 

A literature review reveals a need for further study of the effects of HE as it pertains to 

hydrogen storage. Additionally, when considering the construction of a hydrogen tower, 

it must be considered whether or not the value of hydrogen stored at the turbine tower 

justifies the storage cost. NREL is currently evaluating the value of storing hydrogen in 

turbine towers as part of its WindSTORM study. 

References 

ASME Boiler and Pressure Vessel Code. (2001). New York, NY: The American Society 

of Mechanical Engineers. 

Bain, A.; Barclay, J.; Bose, T.; Edeskuty, F.; Fairlie, M.; Hansel, J.; Hay, D.; Swain, M.; 

Ohi, J.; Gregoire Padro, C. (1998). Sourcebook for Hydrogen Applications. Quebec, 

Canada: Hydrogen Research Institute; Golden, CO: National Renewable Energy 

Laboratory; NREL/BK-540-24778. 

Cox, K. E.; Williamson Jr., K.D. eds. (1977). Transmission and Storage. Hydrogen: Its 

Technology and Implications, Vol. II, Cleveland: CRC Press. 

Fingersh, L. J. (2003). Optimized Hydrogen and Electricity Generation from Wind. 

NREL/TP-500-34364. Golden, CO: National Renewable Energy Laboratory. 
 9

Gray, H.R. (1974). “Hydrogen Environment Embrittlement: Experimental Variables.” 

Hydrogen Embrittlement Testing. pp. 133-151. Proceedings from the 75th Annual 

Meeting of the American Society for Testing and Materials; 25-30 June 1972, Los 

Angeles, CA; Baltimore, MD: ASTM. 

Kottenstette, R.; Cotrell, J. Hydrogen Storage in Wind Turbine Towers. NREL/TP-500-

34656. Golden, CO: National Renewable Energy Laboratory, 2003. 

Malcolm, D.J.; Hansen, A.C. (2002), WindPACT Turbine Rotor Design Study. 

NREL/SR-500-32495. Work performed by Global Energy Concepts, LLC, 

Kirkland, Washington. Golden, CO: National Renewable Energy Laboratory. 

Mohitpour, M.; Golshan, H.; Murray, A. (2000). Pipeline Design & Construction: A 

Practical Approach. New York: ASME Press. 

Roberge, P. (1999). Handbook of Corrosion Engineering. New York: McGraw-Hill. 
REPORT DOCUMENTATION PAGE Form Approved 

 OMB NO. 0704-0188 

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson 

Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503. 

1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE

September 2003 

3. REPORT TYPE AND DATES COVERED 

Conference Paper 

4. TITLE AND SUBTITLE

Hydrogen Storage in Wind Turbine Towers: Design Considerations; Preprint 

6. AUTHOR(S) 

R. Kottenstette, J. Cotrell 

5. FUNDING NUMBERS

WER3 3250 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 

National Renewable Energy Laboratory 

1617 Cole Blvd. 

 Golden, CO 80401-3393 

8. PERFORMING ORGANIZATION 

REPORT NUMBER 

NREL/CP-500-34759 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORING/MONITORING 

AGENCY REPORT NUMBER

11. SUPPLEMENTARY NOTES

12a. DISTRIBUTION/AVAILABILITY STATEMENT

National Technical Information Service 

U.S. Department of Commerce 

5285 Port Royal Road 

 Springfield, VA 22161

12b. DISTRIBUTION CODE

 

13. ABSTRACT (Maximum 200 words)

The paramount considerations associated with a hydrogen tower are corrosion (in the form of hydrogen embrittlement) and 

structural failure (through bursting or fatigue life degradation). Although hydrogen embrittlement (HE) requires more research

and experimentation, it does not appear to prohibit the use of turbine towers for hydrogen storage. Furthermore, the structural 

modifications required to store hydrogen in a tower are technically feasible. 

We discovered that hydrogen towers have a “crossover pressure” at which their critical mode of failure crosses over from 

fatigue to bursting. The crossover pressure for many turbine towers is between 10 and 15 atm. The cost of hydrogen storage 

per unit of storage capacity is lowest near the crossover pressure. Above the crossover pressure, however, storage costs rise 

quickly. 

15. NUMBER OF PAGES

14. SUBJECT TERMS 

wind energy; wind turbine; wind turbine tower; hydrogen; hydrogen storage 16. PRICE CODE

17. SECURITY CLASSIFICATION 

OF REPORT

Unclassified 

18. SECURITY CLASSIFICATION 

OF THIS PAGE

Unclassified

19. SECURITY CLASSIFICATION 

OF ABSTRACT

Unclassified

20. LIMITATION OF ABSTRACT

UL 

 NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89) 

Prescribed by ANSI Std. Z39-18 

298-102