Hydrogen storage – Industrial prospectives

The topic of this paper is to give an historical and technical overview of hydrogen storage vessels and to detail the specific issues and constraints of hydrogen energy uses. Hydrogen, as an industrial gas, is stored either as a compressed or as a refrigerated liquefied gas. Since the beginning of the last century, hydrogen is stored in seamless steel cylinders. At the end of the 60 s, tubes also made of seamless steels were used; specific attention was paid to hydrogen embrittlement in the 70 s. Aluminum cylinders were also used for hydrogen storage since the end of the 60 s, but their cost was higher compared to steel cylinders and smaller water capacity. To further increase the service pressure of hydrogen tanks or to slightly decrease the weight, metallic cylinders can be hoop-wrapped. Then, with specific developments for space or military applications, fully-wrapped tanks started to be developed in the 80 s. Because of their low weight, they started to be used in for portable applications: for vehicles (on-board storages of natural gas), for leisure applications (paint-ball) etc… These fully-wrapped composite tanks, named types III and IV are now developed for hydrogen energy storage; the requested pressure is very high (from 700 to 850 bar) leads to specific issues which are discussed. Each technology is described in term of materials, manufacturing technologies and approval tests. The specific issues due to very high pressure are depicted.     

Thermodynamic analysis of the emptying process of compressed hydrogen tanks

During the driving of fuel cell vehicles, the fast depressurization of compressed hydrogen tanks plus the high storage pressure and the low thermal conductivity of carbon fiber reinforced plastic (CFRP) can lead to significant cooling of the tank. This can result in a temperature below −40 °C inside the compressed hydrogen tanks and cause safety problems. In this paper, a thermodynamic model that incorporates the nature of external natural convection was developed to describe the emptying process of compressed hydrogen tanks and was validated by experiments. Thermodynamic analyses of the emptying process were performed to study the global heat transfer characteristics and the effects of ambient temperature, defueling rate, defueling pattern, initial and final density of hydrogen gas, liner and CFRP thickness and the crosswind velocity on the final temperature decreases of hydrogen gas, the inner wall and the outer wall.     

Multi-criteria evaluation of hydrogen storage systems for automobiles in Korea using the fuzzy analytic hierarchy process

In this paper, five hydrogen storage systems for automobiles are evaluated using the fuzzy analytic hierarchy process (AHP) in respect to eight criteria. The hydrogen storage systems for automobiles to be evaluated are 350 bar compressed gas hydrogen, 700 bar compressed gas hydrogen, liquefied hydrogen, metal hydride and chemical hydride. The selected criteria used in the evaluation of five hydrogen storage systems are weight efficiency, volume efficiency, system cost, energy efficiency, cycle life, refueling time, safety and infrastructure. According to the evaluation, compressed gas hydrogen ranks the highest in classification in Korea. Liquefied hydrogen ranks higher than metal hydride and chemical hydride. If the infrastructure for liquefied hydrogen were good in Korea, liquefied hydrogen may rank the highest in classification. Also, it should be noted that the rank of hydrogen storage systems can be changed according to the future technological developments.     

Review on studies of the emptying process of compressed hydrogen tanks

Compressed hydrogen tanks are now widely used for onboard hydrogen storage in fuel cell vehicles (FCVs). However, because of the high storage pressure and the low thermal conductivity of carbon fibre reinforced polymer (CFRP), the emptying of such tanks during driving or emergency release can cause a significant temperature decrease and result in an in-tank gas temperature below the low safety temperature limit of ?40 °C even in warm weather. Once the gas temperature within the tank is lower than ?40 °C, the sealing elements at the boss of the tank may fail, and glass transition of the polymer liner of the type IV tank may occur; both can cause hydrogen leakage and severe safety problems. In this paper, the heat transfer correlations, thermodynamic analyses, computational fluid dynamics (CFD) simulations, experimental studies, and thermal management methods associated with the emptying process of compressed hydrogen tanks are comprehensively reviewed. Future research directions on this topic are suggested.     

Hydrogen tank first filling experiments at the JRC-IET GasTeF facility

Storage of gases under pressure, including hydrogen, is a well-known technology. However the use of hydrogen in vehicles at pressures much higher than those applicable in natural gas cars still requires safety and performance studies with respect to the verification and validation of the existing standards and regulations. The JRC-IET has developed a facility, GasTeF, for carrying out tests on full-scale high pressure vehicle's tanks for hydrogen or natural gas. A typical test performed in GasTeF is the hydrogen cycling, in which tanks are filled and slowly emptied using hydrogen pressurised up to 88 MPa, for at least 1000 times in line with the requirements of the EU regulation on type-approval of hydrogen-powered motor vehicles. The temperature evolution of the gas inside and outside the tank is monitored using a thermocouples array system specifically designed for this purpose. This paper presents the first experimental results on the temperature distribution during hydrogen cycling tests.     

Simulation of hydrogen leak and explosion for the safety design of hydrogen fueling station in Korea

Hydrogen has been used as chemicals and fuels in industries for last decades. Recently, it has become attractive as one of promising green energy candidates in the era of facing with two critical energy issues such as accelerating deterioration of global environment (e.g. carbon dioxide emissions) as well as concerns on the depletion of limited fossil sources. A number of hydrogen fueling stations are under construction to fuel hydrogen-driven vehicles. It would be indispensable to ensure the safety of hydrogen station equipment and operating procedure in order to prevent any leak and explosions of hydrogen: safe design of facilities at hydrogen fueling stations e.g. pressurized hydrogen leak from storage tanks. Several researches have centered on the behaviors of hydrogen ejecting out of a set of holes of pressurized storage tanks or pipes. This work focuses on the 3D simulation of hydrogen leak scenario cases at a hydrogen fueling station, given conditions of a set of pressures, 100, 200, 300, 400 bar and a set of hydrogen ejecting hole sizes, 0.5, 0.7, 1.0 mm, using a commercial computational fluid dynamics (CFD) tool, FLACS. The simulation is based on real 3D geometrical configuration of a hydrogen fueling station that is being commercially operated in Korea. The simulation results are validated with hydrogen jet experimental data to examine the diffusion behavior of leak hydrogen jet stream. Finally, a set of marginal safe configurations of fueling facility system are presented, together with an analysis of distribution characteristics of blast pressure, directionality of explosion. This work can contribute to marginal hydrogen safety design for hydrogen fueling stations and a foundation on establishing a safety distance standard required to protect from hydrogen explosion in Korea being in the absence of such an official requirement.     

Solar powered residential hydrogen fueling station

This paper presents a conceptual design of a solar powered hydrogen fueling station for a single family home in Wallingford, Connecticut, USA. Sixty high-efficiency monocrystalline silicon photovoltaic (PV) solar panels (Total capacity: 18.9 kW) account for approximately 94.7% of the hydrogen home’s power consumption. The fueling station consists of a 165 bar high pressure electrolyzer for on-site production of 2.24 kg/day of hydrogen, three-bank cascade configuration storage tanks (4.26 kg of H₂ at 350 bar) and a SAE J2600 compliant hydrogen nozzle. The system produces 0.8 kg/day of hydrogen for a fuel cell vehicle with an average commute of 56 km/day (Fuel mileage: 71 km/kg H₂). Safety codes and standards applicable at the facility are described, and a well-to-wheel analysis is performed to contrast the carbon dioxide emissions of conventional gasoline and fuel cell vehicles. The energy efficiency obtained by incorporating a solar-hydrogen system for residential applications is also computed.     

Technical assessment of compressed hydrogen storage tank systems for automotive applications

The performance and cost of compressed hydrogen storage tank systems has been assessed and compared to the U.S. Department of Energy (DOE) 2010, 2015, and ultimate targets for automotive applications. The on-board performance and high-volume manufacturing cost were determined for compressed hydrogen tanks with design pressures of 350 bar (∼5000 psi) and 700 bar (∼10,000 psi) capable of storing 5.6 kg of usable hydrogen. The off-board performance and cost of delivering compressed hydrogen was determined for hydrogen produced by central steam methane reforming (SMR). The main conclusions of the assessment are that the 350-bar compressed storage system has the potential to meet the 2010 and 2015 targets for system gravimetric capacity but will not likely meet any of the system targets for volumetric capacity or cost, given our base case assumptions. The 700-bar compressed storage system has the potential to meet only the 2010 target for system gravimetric capacity and is not likely to meet any of the system targets for volumetric capacity or cost, despite the fact that its volumetric capacity is much higher than that of the 350-bar system. Both the 350-bar and 700-bar systems come close to meeting the Well-to-Tank (WTT) efficiency target, but fall short by about 5%.     

Modeling of sudden hydrogen expansion from cryogenic pressure vessel failure

We have modeled sudden hydrogen expansion from a cryogenic pressure vessel. This model considers real gas equations of state, single and two-phase flow, and the specific “vessel within vessel” geometry of cryogenic vessels. The model can solve sudden hydrogen expansion for initial pressures up to 1210 bar and for initial temperatures ranging from 27 to 400 K. For practical reasons, our study focuses on hydrogen release from 345 bar, with temperatures between 62 K and 300 K. The pressure vessel internal volume is 151 L. The results indicate that cryogenic pressure vessels may offer a safety advantage with respect to compressed hydrogen vessels because i) the vacuum jacket protects the pressure vessel from environmental damage, ii) hydrogen, when released, discharges first into an intermediate chamber before reaching the outside environment, and iii) working temperature is typically much lower and thus the hydrogen has less energy. Results indicate that key expansion parameters such as pressure, rate of energy release, and thrust are all considerably lower for a cryogenic vessel within vessel geometry as compared to ambient temperature compressed gas vessels. Future work will focus on taking advantage of these favorable conditions to attempt fail-safe cryogenic vessel designs that do not harm people or property even after catastrophic failure of the inner pressure vessel.     

Analytical model for a techno-economic assessment of green hydrogen production in photovoltaic power station case study Salalah city-Oman

Hydrogen energy will play a credible role to reduce gas emissions in the transportation sector, the storage of energy, and other industrial applications. Moreover, the hydrogen produced from renewable energy sources allows to minimize greenhouse gas and increase the net profit of energy projects. This paper discusses the feasibility of the conversion of solar energy into hydrogen in a Photovoltaic Hydrogen Station (PVHS) in the south of Oman. Then, the sizing of different equipment and hydrogen production estimation in a 5 MWp PVHS is presented. The analysis of the investment cost (IC), the Net Profit (NP), and the Levelized Hydrogen Energy Cost (LHEC) are discussed to investigate the benefit of the project. The energy generated from the PV system and the produced hydrogen is calculated through an analytical model. The PVHS consists of 5 MWp PV panels connected to electrolyzers through maximum power point-controlled converters. The electrolyzers convert the electrical energy and the water into hydrogen. The hydrogen compressed and stored in special tanks can be used later in many industrial applications. The system produces about 90 910 kg of hydrogen per year with an IC of 5 301 760 €. The calculated LHEC is equal to 6.2 €/kg at an interest rate of 2%. The analysis has shown promising green hydrogen production projects in Oman.     

Vehicular storage of hydrogen in insulated pressure vessels

This paper describes an alternative technology for storing hydrogen fuel onboard vehicles. Insulated pressure vessels are cryogenic capable vessels that can accept cryogenic liquid hydrogen, cryogenic compressed gas or compressed hydrogen gas at ambient temperature. Insulated pressure vessels offer advantages over conventional storage approaches. Insulated pressure vessels are more compact and require less carbon fiber than compressed hydrogen vessels. They have lower evaporative losses than liquid hydrogen tanks, and are lighter than metal hydrides.

The paper outlines the advantages of insulated pressure vessels and describes the experimental and analytical work conducted to verify that insulated pressure vessels can be safely used for vehicular hydrogen storage. Insulated pressure vessels have successfully completed a series of certification tests. A series of tests have been selected as a starting point toward developing a certification procedure. An insulated pressure vessel has been installed in a hydrogen fueled truck and tested over a six month period.     

Risk assessment of Hydrogen fueling stations for 70 MPa FCVs

People are placing their hopes on the future of fuel-cell vehicles (FCVs) to replace today's gasoline-fueled vehicles. To encourage the widespread use of FCVs, however, these vehicles must be able to drive a distance of at least 500 km, mileage comparable to today's gasoline-fueled vehicles. To achieve this distance, automobile manufacturers are focusing their efforts on developing new hydrogen fuel tanks that will raise pressure to 70 MPa from the current 35 MPa. At the same time, hydrogen stations will also have to be able to provide 70 MPa compressed hydrogen gas to service these improved FCVs. Regulations for hydrogen fueling stations where pressure is no higher than 40 MPa were established in 2005 in Japan but it goes without saying that these regulations are inadequate for hydrogen fueling stations of 70 MPa.     

Off-grid test results of a solar-powered hydrogen refuelling station for fuel cell powered Unmanned Aerial Vehicles

Fuel cell (FC) propulsion for small (MTOW < 25 kg) Unmanned Aerial Vehicles (UAVs) provides a route for lower capital cost, environmentally friendlier and low noise operation. Most FC-based UAVs tested to date rely on compressed gas cylinders delivered to the point of use and used to refill the UAV hydrogen tanks on-site or chemical hydride systems to produce hydrogen on-board. An attractive alternative option is to produce hydrogen on-site from an off-grid renewable source according to the UAV fuel demand. A prototype off-grid solar-based hydrogen refuelling station for UAVs was developed for that purpose by Boeing Research & Technology Europe. A test program was carried out to evaluate the dynamic response of the hydrogen UAV refuelling system operating in an off-grid manner (disconnected from the AC grid). The system comprises a concentrated photovoltaic (CPV) array, an alkaline electrolyser, a low pressure hydrogen buffer tank and the required power electronics. The electrolyser was connected to the CPV source in an off-grid manner. The results from the off-grid tests are presented in this paper.     

Refuelling scenarios of a light urban fuel cell vehicle with metal hydride hydrogen storage. Comparison with compressed hydrogen storage counterpart

The high price of hydrogen fuel in the fuel cell vehicle refuelling market is highly dependent on the one hand from the production costs of hydrogen and on the other from the capital cost of a hydrogen refuelling station's components to support a safe and adequate refuelling process of contemporary fuel cell vehicles. The hydrogen storage technology dominated in the vehicle sector is currently based on high-pressure compressed hydrogen tanks to extend as much as possible the driving range of the vehicles. However, this technology mandates the use of large hydrogen compression and cooling systems as part of the refuelling infrastructure that consequently increase the final cost of the fuel. This study investigated the prospects of lowering the refuelling cost of small urban hydrogen vehicles through the utilisation of metal hydride hydrogen storage. The results showed that for low compression hydrogen storage, metal hydride storage is in favour in terms of the dispensed hydrogen fuel price, while its weight is highly comparable to the one of a compressed hydrogen tank. The final refuelling cost from the consumer's perspective however was found to be higher than the compressed gas due to the increased hydrogen quantity required to be stored in fully empty metal hydride tanks to meet the same demand.     

Study on hazards from high-pressure on-board type III hydrogen tank in fire scenario: Consequences and response behaviours

Exploration of thermal performances of composite high-pressure hydrogen storage tank under fire exposure were critical issues to reduce the risk of tank rupture. Three bonfire tests of type III tanks of 210 L-35 MPa with full compressed hydrogen were exposed to a pool fire to study the response behaviours in fire scenarios. Detailed data on the tank wall temperature and inner pressure were presented in this work. Prototype bonfire tests for the type III tank indicated the failure pressure limits amounted to 41.1–41.8 MPa (average 41.4 MPa). Two consequences (rupture and hydrogen blowdown) will be caused when the inner pressure beyond this limits in fire scenario. The loading-bearing capacity of the tank reduced nearly 3 times under the prescribed fire condition when compared to its average burst pressure of 123.5 MPa conducted from the hydraulic burst test. Results also shown that fire resistance rating (FRR, time to rupture) of the three tanks were 784, 666, and 596, respectively. The FRR got shorter when the tank was exposed in the engulfing fire in advance at hydrogen blowdown case.     

Hydrogen storage technology options for fuel cell vehicles: Well-to-wheel costs, energy efficiencies, and greenhouse gas emissions

Five different hydrogen vehicle storage technologies are examined on a Well-to-Wheel basis by evaluating cost, energy efficiency, greenhouse gas (GHG) emissions, and performance. The storage systems are gaseous 350 bar hydrogen, gaseous 700 bar hydrogen, Cold Gas at 500 bar and 200 K, Cryo-Compressed Liquid Hydrogen (CcH2) at 275 bar and 30 K, and an experimental adsorbent material (MOF 177) -based storage system at 250 bar and 100 K. Each storage technology is examined with several hydrogen production options and a variety of possible hydrogen delivery methods. Other variables, including hydrogen vehicle market penetration, are also examined. The 350 bar approach is relatively cost-effective and energy-efficient, but its volumetric efficiency is too low for it to be a practical vehicle storage system for the long term. The MOF 177 system requires liquid hydrogen refueling, which adds considerable cost, energy use, and GHG emissions while having lower volumetric efficiency than the CcH2 system. The other three storage technologies represent a set of trade-offs relative to their attractiveness. Only the CcH2 system meets the critical Department of Energy (DOE) 2015 volumetric efficiency target, and none meet the DOE’s ultimate volumetric efficiency target. For these three systems to achieve a 480-km (300-mi) range, they would require a volume of at least 105-175 L in a mid-size FCV.     

Development of hydrogen storage reactor using composite of metal hydride materials with ENG

Hydrogen is widely accepted as a promising energy carrier replacing fossil fuels. In this context hydrogen storage is one of the critical challenges in realizing hydrogen economy which relies on hydrogen as the commercial fuel. Due to very low volumetric energy density of pure hydrogen, it is highly compressed as a gas phase or liquified at extremely low temperature. However, chemically combined state in other materials has advantages in terms of storage conditions and associated safety concerns.The present study focuses on a development of a hydrogen storage applicable to special fuel cell (FC) mobilities such as forklift but not limited to. We adopts a solid-state storage method using metal hydride composite prepared by processing La_0.9Ce_0.1Ni₅ and extended natural graphite (ENG). The isothermal hydrogen absorption/desorption behavior of the composite is measured at 20–80 °C. The results suggest that around 10 bar is sufficient to store 1.2 wt% of hydrogen. A cylindrical reactor is manufactured and experiments are carried out with the fabricated hydrogen storage material by changing operation conditions. The results of satisfaction are obtained in terms of the amount of hydrogen storage (>83 standard liter) and the absorption time (~10 min) under relatively moderate conditions of temperature (~19 °C) and pressure (~11 bar).As for scaling-up, a reactor of 2.0 kWh is designed based on the experimental results. CFD analysis is performed based on the hottest operation conditions focusing on a cooling water flow. The flow pattern and the temperature distribution of the cooling water are expected to be adequate not deviating from the stable operating conditions. CFD would be further applied to optimize the incorporated modular reactors.     

Efficiencies of hydrogen storage systems onboard fuel cell vehicles

Energy efficiency, vehicle weight, driving range, and fuel economy are compared among fuel cell vehicles (FCV) with different types of fuel storage and battery-powered electric vehicles. Three options for onboard fuel storage are examined and compared in order to evaluate the most energy efficient option of storing fuel in fuel cell vehicles: compressed hydrogen gas storage, metal hydride storage, and onboard reformer of methanol. Solar energy is considered the primary source for fair comparison of efficiencies for true zero emission vehicles. Component efficiencies are from the literature. The battery powered electric vehicle has the highest efficiency of conversion from solar energy for a driving range of 300 miles. Among the fuel cell vehicles, the most efficient is the vehicle with onboard compressed hydrogen storage. The compressed gas FCV is also the leader in four other categories: vehicle weight for a given range, driving range for a given weight, efficiency starting with fossil fuels, and miles per gallon equivalent (about equal to a hybrid electric) on urban and highway driving cycles.     

Design of a hydrogen community

This paper discusses the conceptual design of a scalable and reproducible hydrogen fueling station at Santa Monica, California. Hydrogen production using renewable energy sources such as biogas, which accounts for 100% of the total production, has been discussed. The fueling station consists of a direct fuel cell (DFC) 300 fuel cell for on-site generation of 136 kg/day of hydrogen and 300 kW of electric power, five hydrogen storage tanks (storage capacity of 198 kg of H₂ at 350 and 700 bar), four compressors which assist in dispensing 400 kg of hydrogen in 14 h, two hydrogen dispensers operating at 350 bar and 700 bar independently and a SAE J2600 compliant hydrogen nozzle. Potential early market customers for hydrogen fuel cells and their daily fuel requirements have been computed. The safety codes, potential failure modes and the methods to mitigate risks have been explained. A well-to-wheel analysis is performed to compare the emissions and the total energy requirements of conventional gasoline and fuel cell vehicles.