A solar-powered,high-efficiency hydrogen fueling system using high-pressure electrolysis of water: Design and initial results

Hydrogen for fuel-cell electric vehicles (FCEVs) was produced using clean, renewable solar energy to electrolyze water. This report describes the design, construction, and initial performance testing of a solar hydrogen fueler at the GM Proving Ground in Milford, MI. The system used high-efficiency photovoltaic (PV) modules, a high-pressure (6500 psi, 44.8 MPa) electrolyzer, and an optimized direct connection between the PV and electrolyzer systems. This resulted in world-class solar to hydrogen efficiencies as high as 9.3% (based on H₂ lower heating value, LHV). The system could potentially supply approximately 0.5 kg of hydrogen per day from solar power for the average solar insolation in Detroit; more hydrogen would be produced in locations with more abundant sunshine. This is sufficient hydrogen to operate an FCEV for an average daily urban commute. Thus, the solar hydrogen fueler testing served as a “proof of concept” for clean, renewable hydrogen with potential applications including convenient, clean, quiet, small-scale home fueling of FCEVs (that can contribute to the growth of a future FCEV fleet) and fueling in remote locations where grid electricity is not available.     

Development of Korean hydrogen fueling station codes through risk analysis

When hydrogen fueling stations were constructed first time in Korea in 2006, there were no standards for hydrogen fueling stations. Hence the CNG (Compressed Natural Gas) station codes were temporarily adopted. In last three years, from 2006 to 2009, the studies for the development of hydrogen fueling station standards were carried out, with the support of the Korean government. In this study, three research groups cooperated to develop optimized hydrogen fueling station codes through risk analysis of hydrogen production and filling systems. Its results were integrated to develop the codes. In the first step to develop the codes, the standards for CNG stations and hydrogen fueling station were compared with each other and analyzed. By referring to foreign hydrogen fueling station standards, we investigated the potential problems in developing hydrogen fueling station codes based on the CNG station standards. In the second, the results of the high-pressure hydrogen leakage experiment were analyzed, and a numerical analysis was performed to establish the safety distance from the main facilities of a hydrogen fueling station to the protection facilities. In the third, HAZOP (Hazard and Operability) and FTA (Fault Tree Analysis) safety assessments were carried out for the on-site and off-site hydrogen fueling stations—currently being operated in Korea— to analyze the risks in existing hydrogen fueling stations. Based on the study results of the above three groups, we developed one codes for off-site type hydrogen fueling stations and another codes for on-site type hydrogen fueling stations. These were applied from September 2010.     

Risk assessment for liquid hydrogen fueling stations

In recent years, consumers calling for the protection of the environment on a regional and global scale are demanding the use of vehicles that do not emit harmful exhaust. It is anticipated that one response to this demand is the widespread use of fuel cell vehicles (FCVs). In order to achieve this, it is necessary to provide hydrogen fueling stations where FCVs can refuel.     

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.     

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.     

Security risk analysis of a hydrogen fueling station with an on-site hydrogen production system involving methylcyclohexane

Although many studies have looked at safety issues relating to hydrogen fueling stations, few studies have analyzed the security risks, such as deliberate attack of the station by threats such as terrorists and disgruntled employees. The purpose of this study is to analyze security risks for a hydrogen fueling station with an on-site production of hydrogen from methylcyclohexane. We qualitatively conducted a security risk analysis using American Petroleum Institute Standard 780 as a reference for the analysis. The analysis identified 93 scenarios, including pool fires. We quantitatively simulated a pool fire scenario unique to the station to analyze attack consequences. Based on the analysis and the simulation, we recommend countermeasures to prevent and mitigate deliberate attacks.     

Assessment of hydrogen supply solutions for hydrogen fueling station: A Shanghai case study

Shanghai is one of the fastest growing regions of hydrogen energy in China. This paper researched feasible hydrogen sources in both internal and external Shanghai. This study comes up 9 hydrogen production methods and 6 transportation routes, ultimately forms 12 hydrogen supply solutions according to local conditions. The total cost in each solution is estimated including processes of hydrogen production, treatments, storage and transportation based on different transport distance. The results indicate that hydrogen supply cost is above 50 CNY/kgH₂ for external hydrogen sources after long-distance transportation to Shanghai, such as hydrogen production from coal in Inner Mongolia and from renewables in Hebei. The total cost of on-site hydrogen production from natural gas can be controlled under 40 CNY/kgH₂. When the price of wind power reduces to 0.5 CNY/kWh, hydrogen production from offshore wind power cooperating with hydrogen pipeline network has the greatest development potential for Shanghai hydrogen supply.     

Licensing a fuel cell bus and a hydrogen fueling station in Brazil

The Brazilian Fuel Cell Bus Project is being developed by a consortium comprising 14 national and international partners. The project was initially supported by the GEF/UNDP and MME/FINEP Brazil. The national coordination is under responsibility of MME and EMTU/SP, the São Paulo Metropolitan Urban Transport Company that also controls the bus operation and bus routes. This work reports the efforts done in order to obtain the necessary licenses to operate the first fuel cell buses for regular service in Brazil, as well as the first commercial hydrogen fueling station to attend the vehicles.     

Dynamic simulation of the effect of vehicle-side pressure loss of hydrogen fueling process

This study explains the fundamental mathematical equations used for the main component models that are implemented in freely available library for hydrogen fueling station. The paper provides a background to the model formulation and theory, useful for the further investigations of hydrogen fueling stations. The model was verified against a specific manufacturer model, and it was validated by using test data from an actual fueling station. The study works as documentation and validation of the model formulation. The simulation library is used to make a model for investigating how the pressure loss in the vehicle affects the fueling process. Keeping the temperature out of the station constant and fueling to 80 MPa in the compressed hydrogen storage system, the pressure loss in the compressed hydrogen storage system directly correlates to the final temperature. The final temperature increases with increasing pressure losses. It is also shown that with no pressure loss in the vehicle the fueling has no limit in fueling speed as the heat of compression depends on the mass filled and the enthalpy of the mass, and not the filling time.     

PV powered smart charging station for PHEVs

A huge inrush of PHEVs is envisioned in the future. There is a growing risk that, this proliferation in the number of PHEVs will trigger extreme surges in demand while charging them during rush hours. To mitigate this impact, a smart charging station is proposed in which the charging of the PHEVs is controlled in such a way that the impact of charging during peak load period is not felt on the grid. The power needed to charge the plug in hybrids comes from grid-connected photovoltaic generation or the utility or both. The three way interaction between the PV, PHEVs and the grid ensures optimal usage of available power, charging time and grid stability. The system designed to achieve the desired objective consists of a photovoltaic system, DC/DC boost converter, DC/AC bi-directional converter and DC/DC buck converter. The output of DC/DC boost converter and input of DC/AC bi-directional converter share a common DC link. A unique control strategy based on DC link voltage sensing is proposed for the above system for efficient transfer of energy.     

Predicting efficiency of solar powered hydrogen generation using photovoltaic-electrolysis devices

Hydrogen fuel for fuel cell vehicles can be produced by using solar electric energy from photovoltaic (PV) modules for the electrolysis of water without emitting carbon dioxide or requiring fossil fuels. In the past, this renewable means of hydrogen production has suffered from low efficiency (2–6%), which increased the area of the PV array required and therefore, the cost of generating hydrogen. A comprehensive mathematical model was developed that can predict the efficiency of a PV-electrolyzer combination based on operating parameters including voltage, current, temperature, and gas output pressure. This model has been used to design optimized PV-electrolyzer systems with maximum solar energy to hydrogen efficiency. In this research, the electrical efficiency of the PV-electrolysis system was increased by matching the maximum power output and voltage of the photovoltaics to the operating voltage of a proton exchange membrane (PEM) electrolyzer, and optimizing the effects of electrolyzer operating current, and temperature. The operating temperature of the PV modules was also an important factor studied in this research to increase efficiency. The optimized PV-electrolysis system increased the hydrogen generation efficiency to 12.4% for a solar powered PV-PEM electrolyzer that could supply enough hydrogen to operate a fuel cell vehicle.     

Compact fluorescent lighting and residential natural gas consumption: Testing for interactive effects

Replacing incandescent light bulbs with compact fluorescents (CFLs) has traditionally been seen as a cost effective means of promoting energy conservation. Recently, however, the magnitude of energy savings associated with CFLs has been called into question. Specifically, recent findings suggest an “interactive effect” associated with the replacement of incandescent light bulbs with CFLs in the residential sector. In this scenario, the reduced wattage of CFLs, relative to incandescent bulbs, generates less heat, which in turn, requires additional natural gas usage during the heating season. Engineering studies suggest the magnitude of the effect is significant in energy terms, which implies that the energy savings associated with CFLs may be significantly overstated. In this paper, we use billing analysis to test for the presence of interactive effects. Our analysis is based on a comprehensive dataset that includes monthly household electricity and natural gas usage, the number of CFL bulbs installed, the installation date, and a set of household characteristics. Our results suggest that CFLs do indeed save electricity. However, we do not find any support for the hypothesis that CFLs cause increased usage of natural gas.     

The public's acceptance toward building a hydrogen fueling station near their residences: The case of South Korea

South Korea is pushing for advancing the emergence of the hydrogen economy in order to reduce greenhouse gas emissions and promote economic growth. In this regard, a significant expansion of hydrogen charging stations is scheduled, but one of the biggest obstacles to this is the public acceptance of building a hydrogen fueling station near their residences. This article collected the data on the public acceptance toward building a hydrogen fueling station on a nine-point scale from a survey of 1000 people across the country, and analyzed the factors affecting public acceptance employing the ordered probit model. The respondents' approval rate for building a hydrogen fueling station near their residences (48.0%) was slightly higher than twice the opposition rate (23.0%). However, the sum of opposition (23.0%) and neutrality or indifference (29.0%) exceeded half of the total respondents, suggesting that the government's additional efforts were needed to improve acceptance. While some factors positively influenced the public acceptance, others affected it negatively. The various implications that can be obtained from these findings for building hydrogen fueling stations are discussed.     

Predicting demand for hydrogen station fueling

Full function hydrogen stations are a reality; fuel cell electric vehicle drivers can pull up to commercial fueling stations and receive 3–5 kg in less than 5 min, for an approximately 300-mile range. The demand for hydrogen is increasing, driven by an increase in the fueling of public and private fuel cell vehicles. This study describes the development and value of a model that simulates stochastic future demand at a hydrogen filling station. The predictive hydrogen demand model described in this article is trained from mathematical models constructed from actual hydrogen fill count, amount, and frequency data. Future fill probabilities inform the hour-by-hour demand profile and the station state of either “available, ready to fill” or “available, filling”. For example, a prediction for a station generally dispensing 5,000 kg a week on a Friday afternoon at 4 p.m. is 16 fills, totaling 48.7 kg, with a 0.52 proportion of time spent in “available, filling” state yielding 31 min of filling time. This is a first-of-its kind, published study on predicting future hydrogen demand by the time of day (e.g., hour-by-hour intervals) and day of week. This study can be used for hydrogen station requirements and operation and maintenance strategies and to assess the impact of demand variations and scenarios. This article presents the current status of hydrogen demand, the model development methods, a set of sample results. Discussion and conclusions concentrate on the value and use of the proposed model.     

Developing sustainable residential buildings in Saudi Arabia: A case study

This paper assesses the energy and water consumption practices of existing housing in Saudi Arabia, with the ultimate aim of establishing guidelines for delivering sustainable residential buildings in the near future. In order to achieve this aim the current status of a typical Saudi residence (i.e. an apartment complex) is investigated in terms of energy and water consumption using simulation software packages. The paper then examines the prospects for applying various measures to the typical Saudi residence to manage energy and water use more sustainably. This research identifies several design-related faults common to Saudi Arabian house design. These faults contribute to an inefficient use of energy and domestic water resources. Finally, the paper puts forward a set of recommendations and guidelines, design-related and otherwise, to enhance the sustainability of future Saudi residential buildings.     

Energy efficiency in New Zealand's residential sector: A systemic analysis

This paper examines the complexity arising from the multiple, time varying factors that impact energy efficiency in New Zealand's residential sector. Initial problem structuring involved the analysis of behaviour over time of main variables and incorporated stakeholder analysis using a systems approach. Further, a systems model of the problem situation was developed using a participative group model building process. The analysis of the model revealed a set of feedback loops operating in the system identified as responsible for the complexity of the problem situation relating to energy efficiency. The paper concludes by highlighting some of the main results relating to long-term structural changes suggested by the stakeholders involved in this study to change the behaviour of the system.     

A method of identifying and weighting indicators of energy efficiency assessment in Chinese residential buildings

This paper describes a method of identifying and weighting indicators for assessing the energy efficiency of residential buildings in China. A list of indicators of energy efficiency assessment in residential buildings in the hot summer and cold winter zone in China has been proposed, which supplies an important reference for policy makings in energy efficiency assessment in buildings. The research method applies a wide-ranging literature review and a questionnaire survey involving experts in the field. The group analytic hierarchy process (group AHP) has been used to weight the identified indicators. The size of survey samples are sufficient to support the results, which has been validated by consistency estimation. The proposed method could also be extended to develop the weighted indicators for other climate zones in China.     

An integrated system for ammonia production from renewable hydrogen: A case study

This study presents an analysis and assessment study of an integrated system which consists of cryogenic air separation unit, polymer electrolyte membrane electrolyzer and reactor to produce ammonia for a selected case study application in Istanbul, Turkey. A thermodynamic analysis of the proposed system illustrates that electricity consumption of PEM electrolyzer is 3410 kW while 585.4 kW heat is released from ammonia reactor. The maximum energy and exergy efficiencies of the ammonia production system which are observed at daily average irradiance of 200 W/m² are found as 26.08% and 30.17%, respectively. The parametric works are utilized to find out the impacts of inlet air conditions and solar radiation intensity on system performance. An increase in the solar radiation intensity results in a decrease of the efficiencies due to higher potential of solar influx. Moreover, the mass flow rate of inlet air has a substantial effect on ammonia production concerning the variation of generated nitrogen. The system has a capacity of 0.22 kg/s ammonia production which is synthesized by 0.04 kg/s H₂ from PEM electrolyzer and 0.18 kg/s N₂ from a cryogenic air separation unit. The highest exergy destruction rate belongs to PEM electrolyzer as 736.2 kW while the lowest destruction rate is calculated as 3.4 kW for the separation column.     

Experiment and simulation of electrolytic hydrogen production: Case study of photovoltaic-electrolyzer direct connection

Hydrogen as an energy currency, carrier and storage medium can contribute to solve the problem of intermittent availability of renewable energies. In this paper, we study the production of hydrogen by a proton exchange membrane (PEM) electrolyzer (WE) using photovoltaic energy (PV) as source of electricity. Experiments were performed to model and optimize the direct-coupling system. Mathematical and empirical models based on experiments were used to simulate the system. RMSE was about 2% for the PV and WE. Optimization of direct connection was carried out to improve the system efficiency. However, it was noticed that the simulation of the system does not fit well the experimental results. Nevertheless, the RMSE is about 7%. In this study, we emphasize the need to develop appropriate models for hydrogen production system that operates in direct connection mode.     

Renewable electrolytic hydrogen potential in Algeria

The present paper deals with the assessment of the renewable hydrogen production potential in Algeria. The studied system produces hydrogen by electrolysis of water; electricity is supplied by a photovoltaic generator. Adequate mathematical models were used to calculate the electrolytic hydrogen production. Detailed hourly simulations were used to assess the potential for the entire country and to draw it maps. Throughout this study, the influence of the tilt angle of a photovoltaic generator has been investigated. It has been observed that the tilt angle has an impact on solar energy received by the photovoltaic generator, the produced solar electrical power and the rate of hydrogen production. We have calculated the optimal angles to maximize each element. We were particularly interested in the optimal angle to maximize hydrogen production. We found that the solar hydrogen potential for Algeria varies from 0.10 Nm³/m²/d to 0.14 Nm³/m²/d. This potential is quite significant, especially in the arid region of southeastern Algeria. The lowest potential is located in the northeast region. For stand-alone systems, it is important to assess the minimum available level, as their sizing takes into account the most unfavorable case. This level is between 0.07 Nm³/m²/d and 0.13 Nm³/m²/d. This shows that, even for a stand-alone system, the potential is quite high. Finally, we provide robust correlations that allow calculating the potential and the angle of inclination maximizing it for the whole of Algeria.