The feasibility of using geothermal energy in hydrogen production

A feasibility study exploring the use of geothermal energy in hydrogen production is presented. It is possible to use a thermal energy to supply heat for high temperature electrolysis and thereby substitute a part of the relatively expensive electricity needed. A newly developed HOT ELLY high temperature steam electrolysis process operates at 800 – 1000°C. Geothermal fluid is used to heat fresh water up to 200°C steam. The steam is further heated to 900°C by utilising heat produced within the electrolyser. The electrical power of this process is reduced from 4.6 kWh per normalised cubic meter of hydrogen (kWh/Nm³ H₂) for conventional process to 3.2 kWh/Nm³ H₂ for the HOT ELLY process implying electrical energy reduction of 29.5%. The geothermal energy needed in the process is 0.5 kWh/Nm³ H₂. Price of geothermal energy is approximately 8–10% of electrical energy and therefore a substantial reduction of production cost of hydrogen can be achieved this way. It will be shown that using HOT ELLY process with geothermal steam at 200°C reduces the production cost by approximately 19%.     

Feasibility study for hydrogen production using hybrid solar power in Algeria

Hydrogen demand as a clean energy is one of the new energy challenges in the future. Being a very controlled technology, the water electrolysis is more efficient at high temperature level than at low one. This is because of the use of thermal energy which is less expensive than the use of electricity power to produce the hydrogen; the chemical reaction is more activated in these conditions. In this paper, the feasibility of hydrogen production at high temperature electrolyser, using a hybrid solar resource, thermal energy (parabolic trough concentrators) to produce high temperature, steam water and photovoltaic energy for electricity requirements of the HTE, is presented. The described here-after presented in this document guarantees the production of an important quantity of hydrogen at 900 °C. The production rate depends on geographic position, on climatic conditions and on sun radiation. The optimization of the process is strongly related to what preceded these three parameters. Then, we suggest the set up construction in any region allowing maximum extraction of energy based in our simulation results.     

Potential methods for geothermal-based hydrogen production

In this study, four potential methods are identified for geothermal-based hydrogen production, namely, (i) directly from the geothermal steam, (ii) through conventional water electrolysis using the electricity generated from geothermal power plant, (iii) using both geothermal heat and electricity for high temperature steam electrolysis and/or hybrid processes, (iv) using the heat available from geothermal resource in thermochemical processes to disassociate water into hydrogen and oxygen. Here we focus on relatively low-temperature thermochemical and hybrid cycles, due to their greater application possibility, and examine them as a potential option for hydrogen production using geothermal heat. We also present a brief thermodynamic analysis to assess their performance through energy and exergy efficiencies for comparison purposes. The results show that these cycles have good potential and become attractive due to the overall system efficiencies over 50%. The copper–chlorine cycle is identified as a highly promising cycle for geothermal hydrogen production. Furthermore, three types of industrial electrolysis methods, which are generally considered for hydrogen production currently, are also discussed and compared with the above mentioned cycles.     

Geothermal‐based hydrogen production using thermochemical and hybrid cycles: A review and analysis

Geothermal‐based hydrogen production, which basically uses geothermal energy for hydrogen production, appears to be an environmentally conscious and sustainable option for the countries with abundant geothermal energy resources. In this study, four potential methods are identified and proposed for geothermal‐based hydrogen production, namely: (i) direct production of hydrogen from the geothermal steam, (ii) through conventional water electrolysis using the electricity generated through geothermal power plant, (iii) by using both geothermal heat and electricity for high temperature steam electrolysis and/or hybrid processes, and (iv) by using the heat available from geothermal resource in thermochemical processes. Nowadays, most researches are focused on high‐temperature electrolysis and thermochemical processes. Here we essentially discuss some potential low‐temperature thermochemical and hybrid cycles for geothermal‐based hydrogen production, due to their wider practicality, and examine them as a sustainable option for hydrogen production using geothermal heat. We also assess their thermodynamic performance through energy and exergy efficiencies. The results show that these cycles have good potential and attractive overall system efficiencies over 50% based on a complete reaction approach. The copper‐chlorine cycle is identified as a highly promising cycle for geothermal‐hydrogen production. Copyright © 2009 John Wiley & Sons, Ltd.     

Efficient utilization of waste heat from molten carbonate fuel cell in parabolic trough power plant for electricity and hydrogen coproduction

Direct steam generating parabolic trough power plant is an important technology to match future electric energy demand. One of the problems related to its emergence is energy storage. Solar-to-hydrogen is a promising technology for solar energy storage. Electrolysis is among the most processes of hydrogen production recently investigated. High temperature steam electrolysis is a clean process to efficiently produce hydrogen. In this paper, steam electrolysis process using solar energy is used to produce hydrogen. A heat recovery steam generator generates high temperature steam thanks to the molten carbonate fuel cell's waste heat. The analytical study investigates the energy efficiency of solar power plant, molten carbonate fuel cell and electrolyser. The impact of waste heat utilization on electricity and hydrogen generation is analysed. The results of calculations done with MATLAB software show that fuel cell produces 7.73 MWth of thermal energy at design conditions. 73.37 tonnes of hydrogen and 14.26 GWh of electricity are yearly produced. The annual energy efficiency of electrolyser is 70% while the annual mean electric efficiency of solar power plant is 18.30%.The proposed configuration based on the yearly electricity production and hydrogen generation has presented a good performance.     

Hydrogen production through steam electrolysis: Model-based dynamic behaviour of a cathode-supported intermediate temperature solid oxide electrolysis cell

Hydrogen production via steam electrolysis may involve less electrical energy consumption than conventional low temperature water electrolysis, reflecting the favourable thermodynamics and kinetics at elevated temperatures. In the present paper, a one-dimensional model of a cathode-supported planar intermediate temperature solid oxide electrolysis cell (SOEC) stack is employed to study the dynamic behaviour of such an electrolyser. The simulations found that step changes in the average current density cause the stack temperature to alter during both exothermic and endothermic operation. However, the temperature control, by the variation of the air flow through the stack, was predicted to be capable of returning the stack temperature to the initial value. Furthermore, the proposed control strategy is observed to reduce the interim temperature excursions between the initial and final steady states, suggesting that such a control strategy has a good potential to prevent the issues of cell component fracture, and transitions in stack operating mode, which are related to the temperature fluctuations during dynamic operation of an SOEC stack.     

Hybrid systems to address seasonal mismatches between electricity production and demand in nuclear renewable electrical grids

A strategy to enable zero-carbon variable electricity production with full utilization of renewable and nuclear energy sources has been developed. Wind and solar systems send electricity to the grid. Nuclear plants operate at full capacity with variable steam to turbines to match electricity demand with production (renewables and nuclear). Excess steam at times of low electricity prices and electricity demand go to hybrid fuel production and storage systems. The characteristic of these hybrid technologies is that the economic penalties for variable nuclear steam inputs are small. Three hybrid systems were identified that could be deployed at the required scale. The first option is the gigawatt-year hourly-to-seasonal heat storage system where excess steam from the nuclear plant is used to heat rock a kilometer underground to create an artificial geothermal heat source. The heat source produces electricity on demand using geothermal technology. The second option uses steam from the nuclear plant and electricity from the grid with high-temperature electrolysis (HTR) cells to produce hydrogen and oxygen. Hydrogen is primarily for industrial applications; however, the HTE can be operated in reverse using hydrogen for peak electricity production. The third option uses variable steam and electricity for shale oil production.     

Model development and analysis of a novel high-temperature electrolyser for gas phase electrolysis of hydrogen chloride for hydrogen production

In this study, a high temperature electrolyser for the gas phase electrolysis of hydrogen chloride for hydrogen production is proposed and assessed. A detailed electrochemical model is developed to study the J-E characteristics for the proposed electrolyser (a solid oxide electrolyser based on a proton conducting electrolyte). The developed model accounts for all major losses, namely activation, concentration and ohmic. Energy and exergy analyses are carried out, and the energy and exergy efficiencies of the proposed electrolyser are determined to be 41.1% and 39.0%, respectively. The simulation results show that at T = 1073 K, P = 100.325 kPa and J = 1000 A/m², 1.6 V is required to produce 1 mol of hydrogen. This is approximately 0.3 V less than the voltage required by a high temperature steam electrolyser (based on a proton conducting electrolyte) operating at same condition (T = 1073 K, P = 101.325 kPa and J = 1000 A/m²), suggesting that the proposed electrolyser offers a new option for high temperature electrolysis for hydrogen production, potentially with a low electrical energy requirement. The proposed electrolyser may be incorporated into thermochemical cycles for hydrogen production, like CuCl or chlorine cycles.     

Prospects for solar only operation of the hybrid sulphur cycle for hydrogen production

The hybrid sulphur process is one of the most promising thermochemical water splitting cycles for large scale hydrogen production. While the process includes an electrolysis step, the use of sulphur dioxide in the electrolyser significantly reduces the electrical demand compared to conventional alkaline electrolysis. Solar operation of the cycle with zero emissions is possible if the electricity for the electrolyser and the high temperature thermal energy to complete the cycle are provided by solar technologies.This paper explores the possible use of photovoltaics (PV) to supply the electrical demand and examines a number of configurations. Production costs are determined for several scenarios and compared with base cases using conventional technologies. The hybrid sulphur cycle has promise in the medium term as a viable zero carbon production process if PV power is used to supply the electrolyser. However, the viability of this process is dependent on a market for hydrogen and a significant reduction in PV costs to around $1/W_p.     

Performance evaluation of a solarized gas turbine system integrated to a high temperature electrolyzer for hydrogen production

In this paper, the performance of a solar gas turbine (SGT) system integrated to a high temperature electrolyzer (HTE) to generate hybrid electrical power and hydrogen fuel is analyzed. The idea behind this design is to mitigate the losses in the electrical power transmission and use the enthalpy of exhaust gases released from the gas turbine (GT) to make steam for the HTE. In this context, a GT system is coupled with a solar tower including heliostat solar field and central receiver to generate electrical power. To make steam for the HTE, a flameless boiler is integrated to the SGT system applying the SGT extremely high temperature exhaust gases as the oxidizer. The results indicate that by increasing the solar receiver outlet temperature from 800 K to 1300 K, the solar share increases from 22.1% to 42.38% and the overall fuel consumption of the plant reduces from 7 kg/s to 2.7 kg/s. Furthermore, flameless mode is achievable in the boiler while the turbine inlet temperature (TIT) is maintained at the temperatures higher than 1314 K. Using constant amounts of the SGT electrical power, the HTE voltage decreases by enhancing the HTE steam temperature which result in the augmentation of the overall hydrogen production. To increase the HTE steam temperature from 950 K to 1350 K, the rate of fuel consumption in the flameless boiler increases from 0.1 m/s to 0.8 m/s; however, since the HTE hydrogen production increases from 4.24 mol/s to 16 mol/s it can be interpreted that the higher steam temperatures would be affordable. The presented hybrid system in this paper can be employed to perform more thermochemical analyses to achieve insightful understanding of the hybrid electrical power-hydrogen production systems.     

Life cycle assessment of H2 generation with high temperature electrolysis

Water electrolysis is a well-established process for hydrogen production but requires efficiency improvements to reduce costs. High temperature electrolysis (HTE) as a means to higher efficiency was advanced in the EU project RelHY. Through Life Cycle Assessment (LCA), also the environmental performance of five HTE-based hydrogen production systems was evaluated: operation with power and steam from a nuclear plant, continuous and intermittent operation with wind power and water, intermittent operation with natural gas or biogas reforming as back-up. Large scale natural gas reforming (NGR) was used as a reference. The LCA aims to identifying environmental hotspots of HTE plants and comparing their operation. The results show that stack manufacturing has the strongest impact during construction of the HTE plant while the impacts during H₂ production are largely due to power supply. All HTE variants studied lead to less life cycle CO₂-equivalent emissions than NGR. However, only the wind powered HTE variants without back-up use less energy than NGR. The other impacts and flows show different patterns. The results and limitations of the study are discussed.     

Classification of Geothermal Energy Resources in Japan Applying Exergy Concept

Higher demand for energy consumption and importance of environmental issues has encouraged researchers and policy makers to consider renewable energies more seriously. Geothermal resources are a green energy source that can make a considerable contribution in some countries. Japan has the third ranking geothermal energy potential, and its geothermal electricity production is currently eighth in the world. Since the nature of geothermal resources dictates its method of utilization, it is important to categorize available resources. There is no consensus on classification of geothermal resources. Most scientists, from geologist to engineers, agree on the term temperature. However, temperature or enthalpy alone cannot describe the nature of fluids; they can have same temperature with different phases, such as saturated water or saturated steam. Using exergy for resource classification benefits their comparison, according to their ability to do work. In this paper, exergetic classification of geothermal resources was applied to 18 under‐operating geothermal power plants in Japan. Six geothermal fields have high exergy resources according to their SExI values in excess of 0.5. The remaining geothermal fields in Japan are classified in the medium resources zone. Classification results can be used by decision makers as a reference for future geothermal development. Copyright © 2012 John Wiley & Sons, Ltd.     

High-temperature steam electrolysis: Technical and economic evaluation of alternative process designs

A high-temperature water-vapor electrolysis (HTE) unit operating at an average temperature of 1000°C was integrated into a preliminary process design using electrical and thermal energy derived from coal. Process variations with either steam or water feeds under isothermal or nonisothermal HTE operation were considered. Operating and capital costs were estimated for each process flowsheet, with the lowest costs being obtained for operation with high steam conversions in the electrolyzer. Estimated H₂ production costs were compared with estimates obtained from the literature for other H₂ production processes. The estimated HTE H₂ production costs ranged from $0.17 to $0.22 standard m⁻³ H₂ produced ($13–17 GJ⁻¹, using the higher heating value), assuming $1.90 GJ⁻¹ for thermal energy and $13.90 GJ⁻¹ for electrical energy.     

Configuration design and performance optimum analysis of a solar-driven high temperature steam electrolysis system for hydrogen production

A new solar-driven high temperature steam electrolysis system for hydrogen production is presented, in which the main energy consumption processes such as steam electrolysis processes, heat transfer processes, and product compression processes are included. The detailed thermodynamic-electrochemical modeling of the solid oxide steam electrolysis (SOSE) is carried out, and consequently, the electrical and thermal energy required by every energy consumption process are determined. The efficiency of the system is derived, from which the effects of some of the important parameters such as the operating temperature, component thickness of the SOSE, leakage resistance, effectiveness of heat exchangers, and inlet rate of water on the performance of the system are discussed. It is found that the efficiency attains its maximum when a proper current density is chosen. The ratio of the required electric energy to the total energy input of the system is calculated, and consequently, the problem how to rationally operate the solar concentrating beam splitting device is investigated. The results obtained will be helpful for further understanding the optimal design and performance improvement of a practical solar-driven high temperature steam electrolysis system for hydrogen production.     

Hydrogen electrolyser technologies and their modelling for sustainable energy production: A comprehensive review and suggestions

The advancement of hydrogen technology is driven by factors such as climate change, population growth, and the depletion of fossil fuels. Rather than focusing on the controversy surrounding the environmental friendliness of hydrogen production, the primary goal of the hydrogen economy is to introduce hydrogen as an energy carrier alongside electricity. Water electrolysis is currently gaining popularity because of the rising demand for environmentally friendly hydrogen production. Water electrolysis provides a sustainable, eco-friendly, and high-purity technique to produce hydrogen. Hydrogen and oxygen produced by water electrolysis can be used directly for fuel cells and industrial purposes. The review is urgently needed to provide a comprehensive analysis of the current state of water electrolysis technology and its modelling using renewable energy sources. While individual methods have been well documented, there has not been a thorough investigation of these technologies. With the rising demand for environmentally friendly hydrogen production, the review will provide insights into the challenges and issues with electrolysis techniques, capital cost, water consumption, rare material utilization, electrolysis efficiency, environmental impact, and storage and security implications. The objective is to identify current control methods for efficiency improvement that can reduce costs, ensure demand, increase lifetime, and improve performance in a low-carbon energy system that can contribute to the provision of power, heat, industry, transportation, and energy storage. Issues and challenges with electrolysis techniques, capital cost, water consumption, rare material utilization, electrolysis efficiency, environmental impact, and storage and security implications have been discussed and analysed. The primary objective is to explicitly outline the present state of electrolysis technology and to provide a critical analysis of the modelling research that had been published in recent literatures. The outcome that emerges is one of qualified promise: hydrogen is well-established in particular areas, such as forklifts, and broader applications are imminent. This evaluation will bring more research improvements and a road map to aid in the commercialization of the water electrolyser for hydrogen production. All the insights revealed in this study will hopefully result in enhanced efforts in the direction of the development of advanced hydrogen electrolyser technologies towards clean, sustainable, and green energy.     

Thermodynamic assessment of geothermal energy use in hydrogen production

In this study, geothermal-based hydrogen production methods, and their technologies and application possibilities are discussed in detail. A high-temperature electrolysis (HTE) process coupled with and powered by a geothermal source is considered for a case study, and its thermodynamic analysis through energy and exergy is conducted for performance evaluation purposes. In this regard, overall energy and exergy efficiencies of the geothermal-based hydrogen production process for this HTE are found to be 87% and 86%, respectively.     

Hydrogen production by coupling pressurized high temperature electrolyser with solar tower technology

Solar hydrogen production by coupling of pressurized high temperature electrolyser with concentrated solar tower technology is studied. As the high temperature electrolyser requires constant temperature conditions, the focus is made on a molten salt solar tower due to its high storage capacity. A flowsheet was developed and simulations were carried out with Aspen Plus 8.4 software for MW-scale hydrogen production plants. The solar part was laid out with HFLCAL software. Two different scenarios were considered: the first concerns the production of 400 kg/d hydrogen corresponding to mobility use (fuel station). The second scenario deals with the production of 4000 kg/d hydrogen for industrial use. The process was analyzed from a thermodynamic point of view by calculating the overall process efficiency and determining the annual production. It was assumed that a fixed hydrogen demand exists in the two cases and it was assessed to which extent this can be supplied by the solar high temperature electrolysis process including thermal storage as well as hydrogen storage. For time periods with a potential over supply of hydrogen, it was considered that the excess energy is sold as electricity to the grid. For time periods where the hydrogen demand cannot be fully supplied, electricity consumption from the grid was considered. It was assessed which solar multiple is appropriate to achieve low consumption of grid electricity and low excess energy. It is shown that the consumption of grid electricity is reduced for increasing solar multiple but the efficiency is also reduced. At a solar multiple of 3.0 an annual solar-to-H₂ efficiency greater than 14% is achieved at grid electricity production below 5% for the industrial case (4000 kg/d). In a sensitivity study the paramount importance of electrolyser performance, i.e. efficiency and conversion, is shown.     

Economics of hydrogen production and liquefaction by geothermal energy

Seven models are considered for the production and liquefaction of hydrogen by geothermal energy. In these models, we use electrolysis and high-temperature steam electrolysis processes for hydrogen production, a binary power plant for geothermal power production, and a pre-cooled Linde–Hampson cycle for hydrogen liquefaction. Also, an absorption cooling system is used for the pre-cooling of hydrogen before the liquefaction process. A methodology is developed for the economic analysis of the models. It is estimated that the cost of hydrogen production and liquefaction ranges between 0.979 $/kg H₂ and 2.615 $/kg H₂ depending on the model. The effect of geothermal water temperature on the cost of hydrogen production and liquefaction is investigated. The results show that the cost of hydrogen production and liquefaction decreases as the geothermal water temperature increases. Also, capital costs for the models involving hydrogen liquefaction are greater than those for the models involving hydrogen production only.     

High temperature water electrolysis in solid oxide cells

Hydrogen production via high temperature steam electrolysis is a promising technology as it involves less electrical energy consumption compared to conventional low temperature water electrolysis, as consequence of the more favourable thermodynamic and electrochemical kinetic conditions for the reaction. This paper reports on the Solid Oxide Electrolyser Cell (SOEC) performance as function of the operating parameters temperature, humidity and current density. Current–voltage measurements are coupled with impedance spectroscopy, in order to identify the different loss terms in the cell behaviour coming from the electrolyte resistance and the electrode processes. Remarkably high electrical-to-hydrogen energy conversion efficiencies are achieved (e.g., cell voltages of 1.0 and 1.25 V at −1 A cm⁻² and 900 and 800 °C, respectively). Results obtained, moreover, show that an important limitation for the electrolysis reaction, at least at moderate absolute humidity values below about 70 vol.% can be the steam diffusion in the hydrogen/steam electrode.     

A comprehensive review on power-to-gas with hydrogen options for cleaner applications

This review presents the power-to-gas concept, particularly with hydrogen, from renewable energy sources to end-use applications in various sectors, ranging from transportation to natural gas distribution networks. The paper includes an overview of the leading related studies for comparative evaluation. Due to the intermittent/fluctuating phenomena of most renewables, power-to-hydrogen appears to be a promising option to offset any mismatch between demand and supply. It is a novel concept to increase the renewability of fuels and reach a sustainable energy system for future transportation, power and thermal process sectors. Comparisons of different hydrogen production methods fed by several energy sources are made regarding environmental impact, cost and efficiency. The present results show that hydrogen production (with power-to-hydrogen concept) via polymer electrolyte membrane electrolyser has lower environmental effects than other traditional methods, such as coal gasification and reforming and steam methane reforming. The geothermal energy-based system has the lowest levelized cost of electricity during hydrogen production, while natural gas has the highest value. The best option for the plant efficiency is found for high-temperature steam electrolysis fed from biogas, while the lowest efficiency value belongs to polymer electrolyte membrane electrolyser driven by solar photovoltaics, respectively.