An assessment of large-scale solar hydrogen production in Canada

This study presents an assessment on the hydrogen production using a central receiver system coupled to either an electrolyser plant or a thermochemical plant. Systems which are capable of producing 10⁵ and 10⁶ GJ per year thermal energy or about half of this as hydrogen were developed at four locations in Canada: Fort McMurray, London, Moncton and Victoria. For central receiver systems of 10⁵ and 10⁶ GJ per year thermal energy capacity, heliostat fields arranged to the north of the receiver and tower were developed. A code consisting of optical and thermodynamic performance models was developed to simulate the system. For chemical plants, both electrolysis and thermochemical, codes were developed to simulate their thermodynamic performances. Cost models were developed for each subsystem based on the data published in the literature. Two scenarios were used for the heliostat prices: the first with a limited time and production capacity and the second with a quasi-optimized production capacity and production time. Estimates for the costs of hydrogen were then developed. The results indicated that levelized thermal energy costs ranged from $ 17 to $ 55 per GJ, electricity costs ranged from $ 0.2 to $ 0.5 per kWh and hydrogen costs from $ 57 to $ 157 per GJ.     

A critical review on integrated system design of solar thermochemical water-splitting cycle for hydrogen production

The development of clean hydrogen production methods is important for large-scale hydrogen production applications. The solar thermochemical water-splitting cycle is a promising method that uses the heat provided by solar collectors for clean, efficient, and large-scale hydrogen production. This review summarizes state-of-the-art concentrated solar thermal, thermal storage, and thermochemical water-splitting cycle technologies that can be used for system integration from the perspective of integrated design. Possible schemes for combining these three technologies are also presented. The key issues of the solar copper-chlorine (Cu–Cl) and sulfur-iodine (S–I) cycles, which are the most-studied cycles, have been summarized from system composition, operation strategy, thermal and economic performance, and multi-scenario applications. Moreover, existing design ideas, schemes, and performances of solar thermochemical water-splitting cycles are summarized. The energy efficiency of the solar thermochemical water-splitting cycle is 15–30%. The costs of the solar Cu–Cl and S–I hydrogen production systems are 1.63–9.47 $/kg H₂ and 5.41–10.40 $/kg H₂, respectively. This work also discusses the future challenges for system integration and offers an essential reference and guidance for building a clean, efficient, and large-scale hydrogen production system.     

Hydrogen production from solar energy

Three alternatives for hydrogen production from solar energy have been analyzed on both efficiency and economic grounds. The analysis shows that the alternative using solar energy followed by thermochemical decomposition of water to produce hydrogen is the optimum one. The other schemes considered were the direct conversion of solar energy to electricity by silicon cells and water electrolysis, and the use of solar energy to power a vapor cycle followed by electrical generation and electrolysis. The capital cost of hydrogen via the thermochemical alternative was estimated at $575/kW of hydrogen output or $3·15/million Btu. Although this cost appears high when compared with hydrogen from other primary energy sources or from fossil fuel, environmental and social costs which favor solar energy may prove this scheme feasible in the future.     

Solar hydrogen production by hybrid thermochemical processes

In this study, a solar chemical process has been conceived and evaluated. The process is based on the sulfur family cycles in which the thermochemical decomposition of sulfuric acid at high temperature is a common reaction in various processes. The decomposition of sulfuric acid using oxygen as a vector was studied earlier in conjunction with nuclear hydrogen production. In the present study, the process is adapted to couple with a high temperature solar heat source and the problem of intermittent operation has been solved. An assessment is presented on hydrogen production using a dedicated central receiver solar system coupled to the chemical process and the Mark 11 cycle. For 10⁶ GJ per year solar plant, it is found that the overall efficiency of solar hydrogen production is about 38% and the solar hydrogen cost is from 15 to 70$/GJ hydrogen depending on the cost parameters.     

An assessment on hydrogen production using central receiver solar systems

An assessment is presented on hydrogen production using a dedicated central receiver solar system concept coupled to two types of hydrogen producing processes, electrolysis and thermochemical. The study on solar electrolytic hydrogen was carried out using solar electricity and four different electrolytic technologies, namely industrial unipolar 1980 and 1983 technologies, industrial bipolar and solid polymer electrolyte technology. The thermochemical process was the sulphur/iodine cycle which is being developed by General Atomic Co. Systems which is capable of producing about 10⁶ GJ hydrogen per year were developed at the conceptual level and site specific computations were carried out. A general mathematical model was developed to predict the optical and thermal performance of the central receiver system coupled directly to the chemical plant. Cost models were developed for each sub-system based on the database published in the literature. Levelized and delevelized costs of solar hydrogen were then computed.     

An overview of hydrogen gas production from solar energy

Hydrogen production plays a very important role in the development of hydrogen economy.Hydrogen gas production through solar energy which is abundant, clean and renewable is one of the promising hydrogen production approaches. This article overviews the available technologies for hydrogen generation using solar energy as main source.Photochemical, electrochemical and thermochemical processes for producing hydrogen with solar energy are analyzed from a technological environmental and economical point of view. It is concluded that developments of improved processes for hydrogen production via solar resource are likely to continue in order to reach competitive hydrogen production costs. Hybrid thermochemical processes where hydrocarbons are exclusively used as chemical reactants for the production of syngas and the concentrated solar radiation is used as a heat source represent one of the most promising alternatives: they combine conventional and renewable energy representing a proper transition towards a solar hydrogen economy.     

Cost evaluation of two potential nuclear power plants for hydrogen production

Hydrogen is recognized as one of the most promising alternative fuels to meet the energy demand for the future by providing a carbon-free solution. In regards to hydrogen production, there has been increasing interest to develop, innovate and commercialize more efficient, effective and economic methods, systems and applications. Nuclear based hydrogen production options through electrolysis and thermochemical cycles appear to be potentially attractive and sustainable for the expanding hydrogen sector. In the current study, two potential nuclear power plants, which are planned to be built in Akkuyu and Sinop in Turkey, are evaluated for hydrogen production scenarios and cost aspects. These two plants will employ the pressurized water reactors with the electricity production capacities of 4800 MW (consisting of 4 units of 1200 MW) for Akkuyu nuclear power plant and 4480 MW (consisting of 4 units of 1120 MW) for Sinop nuclear power plant. Each of these plants are expected to cost about 20 billion US dollars. In the present study, these two plants are considered for hydrogen production and their cost evaluations by employing the special software entitled “Hydrogen Economic Evaluation Program (HEEP)” developed by International Atomic Energy Agency (IAEA) which includes numerous options for hydrogen generation, storage and transportation. The costs of capital, fuel, electricity, decommissioning and consumables are calculated and evaluated in detail for hydrogen generation, storage and transportation in Turkey. The results show that the amount of hydrogen cost varies from 3.18 $/kg H₂ to 6.17 $/kg H₂.     

Numerical modeling of a bayonet heat exchanger-based reactor for sulfuric acid decomposition in thermochemical hydrogen production processes

Sulfur-based thermochemical hydrogen production cycles represent one of the most appealing options to produce hydrogen from water on a large scale. The Hybrid Sulfur is one of the most advanced thermochemical cycles. The high temperature section of the process, common to all sulfur-based cycles, operates the sulfuric acid thermal decomposition reaction at temperatures on the order of 800 °C. The paper shows and discusses the modeling results obtained for a bayonet heat exchanger based high temperature reactor that decomposes the sulfur compounds into sulfur dioxide and oxygen. A detailed transport phenomena model, including suitable decomposition kinetics, has been set up using a finite volume numerical approach. A preliminary configuration of the reactor, established based on process simulation results and on the initial reactor prototype developed at Sandia National Laboratory, has been examined and simulated. Results, obtained for a reactor driven by thermal power provided by helium flow, demonstrate the effective decomposition performance at maximum temperatures on the order of 800 °C and pressures of 14 bar. For a laminar flow configuration a sulfur dioxide production yield of about 28 wt% (with sulfur trioxide reduction from 69 wt% to approximately 33 wt%) has been achieved, representing decomposition rates practically equal to the corresponding equilibrium values. Limited pressure drops of approximately 2500 Pa have also been achieved in the sulfur mixture region.     

Comparative assessment of hydrogen production methods from renewable and non-renewable sources

In this study, we present a comparative environmental impact assessment of possible hydrogen production methods from renewable and non-renewable sources with a special emphasis on their application in Turkey. It is aimed to study and compare the performances of hydrogen production methods and assess their economic, social and environmental impacts, The methods considered in this study are natural gas steam reforming, coal gasification, water electrolysis via wind and solar energies, biomass gasification, thermochemical water splitting with a Cu–Cl and S–I cycles, and high temperature electrolysis. Environmental impacts (global warming potential, GWP and acidification potential, AP), production costs, energy and exergy efficiencies of these eight methods are compared. Furthermore, the relationship between plant capacity and hydrogen production capital cost is studied. The social cost of carbon concept is used to present the relations between environmental impacts and economic factors. The results indicate that thermochemical water splitting with the Cu–Cl and S–I cycles become more environmentally benign than the other traditional methods in terms of emissions. The options with wind, solar and high temperature electrolysis also provide environmentally attractive results. Electrolysis methods are found to be least attractive when production costs are considered. Therefore, increasing the efficiencies and hence decreasing the costs of hydrogen production from solar and wind electrolysis bring them forefront as potential options. The energy and exergy efficiency comparison study indicates the advantages of biomass gasification over other methods. Overall rankings show that thermochemical Cu–Cl and S–I cycles are primarily promising candidates to produce hydrogen in an environmentally benign and cost-effective way.     

Efficient STEP (solar thermal electrochemical photo) production of hydrogen – an economic assessment

A consideration of the economic viability of hydrogen fuel production is important in the STEP (Solar Thermal Electrochemical Photo) production of hydrogen fuel. STEP is an innovative way to decrease costs and increase the efficiency of hydrogen fuel production, which is a synergistic process that can use concentrating photovoltaics (CPV) and solar thermal energy to drive a high temperature, low voltage, electrolysis (water-splitting), resulting in H₂ at decreased energy and higher solar efficiency. This study provides evidence that the STEP system is an economically viable solution for the production of hydrogen. STEP occurs at both higher electrolysis and solar conversion efficiencies than conventional room temperature photovoltaic (PV) generation of hydrogen. This paper probes the economic viability of this process, by comparing four different systems: (1) 10% or (2) 14% flat plate PV driven aqueous alkaline electrolysis H₂ production, (3) 25% CPV driven molten electrolysis H₂ production, and (4) 35% CPV driven solid oxide electrolysis H₂ production. The molten and solid oxide electrolysers are high temperature systems that can make use of light, normally discarded, for heating. This significantly increases system efficiency. Using levelized cost analysis, this study shows significant cost reduction using the STEP system. The total price per kg of hydrogen is shown to decrease from $5.74 to $4.96 to $3.01 to $2.61 with the four alternative systems. The advanced STEP plant requires less than one seventh of the land area of the 10% flat cell plant. To generate the 216 million kg H₂/year required by 1 million fuel cell vehicles, the 35% CPV driven solid oxide electrolysis requires a plant only 9.6 mi² in area. While PV and electrolysis components dominate the cost of conventional PV generated hydrogen, they do not dominate the cost of the STEP-generated hydrogen. The lower cost of STEP hydrogen is driven by residual distribution and gate costs.     

Prospects of solar thermal hydrogen production processes

This article provides a critical discussion of prospects of solar thermal hydrogen production in terms of technological and economic potentials and their possible role for a future hydrogen supply. The study focuses on solar driven steam methane reforming, thermochemical cycles, high temperature water electrolysis and solar methane cracking. Development status and technological challenges of the processes and objectives of ongoing research are described. Estimated hydrogen production costs are shown in comparison to other options. A summary of current discussions and today's scenarios of future use of hydrogen as an energy carrier and a brief overview on the development status of end-use technologies characterise uncertainties whether hydrogen could emerge as important energy carrier until 2050. Another focus is on industrial hydrogen demand in areas with high direct solar radiation which may be the main driver for the further development of solar thermal hydrogen production processes in the coming decades.     

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.     

Development of the once-through hybrid sulfur process for nuclear hydrogen production

The Once-through Hybrid Sulfur (Ot-HyS) process, proposed in this work, produces hydrogen using the same Sulfur dioxide Depolarized water Electrolysis (SDE) process found in the original Hybrid Sulfur cycle (HyS). In the process proposed here, the Sulfuric Acid Decomposition (SAD) process in the HyS procedure is replaced with the well-established sulfur combustion process. First, a flow sheet for the Ot-HyS process was developed by referring to existing facilities and to the work done by the Savannah River National Laboratory (SRNL) under their reasonable assumptions. The process was then simulated using Aspen Plus with appropriate thermodynamic models. It was demonstrated that the Ot-HyS process has higher net thermal efficiency, as well as other advantages, over competing benchmark processes. The net thermal efficiency of the Ot-HyS process is 47.1% (based on LHV) and 55.7% (based on HHV) assuming 33.3% thermal-to-electric conversion efficiency of a nuclear power plant with no consideration given to the work for the air separation. Hydrogen produced through the Ot-HyS process would be used as off-peak electricity storage, to relieve the burden of load-following and could help to expand applications of nuclear energy, which is regarded as a ’sustainable development’ technology.     

Analysis of solar chemical processes for hydrogen production from water splitting thermochemical cycles

This paper presents a process analysis of ZnO/Zn, Fe₃O₄/FeO and Fe₂O₃/Fe₃O₄ thermochemical cycles as potential high efficiency, large scale and environmentally attractive routes to produce hydrogen by concentrated solar energy. Mass and energy balances allowed estimation of the efficiency of solar thermal energy to hydrogen conversion for current process data, accounting for chemical conversion limitations. Then, the process was optimized by taking into account possible improvements in chemical conversion and heat recoveries. Coupling of the thermochemical process with a solar tower plant providing concentrated solar energy was considered to scale up the system. An economic assessment gave a hydrogen production cost of 7.98$ kg⁻¹ and 14.75$ kg⁻¹ of H₂ for, respectively a 55 MW_th and 11 MW_th solar tower plant operating 40 years.     

Kinetic investigations of the hydrogen production step of a thermochemical cycle using mixed iron oxides coated on ceramic substrates

A two‐step thermochemical cycle for solar hydrogen production using mixed iron oxides as the metal oxide redox system has been investigated. The ferrite is coated on a honeycomb structure, which serves as the absorber for solar irradiation and provides the surface for the chemical reaction. Coated honeycomb structures have already been tested in a solar receiver reactor in the solar furnace of DLR in Cologne with respect to their water splitting capability and their long‐term stability. The concept of this new reactor design has proven feasible and constant hydrogen production during repeated cycles has been shown. For a further optimization of the process and in order to gain reliable performance predictions more information about the process especially concerning the kinetics of the oxidation and the reduction step are essential. To examine the hydrogen production during the water splitting step a test rig has been built up on a laboratory scale. In this test rig small coated honeycombs are heated by an electric furnace. The honeycomb is placed inside a tube reactor and can be flushed with water vapour or with an inert gas. A homogeneous temperature within the sample is reached and testing conditions are reproducible. Through analysis of the product gas the hydrogen production is monitored and a reaction rate describing the hydrogen production rate per gram ferrite can be formulated. Using this test set‐up, SiC honeycombs coated with zinc ferrite have been tested. The influences of the temperature and the water concentration on the hydrogen production during the water splitting step have been investigated. An analysis of the ferrite conversion was performed using the Shrinking Core Model. A mathematical approach for the peak reaction rate at the beginning of the water splitting step was formulated and the activation energy was calculated from the experimental data. An activation energy of 110 kJ mol⁻¹ was found. Copyright © 2009 John Wiley & Sons, Ltd.     

Economic comparison of solar hydrogen generation by means of thermochemical cycles and electrolysis

Hydrogen is acclaimed to be an energy carrier of the future. Currently, it is mainly produced by fossil fuels, which release climate-changing emissions. Thermochemical cycles, represented here by the hybrid-sulfur cycle and a metal oxide based cycle, along with electrolysis of water are the most promising processes for ‘clean’ hydrogen mass production for the future. For this comparison study, both thermochemical cycles are operated by concentrated solar thermal power for multistage water splitting. The electricity required for the electrolysis is produced by a parabolic trough power plant. For each process investment, operating and hydrogen production costs were calculated on a 50 MW_th scale. The goal is to point out the potential of sustainable hydrogen production using solar energy and thermochemical cycles compared to commercial electrolysis. A sensitivity analysis was carried out for three different cost scenarios. As a result, hydrogen production costs ranging from 3.9–5.6 €/kg for the hybrid-sulfur cycle, 3.5–12.8 €/kg for the metal oxide based cycle and 2.1–6.8 €/kg for electrolysis were obtained.     

Uncertainty quantification in a hydrogen production system based on the solar hybrid sulfur process

Water splitting through the Hybrid Sulfur (HyS) process powered by solar energy is a promising pathway to the production of green hydrogen. The main challenges to the development of this process are related to the intrinsic variability of the solar resource, which, besides requiring the deployment of innovative process solutions, introduces significant elements of uncertainty in the plant design.In this paper, the Polynomial Chaos Expansion (PCE) method is applied for the uncertainty quantification (UQ) in this kind of systems. In particular, a forward analysis dealing with the evaluation of the output probability distributions is performed. This is carried out in terms of the input probability distributions, and the analysis is focused on how uncertainty is propagated from the input to the output. Moreover, a comparison between the PCE method and the standard Monte Carlo analysis (using the Latin Hypercube Sampling method) is performed. The obtained results show the advantage of the PCE approach in terms of convergence rate and the number of function evaluations. Finally, a sensitivity analysis through Sobol’ indices has been carried out, which highlighted the influence of each variation in the input on the output.     

An assessment of solar hydrogen production using the mark 13 hybrid process

An assessment is presented of hydrogen production using a dedicated central solar receiver system concept coupled to a Mark 13-V2 hybrid thermochemical process. The system which is capable of producing about 10⁶ GJ hydrogen per year was developed at the conceptual level. The total irradiance at normal incidence was taken as a parameter and varied from 1500 to 2500 kWh m^?2 y^?1 at a location with 30° latitude and 0.1 km altitude. The peak noon irradiance at normal incidence was taken as 0.95 kW m^?2 and the mean total sunshine hours as 2333 h y^?1.A flow sheet of the solar Mark 13-V2 hybrid process was developed to operate using the intermittent heat supply from the central receiver system and the continuous electric energy supply from outside. It was then evaluated using the models for the central receiver system, the solar receiver and the chemical process.It is found that for 2000 kWh m^?2 y^?1 total irradiance at normal incidence, the overall efficiency of the solar Mark 13-V2 process is about 21% and that the cost of the solar hydrogen is about $52 GJ^?1.     

The solar Cristina process for hydrogen production

Hydrogen production using the Cristina process coupled to a dedicated central receiver solar system has been studied. The Cristina process was originally conceived and developed at the Joint Research Center of the European Communities in Ispra to decompose the sulfuric acid and produce the sulfur dioxide necessary for hydrogen production. In the present study, the process has been adopted to an intermittently operating solar heat source to produce the sulfur dioxide during sunshine hours and operate in reverse as a sulfuric acid synthesis process at a required rate to produce high temperature heat during night operation by using a small part of the stored sulfur dioxide. In this manner, the chemical process is operated continuously, hence, thermal inertia and start-up problems have been eliminated.A system has been conceived to produce 10⁶ mole SO₂ per hour, which is coupled to a central receiver solar system producing 10⁶ GJ per year heat operating 2333 hrs per year. The system produces 0.62 × 10⁶ GJ hydrogen per year when coupled to a hydrogen producing step such as Mark 11 or 13 operating 7000 hrs per year and using electric energy supplied from outside.It has been found that the cost of sulfuric acid decomposition by the solar Cristina process is approximately 31 $ per GJ hydrogen. Including the cost of solar heat (approximately 32 $ per GJ hydrogen) and that of hydrogen producing step (approximately 5 $ per GJ hydrogen), the total cost has been estimated to be 68 $ per GJ hydrogen.