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Concentrated solar thermal technology is considered a very promising renewable energy technology due to its capability of producing heat and electricity and of its straightforward coupling to thermal storage devices. Conventionally, this approach is mostly used for power generation. When coupled with the right conversion process, it can be also used to produce methanol. Indeed methanol is a good alternative fuel for high compression ratio engines. Its high burning velocity and the large expansion occurring during combustion leads to higher efficiency compared to operation with conventional fuels. This study is focused on the system level modeling of methanol production using hydrogen and carbon monoxide produced with cerium oxide solar thermochemical cycle which is expected to be CO2 free. A techno-economic assessment of the overall process is done for the first time. The thermochemical redox cycle is operated in a solar receiver-reactor with concentrated solar heat to produce hydrogen and carbon monoxide as the main constituents of synthesis gas. Afterwards, the synthesis gas is turned into methanol whereas the methanol production process is CO2 free. The production pathway was modeled and simulations were carried out using process simulation software for MW-scale methanol production plant. The methanol production from synthesis gas utilizes plug-flow reactor. Optimum parameters of reactors are calculated. The solar methanol production plant is designed for the location Almeria, Spain. To assess the plant, economic analysis has been carried out. The results of the simulation show that it is possible to produce 27.81 million liter methanol with a 350 MWth solar tower plant. It is found out that to operate this plant at base case scenario, 880685 m2 of mirror's facets are needed with a solar tower height of 220 m. In this scenario a production cost of 1.14 €/l Methanol is predicted.

The transition towards a renewable energy-based society is challenged by spatial and temporal imbalances of energy demand and supply. Storage properties and versatility may favor hydrogen to serve as the linking element between renewable energy generation and a variety of sector coupling options. This paper examines four alternative solar-based hydrogen production concepts based on concentrated solar (CSP) or photovoltaic (PV) power generation and solid oxide (SOE) or polymer electrolyte membrane (PEM) electrolysis, namely, CSP-SOE and CSP-PEM, as well as PV-PEM concepts with (PV-PEM I) or without (PV-PEM II) power converters coupling both devices. In this paper, we analyze these concepts in terms of their techno-economic performance in order to determine the levelized cost of hydrogen (LCOH) for the target year 2025, based on different locations with different climate conditions. The analysis was carried out using a broadly applicable computer model based on an hourly resolved time-series of temperature and irradiance. The lowest LCOH was identified in the case of the CSP-SOE and CSP-PEM concepts with 14–17 €-ct per kW per h at high-irradiance locations, which clearly exceed the US Department of Energy (DOE) target of 6 $-ct per kW per h for the year 2020. Moreover, CSP-SOE also shows the highest hydrogen production volumes and, therefore, solar-to-hydrogen efficiencies. Considering the PV-PEM concepts, we found that the application of power converters for the electrical coupling of PV modules and electrolyzers does not contribute to cost reduction due to the higher related investment costs. A further system optimization is suggested regarding the implementation of short-term energy storage, which might be particularly relevant at locations with higher fluctuations in power supply.

Water electrolysis is considered as a suitable pathway for the production of large amounts of hydrogen to be used as energy carrier for electricity storage. Among the existing water electrolysis technologies solid oxide steam electrolysis exhibits the highest electrical efficiency. Moreover, from thermodynamic considerations the efficiency can be further increased when part of the energy demand is provided by the integration of external high temperature heat to reduce the electrical energy for the water splitting reaction. This paper reports on the successful integration of solar heat into a solid oxide electrolyzer. The experimental setup of the prototype system consisting of a solar simulator, a solar steam generator, a steam accumulator and a solid oxide electrolyzer as well as first results with regard to solar steam generation and electrochemical performance of the electrolyzer are presented. Hot steam with a maximum flow rate of 5.0 kgh−1 was produced with the solar steam generator. A small fraction (0.58 kgh−1) mixed with 10% of H2 was supplied to a 12-cell solid oxide electrolyzer stack with approx. 2 kW electrical power. At 770 °C and a current density of −1.25 Acm−2 a steam conversion rate of 70% at 93% electrical electrolyzer efficiency was achieved.

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.

The present research focuses on modeling of solar thermal driven fuel production plant with CO2 and H2O as raw materials to produce synthetic gas (syngas) which is converted into hydrocarbons through Fischer-Tropsch process either with Fe and Co catalyst to produce diesel, gasoline and kerosene. The solar reactor uses cerium oxide (CeO2) as a metal-redox and operates at 1773 K and 1300 K for reduction and oxidation step respectively under non-stoichiometric condition. The plant is analyzed by performing a quasi-steady state simulation under boundary condition that the Fischer-Tropsch reactor should operate with the capacity factor of 0.95 or 8350 hours annually. A storage tank is used to store and regulate the flow of syngas going into the Fischer-Tropsch reactor. Sensitivity analysis is carried out, particularly on solar reactor conversion and solid-to-solid heat exchanger efficiency. Another sensitivity analysis is to combine PV and CSP as the external electricity source. The production cost is finally calculated using annuity method with constant discount rate.

Concentrated solar energy is an ideal energy source for high-temperature energy conversion processes such as concentrated solar power generation, solar thermochemical fuel production, and solar driven high-temperature electrolysis. Indirectly irradiated solar receiver designs utilizing tubular absorbers enclosed by a cavity are possible candidates for direct steam generation, allowing for design flexibility and high efficiency. We developed a coupled heat and mass transfer model of cavity receivers with tubular absorbers to guide the design of solar-driven direct steam generation. The numerical model consisted of a detailed 1D two-phase flow model of the absorber tubes coupled to a 3D heat transfer model of the cavity receiver. The absorber tube model simulated the flow boiling phenomena inside the tubes by solving 1D continuity, momentum, and energy conservation equations based on a control volume formulation. The Thome-El Hajal flow pattern maps were used to predict liquid-gas distributions in the tubular cross-sections, and heat transfer coefficients and pressure drop along the tubes. The heat transfer coefficient and fluid temperature of the absorber tubes’ inner surfaces were then extrapolated to the circumferential of the tube and used in the 3D cavity receiver model. The 3D steady state model of the cavity receiver coupled radiative, convective, and conductive heat transfer. The complete model was validated with experimental data and used to analyze different receiver types and designs made of different materials and exposed to various operational conditions. The proposed numerical model and the obtained results provide an engineering design tool for cavity receivers with tubular absorbers (in terms of tube shapes, tube diameter, and water-cooled front), support the choice of best-performant operation (in terms of radiative flux, mass flow rate, and pressure), and aid in the choice of the component materials. The model allows for an in-depth understanding of the coupled heat and mass transfer in the solar receiver for direct steam generation and can be exploited to quantify the optimization potential of such solar receivers.

High-temperature steam electrolysis (HTSE) consists of the splitting of steam into hydrogen and oxygen at high temperature in solid oxide electrolyzers. Performing the electrolysis process at high temperatures offers the advantage of achieving higher efficiencies as compared to the conventional water electrolysis. Furthermore, this allows the direct use of process heat to generate steam. This paper is related to the FCH JU (Fuel Cells and Hydrogen Joint Undertaking) project ADEL (ADvanced ELectrolyser For hydrogen Production with Renewable Energy Sources), which investigates different carbon-free energy sources to be coupled to the HTSE process. Renewable energy sources are able to provide the high-temperature steam electrolysis (HTSE) process with heat and power. This paper investigates the capability of Concentrating Solar Power (CSP) technologies to provide the HTSE process with the necessary energy demand. The layout of the plant is shown in the following figure. The design of commercial-scale high-temperature steam electrolysis has been carried out. The HTSE plant is coupled to an air cooled solar tower. The configuration and the operating parameters of the solar tower are based on those of the solar tower of Julich (Germany), which is operated by DLR. This paper presents the results of process analysis performed to evaluate the hydrogen production from a HTSE plant coupled to an 80MWth air solar tower. Additionally, the dynamic behavior of the system during energy fluctuations has been analyzed. The receiver-to-hydrogen efficiency (based on the Higher Heating Value of hydrogen) is 26% at a hydrogen production rate of 680 kg/h in steady-state operation. The overall solar-to-hydrogen efficiency is calculated to be at 18%. Moreover, the analysis under transient conditions shows that a steady-state operation of the plant is only possible for 8 h.

The transformation of the energy supply needs further development of energy storage technologies in order to integrate the fluctuating renewable energy. The conversion of renewable wind power into green methane offers a technical approach with the necessary storage and Transport capacities. Thus, the concept of Power-to-Gas which is illustrated here by the coupling of wind energy with a High Temperature Steam Electrolyser (HTSE) and a methanation unit enabling the production of green fuel like hydrogen and methane is presented is this paper. In fact, hydrogen can be used as energy carrier as well for the production of green fuels, like methane which is simpler to store and to transport and which can be thus used as storage medium for the stabilization of the electrical power supply as well as fuel for transport and heat sector. Its production using high temperature electrolysis is able to reduce the carbon dioxide emissions if performed with renewable resources. This is the case if the electricity needed for the HTSE comes from a wind turbine and the CO2 needed for the methanation step comes from biogas. For such a plant, the Location and the boundary conditions have a great importance. Thus, this study considers the coupling of a HTSE with a wind turbine and a methanation reactor, and focuses about the site selection, depending of the geographical and economic considerations. The study is limited first to the European area. Schleswig-Holstein is found as a very good location for this plant. It is one of the regions with the largest wind reserves in Germany. This region has also available a lot of Biogas and meets all the other necessary requirements.

Thermochemical multistep water- and CO2-splitting processes are promising options to face future energy problems. Particularly, the possible incorporation of solar power makes these processes sustainable and environmentally attractive since only water, CO2 and solar power are used; the concentrated solar energy is converted into storable and transportable fuels. One of the major barriers to technological success is the identification of suitable active materials like catalysts and redox materials exhibiting satisfactory durability, reactivity and efficiencies. Moreover, materials play an important role in the construction of key components and for the implementation in commercial solar plants. The most promising thermochemical water- and CO2-splitting processes are being described and discussed with respect to further development and future potential. The main materials-related challenges of those processes are being analyzed. Technical approaches and development progress in terms of solving them are addressed and assessed in this review.

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 MWth 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.

Hydrogen produced from water by concentrated solar power (CSP) is a clean and renewable energy carrier, free of greenhouse emission offering the potential to fully replace fossil fuels. Today’s benchmark water-splitting process is the alkaline electrolysis, which, however, has a relatively low overall efficiency limited by the efficiency of power generation. In comparison, solar thermal processes have the potential to significantly increase the hydrogen yield by about 50%. Direct water splitting can theoretically be driven by CSP but requires technically unfeasible temperatures. Thermochemical cycles separate the water-splitting step into two or more reactions significantly reduce the temperature level and, by this, achieve high thermal efficiencies. High-temperature electrolysis of water is a promising technology for solar thermal water splitting due to its reduced electricity demand and, therefore, higher efficiency compared to room-temperature alkaline or PEM electrolysis. Such processes promise a huge potential for carbon-free and sustainable hydrogen production on large scale, but still major effort is needed to enhance the stability and thus suitability of the materials involved and used at high operating temperature.

A two-step thermochemical cycle process for solar hydrogen production from water has been developed using ferrite-based redox systems at moderate temperatures. The cycle offers promising properties concerning thermodynamics and efficiency and produces pure hydrogen without need for product separation. The process works by cycling stationary ferrite-coated monoliths through sequential oxidation and reduction steps at 1073 and 1473 K, respectively. By using two such monoliths in parallel, it is possible to quasi-continuously produce hydrogen. A prototype solar reactor and peripherals suitable to proof the process concept were developed and have been successfully tested in DLR's solar furnace in Cologne. Repeated cycling operation is possible with a reproducible amount of hydrogen produced. In most cases, a distinct decay of the amount of the evolved hydrogen is observed from cycle to cycle due to inhomogeneous heating of the monolithic absorber in the very first cycles and due to disappearance of the porosity and the associated loss of surface area in later cycles. Results from experimental campaigns with the prototype reactor and simulations with a corresponding reactor model support the development and verification of a process strategy for the continuous production of hydrogen in a larger scale. The tasks include the enhancement of long-term stability of the redox system, the development of an operational strategy and finally the design and development of a 100 kWth pilot reactor to demonstrate the feasibility of the process on top of a solar tower under real conditions.

The objective of HYTHEC-HYdrogen THErmo-chemicat Cycles-is to investigate the effective potential for massive hydrogen production of the S-I thermo-chemical cycle, and to compare it with the hybrid S Westinghouse (WH) cycle. The project aims to conduct flow-sheeting, industrial scale-up, safety and costs modelling, to improve the fundamental knowledge and efficiency of the S-I cycle H-2 production step, and to investigate a solar primary energy source for the H2SO4 decomposition step which is common to both the cycles. Initial reference flow-sheets have been prepared and compared. First data and results are available now on the coupling of S-I cycle with a very high temperature nuclear reactor, scale-up to industrial level and cost estimation, improvement of the knowledge of the HIx mixture (S-I cycle) and membrane separation, splitting of sulphuric acid using a solar furnace, and plant concepts regarding the WH process. (C) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

A very promising method for the conversion and storage of solar energy into a fuel is the dissociation of water to oxygen and hydrogen, carried out via a two-step process using metal oxide redox systems such as mixed iron oxides, coated upon multi-channeled honeycomb ceramic supports capable of absorbing solar irradiation, in a configuration similar to that encountered in automobile exhaust catalytic converters. With this configuration, the whole process can be carried out in a single solar energy converter, the process temperature can be significantly lowered compared to other thermo-chemical cycles and the re-combination of oxygen and hydrogen is prevented by fixing the oxygen in the metal oxide. For the realization of the integrated concept, research work proceeded in three parallel directions: synthesis of active redox systems, manufacture of ceramic honeycomb supports and manufacture, testing and optimization of operating conditions of a thermochemical solar receiver-reactor. The receiver-reactor has been developed and installed in the solar furnace in Cologne, Germany. It was proven that solar hydrogen production is feasible by this process demonstrating that multi cycling of the process was possible in principle.Copyright © 2005 by ASME

An economic evaluation regarding the industrial photosynthesis of fine chemical rose oxide using solar light is given and compared to conventional lamps as light source. A plant reaching a capacity of 100 t/a was designed containing app. 1,900 m2 of parabolic troughs, 1,500 m2 of flatbed reactors or 32 high-pressure mercury lamps doped with Thallium iodide (TlI) as a photounit. The investment and production costs were compared and graded. We reached the conclusion that solar application is more profitable than the lamp driven one.

Solar radiation is the largest indigenous energy resource worldwide. It will gain a significantly more relevant role in covering the energy demand of many countries when national fuel reserves fall short and when demand increases as is expected within the next 10 years. If solar energy is transformed into heat by concentrating and absorbing the radiation, energy can be stored easily. Thermal energy from mirror fields that focus solar radiation not only is able to generate electricity but also can be used to generate storable heat, to desalinate salt water or to synthesise fuels from water and carbon dioxide to store, transport or use them on-site. The application of concentrated solar radiation as a primary energy source can help to decarbonise electricity generation and many other sectors to keep the chance of staying within the 2 °C goal for limiting the effects of global warming. The aim of the present contribution is to give an overview on the state-of-the art of technologies for solar thermal power production and fuel production and to describe the status and outlook of commercial projects and perspectives of market development.

The search for a sustainable, CO2-free massive hydrogen production route is a strong need, if one takes into account the world-wide increasing energy demand, the deterioration of fossil fuel reserves and in particular the increasing CO2 concentration leading to global warming. Thermo-chemical cycles for water splitting are considered as a promising alternative of emission-free routes of massive hydrogen production – with potentially higher efficiencies and lower costs compared to alkaline electrolysis of water. The hybrid-sulphur cycle was chosen as one of the most promising cycles from the ‘sulphur family’ of processes. Different process schemes using concentrated sunlight or nuclear generated heat or a combination of both have been elaborated and analysed by a comparative techno-economic study with regard to their potential of a large-scale hydrogen production. Options for a hybridisation of the energy supply between solar and nuclear have been also investigated, particular focused on the coupling of concentrated solar radiation into a round-the-clock operated process. Process design and simulation, industrial scale-up assessments including safety analysis and cost evaluations were performed to analyse reliability and potential of those process concepts.

The potential of hydrogen to be the energy carrier of the future is widely accepted. Today more than 90% of hydrogen is produced by cost effective technologies from fossil sources mainly by steam reforming of natural gas and coal gasification. But hydrogen is not important as an energy carrier yet — it is mainly a chemical. To finally benefit from hydrogen as a fuel it has to be produced greenhouse gas free in large quantities. Therefore these two tasks have to be connected by a strategy incorporating transition steps. Solar thermal processes have the potential to be the most effective alternatives for large scale hydrogen production in the future. Therefore high temperature solar technologies are under development for the different steps on the stair to renewable hydrogen. This paper discusses the strategy based on the efficiencies of the chosen solar processes incorporating carbonaceous materials as well as processes based on water splitting. And the availability of the technologies. A comparison with the most common industrial processes shall demonstrate which endeavors have to be done to establish renewable hydrogen as a fuel.