Nathalie Monnerie

SOLAR HYDROGEN PRODUCTION BY A TWO-STEP CYCLE BASED ON MIXED IRON OXIDES

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.

Materials-Related Aspects of Thermochemical Water and Carbon Dioxide Splitting: A Review

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.

Technologies and trends in solar power and fuels

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.

Economic Evaluation of the Industrial Photosynthesis of Rose Oxide via Lamp or Solar Operated Photooxidation of Citronellol

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 m 2 of parabolic troughs, 1,500 m 2 of flatbed reactors or 32 high-pressure mercury lamps doped with Thallium iodide (TII) 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.

Potential of hybridisation of the thermochemical hybrid-sulphur cycle for the production of hydrogen by using nuclear and solar energy in the same plant

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.

Solar Thermal Water Splitting

Abstract 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.

Efficient Solar Thermal Processes From Carbon Based to Carbon Free Hydrogen Production

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.

Solar Hydrogen Production by a Two-Step Cycle Based on Mixed Iron Oxides

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