Material analysis for the construction of solar hydrogen generator

The growth of the world population, economy, and standards of living have significantly increased the demand for energy. The need for the development of clean energy sources has hence been on the rise in recent years. Among these, solar power and chemical fuels such as hydrogen have been identified as prime sources of clean energy. The main challenge associated with solar energy has been how to convert solar radiation into useful energy forms to meet consumer demand. One method that has been identified for converting solar radiation to functional energy is the production of clean chemical fuels such as hydrogen. The production of hydrogen gas with the aid of solar energy can be accomplished in three different processes namely; thermochemical, electrochemical, and photochemical (Agrafiotis et al., 2007). Of the three processes, the most efficient is the thermochemical process, which utilizes the sun’s radiation and heat as the energy source for conducting high-temperature reactions, such as water splitting and natural gas reforming. This results in the production of hydrogen gas from fossil and non-fossil fuels.

Solar Thermal Hydrogen Generator

The abundance of solar energy and various sources of hydrogen, such as water and methane, make this process economically and environmentally viable. A solar thermal generating system is used for the production of hydrogen through reforming of methane gas. A typical solar thermal reforming system includes a solar collector/receiver with a concentrator, a solar reactor with concentric tubes, and a water-gas shift reactor (Sheu, Mokheimer, & Ghoniem, 2015). The solar receiver/collector has the function of concentrating and focusing the solar radiation to raise the temperature in the chemical reactor and facilitate the reforming process. The chemical reactor is mainly the chamber where the catalyst assisted reforming reaction occurs to produce hydrogen. The water-gas shift reactor is incorporated in the system to produce pure hydrogen by separating it from carbon dioxide. The efficiency of the solar hydrogen generator is greatly reliant on the materials used to make the individual components.

Material Analysis

The solar collector, receiver, and reactor are the main components of the solar reforming system. The solar collector system generally includes a solar concentrator and receiver. There are four different types of optical setups for the solar concentrator, and they include the parabolic dish reflector, central tower reflector, linear Fresnel reflector, and parabolic trough reflector system (Maridurai et al., 2018). The parabolic dish and central tower systems are best suited for high-temperature reactions. The solar concentrator reflects the sun’s radiation to the receiver hosing the chemical reactor. To ensure the solar collector/receiver system can collect a large amount of solar energy, concentrator should be made of highly reflective materials such as refined glass mirrors or polished, reflective aluminum surfaces. For maximum absorption and retention of the reflected radiation, the solar receiver should be made of black coated outer surfaces and highly conductive inner surfaces (Maridurai et al., 2018). The use of chromium and nickel-based black coatings for the outer surface of the tube ensures the receiver absorbs the complete spectrum of the reflected sun rays.

The inner surface of the receiver tubes should be lined with highly conductive elements such as copper or aluminum. This will ensure the solar collector and receiver system can absorb maximum solar radiation and can withstand the high temperatures required for the reforming reaction. The solar reactor system is usually modeled in the form of concentric tubes in which the reaction occurs (Sheu, Mokheimer, & Ghoniem, 2015). The outer tube consists of a solar receiver surface, and the inner tube includes the reactor. The materials used in the construction of the reactor tubes should be able to withstand the high temperatures as well as be able to handle the catalysts used in the reaction.  Graphite and ceramic membranes are two suitable materials that can be used in the construction of solar reactor tubes (Agrafiotis et al., 2007). The two materials are highly conductive, thus transferring the heat from the receiver more efficiently through radiation and convection. They also offer a suitable surface area for the reaction of the gases with the catalysts used in the reaction.

The water-gas shift reactor is included in the system to facilitate the production of pure hydrogen by separating from the CO2 produced in the reaction. The main consideration in the water-gas shift reaction is the catalyst used at different temperatures for the process (Sheu, Mokheimer, & Ghoniem, 2015). For the high-temperature reactions that occur in the methane reforming process, chromium or iron-based catalysts are most suited. The research on thermal generation of hydrogen using solar energy is, however, still ongoing. This means newer and more suitable materials are being developed by researchers working in the field. The future of renewable energy can, therefore, only get better in terms of the new materials for building more efficient solar hydrogen generation systems.

Works Cited

Agrafiotis, C. C., Pagkoura, C., Lorentzou, S., Kostoglou, M., & Konstandopoulos, A. G. (2007). Hydrogen production in solar reactors. Catalysis Today, 265-277.

Maridurai, T., Irfan, A. A., Vengadesan, E., Loganathan, K., Aminudeen, M., & Ahamed, K. H. (2018). Review of Material aspects of Thermal Collectors. International Journal of Mechanical Engineering and Technology (IJMET), 286-292.

Sheu, E. J., Mokheimer, E. M., & Ghoniem, A. F. (2015). A review of solar methane reforming systems. International Journal of Hydrogen Energy, 1-27.