During the late 90s and the 2000s, hydrogen was one of the most promising candidates as alternative fuel for road vehicles because of its clean combustion. Nowadays, the focus of research has shifted towards synthetic hydrocarbon fuels, such as synthetic gasoline, diesel, kerosene, or fuel methanol, derived from biomass or directly from H2O and CO2. In comparison to carbon-free energy carriers, such as hydrogen or batteries, hydrocarbons offer much higher energy density (per volume) and compatibility with the current global fuel distribution infrastructure.
Multiple approaches have been investigated over the past decades to produce market-competitive solar fuels. Different efforts dealt with the electrochemical pathway, where solar energy is first converted to electricity by means of photovoltaic (PV) or solar thermal systems and successively used to split water and/or carbon dioxide in electrolytic cells. Electrolytic solar-to-H2 conversion can be performed at efficiencies of around 12%. The electrochemical splitting of CO2 is still in its early stages reaching efficiencies of around 6.5% under laboratory conditions.
Another very promising avenue exploits solar-driven high temperature thermochemistry to perform the water and carbon dioxide splitting. The group of Prof. Aldo Steinfeld at ETH Zurich, partner of the present project, is a renown world leader in the solar thermochemical fuel research. Now, a series of innovations promises to radically improve the solar-to-syngas efficiency of the technology from the current 6% to a peak of above 17% and a yearly average of above 15% under realistic operation conditions and with very competitive cost figures. This breakthrough project aims at leveraging more than two decades of top research and to become the first viable large scale solar fuel technology.
In a typical temperature swing redox thermochemical cycle, a suitable material such as ceria (CeO2) is firstly heated to temperatures high enough such that, under sufficiently low oxygen partial pressure (pO2), it reduces (looses oxygen) to a lower oxidation state.
In the second step, the cooled reduced material is exposed to oxygen-containing reactants such as water and/or carbon dioxide, and, at the lower temperatures re-oxidizes spontaneously by stripping them of their oxygen. Therefore, in the case of water and carbon dioxide, the products are hydrogen and carbon monoxide, whose mixture, called synthesis gas or syngas, is the precursor for several hydrocarbon fuel synthesis processes. Once the oxidation phase is completed the cycle is repeated. The redox material acts only as an oxygen “adsorber/desorber” and is not consumed in the process.
Solar energy, which is by far the most widely available source of energy on earth, is an ideal candidate to provide energy for synthetic fuel production. The concentrated solar radiation of CSP technologies can be optimally used to drive high-temperature endothermic reactions in solar thermochemical processes.
Synhelion, after having verified experimentally the working principles of the core innovations at the lab scale, has recently teamed up with the leading energy company Eni S.p.A. to further develop these innovations into a viable commercial technology. The two companies signed a cooperation agreement on June 22, 2017. The collaboration targets, among others, the development of pilot plants at different scales until the technology is completely industrialized.
The activities of Synhelion are carried out in collaboration with the leading players in the field.