Solar energy-driven hydrogen production

Promovendus/a: Yimin Deng

Promotor(en): Prof. dr. ir. Raf Dewil, Prof. Jan Baeyens

The climate emergency requires urgent actions to reduce the global average temperature increase to below 1.5 oC. Nations commonly agree on necessary measures to reach zero greenhouse gas (GHG) emissions by the mid-century. Renewable electricity-based fuels and chemicals are expected to play an ever-growing role in future sustainable energy solutions and are crucial for their progressive de-fossilization. Hydrogen-based options are expected to be part of the solution and may even be the major solution in the longer term. When dealing with the valorization of hydrogen, two main issues need to be considered, i.e. the growing market for H2, and the “green” feedstock that should be used to produce H2. The demand for H2 continues to increase. It is expected to increase to 1423 M$ by 2026. Being mostly fossil fuel-based, the production of H2 is responsible for CO2 emissions of around 830 million tons per year.

Research Methodology

An alternative H2-production route would be using “green” feedstock to replace fossil fuels and renewable energy to supply the reaction heat. The first part of the present research investigated this alternative route through firstly using bio-based methanol or ethanol, or ammonia from digesting agro-industrial or domestic waste. The catalytic conversion of CH4 to C and H2 is moreover examined as a possible option to decarbonize the natural gas grid. Secondly, the water splitting by reversible redox reactions is examined in detail. Although these alternative H2 production methods will be proven technically and economically viable, their moderate to high endothermicity requires the use of a “green” energy supply, where renewable energy appears to be the most indicated option. The application of renewable heat or power was therefore thirdly investigated in the Ph.D. research, with a special focus on using Concentrated Solar Tower (CST) technology, both in a base-load and in a peaker operation mode.

Results & Conclusions

The assessments indicate that the solar thermochemical production of hydrogen can be competitive with the electrolyzer using solar-generated electricity, and, under certain conditions, might become competitive with conventional fossil-fuel-based processes at current fuel prices. The weaknesses of these economic evaluations are related primarily to the uncertainties in the viable efficiencies and investment costs of the various components due to their potential early stage of development and their economy of scale. Further development and large-scale demonstration are required. The design recommendations and tentative economic balances should be proven at pilot-scale. This research has provided conclusions positive enough to incite other researchers and even R&D centers to continue this research.