(93d) Efficient Hydrogen Production from Solar Thermal Energy Via High Temperature Water Electrolysis

With the rapid growth in world population and increasing demand for life quality, human beings are continuously exerting immense pressure on our global energy resources. However, even with development in renewable energy application, the world energy consumption is still largely dependent on fossil fuels, which have brought environmental issues such as greenhouse gas emission and might be deprived in a foreseeable future. Switching energy resources to renewable energy will be crucial to the global energy challenge and solar energy is the promising because of its abundance and wide availability at most locations in the world. Due to the limitations on land area that can be dedicated to solar energy harnessing and the uncontrollable intermittencies in the solar energy supply, technologies are highly desired to fully utilize the solar energy that can be harnessed and convert or store it in the form of electricity, chemicals, etc. With its high energy density and zero greenhouse gas emission, hydrogen is the key energy carrier in a sustainable future. Hydrogen production from solar energy has been studied by many researchers by either thermochemical or electrolysis method.

Here we introduce a process design strategy for the production of hydrogen by high temperature water electrolysis using concentrated solar thermal energy. High temperature water electrolysis is realized by using solid oxide electrolysis cell (SOEC). SOEC requires both electricity and heat input to enable the energy balance of the water splitting process. We utilize solar thermal power production cycle to supply the electricity the SOEC requires. Meanwhile, water is heated by concentrated solar energy to reach the SOEC operation temperature before electrolysis. The power generating and hydrogen production processes are integrated, allowing electricity flow and heat transfer between the two cycles. Process simulations for the proposed integration are performed in an integrated Matlab and Aspen Plus platform.

Considering the electricity and power input as well as the overpotential of the SOEC, different operation modes of SOEC, including thermoneutral, endothermic and exothermic operations, could largely affect the efficiency of hydrogen production. Therefore, different operation modes of SOEC are investigated and various process designs are examined accordingly to figure out the most efficient process under various circumstances. In this way the most promising solar thermal hydrogen production process could be designed and flexibility of operation conditions could also be identified.