Development, validation and characterization of a reversible SOFC/SOEC system for green hydrogen generation from PV renewable energy sources.

Nowadays, the reduction of greenhouse gas emissions to minimise the effects of climate change and the increase of energy independence from geopolitically unstable countries are highly relevant aspects. To achieve these targets, it is necessary to increment the use of Renewable Energy Sources (RES). However, intermittent energy production is a well-known drawback of some of these sources, such as wind and photovoltaic systems. Consequently, it becomes important to find more efficient and reliable storage systems. Hydrogen technologies can play a significant role in the future energy transition scenario. In this regard, the technology taken into consideration in this work is the reversible Solid Oxide Cells (rSOCs). The latter is an electrochemical cell able to perform a reversible transformation using the same technology and materials. When used in Solid Oxide Electrolysis Cell (SOEC) mode, it transforms electricity into hydrogen through steam electrolysis, while in Solid Oxide Fuel Cell (SOFC) mode it generates electricity from hydrogen. In particular, rSOCs achieve high efficiency electrolysis by working at high temperatures and a good round trip efficiency. However, there is still research to be done to increase the durability and reliability of these systems. This work starts with a general overview of fuel cell technology. Then, the prototype developed within the Institut de Recerca en Energia de Catalunya (IREC) laboratories is presented, describing in detail the auxiliary components that complete the overall Balance of Plant. It is followed by a description of the protocol that led to the characterization of the SOFCMAN stack module working within the prototype set-up. The module used has a nominal input power of 1kW in SOEC mode and a nominal output power of 0.5 kW in SOFC mode. For its validation, polarization tests (both in SOFC and SOEC mode) and reversibility tests were performed, obtaining current-tension (i-V) characterisation curves. Finally, using solar profiles from the energy production of photovoltaic panels, some tests were carried out to prove the possibility of using this system as a hydrogen storage technology. Using the surplus of electricity generated by the photovoltaic panels, it is possible to produce hydrogen exploiting the rSOC prototype. The equivalent quantity of obtained gas through electrolysis (no hydrogen tank used in this prototype version) could be used later to meet the energy demand when the availability of renewables is lacking.