The 2.6 MWel,AC unit presented in this article comprises a 2.4 MWel,AC high temperature steam electrolyser and a 0.2 MWel,AC hydrogen processing unit. The system is based on Sunfire's “Gen-2” solid oxide technology. The unit is made of 12 modules and is designed to deliver a flow rate of hydrogen of ≥ 60 kg/h. Each module went through a factory acceptance test and all passed the quality criteria at the first time, and could subsequently be shipped to Rotterdam, to be installed at NESTE renewable products refinery. They were able to demonstrate an electrical efficiency above 86 %el,LHV as expected with this technology. The HPU, responsible to process the hydrogen produced to meet the quality and pressure criteria of the refinery process, has been designed by Paul Wurth and its components also passed the factory acceptance tests with success. On NESTE side, the plot has been prepared in Rotterdam refinery, to receive the HTSE and HPU units and to provide the requested power line and other utilities. The whole unit has been successfully installed on site and the commissioning performed.
In parallel, long term stack tests were performed at laboratory scale in order to assess the technology performance and durability. Two types of stacks, made of either electrode or electrolyte supported cells, at two scales, a few kW and up to 10 to 20 kW scale, have been tested over durations up to 8 kh. Thanks to a smart operation strategy adopted for all stack types and sizes and consisting in compensating degradation by a stack temperature evolution over time, it has been shown that they could be operated over those durations without any hydrogen production loss, the current density being kept constant over the whole duration. This operation strategy is the one which will be used for the operation of the pilot.
Thanks to stack design improvement, the latest generations were able to operate at higher current densities, respectively – 0.79 A/cm² for the “Gen-3” electrolyte supported stack prototype and – 0.92 A/cm² for electrode supported stacks, with a lower degradation rate despite the higher current density. Those results are encouraging for the next generations of the technology, of which the maturity and size of units installed are expected to grow hugely over the next years.
