Efficient water splitting via a flexible solar-powered Hybrid thermochemical-Sulphur dioxide depolarized Electrolysis Cycle

HySelect will demonstrate the production of hydrogen (H2) by splitting water via concentrated solar technologies (CST) with an attractive efficiency and cost, through the hybrid sulphur cycle (HyS). The HyS consists of two central steps: the high temperature -yet below-900C -decomposition of sulphuric acid forming sulphur dioxide (SO2) and the subsequent low temperature (50-80C) SO2 depolarised electrolysis (SDE) of water to produce H2. HySelect will introduce, develop and operate under real conditions a complete H2 production chain focusing on two innovative, full scale plant prototype core devices for both steps of the HyS cycle: an allothermally heated, spatially decoupled from a centrifugal particle solar receiver, sulphuric acid decomposition-sulphur trioxide splitting (SAD-STS) reactor and a sulphur dioxide depolarized electrolyser (SDE) without expensive Platinum Group Metals (PGMs). Furthermore, a heat recovery system will be integrated to exploit the temperature difference within the cycle and boost the overall process efficiency. In the course of the work, non-critical materials and catalysts will be developed, qualified and integrated into the plant scale prototype units for both the acid splitting reactor and the SDE unit. Experimental work will be accompanied by component modelling and overall process simulation and culminate with a demonstration of the complete process integrating its key units of a 750kWth centrifugal particle receiver, a hot particles storage system, a 250kWth SAD-STS and a 100kWe SDE into a pilot plant. Testing for a period of at least 6 months in a large-scale solar tower, driven with smart operation and control strategies, will establish the HySelect targeted efficiency and costs. Finally, an overall process evaluation will be carried out in order to assess the technical and economic prospects of the HySelect technology, directly linked to the know-how and developments of the sulphuric acid and water electolysers industries.