Solar hydrogen by high-temperature electrolysis: Flowsheeting and experimental analysis of a tube-type receiver concept for superheated steam production

Abstract

High-temperature electrolysis (HTE) offers the potential of considerably higher efficiency than conventional alkaline electrolysis when producing hydrogen from water by solar energy. The production rate of the alkaline electrolyzer process is limited since the whole energy demand is covered by electricity. By contrast, in HTE part of the energy can be introduced as high temperature heat from concentrated solar power (CSP) leading to a significantly higher process efficiency. In the internal project SoHTEk a solar tube-type receiver to superheat steam to 700 °C for HTE was developed. The receiver was operated in DLR’s solar simulator with up to 5 kg/h of steam reaching an outlet temperature of about 700 °C at a thermal efficiency of 40 % and a solar power of about 4 kW. In addition, a flowsheeting analysis was carried out of a HTE process with direct steam generation on a solar tower. Simulation of the process at steady-state yielded a thermal-to-hydrogen efficiency of 26 %. A subsequent sensitivity analysis indicated the potential to reach efficiencies of 38 % and more.