Techno-Economic Evaluation of the Integration of High-Temperature Electrolysis With Geothermal Energy for Low-Carbon Hydrogen Production

Abstract

Abstract In this paper, the integration of geothermal energy with high temperature electrolysis to produce low-carbon hydrogen is investigated. Geothermal energy provides a stable energy flux, allowing to achieve high electrolyzer utilization factors, the compatibility with industrial processes and reduced load oscillations on electrolyzers. If steam-fed high temperature electrolysis is employed a highly efficient low-temperature heat exploitation process is made possible, with an electrolysis electrical efficiency above 80 % on LHV basis. The study identifies the best design for the integration of high temperature SOEC (Solid Oxide Electrolysis Cell) electrolysis technology and geothermal energy and provides a techno-economic assessment, computing its performance and the Levelized Cost of Hydrogen (LCOH). To feed the 3 MW electrolyzer the system exploits a hot geothermal fluid, both to generate steam and power (via ORC). A model of the system is set up with Aspen Plus software. A set of low-enthalpy geothermal resources ranging from 85 °C to 160 °C are considered. The two technologies work synergistically, leading to an efficient and stable hydrogen production. The use of SOEC electrolysis allows to produce 34 % to 38 % more hydrogen than alkaline electrolysis. The economic evaluation shows an exponential increase in the geothermal plant specific Capex for decreasing geothermal resource temperature, leading to an analogous trend in the LCOH. A benchmark case is defined coupling a PEM electrolyzer with a PV plant. The LCOH grows from a value 15 % lower than the benchmark in the 160 °C geothermal brine case, to a value 20 % higher than the benchmark in the 85 °C case. The breakeven point is found at 98 °C. This promising result is even more valuable considering the high dispatchability and stability of the output.