(325d) Techno-Economic Assessment of Heat Integration from Concentrated Solar Thermal Energy into Solid Oxide Electrolysis for Green Hydrogen Production

In the Paris Agreement of 2015, 196 countries agreed to take action to mitigate climate change and limit global warming to below 2°C. To achieve this goal, countries aim to decarbonize their energy sectors as much as possible. The use of green hydrogen may play a vital role in reducing the emissions of ‘hard to abate’ sectors like fertilizer production, ore processing and long-distance transport. It could also be used in long term energy storage to mitigate the variable nature of renewable energy sources.

Problem statement

Green hydrogen can be produced with water electrolysis that utilizes renewable electricity to split water into hydrogen and oxygen. The cost of green hydrogen electrolysis is currently still significantly higher than steam methane reformation which produces a lot of carbon dioxide. The highest contribution to the levelized cost of hydrogen is the cost of renewable electricity. The electricity demand for electrolysis can be reduced if heat energy is supplied by vaporizing water before it enters the electrolyzer. High-temperature solid oxide electrolysis cells (SOECs) that uses steam at 700-1000°C has the highest electrical efficiency compared to other low temperature water electrolyzer technologies. The high efficiency is a result of the faster reaction kinetics due to the higher temperature. This work investigates the technoeconomic impacts of integrating concentrated solar thermal (CST) energy into a hypothetical SOEC plant to determine if this integration could produce more cost-effective green hydrogen compared to using only electric heating.

Motivation

Technoeconomic analyses on the integration of SOEC plants with concentrated solar thermal energy have been previously documented in literature. However, limited attention has been given to the direct technoeconomic comparison between solar heat integration and electric heating. To the authors’ best knowledge, there is no published literature on the direct comparison with using transient weather data to simulate annual production of hydrogen for both cases.

Methodology

This work modelled a 100 MW hypothetical SOEC plant with wind farm, photovoltaic plant, and a CST plant. Two systems are compared: one where heat is supplied via CST and the other where electric heating is used. Both systems source electricity from a photovoltaic and wind farm. A mathematical model of the SOEC has been created based on the work of previous published literature that uses area specific resistance to characterize the SOEC. A balance of plant model around the SOEC was built in Ebsilon Professional software that includes the compression and purification of the produced hydrogen to 30 bars. Both systems were modelled with one year of hourly variable weather data for a predefined location to determine annual hydrogen production.

Expected results

The primary question that will be answered in the presentation is whether CST makes sense in this system or not. The presentation will cover the economic comparison based on the levelized cost of produced hydrogen of the two systems. Additionally, the presentation explores the effects of changing operating conditions of the SOEC at both cell and balance of plant levels and their implications on heat integration and the levelized cost of hydrogen.