Researchers from the Cologne University of Applied Sciences in Germany have assessed Germany's potential to produce green hydrogen via a decentralized approach based on solar PV and electrolyzers under different scenarios. They have found that this combination is already competitive with blue or gray hydrogen generated via fossil fuels.
Their work focused on alkaline electrolyzers, which they described as a mature technology available at megawatt scale, and proton exchange membrane (PEM) electrolyzers, which they defined as a relatively new technology available for small-scale applications.
“Although alkaline electrolysis is a preferred technology, PEM electrolysis is slowly catching the attention of researchers,” they said.
As a case study site, the scientists selected Cologne, where several companies are producing and consuming hydrogen and where hydrogen demand at refueling stations is currently increasing. They assumed the utilization of a solar-powered electrolyzer with a rated production capacity of 21.36 kg/day. The alkaline device was designed to have an installed power of 49 kW and the PEM electrolyzer a capacity of 62 kW. Output pressure for the latter was indicated at 29.9 bar and for the former t 9.9 bar.
Six different scenarios were considered: an alkaline electrolyzer powered by an off-grid PV system with a capacity of 2.6 MW and a battery backup with a capacity of 7,250 kW; a PEM electrolyzer powered by a 3.3 MW off-grid PV system with a battery with a capacity of 9,125 kWh; an alkaline electrolyzer powered by an 850 kW grid-connected solar array; a PEM electrolyzer powered by a 1 MW grid-connected PV installation; an alkaline electrolyzer powered by a 680 kW off-grid PV system with a battery backup of 1,500 kWh and with limited operational time; and a PEM electrolyzer powered by a 950 kW off-grid PV system with a battery backup of 2,000 kWH and limited operational time.
For the last two scenarios, the electrolyzer's operating hours were selected to match with the actual time of solar generation. The levelized cost of hydrogen was evaluated considering the initial investment for building the systems, annual operation costs, annual hydrogen production, discount rate, and system lifetime, which was 20 years for all scenarios.
The higher LCOH was found to be that of electrolyzers powered by off-grid solar, which the scientists explained with the higher costs coming from deploying a battery backup.
“In the off-grid limited operations scenario, the system size is reduced, but the LCOH is still high,” they said, noting that the best performance was achieved by grid-connected solar powering the alkaline electrolyzer, which reached an LCOH of 6.23 €/kg.
For the purpose of comparison, the PEM electrolyzer powered by off-grid solar achieved 57.61 €/kg.
“The results clearly show the fact that the idea to run the electrolyzers 24 hours a day and round the year in off-grid mode is not economically feasible as the hydrogen produced is very expensive,” they said.
Their work also provides a model for system sizing and allows for the calculation of the LCOH anywhere in the world by changing the relevant input parameters. They presented it in the paper “Hydrogen as energy carrier: Techno-economic assessment of decentralized hydrogen production in Germany,” which was recently published in Renewable Energy.
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