Abstract
This work presents a review of life-cycle assessment (LCA) studies of hydrogen electrolysis using power from photovoltaic (PV) systems. The paper discusses the assumptions, strengths and weaknesses of 13 LCA studies and identifies the causes of the environmental impact. Differences in assumptions of system boundaries, system sizes, evaluation methods, and functional units make it challenging to directly compare the Global Warming Potential (GWP) resulting from different studies. To simplify this process, 13 selected LCA studies on PV-powered hydrogen production have been harmonized following a consistent framework described by this paper. The harmonized GWP values vary from 0.7 to 6.6 kg CO2-eq/kg H2 which can be considered a wide range. The maximum absolute difference between the original and harmonized GWP results of a study is 1.5 kg CO2-eq/kg H2. Yet even the highest GWP of this study is over four times lower than the GWP of grid-powered electrolysis in Germany. Due to the lack of transparency of most LCAs included in this review, full identification of the sources of discrepancies (methods applied, assumed production conditions) is not possible. Overall it can be concluded that the environmental impact of the electrolytic hydrogen production process is mainly caused by the GWP of the electricity supply. For future environmental impact studies on hydrogen production systems, it is highly recommended to 1) divide the whole system into well-defined subsystems using compression as the final stage of the LCA and 2) to provide energy inputs/GWP results for the different subsystems.
Highlights
With the increased interest in hydrogen as a sustainable fuel, the life-cycle environmental performance of its production is gaining importance
The average global warming potential (GWP) of all reviewed studies is 3.71 kg CO2/ FUhar and the median of 3.69 kg CO2/FUhar. These differences between original and harmonized GWP are mainly caused by the harmonization of the compression stage, which resulted in extra emissions of 0.24 kg CO2/functional units (FU) on average
The GWP upon compression had to be accurately quantified, to recalculate the original GWP to FUhar and the emissions caused by liquefaction were subtracted, causing lower GWP of FUhar compared to original results
Summary
With the increased interest in hydrogen as a sustainable fuel, the life-cycle environmental performance of its production is gaining importance. Hydrogen is generally considered to be a clean fuel because of the absence of emissions during its use. The predominant production processes of hydrogen have been steam methane reforming and coal gasification, both of which, due to the use of fossil fuels, result in the emission of a large amount of greenhouse gases, which are by-products of hydrogen production (Bundesministerium für Wirtschaft und Energie (BMWi), 2020; IEA, 2019). Life-cycle assessment (LCA) can be used to measure and compare the sustainability of GWP of PV-Powered Hydrogen Production different hydrogen production chains. LCA is generally defined as a compilation and evaluation of the inputs, outputs and potential environmental impacts of a product system throughout its life cycle following DIN 14040 and DIN 14044 (DIN 14040, 2006; DIN 14044, 2006)
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