When Bigger Is Not Greener: Ensuring the Sustainability of Power-to-Gas Hydrogen on a National Scale.

As the prices of photovoltaics and wind turbines continue to decrease, more renewable electricity-generating capacity is installed globally. While this is considered an integral part of a sustainable energy future by many nations, it also poses a significant strain on current electricity grids due to the inherent output variability of renewable electricity. This work addresses the challenge of renewable electricity surplus (RES) utilization with target-scaling of centralized power-to-gas (PtG) hydrogen production. Using the Republic of Korea as a case study, due to its ambitious plan of 2030 green hydrogen production capacity of 0.97 million tons year-1, we combine predictions of future, season-averaged RES with a detailed conceptual process simulation for green H2 production via polymer electrolyte membrane (PEM) electrolysis combined with a desalination plant in six distinct scale cases (0.5-8.5 GW). It is demonstrated that at scales of 0.5 to 1.75 GW the RES is optimally utilized, and PtG hydrogen can therefore outperform conventional hydrogen production both environmentally (650-2210 Mton CO2 not emitted per year) and economically (16-30% levelized cost reduction). Beyond these scales, the PtG benefits sharply drop, and thus it is answered how much of the planned green hydrogen target can realistically be "green" if produced domestically on an industrial scale.

Techno-economic and environmental assessments for sustainable bio-methanol production as landfill gas valorization.

With the regular increase in global solid waste, landfilling is intensively used for waste disposal. However, landfill gas (LFG) produced as a byproduct during waste decomposition in the landfills is a serious problem since it leads to damage to the eco-systems. Accordingly, it has been highlighted to convert LFG into other value-added chemicals. In this study, LFG utilization was studied in terms of conversion into methanol (MeOH) by considering different scenarios of LFG utilization. Techno-economic analysis and environmental assessment were performed to identify the economic feasibility and environmental impact of each case. From the economic analysis, bio-MeOH production costs of 879.16, 724.52, and 1,130.74 $ ton-1 for case 1, 2, and 3 was estimated with the economic infeasibility, while substantial cost reduction through projected cost analysis can lead to economic competitiveness (449.52 $ ton-1 for case 2 and 595.76 $ ton-1 for case 3). In sequence, the quantitative environmental impacts in terms of climate change impact were 2.360, 0.835, and 0.605 kg CO2-eq kg MeOH-1 for cases 1, 2, and 3, respectively. Based on the results of two analyses, a multi-criteria decision analysis was conducted to investigate the acceptable case of bio-MeOH production in the economic and environmental aspects. It can be concluded that the most feasible case depends on decision-makers if only economic and environmental criteria were considered. Therefore, dry reforming and membrane separation of LFG have considerable potential for bio-MeOH production in terms of LFG utilization for high weighting of economic and environmental aspects, respectively.