(630a) Advancing Towards a Net-Negative Carbon Economy: Integrating Solid Direct Air Capture with Green Hydrogen Production for Economic Enhancement

The urgent need for a sustainable energy system has catalyzed widespread initiatives to reduce carbon emissions, with carbon dioxide being a primary target [1]. A leading solution in this endeavor is Direct Air Capture (DAC), a technology engineered to directly remove carbon dioxide from the atmosphere [2]. Within the realm of DAC, the Temperature-Vacuum Swing Adsorption (TVSA) technique, utilizing solid absorbents, stands out for its energy efficiency [3], quick response times [4], and its synergy with fluctuating renewable energy sources [5].

Simultaneously, green hydrogen (GH) is gaining traction as a key sustainable energy vector. GH is hydrogen produced through renewable energy-driven water electrolysis, with Proton Exchange Membrane (PEM) electrolyzers noted for their versatility [6]. Furthermore, green hydrogen and e-fuels are emerging as critical elements in the envisioned sustainable energy ecosystem, especially for clean energy applications in transportation and heating [7]. There's a concerted research focus on generating green hydrogen from renewable resources and converting it into e-fuels such as methane [8] or methanol [9], using the carbon dioxide captured by DAC technologies. E-fuels are particularly advantageous for their compatibility with existing energy distribution and utilization infrastructures.

However, the primary obstacle to the widespread adoption of these energy systems is their high costs, exacerbated by the intermittent nature of renewable energy sources. This intermittency necessitates substantial investments in infrastructure and results in notable energy losses, affecting the overall efficiency of these technologies [10]. Overcoming these challenges related to cost and efficiency is crucial for the practical implementation of these innovative energy solutions.

Our research proposes the integration of solid DAC systems with GH systems through the concept of sector-coupling to overcome the prevailing challenges of high costs and energy efficiency. Unlike GH systems, which require a consistent and stable energy input, solid DAC systems boast operational flexibility. They can capture a predetermined amount of CO₂ within a set timeframe, allowing for their strategic shutdown during energy deficits and reactivation in times of surplus. This flexibility aligns energy usage with availability, optimizing the combination of GH production and CO₂ capture to enhance both efficiency and sustainability. Moreover, the shared use of power sources and energy storage in a sector-coupled system could lead to further economic gains.

The literature on sector-coupling highlights its potential for the synergistic integration of renewable energy systems, aiming for both economic and efficiency improvements. Furthermore, hydrogen is increasingly seen as a viable option for long-term energy storage in grids that depend heavily on variable renewable sources. Sector-coupling, especially in industrial contexts like cement and steel production or waste incineration, can lead to significant CO₂ emission reductions. For instance, Rafael et al. demonstrated that sector-coupling could achieve annual CO₂ emission reductions of up to 860 Mt in Europe—about 27% of its greenhouse gas emissions—while potentially halving the costs compared to standalone carbon capture and storage (CCS) technologies [11]. This emphasizes the critical role of integrating systems for attaining net-zero or even net-negative emissions in industrial sectors. Another study using the PyPSA-Eur-Sec-30 model focused on the broader integration of renewable energy across Europe, underscoring the importance of sector-coupling and enhanced cross-border transmission networks for achieving a 95% reduction in CO₂ emissions by 2050 [12]. Technologies like battery electric vehicles, power-to-gas units, and long-term thermal storage are key to this vision, with research suggesting that prioritizing power-to-hydrogen pathways could improve renewable energy use and lower total system costs, particularly in ambitious decarbonization scenarios [13].

Although sector-coupling is increasingly recognized for its ability to enhance the efficiency of renewable energy systems, there remains a significant research void concerning the integration GH systems with solid DAC technologies. This oversight presents a unique opportunity to not only improve the efficiency and economic viability of renewable energy and GH projects but also to foster the growth and acceptance of DAC technologies.

This paper posits sector coupling as a revolutionary approach to tackle the challenges at hand and drive progress towards a net-negative carbon economy. By delving into the economic and energy efficiency outcomes of sector coupling, especially its effect on the production dynamics between carbon dioxide and hydrogen, this study aims to shed light on its prospective advantages. It further explores the impact of various techno-economic factors, such as the operational flexibility of heat pumps and the cost implications of installing DAC units, on the design and economic viability of integrated energy systems.

By conducting a comprehensive analysis on an hourly basis, taking into account weather variability throughout the year, this research aspires to significantly enrich the conversation around sustainable energy systems. Our goal is to advance the understanding and adoption of these systems within both the academic community and the industrial sector, emphasizing the practical implications and benefits of sector coupling in enhancing the viability and efficiency of renewable energy initiatives.

[Reference]

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[3] Erans, María, et al. "Direct air capture: process technology, techno-economic and socio-political challenges." Energy & Environmental Science 15.4 (2022): 1360-1405.

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[10] Kim, Sunwoo, et al. "Multi-period, multi-timescale stochastic optimization model for simultaneous capacity investment and energy management decisions for hybrid Micro-Grids with green hydrogen production under uncertainty." Renewable and Sustainable Energy Reviews 190 (2024): 114049.

[11] Castro-Amoedo, Rafael, et al. "On the role of system integration of carbon capture and mineralization in achieving net-negative emissions in industrial sectors." Energy & Environmental Science 16.10 (2023): 4356-4372.

[12] Brown, Tom, et al. "Synergies of sector coupling and transmission reinforcement in a cost-optimised, highly renewable European energy system." Energy 160 (2018): 720-739.

[13] He, Guannan, et al. "Sector coupling via hydrogen to lower the cost of energy system decarbonization." Energy & Environmental Science 14.9 (2021): 4635-4646.