Energy transition and its link to Green Energy Resources

Cities play a pivotal role in driving climate change, responsible for a staggering 70% of greenhouse gas emissions (GHG). In Europe, residential energy consumption accounts for around 40%, with heating and domestic uses alone contributing to 31% of the overall energy usage [1]. As global population continues to surge, projections indicate that by 2050, over two-thirds of the world's inhabitants will reside in urban areas [2]. This urbanization trend, coupled with the imperative to limit global temperature rise to below 2 degrees Celsius [3], underscores the urgent need to overhaul our current energy paradigm, which heavily relies on fossil fuels.

In response to these challenges, the United Nations has articulated the 17 Sustainable Development Goals (SDGs). These goals encompass a comprehensive approach to tackle various issues, with Goal 7 focusing on Affordable and Clean Energy, and subsequently, Goal 1 on Poverty, Goal 3 on Good Health and Well-Being, and Goal 11 on Sustainable Cities and Communities [4]. Realizing these SDGs necessitates rapid advancements in zero-emission electricity solutions for not only industries but also residential sectors and transportation, particularly as the shift towards electric mobility strains existing power networks [5].

Amidst these circumstances, Energy Storage Systems emerge as a crucial facet of the transition to sustainable energy models. While photovoltaic and wind systems show promise, their intermittent nature cannot single-handedly meet household energy demands. Li-ion batteries, anticipated as a linchpin in the energy transition, offer scalability and integration across a spectrum of applications, from mobility to housing infrastructure [6]. Yet, I hold the conviction that Hydrogen (H2) will assume a pivotal role in the short-term energy transition landscape. Distinguished by its eco-friendly attributes, Green Hydrogen provides a scalable energy storage solution for renewable facilities [7]. Notably, fuel cells exhibit an impressive efficiency of around 60%, outstripping the lackluster 34% efficiency of fossil fuel systems. Fuel cells not only generate electricity but also yield water as a benign byproduct [8].

Green H2 process:

The key aspect of green hydrogen it is that it has been obtained through the use of renewable energy, such as Solar energy and Wind energy. Figure below shows the whole chain to produce green H2 based on electrolysation. This process has more aspects but I have considered the Electrolysis and Hydrogen and Oxygen Production as the most important. Now, I will defined both of them:

  • Electrolysis Process: Electrolysis of water is conducted within a device known as an electrolyzer. It involves two electrodes submerged in water and separated by a conductive electrolyte. By applying a continuous electric current, the electrodes function as a cathode (where hydrogen is produced) and an anode (where oxygen is produced).

  • Hydrogen and Oxygen Production: At the cathode, hydrogen ions (protons) gain electrons and transform into molecules of gaseous hydrogen (H2). At the anode, oxygen ions (originating from water molecules) lose electrons and form gaseous oxygen (O2). The overall reaction is:

 2H2O -> 2H2 + O2


The role of green H2 to achieve net-zero emissions process:

Green hydrogen, produced through renewable energy-driven electrolysis, plays a vital role in achieving net-zero emissions. Its versatility as a clean energy carrier makes it invaluable for sectors challenging to electrify directly, such as heavy industries and aviation. Additionally, it contributes to grid stability by providing flexible load balancing, can be stored for intermittent energy supply, and aids in transitioning industries and transportation toward lower or zero carbon emissions. Furthermore, green hydrogen aligns with global climate goals by replacing fossil fuels in various applications, including fuel cells for electricity generation and energy-intensive processes. Its potential for international cooperation and trade in renewable energy resources makes it a linchpin in the endeavor to combat climate change, providing a cleaner, sustainable energy source across diverse sectors and driving the world closer to a net-zero emissions future.

In essence, effecting an energy transition necessitates acknowledging that a singular solution cannot effectively counter the intricate climate-energy quandary. Rather, the amalgamation of multiple solutions is key to navigating the escalating climate crisis. I posit the adoption of hybrid systems, encompassing hydrogen, Li-ion batteries, wind turbines, and solar PV panels, as a means to satisfy energy requisites ranging from individual residences to compact neighborhoods, including mobility needs. This synthesis of resources, propelling the decarbonization of urban centers, envisions self-sufficient microgrids that guarantee a consistent energy supply. Fuel cells and hydrogen storage mechanisms epitomize this pursuit of emissions-free energy autonomy.


[1] energía y turismo. E. (IDAE, Instituto para la diversificación y Ahorro de la Energía). Ministerio de industria, ‘Consumos del sector residencial en España Resumen de Información Básica’, 1, vol. 1. pp. 1–16, 2014.

[2] J. García López, R. Sisto, J. Lumbreras Martín, and C. Mataix Aldeanueva, A Systematic Study of Sustainable Development Goal (SDG) Interactions in the Main Spanish Cities. Springer International Publishing, 2021. doi: 10.1007/978-3-030-57764-3_5.

[3] F. H. Supervisor and H. Geography, ‘Investigating “ Improved quality of life ” Assessing social dimensions of GrowSmarter - a smart city project in Stockholm’

[4] T. Castillo-Calzadilla, M. A. Cuesta, C. Olivares-Rodriguez, A. M. Macarulla, J. Legarda, and C. E. Borges, ‘Is it feasible a massive deployment of low voltage direct current microgrids renewable-based? A technical and social sight’, Renewable and Sustainable Energy Reviews, vol. 161, no. January, p. 112198, Jun. 2022, doi: 10.1016/j.rser.2022.112198.

[5] D. F. Dominković, I. Bačeković, A. S. Pedersen, and G. Krajačić, ‘The future of transportation in sustainable energy systems: Opportunities and barriers in a clean energy transition’, Renewable and Sustainable Energy Reviews, vol. 82. Elsevier Ltd, pp. 1823–1838, Feb. 01, 2018. doi: 10.1016/j.rser.2017.06.117.

[6] M. Nasir, H. A. Khan, A. Hussain, L. Mateen, and N. A. Zaffar, ‘Solar PV-based Scalable DC Microgrid for Rural Electrification in Developing Regions’, IEEE Trans Sustain Energy, vol. 3029, no. c, pp. 1–9, 2017, doi: 10.1109/TSTE.2017.2736160.

[7] D. O. Akinyele and R. K. Rayudu, ‘Review of energy storage technologies for sustainable power networks’, Sustainable Energy Technologies and Assessments, vol. 8, pp. 74–91, 2014, doi: 10.1016/j.seta.2014.07.004.

[8] R. A. Huggins, Energy storage: Fundamentals, materials and applications, second edition. 2015. doi: 10.1007/978-3-319-21239-5.

[9] P. B. Mary

Keywords: Renewable energy, electrolysis, decarbonization, sustainable fuel, clean energy, hydrogen production, net-zero emissions, green technology, industrial transition, climate solutions.

Tony Castillo-Calzadilla,

Researcher Assistant 

PhD of Engineering by University of Deusto, Spain

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