TL;DR
- The power-to-gas concept converts surplus renewable energy into methane (CH₄) via the Sabatier reaction:
4H₂ + CO₂ → CH₄ + 2H₂O. - Methane can be injected into existing gas networks for energy storage and distribution.
- The process shows:
- Technical feasibility: Energy loss of ~4% for CH₄ production (excluding H₂ and CO₂ generation).
- Economic challenges: High costs of CO₂ supply and renewable energy limit financial viability.
- Environmental benefits depend on sourcing CO₂ from biogenic or atmospheric sources rather than fossil fuels.
- Further research is required to:
- Optimize efficiency and reduce costs.
- Explore policy incentives and market opportunities
What is power-to-gas?
A power-to-gas concept assumes that we can use the energy from renewables during the period of reduced demand to produce hydrogen via electrolysis. To avoid the need for hydrogen compression and storage, produced hydrogen is then combined with CO2 to produce CH4. This is the so-called Sabatier reaction or CO2 hydrogenation reaction. The produced CH4 can be then injected into the existing gas networks, as shown in Figure 1 below.
Fig. 1: Representation of the power-to-gas network [1]
This process follows the reaction below:
4H2 + CO2 → CH4 + 2H2O
Is the power-to-gas process technically viable?
As you may know, process design, techno-economics and life-cycle assessments form a substantial part of my consulting and teaching activities. To refresh the curriculum of my modules, I’ve started developing new industrially-inspired case studies – methanation appeals to be an interesting concept from the process design point of view, and that is why I selected it as the very first case study to develop this year (much more to come!).
Fig. 2: Process flow diagram for methanation process
You can see the initial process design I developed in DWSIM, assuming both CO2 and H2 need to be compressed to the reaction pressure. Is this process feasible then?
Well, my initial analysis showed that this process would consume 0.59 kWh (2.12 MJ) of renewable energy to produce 1 kg of CH4 – and this doesn’t account for the energy required for H2 or CO2 production. Considering the heating value of methane of 55 MJ/kg, we are looking at the energy loss of about 4% for this process itself.
Economics and environmental performance of power-to-gas
Finally, it’s important to talk about the economics and environmental performance of such a concept. I’m yet to complete the full assessments and optimization of the layout, but my previous work can shed some light on these aspects.
Fig. 3. Economic viability of power-to-gas concept [2]
In my previous collaborative work with the research group led by Prof Luis Romeo [2], we evaluated the techno-economic viability of the power-to-gas process integrated with the oxy-combustion process for CO2 supply.
The economic analysis (Figure 3), showed that because of the costs associated with CO2 supply, the power-to-gas project may not be viable under the conditions we considered. This would, of course, change considering the recent changes in carbon markets.
And this brings me to the final point – the environmental implications. Naturally, we would like to use CO2 captured from the power plants so that we could add more value to it. But if that CO2 comes from the combustion of fossil fuels, then we merely shift the emission point. Sure, we could create economic value through this process, but it would not help us solve the global warming challenge.
So where such CO2 could come from? We would need to consider biogenic and atmospheric sources, but this would definitely have implications on process economics.
More work is needed – happy to collaborate!
Conclusions
In summary, while the power-to-gas process demonstrates technical promise with manageable energy losses, its economic and environmental viability remains contingent upon advancements in CO₂ sourcing and reductions in associated costs. Further research and optimization are necessary to enhance the overall efficiency and economic attractiveness of the system. Collaborative efforts and continued exploration of innovative solutions will be essential to overcome the current barriers and fully harness the potential of power-to-gas technologies in the transition to a sustainable energy future.
PS: If you need consultancy or training in process design and process economics, green energy transition, industrial decarbonisation, and carbon removal technologies, I am open to discussing how we can collaborate together!
References
1. Bailera M, Lisbona P, Llera E et al. Renewable energy sources and power-to-gas aided cogeneration for non-residential buildings. Energy 2019;181:226–38.
2. Bailera M, Hanak DP, Lisbona P et al. Techno-economic feasibility of power to gas–oxy-fuel boiler hybrid system under uncertainty. International Journal of Hydrogen Energy 2019:9505–
Frequently Asked Questions:
Power-to-Gas and Methanation Process
1. What is the power-to-gas concept?
The power-to-gas concept uses surplus renewable energy to produce hydrogen (H₂) through electrolysis. The hydrogen is then combined with carbon dioxide (CO₂) in a reaction known as the Sabatier reaction to produce methane (CH₄). This methane can be injected into existing gas networks, providing a way to store and transport renewable energy.
2. What is the Sabatier reaction?
The Sabatier reaction is a chemical process where CO₂ reacts with H₂ to produce CH₄ and water (H₂O):
4H₂ + CO₂ → CH₄ + 2H₂O
This reaction is exothermic, meaning it releases heat, and it requires specific catalysts and operating conditions to achieve efficient conversion.
3. How efficient is the power-to-gas process?
The initial analysis indicates that the process consumes 0.59 kWh (2.12 MJ) of renewable energy to produce 1 kg of CH₄, resulting in an energy loss of approximately 4%. However, this does not include the energy required to produce H₂ and CO₂, which affects overall efficiency.
4. Is the power-to-gas process economically viable?
Economic viability depends on several factors, including the cost of renewable electricity, hydrogen production, and CO₂ supply. Current analyses show that high costs associated with CO₂ supply, particularly from fossil fuel combustion, can render the process unfeasible. However, changes in carbon markets and alternative CO₂ sources may improve its economic outlook.
5. What are the environmental benefits of power-to-gas?
The environmental benefits depend on the source of CO₂. Using CO₂ from biogenic or atmospheric sources supports a circular carbon economy and helps mitigate climate change. However, using CO₂ from fossil fuel combustion shifts emissions without reducing net greenhouse gas levels.
6. Where can the CO₂ for this process come from?
CO₂ can be sourced from power plant flue gases, industrial emissions, or biogenic and atmospheric sources. While fossil-based CO₂ is more readily available, it does not offer net emissions reduction. Biogenic and atmospheric CO₂ sources are more sustainable but often come with higher costs and technological challenges.
7. How does power-to-gas compare to other energy storage solutions?
Power-to-gas offers the unique advantage of utilising existing gas networks for energy storage and distribution. Unlike batteries, which are limited in storage capacity and duration, power-to-gas can store large amounts of energy for extended periods. However, its efficiency and cost-effectiveness are lower compared to some battery technologies.
8. What are the next steps to make power-to-gas more viable?
Further research is needed to:
- Improve the efficiency of the Sabatier reaction.
- Optimize the integration of hydrogen production and CO₂ capture.
- Reduce the cost of renewable energy and CO₂ supply.
- Explore policy and market incentives to support deployment.
9. Can I collaborate on research in this area?
Yes, collaborations are welcome! If you’re interested in working on process design, optimization, or techno-economic and environmental assessments, feel free to reach out.
10. Why did you choose methanation as a case study?
Methanation is an industrially relevant and technically challenging process that showcases key aspects of process design, optimization, and sustainability assessment. It serves as an excellent example for educational purposes and aligns with my expertise in process design and consulting.
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