Electrofuels in a circular economy: A systems approach towards net zero
Davis Rusmanis, Yan Yang, Aoife Long
Energy Conversion and Management
School of Mechanical and Manufacturing Engineering

There is no silver bullet solution when it comes to decarbonising hard-to-abate sectors such as transport, waste management and agriculture. Full electrification will not satisfy all long-distance haulage vehicles nor the production of agri-products such as milk and cheese. We need holistic approaches to move towards net zero GHG emissions, facilitated by a circular economy integrating carbon capture and utilisation technologies and novel negative emissions technologies.

One method for progressing towards net-zero can be formed through the production of electrofuels. Recent projections have shown the Irish electricity grid will be operating at 80% renewable electricity by 2030. Whilst this is crucial, renewable wind and solar power introduces the issue of variable renewable energy (VRE) production which can cause the mismatch of energy production and energy demand. If no means for energy storage is available, electricity is curtailed or constrained. Battery technologies can help alleviate this variability of production but are limited by low storage capacity and low discharge time. 

Electrofuels (or power-to-X systems) are a potential flexible energy storage solution complimenting VRE sources. These electrofuels can be gaseous (hydrogen, methane) or liquid (methanol, Fisher-Tropsch diesel), enabling stable, energy dense, and relatively inexpensive forms of energy storage. Previous studies have shown the viability of hydrogen (H2) production from VRE, relying on bidding strategies to determine the levelized cost of energy for production of H2, offering viable pathways for green H2 in a sustainable green economy.

In this DCU research collaboration, the authors propose a novel cascading, circular economy system, that is based on the production of electrofuels through the capture of otherwise curtailed electricity. The aim of the system is to provide opportunities for improved decarbonisation of the hard-to-abate sectors, such as transport, agriculture, water, and the energy sector. The system-of-systems approach, as illustrated in, is proposed to demonstrate how the hard-to-abate sectors could be tackled in a future strategy that strives to reach net-zero by reducing multi-sectoral emissions.

Our analysis considers the feasibility of such a system at an industrial site in Co. Cork, Ireland. The site has two existing 3-MWe wind turbines, and is nearby a large wastewater treatment plant with adequate gas and electricity infrastructure situated in the locality. The proposed system underlines the importance of situating electrofuel systems at opportune locations such as municipal wastewater treatment plants, which are frequently co-located with AD plants to process sludge waste. Municipal wastewater treatment plants exist in almost all urban locations and are often situated near existing grid infrastructure (gas and electricity), making wastewater treatment plants strategically optimal locations to produce electrofuels, synergising the three sectors of water, gas and electricity.