This section relates to the relevant consideration for the early adaption of e-methane as an alternative fuel.
The main feedstocks for producing e-methane are low emission electricity, water, and CO2. For low emission electricity, mature technologies like solar, wind and hydro are in place but not at the scale required. Key challenges in the production of e-methane therefore remain availability of power-to-X (P2X) technology and scaling of low emission electricity. Main cost drivers for e-methane production are the costs for low emission electricity, along with the cost of the electrolyzers needed for hydrogen production. Furthermore, a renewable source of CO2 is essential for producing e-methane, but qualified renewable CO2 point sources will most likely not be available in the scale needed which may also drive cost. Biogenic CO2 point-sources (CO2 released as a result of combustion or decomposition of biomass and its derivatives) may have limited availability, and Direct Air Capture (DAC) is even more expensive. The potential use of nuclear electricity for e-methane production remains uncertain and an area for further exploration.
Methane synthesis based on natural gas or coal gasification is a mature technology but using renewable electricity as the main feedstock is new and a cost driver. Commercially mature electrolyzers (such as alkaline and PEM) are currently too expensive and inefficient to make e-methane a competitor to other alternative fuels and fossil fuels. Global electrolyzer production capacity is not ready for massive power-to-X roll-out in large scale and record pace construction of new large-scale methane plants is required if e-methane is to have a significant role in decarbonizing shipping. The size of e-methane plants is likely to be limited by the scale of CO2 source supply, thereby diminishing economies of scale, and increasing the cost of e-methane.
Fuel supply logistics and bunkering are well established for liquefied natural gas (LNG). Given that methane is the main constituent of LNG, e-methane is not representing any fundamentally new challenges in fuel storage, logistics and bunkering. If methane expands further as a shipping fuel, the port infrastructure for methane-based marine fuels must expand. Safety and all relevant operating procedures are already in place to deal with e.g. explosion risk. A remaining challenge at terminals and during bunkering of methane is the low boiling point resulting in a latent risk of boil-off. Well-to-wake emissions accounting will require strict control with methane venting or release in the entire supply chain.
Liquid storage of methane requires advanced cryogenic storage systems at -163C, but technologies for storing and converting methane onboard vessels are commercially available. Internal combustion engines (ICEs) using methane are currently adopted in the current liquified natural gas (LNG) fleet. Different ICE technologies including dual-fuel high-pressure and low-pressure two-stroke engines and four-stroke engines are currently used with varying cost, efficiency, and emissions. Furthermore, methane-fueled fuel cells are coming on the market with multiple smaller-scale demonstrators ongoing.
Currently, hundreds of LNG-fueled vessels are in commercial operation. If regulations and safety management practices are followed, no obstacles remain regarding safety and onboard operations for major scaling of methane as a maritime fuel. However, it will require attention to crew competence development for un-familiarized operators.
Methane combustion does release CO2 – but with e-methane providing significant negative value for well-to-tank emissions, a greenhouse gas emissions benefit is clearly obtained from a well-to-wake perspective. High-pressure two-stroke engines have very low methane slip (~0.2%). Other engine types (such as low-pressure two-stroke and 4-stroke engines) have higher methane slip (up 3-4%). Methane slip should be reduced through regulations that incorporate methane into a CO2-equivalent methodology combined with further development of onboard emission reduction technologies like catalysts.
Well-to-wake greenhouse gas quantification for methane (or LNG) is not developed in appropriate regulatory bodies such as the European Union (EU) or International Maritime Organization (IMO). Well-to-wake methane emissions remain a concern to be properly managed and enforced.
Life cycle assessment policy needs to be developed. Regulating the climate impact of fuel use from a life cycle perspective offers the industry the opportunity to establish sustainable fuel production and consumption patterns. By regulating the upstream (well-to-tank) climate impact, fuel users can select fuels with solid sustainability credentials. Regulation from a life cycle perspective also reduces the risk of burden shift of climate impact from the downstream (tank-to-wake) part of the value chain to the upstream. This is an important consideration for alternative marine fuels whereby much of the climate impact resides in well-to-tank activities.
The well-to-tank contribution for e-methane requires strong focus – including monitoring and enforcement of fugitive emissions up-stream as well as onboard combustion. Methane to be a regulated vessel emission with required levels set to promote further technology development and adoption of low-methane slip solutions. Vessel methane emission regulation to be implemented at the EU level and is currently under discussion at IMO.
LNG and methane-based marine fuels: Prospects for the shipping industry - Documentation of assumptions for NavigaTE 1.0 (2021)