# Comparative Analysis of Marine Alternative Fuels for Offshore Supply Vessels
## 2 Methodology
### Fuel Availability  
Figure 7 illustrates the fuel production sites that are available in Scotland, but only inland locations are included. The availability of fuels based in Scotland is taken into account when scoring the matrix.  
Ammonia is primarily produced from fossil fuels, but Scotland has green and blue hydrogen production sites, with more expected due to GHG reduction policies. While ammonia production infrastructure is sufficient, the lack of bunkering facilities remains a key barrier to its adoption in shipping.  
Hydrogen can be produced from various energy sources without major capacity limitations. Green hydrogen is essential to avoid GHG emissions from grey hydrogen production. While 95% of global hydrogen comes from fossil fuels, Scotland has significant green and blue hydrogen production capacity. However, the lack of bunkering infrastructure is a key challenge for using hydrogen as a future marine fuel.  
Biodiesel has the advantage of being classified as a drop-in fuel and can be easily applied to ships. However, the current production capacity is very limited, especially rare in green biodiesel. On the other hand, bunkering infrastructure of conventional fuels can be shared considering the characteristics of these fuels.  
Methanol is not yet a major marine fuel, so bunkering infrastructure is limited. However, building infrastructure for methanol is expected to be easier than for hydrogen or ammonia. With existing production infrastructure, methanol production can scale up easily as demand increases.  
As the number of ships using LNG as fuel increases, LNG bunkering infrastructure is gradually being established around the world. However, the UK currently lacks the infrastructure for LNG bunkering, especially in Scotland, where there are no LNG ports, which poses challenges to fuel applications in terms of infrastructure. In addition, LNG production is not well settled in Scotland.  
Figure 7: Fuel production sites in Scotland.  
Onshore power supply infrastructure is well developed, but few ships use batteries as their main propulsion, and the energy density of electric power limits its application to sea-going vessels, resulting in limited charging infrastructure. Scotland, however, has ample green electricity production from renewables, generating more than half of its electricity this way, which also supports the production of green ammonia and hydrogen. As shown in Figure 8, more than half of total electricity is generated by renewable energy. Based on this, green ammonia and hydrogen can be produced in Scotland as well.  
Table 17 summarises the results of ratings associated with fuel availability in consideration of fuel types, infrastructure available, and production capacity for various propulsion systems.  
\begin{table}
\begin{tabular}{p{113.8 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt}} \hline \hline \multirow{2}{*}{**Fuel**} & \multirow{2}{*}{**Case**} & \multirow{2}{*}{**Fuel Type**} & \multicolumn{2}{c}{**Fuel Availability**} \\ \cline{3-5}  & & & **Infrastructure (Bunkering)** & **Production Capacity** & **Total** \\ \hline \multirow{8}{*}{Ammonia} & Grey & 2 & 4 & 6 \\ \cline{2-5}  & Mechanical propulsion & Blue & 2 & 4 & 6 \\ \cline{2-5}  & Green & 2 & 4 & 6 \\ \cline{2-5}  & Grey & 2 & 4 & 6 \\ \cline{2-5}  & Electric propulsion & Blue & 2 & 4 & 6 \\ \cline{2-5}  & Green & 2 & 4 & 6 \\ \cline{2-5}  & Electric propulsion + battery & Grey & 2 & 4 & 6 \\ \cline{2-5}  & Green & 2 & 4 & 6 \\ \cline{2-5}  & Fuel cell (PEMFC) + battery & Blue & 2 & 4 & 6 \\ \cline{2-5}  & Green & 2 & 4 & 6 \\ \hline \multirow{2}{*}{Hydrogen} & Grey & 1 & 4 & 5 \\ \cline{2-5}  & Fuel cell (PEMFC) + battery & Blue & 1 & 4 & 5 \\ \cline{2-5}  & Green & 1 & 4 & 5 \\ \hline \hline \end{tabular}
\end{table}
Table 17: Rating numbers for fuel availability.  
Figure 8: Electricity production by sources in Scotland.