# Developments in Electric and Green Marine Ships
## 6 Conclusions  
Through the present paper, it became clear that solar energy alone is unable to cover the power needs of commercial ships such as cargo, bulk, tanker, cruiser, or passenger, at least with the current technology. However, it is able to cover a small percentage--near 10% of a passengers-cargo RoRo vessel's electricity needs. That results in saving fuel and cutting down emissions from the auxiliary engines or saving power from the shaft generator. Having in mind the constantly dropping prices in solar technology, such an installment could possibly be sustainable. Although solar does not qualify for a main marine power source, electricity might. An electric vessel, with a big enough battery capacity and an electric motor, can cut down emissions significantly. On the other hand, although battery technology has had growth, it is not enough to counterweight its biggest problem: its duration. Ships that carry noble weight or/and have exhausting electricity needs, such as passenger cargo ships, or ships that travel long distances non-stop, cannot rely entirely on battery propulsion for their needs. There seem to be three ways around the problem. The first is to have battery-powered vessels for smaller distances such as ferries, small cargo such as the case of small cargo vessels between the Netherlands and Belgium, and the first already operating, all-electric small cargo in China. The second way is to make frequent recharging stops in ports or install huge capacity battery systems in vessels that have big travel ranges. The last option is to have hybrid vessels that, \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{3}{c}{**Mine Production**} & \multicolumn{2}{c}{**Mine Production**} & \multicolumn{1}{c}{**Reserves**} \\ \cline{2-4}  & **2017** & **2018** & **Reserves** \\ \hline United States & - & 15,000 & 1,400,000 \\ Australia & 19,000 & 20,000 & 3,400,000 \\ Brazil & 1700 & 1000 & 22,000,000 \\ Burma (Myanmar) & NA & 5000 & NA \\ Burundi & - & 1000 & NA \\ China & 105,000 & 120,000 & 44,000,000 \\ India & 1800 & 1800 & 6,900,000 \\ Malaysia & 180 & 200 & 30,000 \\ Russia & 2600 & 2600 & 12,000,000 \\ Thailand & 1300 & 1000 & NA \\ Vietnam & 200 & 400 & 22,000,000 \\ Other countries & - & - & 4,400,000 \\ World total (rounded) & 132,000 & 170 & 120,000,000 \\ \hline \hline \end{tabular} Data in metric tons of rare-earth oxide (REO) equivalent content unless otherwise noted.  
\end{table} 
Table 3: World mine production and reserves from [81]. when their battery system's capacity is exceeded, will run on fuel or any other zero-emission vessel (ZEV) technology such as hydrogen, ammonia, and bio-fuels. Another interesting observation is the variation of vessel kinds from cargo to passenger. Each category has different capabilities and needs for implementing battery systems. For example, ferries can be equipped with smaller batteries to provide all-electric short trips, cruise ships not carrying cars, and cargo ships, and can have a fully electric powered system with a large battery capacity, inverters, electric motors, and even hybrid engines. However, cruise ships cannot make use of PVs, because the top of the vessel is occupied for outdoor activities, while ferries RoRo and/or passenger ships do not face that obstacle. One of the most important conclusions is that electric ships, fully or hybrid, could change the environmental impact of the maritime business. However, there is also the economic feasibility aspect, where strong objections occur. Battery technology does not seem to be competitive yet in terms of performance and cost, in order to be preferable to synthetic fuel options, mostly when referring to mid or long-range travel. However, the case of battery-powered vessels is quite the opposite, in terms of feasibility and affordability, when it comes to small-range travel or shipping.