# Developments in Electric and Green Marine Ships
## 4 Calculating onboard PVs and Battery Capacity
That is a contributing factor that leads the present research to different type of ships. The next category of ships that will be researched is passenger/RoRo cargo ships. Such ships are commonly used for commercial purposes, carrying a big number of passengers and cars for journeys ranging from 2 to 9 h. The main difference between cruise ships and ferries is that the latter are smaller, not only in terms of length, but also in number of docks. Furthermore, ferries do not make any particular use of the top of the ship, especially the kind of use that could make the installment of solar panels impossible. For the above reasons, the possibility of an efficient installment in a ferry ship is greater than that in a cruiser. Figure 8: Voyager’s power distribution as a percentage of the total power requirements. As with the cruise category, where a specific ship was chosen, the same logic applies to the ferry category. The chosen ship is the Nissos Mykonos, Hellenic Seaways, which is is 141 m long and 41 m wide. Assuming that the useful length and width, in terms of installing solar panels, are:  
\[{L_{\text{ship}}}^{u}=135\text{ m},\,{W_{\text{ship}}}^{u}=38\text{ m} \tag{5}\]  
The useful area for panels to be installed is \(A_{TP}=5130\text{ m}^{2}\), which translates to a total of 3206 solar panels. That amount of panels will have a total output of almost 0.6 MW. Noticeably, the ferry's power consumption is significantly smaller than Voyager's. The exact amount of the total power required by the Nissos Mykonos is 32 MW. Taking into account that the ferry is providing the same kind of services with a cruise ship, but on a smaller scale, a similar power distribution can be assumed. Hence, knowing that 32 MW is the total power required, leads to an approximate 8 MW required for electrical generation. Therefore, an installation of solar panels at the top of Nissos Mykonos would theoretically cover 1.88% of the total power, or 7.5% of the power needed for electricity generation. These results, although being satisfactory, are far from being able to provide even half of the total power required for the ship's operation. By focusing on the optimistic idea of having commercial ships operating only on solar energy, another idea emerged. A PV system would certainly require battery storage through which energy will be provided to the ship. Therefore, it is assumed that batteries are an essential installation. However, if the batteries had a bigger capacity, they could store more energy than just the amount provided by the solar panels. The available space on a ship, as mentioned before, forbids the installation of more panels to cover a bigger percentage of the total power requirements, but doesn't forbid the installment of more batteries. It is worth mentioning that cruise ships, as well as RoRo-passenger vessels, are among the most power-intensive vessels. The average power of the engines of such vessels is able to power small cities. In addition to that, they do also have higher electricity needs compared to other vessels. Therefore, satisfactory battery installments for cruise or RoRo-passenger ships could also be appropriate for other vessels such as cargo, etc., which have significantly smaller power needs. The new scenario consists of two main parts. Part one considers the installment of a battery system that is quite large in order to be available to provide a substantial amount of energy. Part two considers separating the production of power--the solar panels--from the storage system: the batteries. The main idea is that having the batteries on board the ship is essential; however, charging them can happen either on board or off board as well. Expanding on this, there could be a charge point in each port; then, once the ship docks, it could charge with the required energy for the upcoming trip. On this occasion, once the ship reaches the port, it could plug in and charge. The amount of energy drawn while charging could power the ship's needs for travel.