Study of New Consequences on Small Ferries Stability of Li-Po Batteries for Hybrid Propulsion

The Hybrid Propulsion is a reality now and is increasing its diffusion more and more. The basic concept of Hybrid Propulsion is the use of battery packs to store energy, and consequentially operate the propulsion system of the ship, in order to have zero emission navigation, especially in areas of environmental interest.This solution is especially important in small ships, where the limited Power, required for propulsion at low speed, can be easily provided by battery packs.This kind of propulsion makes extensive use of Li-Ion or Li-Po batteries, storing high quantities of energy (MWh); furthermore, the propulsion systems are usually operating with high voltage (660V or more) to guarantee an adequate efficiency to the system.On one side the Lithium based batteries offer a good capability storing energy, especially compared with Lead Acid batteries, but on the other side there is a risk of an explosion in case of overheating.The size of batteries used for propulsion is larger than the size of the batteries normally installed on board and this has a strong impact on the fire risk and on the consequent solutions to maintain safety.This paper will investigate the consequences of the hybrid propulsion in small ships, considering the State of Art of Rules regarding several points of view: the fire safety and the possible solutions adopted regarding Li-Po batteries. The study will consider the case study of a small passenger ship, and the available informations for fire protection in case of onboard batteries, also examining the general arrangement adopted and the position of the Li-Po batteries, and the consequences on the project. The results will arise some interesting questions as the possible problem of flooding of batteries and consequent damage. In fact, it s true that the manufacturer of batteries are providing the battery pack with protection for overheating but must still be considered the risk of overheating coming from a fire on board or the possibility of the physical damage of the battery pack as consequence of a collision.