For electric propulsion systems, batteries are the lifeblood of war. With the development of electric vehicles, whether boats or cars, technologies are evolving rapidly. We therefore wanted to discuss with a specialist to better understand the issues at stake. Christian Hallberg, Oceanvolt's sales manager, was kind enough to answer our questions.
BI: First of all, can you remind us of the first steps of the electric motor in the nautical industry and the problems encountered?
CH : In 2009, the first electric Lagoon 420 catamarans were equipped with lead-acid batteries. This technology, if successful, has several important disadvantages, which have been a barrier to the development of electric pleasure craft.
The acceptable discharge rate for a lead-acid battery must not exceed 50 to 60%. In order to ensure a good autonomy, the battery fleet must therefore be very large, which results in a high on-board mass. A large part of the engine power is then used to transport batteries. This technology is acceptable on heavy river shuttles as it has been operating for years, but not on recreational boats. On the first electric catamarans, the power required was underestimated, which led to the equipment being used beyond its capacity, at the risk of degrading it.
Lead-acid batteries do not allow temperature monitoring. The risk of overheating that would damage the battery is not controlled. The boat may therefore suddenly find itself without propulsion without this being anticipated.
Finally, the limitation to a low DC voltage leads to high amperages. This increases the risk of overheating and battery stress.
BI: What has the arrival of Lithium-Phosphate batteries brought in terms of technology?
CH : The new Lithium-Phosphate technology has brought two major advances in terms of weight and safety. For an equivalent capacity, a Lithium-Phosphate battery is 4 times lighter than a lead-acid battery. The absence of reactive components makes it the safest technology. While other solutions such as NMC (Nickel Magnesium Cobalt) batteries have a higher energy density, they are more reactive and require liquid cooling, which is complex to install.
When sizing a battery, the acceptable charge and discharge current must be considered. The battery must be able to cope with high stress over a short period of time, for example when carrying out port operations at full power. Thanks to Lithium-Phosphate, this permissible discharge current is 10 times higher than that of lead-acid batteries, which makes it possible to reduce the battery fleet. In addition, since the permissible charging current is generally estimated at half of the discharge current, the charging time is shorter for Lithium-Phosphate batteries.
From the point of view of use, safety has also increased. We have to be careful about the type of BMS (Battery Management System) used, because it's a bit like a jungle in all this. With existing active systems, it is now possible to monitor cell parameters separately and react to automatically isolate a defective element. The other cells continue to operate and the boat remains manoeuvrable.
BI: From an economic point of view, electric propulsion remains expensive. Do you think the automotive market can help boating?
CH : The price of lithium-phosphate batteries is still high. Today we are at 950 euros / kWh. Storage now represents half of the investment in an electric propulsion system for a boat. The explosion in the electric car market will help to lower this price, even if the technologies will not always be the same in the short term. For safety reasons in the marine environment, voltage limitation is a major technical difference.
Beyond the economic aspect, R&D in the automotive industry will help batteries to become more environmentally friendly, as they are currently far from being green...
In the end, there will necessarily be convergence. The best batteries for the automotive industry will also be those for recreational use.
BI: How do you see the future for electric propulsion in the nautical industry and for Oceanvolt?
CH : The main technical issues remain weight and voltage limitation.
For both yachting and automobiles, things are moving faster than analysts predict. Within 5 years, I think we should have gained 50% on both the price and the weight of the batteries. The hybrid and all-electric should be the basic proposal for the majority of sailboats. Then, as soon as an efficient fuel cell allows it, we will do without diesel engines.
On the Oceanvolt side, we are the driving force behind this movement. We are already working with several of the largest yacht builders, in France and abroad, to offer our electric motors as a basic offer.