Hybrid use cases for Batteries on Ships
The figure below shows the percentage of pure electric, hybrid, and plug-in hybrid ships of the total number of battery powered ships delivered per year. Most battery powered ships delivered in 2010 were pure electric. This has changed to only a small percentage of battery powered ships being pure electric, and a majority of hybrid and plug-in hybrid ships. The number of fully battery powered ships is increasing, but with current available battery technology, most ships in the world are more suitable for hybrid solutions. So, let’s have a look at all the different hybrid use cases for batteries on ships.
Batteries can be used to increase operational safety and to add redundancy to the system by using them for blackout prevention, or as spinning reserve. Often applied on ships with dynamic positioning capabilities, batteries can be installed to delete the requirement of having an additional generator running in case one of the active generators fails. This results in direct fuel savings by reducing the number of running generators, but also saves on maintenance costs for the generators
If you have installed batteries as spinning reserve, they will only be used occasionally. Therefore, it is beneficial to investigate what else you can use the batteries for. Often the next step is to use the batteries for peak shaving. By using the batteries to support the generators at the highest peak loads, you can reduce the fuel consumption of the generators as well as the maintenance costs. It might even be possible to install a smaller generator, reducing your capital expenses.
Accelerating with a ship requires a significant amount of power and can often be one of the most power consuming parts in a ship’s operational profile. Batteries can be used for ramp support to assist the gensets while accelerating the ship. This can reduce the required generator size, reduce maintenance, and increase the acceleration speed of the ship. After reaching the desired cruising speed, the gensets can temporarily run at a higher load than the demand to recharge the batteries. On ships with gas engines, quickly ramping up can be a challenge as well. Batteries can provide a stable load profile on the engines, making sure they don’t stall.
Temporarily increasing the performance of a ship is doesn’t have to be restricted to ramping up when accelerating. Batteries can also be used for a boost function, increasing the speed or bollard pull for a specific amount of time. Most ships operate only a fraction of their time at maximum power. Therefore, it can be interesting to use batteries to help the genset with a boost, reducing the required generator size. This can result in a higher performance of the vessel, with smaller main engines or generators.
Batteries can also be used over a longer period in hybrid applications. Generators have an optimal load at which they perform the most efficient. However, the ship’s power demand usually fluctuates, making it difficult to keep the generators in at their optimal load. Batteries can be used for load levelling to keep the generators at a stable load, discharging the batteries when the demand is high, and charging the batteries when the demand is low. This can reduce the fuel consumption of the gensets, as well as the required maintenance.
Although for many ships currently battery technology is not sufficient as only source of energy, batteries can be enough to power the ships for short parts of the journey. Zero emission operations in ports or other areas with emission restrictions are possible with the technology of today. This can have a significant impact on local air quality around ports and urban areas. Combine this with a shore power connection for the most efficient source of energy for your ship.
Power regeneration is not as easy for ships compared to battery powered road vehicles. However, there are certain ship types where this is possible. For example, on ships with onboard lifting equipment. All the above use cases are feasible in combination with future alternative fuels and can make sense combined with fuel cells as much as with generators. The starting point is usually to begin with electric propulsion and identify the low hanging fruit for battery use cases. By constantly improving the collaboration between onboard power systems, the number of use cases for the battery can be expanded and the energy efficiency can be increased.