A. Stationary – Hybrid GEN/BAT for electrical loads
B. Low Speed – Propulsion and electrical loads from Hybrid GEN/BAT
C. Cruise – Mechanical propulsion, Hybrid GEN/BAT electrical loads
D. Performance (Boost) – Combined mechanical and electrical propulsion/loads from Hybrid GEN/BAT
The main purpose of these modes provides operational flexibility to ensure the optimal engine load, performance and efficiency.
Fuel Saving and CO2 Reductions
Whilst we now know fuel can be saved by running diesel engines at optimal loads, the more difficult question to answer is; by how much?
One DNV study ‘Electrical Energy Storage For Ships, published in 2020’ suggested that the ‘fuel saving potential’ for yachts was around 5 – 10%. Engine manufacturers and yacht builders tend to be a little more “optimistic” with the potential savings and benefits often using emotive words to describe their benefits.
Where you measure the ‘delta’ from matters, as using the extremes will result in significant differences in SOFC, but may not reflect the real-World use – the time the engines spend at least efficient load may have very limited effect on overall consumption.
It is important not to focus on the headline figure, but to evaluate the potential savings across a range of speed and load scenarios that are expected with the yachts use. The engines technical files will help identify the real savings.
Is It Worth It
The evidence confirms that a well-designed ‘Hybrid’ system can have a positive impact today in terms of more efficient yachts and reduced fuel consumption. According to the IMO fuel coefficient, every ton of MGO/MDO emits 3.206 tCO2. So, on that metric alone, the answer would have to be yes.
Unfortunately a ‘Hybrid’ yacht will be more expensive which no doubt affects more widespread use. When viewed purely on a cost/benefit basis, it may be hard to justify the extra cost against the potential fuel savings, and reduced operational costs due lower engine hours and extended maintenance intervals. Depending on use, the break even point may be a many years away and lay outside the envisaged ownership timescale. So as long as it’s an ‘option’ from builders cost will probably trump environment.
In the evaluation process, it worth considering the cost of diesel fuel may increase in the future due to carbon tax, and renewable fuels such as HVO (drop-in diesel) will be significantly more expensive. So, the additional cost today, may be sound investment for the future?
Finally, whatever energy is used in the future, it will likely be less energy dense than diesel fuel, and certainly more expensive. This means power management and efficiency will become even more critical and Hybrid technology will remain a fundamental component, especially in mixed energy solutions.