Life Cycle Assessment Report of the SOFC-Battery Genset for Cruise Ship

The NAUTILUS project is developing a low-emission energy system tailored for long-haul cruise ships, with the aim of reducing greenhouse gas (GHG) emissions by 50% and nearly eliminating all other diesel engine exhaust gas emission components.

The genset concept comprises an LNG fuelled Genset based on Solid Oxide Fuel Cell (SOFC) hybridized by a battery, coupled with existing Internal Combustion Engine (ICE) generators. The ICE generators will be gradually replaced by SOFC – battery Genset in the vision to have the cruise ship fully powered with the hybrid Genset. The fuel flexibility of the SOFC-based system is a key benefit so for further enhancing emission reduction the Genset system is planned to be fuelled by alternative fuels in the future.

Apart from drafting and verifying the technical aspects of the Genset concept, the project is conducting analyses to evaluate various aspects of the novel marine energy system. One completed analysis is the Life Cycle Assessment (LCA) of the proposed technology solution, assessing the overall environmental impacts of an integrated marine energy and propulsion system based on SOFC-Battery hybrid gensets using LNG as fuel. Additionally, other potential future fuels that were previously identified in the project were assessed. The assessment methodology adhered to ISO 14040 and 14044 standards for LCA and was conducted by the VTT Technical Research Centre of Finland.

The SOFC-battery hybrid Genset is expected to have the potential to comply with emission regulations set by the International Maritime Organisation (IMO), setting thresholds at 50% lower Greenhouse Gases (GHGs) and 99% lower pollutants (SOx, NOx, and Particulate Matter) compared to commonly used fuels. The NAUTILUS project goal is to comply with these emissions targets set for 2030. In the LCA, the performance of SOFCs with a list of fuels was compared to the performance of an Internal Combustion Engine (ICE). The selection of SOFC relevant fuels was previously determined in another analysis within the project (D7.2 - Genset performance report with future fuels). Promising energy sources for the marine sector were identified based on various criteria, resulting in a short list that includes ammonia, hydrogen, methanol, LNG, and Diesel (synthetic Fischer-Tropsch diesel). For more information, refer to D7.2  

The Life Cycle Assessment compared the system's performance with the different fuels in three operation modes: at berth, at sea, and manoeuvring, based on the percentage of hours spent in each mode during the cruise, provided by cruise operators. Six environmental impact categories were selected for study, considering the relevance to the technologies under scrutiny. The selected categories include impacts on climate, air quality, water systems, and resource availability. Other impacts, such as those on human health from particulate formation, may be considered in a later stage of the NAUTILUS project.

Environmental Impact Categories studied in the LCA

Global warming potential (GWP)

Global warming potential is based on the potential of each greenhouse gas to warm the atmosphere once emitted. It is measured in carbon dioxide equivalents (CO2e) by multiplying the inventory results of each greenhouse gas with conversion factors given by Intergovernmental Panel on Climate Change. The factors describe the global warming potential of emissions within the next 100 years, allowing for the summation and reporting of a product's carbon footprint.

Figure 1 total global warming potential results of fuel production and use for the studied fuels in SOFC system comparing them to the reference ICE systems.

Acidification potential (AP)

Acidification is caused by sulphur dioxide and nitrogen oxide emissions. These oxides react with the existing water vapor in atmosphere and form acids which fall back to the earth in the form of rain, snow, or aerosol. Acidification damages the environment, endangers certain living organisms and also has negative effect on structural resilience of building constructions.

Abiotic depletion of resources potential (ADP)

Abiotic depletion of resources potential measures the consumption of non-biological resources, specifically minerals, metals, and fossil fuels. It assesses the potential depletion of abiotic resources based on factors like the availability of resources and extraction rates.

Eutrophication potential (EP)

Eutrophication potential refers to the likelihood of eutrophication occurring in water ecosystems when organic compounds and nutrients are enriched in water ecosystems. This situation increases production of plankton and other water plants resulting in reduced water quality.

Photochemical oxidant formation (POF)

While ozone is protective in the stratosphere, it is toxic to humans in ground level in high concentration. Photochemical ozone, also called “ground level ozone”, is formed by the reaction of volatile organic compounds and nitrogen oxides in the presence of heat and sunlight, key component of photochemical oxidation.

The results of the LCA study

SOFC-battery hybrid genset is expected to have potential to comply with the emission regulation of IMO for 2030 - 50% reduction of GHGs and 99% reduction of other pollutants (SOx, NOx and PM) compared to the commonly used fuels, mainly HFO. The impact of SOFC fuels compared to ICE were evaluated against Environmental impact categories. The LCA results for the SOFC system were compared to ICE systems, with calculations performed for the five fuels listed previously, taking into account their electrical and heat efficiencies. In comparison to ICE diesel (NOx tier II) and ICE HFO, a 99% reduction in pollutants (SOx, NOx, PM) is possible for almost all selected fuels, except conventionally produced ammonia and hydrogen, which slightly exceed the threshold. In other impact categories where SOx, NOx, and PM emissions are relevant, such as freshwater eutrophication, all but one (LNG) of the studied SOFC fuels fail to have a positive impact compared to ICE diesel (NOx tier II). LNG potentially has a lower impact in this category, but the 99% reduction in pollutants is not achieved.

When comparing pollutants (SOx, NOx, and PM) between SOFC and ICE diesel (NOx tier III) or ICE LNG, the reduction potential is significantly lower. Against diesel (NOx tier III), the best SOFC options appear to be green hydrogen, bio-methanol, and green ammonia, with green hydrogen potentially being the best option in most impact categories. ICE LNG exhibits the lowest impacts among all reference ICE technologies in all studied impact categories. The reduction potential of SOFC with different fuels is approximately the same as when compared to NOx tier III diesel. Within the studied categories set for the LCA analysis only green ammonia, green hydrogen, and bio-methanol has potential to achieve the targeted 50% reduction in GHG emissions compared to ICE references.

The NAUTILUS project represents a significant step forward in designing a low-emission energy system for long-haul cruise ships. The completed Life Cycle Assessment (LCA) is an initial step in assessing the environmental impacts of novel technology, but other measurements will follow within the duration of the project. The complexity of the problem reveals the necessity for a more detailed and data-driven examination. Efforts to prove system's compliance with emission targets will be concluded in D7.5 at the end of the project where actual measured data from the Genset concept will be taken into account. This step would help to bridge the gap between theoretical potential and real-world application.

This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 861647.

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