Technologies such as solar PV, proton-exchange membrane (PEM) fuel cells and hydrogen can be used to reduce CO2 and particulate emissions in marine vessels such as large cruise ships, which are usually driven by diesel reciprocating engines, according to a new case study by a group of Swedish researchers.
In Hybrid solar PV/PEM fuel Cell/Diesel Generator power system for cruise ship: A case study in Stockholm, the scientists argued that much needs to be done to further reduce greenhouse gas emissions and oil pollution, despite technological developments in diesel engines that have already facilitated huge fuel savings. Without further action CO2 gas emissions from large marine transport vessels could rise by 50% to 250% by 2050, they warned.
One viable way to reduce greenhouse emissions is to integrate renewable energy technologies – or renewable fuels such as biodiesel, biogas, hydrogen, liquefied natural gas (LNG), methanol and ethanol – into existing ships or new vessels. Solar PV, which has already been identified by other researchers as the best renewable energy technology to power commercial ships, could be installed in the upper decks of vessels.
The proposed propulsion system for the case study would be powered by PV panels, PEM fuel cells, an electrolyzer for H2 production, an aH2 storage tank, and an inverter. The system would be designed to serve the main and auxiliary hourly AC loads of a cruise ship.
The Swedish researchers simulated different renewable power systems to identify the best low-cost solutions, based on set constraints. As a benchmark, they used a cruise ship operating in the Baltic Sea between Stockholm and Mariehamn, in Finland's Åland archipelago. They assumed the vessel consumed 22,987 kWh of auxiliary power per day, including lighting, heating and ventilation systems, and then experimented with different renewable power systems to identify the best solutions. They concluded that four 2760 kW auxiliary diesel engines would be necessary.
However, the researchers have also proposed a renewable power system architecture featuring a 1,000 kW PEM fuel cell, a 5,850 kW diesel generator, a 1,200 kW solar PV system (3,636 solar panels), a 1,083 kW converter, a 2,000 kW electrolyzer, and a 500 kg hydrogen tank.
“The energy production from the system is: 9.44% (1,941,871 kWh/year) from the PV system, 4.39% (902,374 kWh/year) from the PEM fuel cell, and 86.17% (17,734,133 kWh/year) from the generator,” they said. “All the energy produced from the distributed generation is consumed by the cruise ship electrical load (90.5% or 18,621,578 kWh/year) and the Electrolyzer for hydrogen production (8.64% or 1,777,417 kWh/year).”
The researchers estimated the total cost of the system at around $4.5 million, with the solar component accounting for about $1.44 million. They estimated the lifetime cost of electricity at $260/MWh.
The generator and solar panels would supply most of the power during the day, while the diesel engine would kick in at night, supported by the PEM fuel cell systems. This would reduce greenhouse and particulate emissions from the diesel generators by around 9.84%, with solar accounting for 9.44% of onboard electricity consumption and the PEM fuel cell covering roughly 4.39%.
“The results obtained in the course of this study are for the cruise ship located in Stockholm (Sweden) where the solar irradiance is low (2.87 kWh/m2/day),” the researchers said. “The integration of renewable energy systems for cruise ships and ferries will produce better results with higher renewable fractions, lower emissions and lower cost in regions where the solar irradiance is higher such as the desert regions.”
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