Study’s results published in prestigious international scientific journal
Today’s shipping industry is the world’s eighth largest source of CO2 emissions, and the goal of the International Maritime Organization (IMO) until 2050 is to reduce those emissions by at least 50% over the year 2008. With regard to this issue, a researcher from the Polytechnic School of the University of São Paulo (Poli-USP) set out to find alternatives for improving the energy efficiency of maritime vessels used by the petroleum and natural gas industry. One was found to achieve a reduction of about 10% in both CO2 emissions and fuel consumption. The study was recently published in the prestigious international scientific journal Energies, which is dedicated to the subject of electrical energy.
“The proposal works with the concept of adapting the ship. The main generators, which were original to the vessel, are maintained, but we also use complementary energy sources: auxiliary generators, batteries, and fuel cells,” explains São Paulo electrical engineer Giovani Giulio Tristão Thibes Vieira, the lead author of the article. “The main objective of our work was to analyze the ideal configuration of a ship’s power system, taking into account the use of three types of batteries and fuel cells with hydrogen tanks of assorted sizes. In our search for these answers, we evaluated all possible combinations among them.”
Hot topic – The discussion of means for reducing CO2 emissions of ships is a hot topic around the world, as Vieira points out. He is currently studying at Aalborg University, in Denmark. The invitation came in reaction to an article he wrote in 2019 for the RCGI Hybrid Energy System for Ships project, coordinated by Professor Bruno Souza Carmo, from Poli-USP.
“Interest in this topic has been growing, worldwide, since the late 2000s. In 2008, the International Maritime Organization (IMO) decided to reduce the global limit on sulfur oxide emissions resulting from fuel combustion by the world’s merchant fleet. Later, an IMO 2020 regulation established that the sulfur content limit in ships’ fuel be lowered from 3.5% to 0.5%. In such designated emission control zones as the Baltic Sea and the United States, the limit is already 0.1%,” Vieira says.
One short-term solution to help ships adapt to lower CO2 emissions is to take advantage of a retrofit. According to Vieira, there are companies throughout the world that produce a type of container that houses battery packs with their management and protection systems, as well as converters. “The container also has internal temperature control. This solution is ready to be installed on ships,” he says. The scholar also says studies show that 50% of the ships in activity in the world, today, will continue to operate until 2030. “We researchers need to think of short-term solutions so that these vessels can adapt to a new reality and reduce CO2 emissions. This study brings to light some of the possibilities.”
Vieira estimates that the use of batteries may be a short-term solution, because the fuel cell, being relatively new, is a technology that is not very accessible from an economic point of view. Therefore, in addition to the emissions issue, the study also dealt with battery lifespan. “Batteries help to reduce emissions at two different moments. They discharge when demand is low and replace the main generators when they would operate in lower efficiency situations. These batteries are then charged so as to raise the generator’s total charge factor, which generally leads to better efficiency conditions,” he explains. However, the process of charging and discharging causes wear and tear on the battery. “A battery with more charge and discharge cycles has a shorter lifespan, and this financial impact needs to be evaluated,” he concludes.