The demand for green ships has grown significantly, driven by efforts to reduce greenhouse gases (GHG) and produce eco-friendly vessels. Since the introduction of IMO energy efficiency indexes, the maritime industry has focused on solutions such as voyage optimization, energy management, innovative hull designs, electrification of energy systems, and alternative fuels to reduce fuel consumption. On the other hand, the task for greater energy efficiency improvements has triggered stricter legislation constraints leading the classification societies to issue new rules and regulations. Progress toward fully electric vessels is accelerating, with advancements in electrical systems that enhance both robustness and flexibility. The European-funded project “RETROFIT55” is an example of these efforts, focusing on improving vessel performance also through electrical solutions. Key innovations include the installation of shaft generators, which improve the ship’s design efficiency indices. Additionally, the project studies the benefits of installing photovoltaic (PV) panels on ships to provide green auxiliary power, further enhancing energy efficiency. A case study using actual ship data from project partners highlights these advancements, demonstrating the potential for improvements in efficiency and sustainability in the maritime industry.