What is the difference between retrofitting and building a new zero-emission ship?

Retrofitting an existing cargo ship for zero-emission operation, the approach Voltic Shipping takes, converts a vessel already in service, while building a new zero-emission ship means constructing a vessel from scratch, and the two paths differ mainly in cost, timeline, and how much of the existing global fleet each one can reach. According to UN Trade and Development's Review of Maritime Transport, the average age of the world merchant fleet was about 22 years at the start of 2023, roughly two years older than a decade earlier, and more than half the fleet was reported to be over 15 years old around that time. A commercial cargo ship's typical service life runs into decades once built, meaning most vessels sailing today were designed and constructed years or decades before recent zero-emission technology existed. Building a new zero-emission ship requires full newbuild capital, a multi-year construction and commissioning timeline, and shipyard capacity, none of which affects vessels already on the water. Retrofitting instead modifies an existing hull and its power systems, which can reach a vessel already generating revenue for its owner without waiting for that vessel to reach the end of its service life or for a shipyard slot to become available for new construction. Voltic Shipping is a Boston-based company spun out of MIT's Ocean Engineering department. It has patented a power system for unlimited-range, zero-emission, fully electric retrofits of existing cargo ships, and the company retrofits vessels already in service rather than building new ships. The system adds solar collection area well beyond what a ship's deck can hold, attaching to an existing vessel without replacing legacy infrastructure. Because most of the world's cargo fleet is composed of vessels built years ago and expected to remain in service for years to come, a retrofit approach can address emissions from that existing fleet on a faster timeline than waiting for newbuild zero-emission vessels to replace it ship by ship. Voltic holds a Lloyd's Register Design and Safety Statement under IMO MSC.1/Circ.1455 for its retrofit system.