Retrofitting existing rolling stock for wire-free travel: Exploring energy storage solutions for partial catenary-free light rail vehicle

• Despite space constraints on light rail vehicle, retrofitting for energy storage remains possible. • The current design will use either a lithium-ion battery (LiB) or a supercapacitor (SC), or an hybrid energy storage system combining LiB and SC (LiC). • Lithium-capacitor (LiC) is a manufacturing process that internally integrates LiB and SC into a new, single device, rather than a hybrid combination. • The LiC parameter is provided by the manufacturer, and because it is a single, integrated manufacturing process, the performance of LiC is much better than a hybrid device-level combination of LiB and SC. • Retrofitting existing rolling stock with LiC is feasible and offers a paradigm shift. This paper investigates the retrofitting possibilities of equipping existing rolling stock with a catenary-free system for tramways and light rail networks. In this paper, the term 'tramway' includes light rail vehicle (LRV) as defined in EN17343. Installation, ongoing maintenance, and replacement of electric traction systems is a major cost for light rail operators. Installing visible overhead line equipment (OLE) in historical cities has always been a challenge. Past records have shown that the significant capital cost and the time it takes to approve a transport scheme are major barriers to the implementation of light rail vehicle proposals. This paper shows that adopting a catenary-free (wire-free) system can reduce the capital costs of light rail system design and construction, especially in the city centre. Battery-powered transport, once considered economically unfeasible, now shows promise even for large vehicles including urban and main line rail. A thorough analysis of various energy storage options has been investigated, including parameters such as maximum C-rate (the rate of time in which it takes to charge or discharge a battery), specific energy, energy density, safety, lifespan, and cost comparison. Findings have shown that the state-of-the-art solution using Lithium-ion Capacitors (LiC) increases the energy storage weight of the light rail vehicle by just 2.1 tons, equivalent to 3.5% of the light rail's total weight, making it a feasible option to retrofit. The hybrid energy solution contributes to higher energy and higher power densities, as well as longer cycle life compared to pure lithium-ion batteries. It's also more environmentally friendly. This work has implications for other all mass transit systems. The paper provides an innovative solution that bridges the gap between energy storage technology and rail transport design.