The overall aim of this project is to establish a generic modelling platform for the design and operation of zero-emission MW-scale hybrid electric energy systems, with a particular focus on maritime transport applications. The project seeks to integrate battery and fuel cell degradation models with operating strategy models to minimize the total cost of ownership (TCO) of hybrid battery/fuel cell systems. The modelling approach used here, to simulate battery and fuel cell degradation, takes advantage of empirical modelling methods already established in the scientific literature. This approach offers three distinct advantages over alternative multi-physics models, in that empirical degradation models are (i) computationally efficient, (ii) can be integrated into other modelling frameworks, and (iii) can support the quick parameterization of different systems.Real-life battery and fuel cell degradation data, collected using state-of-the-art materials, was used to quantify the model parameters and validate the proposed degradation models. A variety of advanced in-situ electrochemical characterization methods have been employed to quantify the relevant parameters at the beginning-of-life and again after various stages of ageing to determine degradation rates of the relevant parameters.The second aspect of this project is the implementation of a technoeconomic optimization model that combines the data-driven degradation models with additional inputs such as operating conditions, operational profile (i.e., drive cycle), cost of hydrogen, cost of electricity, etc. to design optimal hybrid battery/fuel cell systems and determine optimal control strategies to minimize degradation and total cost of ownership over the system lifetime.This talk will focus on the advanced in-situ electrochemical techniques that have been used to extract fuel cell degradation parameters and provide an overview of both the empirical degradation and technoeconomical models. Finally, we will present the optimization results obtained using our platform for the implementation of a hybrid energy system in a coastal Norwegian ferry.