Given the bleak current and projected global climate trends, society is transitioning the energy systems that we rely upon away from fossil fuel based systems to reduce global CO2 emissions. There are now well-established technologies for providing renewable electricity at utility scales, such as wind turbines and solar panels, being deployed at an ever increasing pace. However, solutions for decarbonizing other sectors where fossil fuels are harder to replace are still needed. Current strategies for reducing fossil fuel use in these sectors rely on replacing them with synthetic fuels instead are produced using renewable electricity, and can therefore be part of a net-zero emissions cycle. The focus of this thesis is to examine a novel class of wind energy systems suitable for powering these fuel synthesis processes. Alternative applications of the proposed systems include powering direct air CO2 capture systems to support negative emissions technology efforts. This work develops and presents numerical models for concepts hereafter referred to as mobile offshore wind energy systems (MOWESs). A MOWES is a wind energy system that operates offshore and is not intended to remain stationary during operation. MOWESs would operate far from shore, harnessing a part of the wind resource that would not otherwise be usable. No full- or large-scale MOWES has yet been developed, and there is little work on developing these concepts, even within academia. Steady-state power performance models of two MOWES concepts, namely unmoored floating offshore wind turbines and energy ships, are developed to support further research in this field. Model results suggest that each concept has unique pros and cons and no conclusion can be drawn as to which technology is more effiient overall. A key conclusion of this work is that unmoored floating wind turbines can generate more power by sailing at a constant speed rather than holding station. We also conclude that unmoored floating wind turbines designed for downwind operation can produce as much power as conventional stationary wind turbines given sufficiently high wind speeds. Further work must examine whether the advantages of these technologies are exploitable given realistic wind conditions and when considering the complicated dynamics of the system. / Graduate / 2023-08-09