Dynamic rating is an approach which implies to operate an electrical network closer to its thermal limits. This approach may be very beneficial for wave farms, as they are expected to present a highly fluctuating electrical current profile while benefiting from the large thermal inertia of the soil where their export cable will be buried. However, as the implementation of this approach is still in its infancy for offshore wind farms, it may be expected that the first wave farms, under the form of small-scale test sites, will be sized with respect to electrical current limits at a first stage. This sizing may be upgraded at a second stage when design methods will have included dynamic rating. However, this raises the question of the economic feasibility of this two-step approach, which is studied in this paper. Also, performing such a techno-economic analysis requires developing an electrothermal model of the export cable able to represent its transient response in a sufficiently precise manner while requiring also a reasonable computing time. In this perspective, a comparative analysis between several electrothermal modelling methods is also described in this paper.