## 4 Consideration about Economic Sustainability  
In order to assess economic sustainability, all of the evaluations of the LCoE for the offshore floating wind plants, as for any other generation technology, have to be compared to selling prices of the energy during the plants lifetime. In the past decades, incentive mechanisms were in place for the renewable generation. Most of them are based on a fix fid-in tariff for all of the (previously defined) lifetimes of the plants. The lifetimes for the wind plants are usually set in 20 years for onshore plants and 25 years for offshore ones. Most of the present generated wind electricity is paid with this tariff. In many countries, including Italy, this mechanism is still in place. The access to the incentive tariff usually takes place through downward auctions. For example, the base tariff for the onshore wind and photovoltaic plants in the 2019 auction in Italy was \(70\) \(\upxi\)/MWh. However, the incentive mechanisms will experiment a gradual decrease until they disappear. One of the new mechanisms to sell renewable energy is the power purchase agreement, where a private subject will buy renewable production at a fixed price for a given period. The period is usually shorter (or significantly shorter) than the lifetime of the plant. At the end of this period, the agreement can be renegotiated. The renewable energy can also be sold directly in the electricity market, however, this market needs a strong redesign to not penalize too much the fluctuating renewable generation (typically solar and wind generation). At present, the market works on \"demand and supply\", so countries with very high fluctuating renewable production could experience situations in which the price of electricity falls to zero, or even becomes negative, i.e., the noon of a windy day in the summer. This is, for example, what many countries, such as Italy, experimented during the coronavirus disease 2019 (COVID-19) pandemic lockdown [33]. Many production facilities were closed and the electricity demand deceased significantly. Therefore, the penetration of the renewable reached the highest even value, but the prices dramatically fell. This will occur more often with the expected increase of wind and solar plants in the next decades, without intervention on the electricity market structure. Some mitigations can be obtained storing the excess of wind production directly with storage systems (batteries); however, these system are still of quite small size compared with the average wind plant one, expensive [34], not completely reliable, and there is no clear regulation about them. Many other storage systems, i.e., pumping the water up in the big hydro plants or offshore compressed air energy storage (CAES) [35], can be associated to wind production, but they are strongly dependent on the presence of already operating plants and/or on the morphologic characteristics of the geographical area. Another way of using the excess of production is the generation of hydrogen or other gaseous fuels. This is the so-called \"Power to Gas\" option [36]. Wind generation can also contribute to the recharge of electrical vehicles, which are seen as distributed storage in a future \"vehicle to grid\" scenario [37]. Wind generation can also contribute to distributed generation in isolated small grids, such as the small island ones [38] or the energy supply of offshore oil and gas platforms, such as the Tampere Hywind floating wind plant [39]. In a future vision of smart grids, wind generation can also contribute to supply energy to an \"aggregate\" of production and demand that is seen as a unique subject by the grid. The aggregate has the purpose to use the generated energy in a smart way inside the aggregate and mitigate the variability of what is send to the grid. In Italy, tests of small aggregate are already in place [40]. Moreover, wind generation can contribute to the frequency regulation of the power grid [41].