## 2 Background
### Main Drivers and Barriers
Authors have also pointed out that a techno-economic analysis of energy alternatives is not sufficient to explain RES diffusion and the barriers to their adoption [39; 40]. Recent broader perspectives incorporated behavioral and social aspects to evaluate potential barriers for the deployment of PtG [19]. Thus, the involvement of stakeholders is a priority in the short term for renewable gas technology [36]. In this topic, the theoretical framework of the policy mix maps the contextual dynamics from the stakeholders' vision with a double objective: to provide transition contracts and to define barriers in a changing socio-technical environment [41]. From the demand-side, it is expected that the current users of natural gas will readily accept this technology despite their diversity (domestic appliances in buildings, industrial sector, heat and PtG turbines, compressed natural gas, etc.,). Unlike hydrogen, it is not necessary to update the gas network or other appliances for PtG, and there are no cost or technical limits for either the distribution or the current appliances for natural gas use. Currently, regulation is another barrier to PtG deployment because the regulatory framework defines conventional commercial deployment models, but providers and consumers must act in a circular model in the future. The increasing integration of distributed renewables requires specific regulation to reach economic feasibility. Thus, incentives are seen as key policies to achieve this objective. Previous instruments aimed at promoting RES were based on primary instruments (feed-in tariffs or quotas with tradable green certificates), and secondary instruments (soft loans, fiscal incentives, or investment subsidies) [42]. Feed-in-tariff schemes are very common in the European Union to support PV systems connected to the grid because they are integrated in policy mechanisms to encourage investments in RES by offering long-term contracts to generation from renewables [43]. In recent decades, different governments promoted specific policies based on the feed-in tariff scheme, tax incentives or renewable portfolio standards, capital grants, soft loans, R&D, or demonstration projects to introduce large-scale RES into power markets [44]. Although the feed-in tariff scheme is now less justified, mainly because of the reduction of the costs of PV systems [45], these mechanisms could be updated to support PtG development in the future. Nonetheless, some authors argue that the conviction about the technical suitability of the investment opportunities plays a substantially more important role in driving investment than the perceived effectiveness of existing policies [39]. Generally, consumers provide public support for green electricity via their electricity bills. In particular, in countries in which RES generation has significantly increased, such as Spain [46], there is a concern that this support places a significant cost on consumers [47], which must be taken into account by policymakers. As a general remark from the analysis of the potential incentives to PtG, we find that the relevance of economic barriers related to investment would be reduced if we considered the PtG process as a new concept of CO\({}_{2}\) hybrid storage based on renewables. Some of the synergies of these hybrid systems are already being tested under real conditions (e.g., PtG-Amine scrubbing, PtG-wastewater treatment). In addition, the efficiency of these systems could be optimized by symbiosis of industrial sectors and their waste streams, thus improving the consumption of resources and the investment in new equipment. Others synergies have been studied, e.g., PtG-oxyfuel using simulations of the combustion processes [48; 49] and PtG-Electrochemical hybridization [50]. In this context, it is clear that PtG should be part of a strategy toward the CE that would benefit its deployment. The development of collaborative business models and synergies with other energy sectors is also a priority for the deployment of PtG [51].