## 4 Discussion  
There are many communities in the world still suffering from lack of fresh water. Many of these communities also face problems regarding access to electricity. Desalination has proved to be a mature cost-effective technology to locally produce the needed fresh water using sea or brackish water. The two most important factors affecting the environmental outlook of desalination are brine treatment and disposal and the energy consumed. As far as brine treatment and disposal is concerned, many efforts are taking place worldwide to minimize the desalination's environmental footprint [53; 54; 55]. This paper is focused on the energy aspect of desalination. RE costs have been declining heavily during the past decades providing the world with a clean alternative to fossil fuel based energy [56]. Global policies around the world related to sustainable development, climate, and energy as the UN Sustainable Development Goals [1], Paris Agreement [57], the European Green Deal [37], and the African Union Energy Transition strategy [58] are driving defossilization efforts. RO desalination coupled with renewables can address cost-effectively the current issues in terms of water scarcity, while minimizing the environmental footprint of the process. In this paper, it has been showcased that desalination powered by renewables can be deployed in practically any location on earth having access to sea or a brackish water source. Moreover, the use of renewables mostly in the form of PVs provides a simple and mature solution to employ green energy. It is highlighted that even in the cases that connection to the grid is possible, it is preferable to also deploy a PV system under a net-metering or comparable scheme depending on the country (e.g., net-billing). Keep in mind that for Greece, the current net-metering benefit is around USD 0.13/kWh, while the last auctions for PV parks ended with an average price around USD 0.05/kWh, highlighting the profitability of the net-metering scheme, taking into consideration that the installations can be up to 3 MWp. While the wind turbines can be more cost-effective than PVs in cases of high wind potential, especially for wind turbines not under the \"small wind turbines\" scheme (in Greece up to 60 kW which is also the limit for wind energy under the net-metering framework) the needed licenses and environmental permits can become a burden to the desalination plant developer, hence the priority given to PV installations. Based on the outcomes of this study (Table 3 and Figure 5), the following recommendations can be made:  
* Project developers should employ energy recovery for sea-water desalination plants and a techno-economic study to be made for brackish water plants, since the salinity of feed water greatly affects the impact of energy recovery. * Project developers should employ a RE system in addition to the desalination system. For grid connected plants the easiest approach is to use a PV plant connected under a net-metering or comparable (e.g., net-billing) scheme. * For cases where there is either no space for the optimal size of PV installation to meet the load under a net-metering or comparable scheme or the needed PVs are beyond the maximum allowed by the regulatory framework, it is advised that the maximum feasible installation is realized. * Distributed energy storage in a grid connected system ought to be investigated only in cases that the regulatory framework provides relevant incentives. * Autonomous systems are technically feasible, but more expensive than grid-connected including renewables under net-metering schemes and ought to be deployed only in cases where grid connection is either more expensive due to distance and topography or simply not existing. * Larger desalination plants operating for less hours during the day are more cost-effective in autonomous scenarios. * When a low-enthalpy geothermal power source is available near the installation site it is strongly advised to investigate its possible use for autonomous systems.