# Future Renewable Energy Communities Based Flexible Power Systems
## 2 Management of Energy Resources  
For a better understanding of how the management of energy sources is important, it is essential to clarify that there are conventional or traditional sources, which are hydraulics, fossils, and nuclear sources. They are considered so for their long history of large-scale use. In turn, alternative sources are the primary sources of unconventional energy in their origin, means of extraction, recovery cycle, and forms of use. Finally, non-renewable sources are those found in finite quantities in natural deposits or mines, such as oil, uranium, and coal (which have a long recovery cycle). All these sources are renewable only if the period of time is considered; they need to recompose themselves in days or millions of years, see Figure 1. Nevertheless, not all sources can be used in a city for practical reasons as presented in this paper. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Reference**} & **Future Types of Energy** & \begin{tabular}{c} **Power-** \\ **Electronic-** \\ **Based** \\ \end{tabular} & \
\begin{tabular}{c} **Sources of** \\ **Flexibility** \\ \end{tabular} &
\begin{tabular}{c} **Prosumers’ and** \\ **Communities’** \\ **Management** \\ \end{tabular} \\ \hline
[8] & ✓ & & & & \\ \hline
[9] & & & & ✓ \\ \hline
[10] & & & ✓ & ✓ \\ \hline
[11] & & & ✓ & ✓ \\ \hline
[12] & ✓ & ✓ & & \\ \hline
[13] & & ✓ & & \\ \hline
[14] & & & & ✓ \\ \hline
[15] & & ✓ & ✓ & \\ \hline
[16] & & & ✓ & \\ \hline
[17] & & & ✓ & \\ \hline
[18] & & & ✓ & ✓ \\ \hline
[19] & & & ✓ & ✓ \\ \hline
[20] & & ✓ & & \\ \hline Our paper & ✓ & ✓ & ✓ & ✓ \\ \hline \hline \hline \end{tabular}
\end{table} 
Table 1: Some existing works discussing solutions for future power systems. As the access to alternative sources increases along with the demand for electrical energy, its historical value chain is transitioning to a new energy landscape, here introduced in the concept of Smart-Cities. The definition of Smart-City refers to an urban area able to manage its connected electric devices with resilience, robustness, and affordable cost. The use of such devices means that the distributed energy resources are based on renewable energy, energy storages, electric vehicles, smart-meters, and centralized controllers. Therefore, these devices must be equipped with Internet-of-Things technology. A condition to realize Smart-Cities is that residences, buildings, and industries should also be smart in a sense [6]. It is important to state at this point that, different from conventional energy sources, renewable energy such as photovoltaic and wind power have very specific generation periods and cannot be activated just on demand. Therefore, the intermittent behavior of the primary source of DG as well as the power mismatch between photovoltaic and wind power systems (PV and WP) and loads are challenges faced by the creators of Renewable Energy Communities and eventually Smart-Cities. In this context, means of energy storage such as Battery-Based Storage Systems (BSS) appear as prominent candidates to ensure energy supply in moments of low solar irradiance. In these cases, the use of large hydropower plants, coal, public network, and fuel as storage means rather than ordinary power generation should be considered. As a result, buildings with PV systems and BSS may maximize the usage of solar energy, reducing the emission of polluting gases [1]. Flexible electrical power systems require battery storage systems to perform functions other than its basics, known as ancillary services. Some examples are the reduction of power distribution losses, operation at minimum costs, improvement of stability and improvement of power quality. To perform ancillary services, in general, the BSS does not have its storage energy compromised. In other words, the BSS does not process active power during execution of ancillary services, except the losses. Therefore, conceiving of an interactive storage structure is very important for the realization of renewable energy communities. Figure 1: Energy depletion curves.