The transition toward decentralized and renewable energy systems in buildings increases the need for energy sharing mechanisms that reduce mismatches between local generation and demand while maximizing self sufficiency. Renewable Energy Communities (REC) are legal entities that allow individuals to collectively produce, consume and share renewable electricity within a defined geographical perimeter. Unlike traditional aggregation schemes, where energy flows unidirectionally from large scale producers to end users, RECs enable virtual sharing of locally generated renewable energy through the public distribution grid. By aligning local production with consumption, they enhance self consumption, foster renewable deployment, mitigate variability from distributed generation and reduce dependence on centralized imports, with associated economic benefits for members.