Energy is an essential factor that must not be overlooked in discussions concerning mitigating and confronting effects associated with human-induced climate change. This work delves into the Chilean and Brazilian energy transitions, scrutinizing just and sustainable aspects, primarily in the local context. The study highlights and compares the experiences of both nations' on-grid energy communities. The methodological pathway comprises three phases: examining regulatory frameworks, assessing on-grid energy communities’ infrastructure in both countries and delving into emerging energy cooperatives. Our findings suggest that on-grid energy communities have the potential to foster a more widespread sustainable energy transition, especially when established as cooperative entities. However, there are no easy solutions to date, as justice and democracy are not guaranteed if stakeholders are not adequately engaged. Although there are fewer cooperative cases in Chile, all show a cross-cutting involvement of different members of society, while some Brazilian cases do not.