App and a digital platform to operating energy communities in buildings or districts with collectively self-consumption of solar. A “behind-the-meter” energy community, could be a large apartment building or cluster housing with collective power buy, solar PV, battery storage, and EV chargers. When a building has such installation, new needs, and opportunities arise. Enyday provides a solution for buildings with smart invoicing to ‘self-manage’ the collective electricity usage with significant savings while providing a community application engaging and nudging neighbors to consume energy in a sustainable and responsible way.