Exhibit 21 - Subsidiaries of the Registrant Subsidiary corporations serving as general partners or managers of limited liability entities are listed with those entities. Name of Subsidiary Type of entity Jurisdiction of organization Ridgewood/Providence Power Partners, L.P. limited partnership Delaware Ridgewood/Providence Corporation corporation Delaware Ridgewood/Maine Hydro Partners, L.P. limited partnership Delaware* Ridgewood Maine Corporation corporation Delaware* *50% owned by Registrant Ridgewood Pump Services Partners IV, L.P. limited partnership Delaware Ridgewood Pump Services IV Corporation corporation Delaware