The diversity of communities was mentioned previously. Because of that, it might be helpful to think about different ways individuals and communities consume information and in turn are motivated. I would think different motivations would resonate more strongly with different individuals and different communities, and at different times. An interactive matrix might help users/communities more easily access the motivations/incentives most immediately relevant and applicable to that user.
Have you considered partnerships with Universities? A university with a strong sustainability or renewables program could create a practicum course where graduate students received course credit for being Ambassadors? This approach could begin to build important relationships with the possibility that some Ambassadors moving towards an Angel role as they move through their careers. It would also connect the project with a large network, particularly if the involved universities were strong research universities.