It is about ownership, does the community own the energy and/or the energy generation company. It s not actually about whether its green or not, although the energy is likely to be green to attract community investors. The community could be virtual or local - so it would be possible for people in an inner city to run and own a off shore wind turbine, get the grid to transport the energy, for a premium, and deliver it to their inner city street. For the most part though the projects are going to be local and for local people use.
Since these groups are in effect mutual "banks" they will also slowly bring back a balanced finance sector. As with industrial revolution and the emergence of locally own banks , as building societies, that were the main building block of social improvement financially, here we have a similar possibility with energy as the currency. - yes it is potentially that important.
It is about a group of locals, who have no political intentions, wanting to put something back to help their local community. Their reasons could be many fold but typically cover, energy saving, energy generation, creating a sustainable revenue stream, improving the environment, creating a more 'joined up' community and improving energy awareness. As most community groups are typically 'non-political' they are able to engage with and more easily obtain the support from all organisations (such as Parish, Borough, County Councils etc). These Community Groups create a vision and passion that is difficult to challenge - it is the opposite of NIMBYism - so this should be encouraged, developed and supported. Maybe we call it SCIMBY (Support Communities In My Back Yard)!
Yes, I think it is about ownership too. There are other ways of structuring it, but the vast majority are Cooperative or Community Benefit Societies. Indeed one definition could be "a community energy scheme is a Cooperative or Community Benefit Society that sells shares to raise money for (local, renewable) energy production (and saving - remember it is nearly always cheaper and easier to use less energy than it is to generate more by any means)
Not hard to define:
Community Benefit Societies, Co-ops & Community Interest Companies that have generating or saving energy as part of their core aims and due to their legal structure have to directly benefit the community. Other types of schemes claiming to benefit the community just have to adopt one of those structures.