The current architecture of the power grid is outdated and will not provide the means to deal with the decentralization of energy sources. The smart grid is a newly envisioned architecture for the power grid that should solve the weaknesses in the current grid. One application that is part of the smart grid vision is the microgrid: a coalition of prosumers that is able to operate either in parallel to the power grid or isolated from it.

In this work we investigate how these microgrids should be formed in order to maximize their usability while at the same time preserving the freedom of choice for participants. We apply a game theoretic perspective to simulate the choices of individual users. This results in a problem that combines the notion of core stability and maximization of social welfare. For this problem we provide a complexity proof, followed by a relaxation of core stability, $k$-stability, by limiting the available knowledge for participants. Finally we produce our own distributed algorithm which can act as a heuristic.