Energy is a key issue when it comes to mitigating anthropogenic climate change. However, renewable energy is not necessarily sustainable, it largely depends on the modes of production and distribution. Agrofuels, offshore wind farms, or large solar projects in the Sahara are mainly means to increase profits of big energy companies, have a negative impact on food supply or the environment, and some are not even CO2 neutral. As long as the power supply is in the hands of large corporations no significant progress can be expected with regard to a reduction in energy consumption and an affordable energy supply for all. However, renewable energy sources are ideal for the decentralization and democratization of energy supply. If citizens take their control into their own hands, regionally appropriate supply structures with a suitable energy mix can be set up. Using the example of initiatives in Berlin and Potsdam, the advantages and disadvantages of participatory municipal enterprises and citizen cooperatives will be discussed.