According to professor Nomad of the Netherlands, never

There, the waste material is brought to normal air pressures and a yeasting reaction starts - producing methane and CO2 which can be used to produce electricity. The first estimates predict that about 10 percent of the houses (so 3 out of a total of 32) can be sufficiently powered this way.

Or are you wondering how large a community has to be before it can build the infrastructure necessary for 10% of its energy to come from poop?

Those whom the Gods wish to destroy They first make mad. -- Euripides