The invention relates to a system for showing the origin of a certain amount of electrical energy generated by a first method, which is transported via a network which is also adapted to transport energy generated by a second method, wherein the system comprises: at least one device for producing certificates which represent a quantity of energy generated by a first method; a system for transferring the thus produced certificates to consumers from the network; at least one measuring and interrupting device for connecting between the network and a user of electrical energy for proportionally reducing the energy representing the certificate in accordance with the electrical energy flowing through the device and for transmitting electrical energy when the certificate represents energy generated by the first method.