Energy certificates, also called "green certificates", are in this context securities facilitating trade with environmental values of the electricity produced from renewable energy sources. A energy certificate is a certificate issued when 1000 kWh (= 1MWh) electricity from a renewable energy source is produced. Electricity from many production devices are fed in to the grid, and we do not know which of them each houshold gets their electricity from. Therefore, certificates, independent of the physical flow in the grid, are used to keep track of who gets electricity from what production device.

We do not know where the electricity flows, however, we know where the money goes.