The Renewable Energy Sources Act (EEG) was introduced in 2000 as a central component of the German energy transition. The goal behind the EEG is to gradually achieve 80% of the electricity supply from renewable energies by 2050 and thus increase the proportion of renewable energies in the German gross electricity consumption (§1 EEG 2017). The EEG guarantees plant operators of renewables a fixed energy buy-back price in ct / kWh for 20 years from the date of commissioning. State funding for the first plants will therefore end in 2021. The so-called Power Purchase Agreements can be a new instrument for the economic operation of these old systems, regardless of the EEG funding.